Bartelised scopes

[bojan]

Any Bartelised scopes out there?
There may be plenty of tricks and solutions to be shared....:)

[Rod]

Hi Bojan,

I am trying to set implement a Bartels stepper system on my 12 inch F5 newt. I have the electronics and have modified my dob mount (a flex rocker for a 12 inch F5). I can't decide on the best reduction system but I am leaning towards epoxy gears because becuse my machine skills and equipment are limited. I would love to correspond with anyone doing a similar project. I am in Mt Martha on the Mornington Peninsula.

Rod.

[bojan]

Hi Rod,
so it seems there are two of us :-)
My reduction is made of two worm gears (1/180) that I found in the misc bin in my friend's machine shop.. He found them on some other waste and decided he should store them for a while :-)
Also, the telescope's hor wheel rides on the 12mm shaft, driven with the worm gear..
I have seen a lot of epoxy gear solutions on the web and this is something I would have adopted if I had not have this solution.
Just be careful how the whole thing is put together, you will want to have the same portability as it was before bartelization.
Apart from couple of hickups with the software ( I have some funny issues with encoders, but I managed to circumvent the problem, partly with the help from yahoo group and Mel himself), the system works great, and it does not cost heaps of dollars, like some commercial systems out there, the price/performance ratio is excellent.
Good luck with your project :-) I would be very glad to assist, if you need any help :-)

[Rod]

Thanks Bojan,

I do have a question at this point. It sounds like you used friction rollers to drive the scope. Did you have any problems with microslippage? Or did the encoders fix that? It's the reports of microslippage that put me off the roller system but if encoders fix it, I would seriously consider it.

Thanks,

Rod.

[bojan]

I do not have a problem with any kind of slippage, but on the other hand, all depends on what you want out of the system.
For up to one hour of tracking and visual, there are no problems. System accepts commands from guider, so that should correct the possible problem 100%.
Since I do not have permanently mounted telescope, whenever I use it I just level it and then point to a known star and reset its coordinates, this is good enough for majority of my purposes at the moment.
For GOTO I had some problems in the past with slippage in the azimuth butthis was because of the design specifics (I am using a roller reduction and at the beginning there was not enough pressure in one direction. I believe I sorted this out with different design approach.
I never noticed any problems on altitude axis, where the telescope rides on the axis with its full weight.
BTW, I know for sure that many professional instruments are using friction roller reduction, it is cheap and there are no periodic error, inherent to gears.
Encoders should correct for slippage, however this will depend on their resolution.. and this is an area where I have some problems (oveshooting when telescope is returning to the correct position when encoders indicate the slippage, and that problem seems to be specific to my system only, since nobody in the bartels community knows what is the cause and cure).
Nevertheless, I am using encoders only as an input to a new position, when I want to observe something on the other direction during starparties (without encoders, I should either slew to the new position with motors which takes a long time - or I should stop tracking, then point to the new object, then I find that object in the data base, then reset to the new coordinates - all this takes a long time as well).
The easiest way to hop to a new object is the same as with conventional dobson: just stop tracking, push the scope to a new direction (encoders are updated every second automatically) and when there, start tracking again. GOTO function I am using for close objects within couple of degrees, and only when I am looking for them because I do not know exactly where they are.

[bojan]

As far as field rotation is concerned, I have not implemented it yet, but it is in my plans for the near future (when I get my Canon 400D).
So far I was using B/W Quickcam for shots up to 30 secs focally, with tracking and no guiding, and there were no problems observed :-)
Afocal avi's with my Kyocera were also OK :-) I had bigger problems with atmospheric turbulence and vibration (after touching something) than with tracking.

[Rod]

Thanks Bojan,

Sounds like a great system! I hope I can have a look at it one day.

Rod.

[bojan]

It is all about Mel Bartels s/w.... :-)

[bojan]

To give you a better idea of tracking accuracy, attached here is 10s prime focus shot of trapezium....
It is not a great image really, mainly because it was very windy and the seeing was terrible ... but it indicates that the tracking was OK during that time.
I think I posted on the forum before the longer exposure of Proxima (20 ~ 30sec), no traces are visible on it either.

[Lex]

what do you mean by prime focus
Lex

[iceman]

Prime Focus means the camera is attached to the scope instead/in-place of the eyepiece.

The light path is focused on the CCD/CMOS of the camera, rather than focused by the eyepiece.

[GReilly]

mmm Am I allowed to disagree? :-) If you put the camera where the diagonal is..... I think that is Prime Focus.
Yours,
Greg Reilly

[bojan]

Actually, in Newtonian telescope case, the prime focus is where it would have been if there were no secondary mirror.. so you are right to the certain degree (you missed by the radius of the tube..).
But since the secondary mirror does not change the optical properties of the system (apart from moving the focus point outside the tube and flipping sides of the image) , Mike is also right :-)
So, both of you are right if we assume we are talking about Newtonians :-)
And, if we want to be really correct in naming things here, this should be called "Newtonian focus"...

[pmrid]

Hi Bojan,
I just saw your original (2 years ago) post. I'll add myself to the list of the Bartelised.
I'm in the process of a grand refurbishment of a 16" Dob I bought last year - OK, so I'm slow - and would be grateful to be able to share some experiences and solutions with others who have done a Bartels implementation.
The mount for this scope is a heavy blighter, made from 2" box section sleel and steel plate. I'll attach a few photos.
The key to it is in the drives of course. The base of the mount has 3 wheels to which I have added a screw-down levelling system and a bearing or two. It is pullable but without dissasembly, an absolute beast to move anywhere far from home.
The Alt bearing is identical to the Az and is mounted on one arm of a yoke - with a slave shaft and bearing on the other side. I had a hell of a time getting all these to run true because the mount - while solidly built, was out of whack in several directions.
The drives in both Alt and Az are 200-step steppers run into a 25:1 reduction box and then through a worm drive to a 180-tooth gear driving a shaft on which the scope turns. My maths says this gives a 1.44 arc/second per step. But I am suffering major brain-fade when it comes to the software controlling these motors.
I bough a ready-made board from Mel (with the motors also) and although it has a field rotation capability as well as focus control, I don't use either yet - there isn't much point in getting the focus right if the thing can't track and slew.
So may I ask if anyone has been through the process of working out the Config.dat file for the Bartels software and is still sane.

[bojan]

Hi Pmrid
Welcome to the club (of bartelized scopes) ;)
Your machine looks great!
As far as config.dat is concerned, we (Rod and myself) are still sane and sound.. and the thing even tracks !
I also do not use field rotation (this is only for photography anyway and I am using mine for visual at the moment.... for photography I will mount my newtonian on Bartelized EQ6 one day).
Focus control via PC is also somewhat too much of an overkill... but with the rest of the settings there were not so many troubles.
And I never bothered to fine tune microsteps, as I found the major source of un-smoothness of the motor rotation comes from the fact that the PC I am using has 100MHz processor (it should be at least 200MHz or over).

[pmrid]

Thanks for the reply. The problem I have with the motors/drive system on both axes is that when I use the handpad to slew, or use the Scope program to do the same thing, the motor seems to accelerate up to a point (quite quickly - only a second or two) when it makes sort of rattling noise and doesn't seem to have any torque. It isn't a problem with the gears or whatever, they are now well balanced and run freely and smoothly. It is in the way Scope the software is controlling the motors.
Did you have to make many changes to the Config.dat file to get your system operating?

Peter

[bojan]

Your problem is in this area:

[*** halfstep section ***]
HsRampStyle 1
HsTimerFlag 1
MaxDelay 2000
MinDelay 600
HsDelayX 1
HsRampX 1
InterruptHs 100
HoldReps 10
HsOverVoltageControl 0
MaxConsecutiveSlews 5

Your MinDelay is probably too short, this controls the max speed of the motor. If the max speed is set too high, the motors can not cope and they will stall (as they apparently do) .
set this var to higher value (until the motors run OK on maximum speed).
Also, you can try to change the HsRampX, set it to 1 (as above), this will result in lower acceleration.

Also, check the power supply voltage, maybe it is too low?

Yes, I have to have some changes, mainly in above area, then to adjust the gear ratio (AltFullStepSizeArcsec and AzFullStepSizeArcsec).
Also I needed to adjust microstep parameters (I am using 24V and my motors are 15V or so) to lower the motor current. But this was done later it was not essential, like HS parameters.

Good luck :-)

[Rod]

Hi Peter,

I have had this sort of a problem. I found it to be a loose connection to the stepper motor or a crossed wire.

I didn't find adjusting msconfig too difficult to get slews happening. I just entered rather large numbers in mindelay (over 800) and maxdelay (over 2000) and gradually reduced them to the point where the motors stalled and then just incresed them slightly (to stop the stalling). Slews are a little slow on mine - just under 2 degrees per second.

Keep at it. It looks like a very rugged mount.

Rod.

[pmrid]

Hi Rod, and many thanks. I'll report back. But for now have to go earn a living (darn it but it does interfere with the good stuff doesn't it?). I'll be offshore now until mid-July. But I'll resume the challenge then.
cheers and thanks again.

Peter

[pmrid]

Amusing the way fate steps in and solves problems for you. I just managed to cook the circuit board on my Bartels stepper controller system - not entirely sure how I managed that but for now, the scope can go back to sleep while I cool off a bit.
Peter

[MrB]

I'll throw another vote in for stalled steppers.
As mentioned, increase the ramp up time(acceleration) and decrease max step rate.
Note: no experience with Bartelising a scope or using his software(except for a casual look at it a few years ago) but plenty stepper experience(CNC).
Also, have a look around for better steppers, most steppers can handle a few hundred RPM no load and much less when loaded, sadly people accept this as the norm, but there are newish chinese made steppers that get up to 10,000 RPM(!) no load, and still handle over a thousand RPM when loaded. Very popular with the CNC guys. Approx $50-$80 each depending where you get them, plus extra spent on beefing up your power supply.

[tnott]

When looking at installing a GOTO system for the 16" Tridob (though eventually I went with a commercial unit to avoid having to use a laptop), I did lots of research and a bit of experimenting of my own. Basically, a friction drive will always have some microslippage, especially when slewing rather than tracking, so you either need to have encoders attached to the axes to "update" the position of the scope or make sure the drive system uses some sort of geared arrangement to avoid pointing errors.

For example, the Servocat system uses a knurled wheel that presses a bit into the wood of the ground ring for the AZ and a cable wound twice around a roller for the ALT. It needs the encoders mounted on each axis to make it a "closed loop" system, with the Argo Navis or Sky Commander telling it where it is pointing and correcting for any slippage.



Precise Goto seems to need more accuracy than just OK tracking.

[Rod]

Hi Tim,

Thanks for your comments. I should update where my scope is at since this post was resurrected. I have nearly finished 'bartelising' it. Bojan says it looks ready to test under the stars but the weather has been terrible lately so I haven't had a chance.

I went with the epoxy gears solution. At this stage, no encoders are fitted but I have bought a pair and intend to install them when I have the rest of the system ready. Strictly speaking they are not necessary in a geared system as you say. I want them mainly for public star parties where the scope can easily get knocked out of position.

I have been following your articles about your tri-dob. It looks great! Could you explain a little more about the cable drive on the altitude. I have read about cable drives but can't visualise how they work.

Regards,

Rod.

[Rod]

Hi MrB,

You have me interested in your comments on stepper motors. Which brand are you refering to? I know a lot of people like Vexta steppers. Where can you get them at the price you mentioned?

Thanks,

Rod.

[Rod]

Sorry to hear that Peter. I hope not too much damage was done.

Rod.

[MrB]

Hi Rod,
The steppers come under different names and code numbers from different vendors but seem to be of the same manufacturer or 'clones'.
The cheapest Aussie supplier I have seen is Oceancontrols with their MOT-122 (http://www.oceancontrols.com.au/motors/stepper/hp_bipolar_stepper_motors.htm) for $79 being the fastest. Check their pdf file for motor comparisons(within their own range).
The cheapest I have seen anywhere is a UK vendor, Arc Euro Trade, with their 180Ncm motor (http://www.arceurotrade.co.uk/Catalogue/Stepper-Motors) (£18, around $40 aussie)being the most popular with CNC conversions. They have an even smaller motor that may be suitable for smaller scopes for only £10.
I'm sure the same thing may be cheaper elsewhere, in the US or on EBay for example(I don't use EBay anymore so don't know..).
Keep in mind that the holding torque quoted for stepper motor's is a pretty useless indication of a motor's suitability for scope driving if the scope has a worm and wheel drive, instead, go for the motor who's datasheet shows the fastest step rates and best dynamic torque. (ie, high current rating/low inductance) The high current rating will likely need a chopper stepper drive unless you want to use some massive resistors as heaters on those cold nights! :D
(eg: standard(linear) stepper drive with 40v supply and 5v 2A motors = 70Watt resistor minimum)

As an example, the steppers I use on my milling machine(and will be replacing in the not too distant future) are Step-Syn brand(Sanyo Denki) nema23's with a 117oz-in torque rating, but have such high inductance that they are very slow compared to newer motors of the same size and torque rating. I could possibly even use smaller motors.

[tnott]

The driven altitude fin has a 1.2 mm cable screwed onto one end which runs along the curved length then wraps around a roller twice. It then connects to a spring, which is connected to a small toggle lever.

When the lever is engaged the friction of the cable around the roller drives the scope (like a horse's reigns outside a saloon in a Western). When the lever is disengaged the cable slips so the scope can be moved manually. A notch is made in each end of the bearing (to stop it slipping off) and a channel made in the teflon it sits on.

The cable also winds from side to side a precise amount depending on the width of the cable, as well as the circumference roller and the alt bearing. Mine needed a custom one.

Attached are some photos of more "standard" scopes

[Rod]

Thanks Tim for the explanation.

Thanks MrB for stepper suggestions. Unfortunately , the Oceancontrols steppers are all bipolar. Mel's system is designed for unipolar motors.

Regards,

Rod.

[bojan]

Rod,
It is possible to use bipolar motors with Mel's software.
Of course, the driver electronics must be differently designed, it should have "bridge drivers" instead of single transistor switch for each motor terminal.
The bridge stage uses 4 transistors per coil, so basically you need twice as many transistors (plus two small ones as drivers/inverters, so this is 6 per coil, 12 per motor). This is not a problem to build, though.

However, I would not worry too much about all this.
Because there is always something better behind the corner.. .. and if you chase the perfection, you will always try to improve but never really use and enjoy what you already have ;)

EDIT:

I just had a look at data sheets (Oceancontrols steppers). 6-leads motor is unipolar, so you do not have to modify Mel's driver box.

[MrB]

I think the Oceancontrols data sheet is a modified version of the motor manufacturers sheet, yes it does include the unipolar motors but if you check the part numbers, OC only stock the bipolar motors.

Yes bipolar motors will work if the hardware is modified, though with these high current motors a chopper(PWM) drive is preferred.
These are reasonably cheap now but need step/dir input, I can't remember if Mel's software generates step-phase or Step/Direction outputs?

True, not worth worrying about, unless you find current slew rates extremely painful ;)

[bojan]

Hmm. you seem to be right re data sheets.

Mel's software does not generate step/dir signals (actually it does but only for field rotator). However, it does generate PWM signals, just like choppers (without current feedback though), for microstepping, and the max value for motor current can be adjusted via microstepping parameters menu.

[DaveGee]

I just found this thread.

I Bartelised my GEM (10"f5 newt.) about 15 months ago now. I had to beef the voltage to 24 volt (12volt steppers) to get decent slew speeds. But other than than that, the scope works fine.

My final drive is by roller and I suppose it slips a little but it's no big deal as I make sure I sync on a nearby bright star before slewing to my target, especially after a polar flip.

I'm very happy with the rig.

There are pictures of my scope all over IceInSpace but to make it easy here are some again.

[bojan]

Dave, this mount looks really impressive!
You must have an access to a very decent workshop, or you must have a good friend (like I do but mine does not have as much free time and interest in those things as I would like him to :-) )

[MrB]

Bewdiful, all you need then is 4 more transistors(and diodes) to modify for H-bridge drive and a higher voltage supply :D

[bojan]

Exactly :thumbsup:

[pmrid]

Dave,
I'm blown away by that GEM. Did you build it yourself? Is it possible to access any engineering drawings?
Peter

[pmrid]

Hello Rod,
well, I'm back and the new PCB has arrived from Mel Bartels, along with a few of the MC3479 field rotator chips (the ones I blew when I cooked the previous board). It looks as though the old board is OK with a new chip swapped in. Sadly I also cooked the printer port on the old Compaq I was using. I am definitely older and wiser. I realize now that I disobeyed one of the key instructions in the Manual - I hadn't connected up the motors to the PCB etc before powering up the board.
I have an AstroFest this weekend (in Qlod) and had hoped to finally give this big 16" scope it's first light there. But chances of getting it all set up in time are diminishing - so the forecast of continuing showers is almost a relief.
Peter

[Rod]

Hi Peter,

Welcome back. Good to hear your board is going OK now. Too bad about the parallel port. Do you need an old laptop? If so PM me. I have one spare I don't need.

My system is nearly ready too. I have learnt that it is something you can't rush.

Rod.

[pmrid]

Thanks Rod,
and thanks for the offer of a laptop. I'm OK there, thanks to a couple of grandsons who go through laptops like they do sox. I get their cast-offs that are generally quite useable.
Now that I'm back in action, I am still at the very beginning of the learning curve with Bartels system I'm afraid and in need of a bit of help with something seemingly very simple but ...
In the setup, in defining my local site, I have enterer Lat and Long for my site here in Qld as -27 Lat and 153 Long but for some reason, the system seems to think I'm somewhere in the northern hemisphere because any goto commands generally see the scope move towards a nadir position.

Is there some trick to entering Lat and Long for a southern hemisphere location?

Peter

[Rod]

Hi Peter,

You are a little ahead of me on this. I have actually been thinking about the same problem. Andy Martyn used to have a great site about his Bartelised scope. He had the following info on it which I hope helps:

"A note for those of us in Australia that the time zone should be a negative number to get the sidereal time right and that the longitude should be positive. Thus for my location in Melbourne at 145.06855E 37.81029S the values are:


Longitude 214.93 145, Latitude -37.81O29. TZ -10."


Does that answer your question?


If not, I'm sure Bojan would be able to advise you.




Rod.

[bojan]

Rod,
You are exactly right.
The relevant part of config.dat should look like this (it is for my position in Melbourne):

[*** astronomical times section ***]
LatitudeDeg -37.853050
CMOS_RTC_Access 0
LongitudeDeg 214.931450
Height 0.000000
Tz -10.000000
DST 0

Of course, system time must also be correct.
And do not forget to initialise the scope properly..
I am using very simple method, but it is very accurate (for me):
First I make sure the whole thing is in level (by means of bubble level).
Then, I point the scope to CSP (celestial south pole, near sigma Octans) which is my home position.

[*** mount section ***]
GEMFlipPossible 0
AutoGEMFlip 0
AutoGEMFlipOnFuzzDeg 0.000000
AutoGEMFlipOffFuzzDeg 0.000000
Siderostat 0
HomeAltDeg 37.853050
HomeAzDeg 180.000000
MsArcsecSec 50


[*** coordinate conversion section ***]
Current.Alt 37.853050
Current.Az 180.000000


Then, I start the scope program. When it is up and running, I can move it freely wherever I want/need, since I have encoders.
I very rarely use Goto (except for difficult things I do not know exactly where they are), most of the time I just use tracking.

If you do not have encoders. I suggest you move the scope to a nearby star, reset coordinates to it (from existing data base, or, I usually prepare the file with objects I want to observe the day before) and then GoTo from there. It will be quicker (because the scope will have to do shorter slew) and more accurate.


I hope this will help :-)

[pmrid]

That helps a lot. Thank you.
Peter

[pmrid]

Thanks again, Rod. I'll test this out tonight - weather permitting. I don't pretend, for a moment, that I understand why it works. But so long as it does ..

Peter

[pmrid]

Well, the day has arrived. I have now finished installing the new Bartels board and finished a rebuild of the mount and all the associated electrics. I wanted to reduce cable clutter and this meant building as much as possible onto the mount itself. Here's the result.
Thanks to Road and Bojan for their helpful advice.
Peter

[bojan]

It looks impressive :thumbsup:
Now, only a clear skies are needed

[Rod]

Looks good Peter. Let us know how it goes under the stars.

Rod.

[kinetic]

Hi Bojan, fellow Bartelisers:)

I Bartelised my homemade GEM ages ago but it is always a work
in progress.
Originally it was on an old 486 machine but has run for about 10
years on an old Compaq P120 (original HD still going strong).

I can vouch for the stalling on high slew speeds.
As mentioned , I tweaked Ramp up and Down settings until
there was a stall, then backed off a little.
I made the whole sytem from the ground up, adding remote
control over fibre from inside my house. ( I do fibre for a living).

My steppers run are 12v and 15v for RA and Dec respectively but run
on 24v with inline resistors for smoother steps.
I can post my Config.dat file if you like, to compare settings.
Also, the Scope-drive forum on Yahoogroups is a goldmine.
Many very smart Bartelisers out there with answers.
Mel himself is always quick to answer also.

Some key parts of the setup in the pic attached.

regards,
Steve B.

[pmrid]

Hi Steve,
that's a pretty professional-looking rig and observatory. A couple of things - the mount - looks solid and simple - make it yourself? And the Optic: I'm fascinated by the optic connection to the house and wonder if you could give us a bit more detail on how you did that and how it operates.

Peter

[bojan]

Hi Steve, looks impressive..
I have some plans to Bartelize my EQ6 one day :-) When I have permanent site with dome etc (if it ever happens)
As it is now, it does what I need, so I am not in a hurry.
Yes, Yahoo group was very helpful to me as well. Mel is always there and he also responds to private mail on the subject. He is one of the guys who definitely deserves to be honored as the one of a few who did not take his personal interests as number one when deciding on how to best contribute to the cause of ATM and amateur astronomy in general, IMO..

[bojan]

Hi Steve,
I noticed on your picture you marked serial mouse encoders... Are you using mouse driver or David Ek's box?
I use mouse driver (Gmouse.com), but I have a problem here, it seems the mouse interrupt handling does not work properly and very often the position is not updated while tracking and/or slewing.
Currently, when I want to move the scope, I have to stop tracking, to avoid problems - automatic returning to a position that scope thinks is current and correct and which is not because of missing interrupts (well, that is my theory).
So I plan to mount the David Ek's box (which keeps current scope position in its own controller's memory and sends it to main computer on request), but since I can live with the workaround, and since I am lazy, the box is still on my table, waiting to be mounted and used..
This is the only problem I have with bartels system and it was not resolved on forum (yet). Perhaps because not many people are using mouse driver and this s/w bug is simply ignored?
Yes, it is a work in progress :-)

[kinetic]

Bojan,

When Mel first introduced mouse encoders years ago, I added it to the
DEC axis only.
Later I added it to the RA axis too although I turn it on and off
depending on what I'm using the scope for.
I use a mouse driver without accelleration (the floppy you see sticking
out the laptop is the backup mouse driver).
I searched for ages to find a mouse driver that was glitch free.
Basically, once I setup the mouse increments in Config.dat, turn on encoders, I can track and slew with the DEC readout giving me an
update on screen.
If I stay the driven side of my backlash, I'm ok.
If I go backwards and introduce some backlash take-up, I get positioning
errors.
So to keep it simple it is only mostly used as a 'push to' goto function.
I set on a known star in stars.dat.
Do an equatorial co-ordinates reset.
Then push the scope until I am at my desired GOTO location.
(I can drive there with the handpad, but it all depends what side
of the backlash I am on).

[kinetic]

Hi Peter,
Mount is very old, my father made it when I was an apprentice.
I added the RA stepper drive, the DEC stepper drive and most other
functions.
It has a mixture of manual setting circles and digital (mouse encoders).
I made my own PCBs for the Scope-drive circuit including the handpad.
The handpad can plug in at several places including local (within the dome), or via optocouplers over the fibre( inside the house or shed).
I use VNC to control K3ccdtools over an ethernet link to the house but
mostly from locally within the dome.
I have never tried LX200 over serial or ASCOM methods.


The Adelaide weather, especially during winter, is so changeable that
I can never go inside and afford to forget the dome for even 10mins :)

Bojan: I agree with your comments re: Mel.....a truly inspiring gentleman.

regards,
Steve B.

[Rod]

Hi all,

This thread has been quiet for a while so I thought I would add a few pictures of my Bartelised scope. I finished it recently and have been testing it out - most recently at the ASV starbeque at Heathcote.

It is a 12 inch F5. I have used epoxy moulded gears for the reduction system. It tracks well and I am told is relatively quiet (for a stepper system!). I need to work on the goto side of the mount. I can usually get objects within a wide field eyepiece if the slew is not too long.

Obviously this is not a highly engineered mount so I am happy with these results. I am going to look into the error correction options in Mel's software to see if I can improve the gotos. I use the DOS version of Guide as a planetarium program for this system.

My only real problem at the moment is that I keep blowing the fuse going to the circuit board. I am going to replace the power cable and if that does not help a friend suggested I try the current limiting circuit.

I hope this is of interest. Any comments or suggestions welcome.

Rod.

[bojan]

Hi Rod, this look fantastic :-)

As for blowing the fuse, you must find the reason for this.
Current limiting approach will help (so the fuse will stay in one piece), but if you have an intermittent short somewhere, you will still have system malfunctioning due to intermittent power..

[Rod]

Hi Bojan,

Thanks for the comment and your advice while I was building this. The fuse is no longer a problem. I replaced some dodgy wiring and all is well there now. I do have the current limiting circuit to allow faster slews. Gotos are reasonably good for a wood and epoxy mount. I can get all objects in the field of view of a low power eyepiece. Tracking is always more than adequate for visual observing. The only issue I have is that gotos sometimes become less accurate after 3 to 4 hours. If I re-initialise on 2 stars then everything is fine again.

I am currently in the Northern Territory observing with my new travelscope while on holidays. Skies are great although we have had clouds the last couple of days. I miss the tracking and ease of locating objects with my Bartelised scope.

Rod.

[Rod]

I think I have blown one or more transistors on my circuit board. Last night I left my scope unattended while in tracking mode. While I was away the laptop shut down while the board was on. Unfortunately I can no longer slew in altitude and the motor just makes a faint buzz sound in tracking mode. I replaced the hex inverters but still have the same problem. I tried another computer and had the same problem so it is not the parallel port.

I am thinking I should replace one or more of the darlington transistors on the altitude side. I am using TIP102s but I have 4 TIP122s which I believe can be used instead. Should I just replace all 4 on the altitude side or is there a simple way to identify which of the transistors is damaged? I have a cheapo multimeter but I am pretty ignorant when it comes to electronics - can do basic soldering though.

Thanks,

Rod.

[bojan]

Hi Rod,
There is no need to replace all of them...

The easiest way to test the transistor is with Ohm-meter.. and transistor outside the circuit (but it should work with transistor soldered in place as well). However, the multimeter should have high enough test voltage, to deal with Darlingtons. Try using Mohm range if diode test doesn't work.

You should have low resistance from Base to Emitter, and from Base to Collector (Tab).
However, in opposite direction you should have high resistance.

From Collector to Emitter you should have high resistance, while in the opposite direction, you should have low (because of build-in protection diode).

Try to experiment with the TIP122 you have, not mounted.

The data sheet is here:
http://www.fairchildsemi.com/ds/TI%2FTIP122.pdf

If you have problems, give me a ring or PM me.
Or you just replace all of them.
Later, you can separate survivors from casualties :-) ..

[DaveGee]

Hi Rod,

If scope.exe loses control of the switching, the full current that the supply can give could go through the board and to the motor(s) and the weakest link get's a workout.

Have you tested that the motor is OK? Try swapping it with the other working motor. You say that the motor buzzes, then I guess that some of the trannies/coils are OK, otherwise if it was completely dead, then all the trannies/colis have been nuked.

If you need another board or motor, just shout. I have a spare.

[Rod]

Hi Dave and Bojan,

Thanks for your advice and generous offers. I am embarrassed to say that after looking more closely, the problem was a blown fuse on the overvoltage circuit. I have the overvoltage circuit installed to allow faster slews. I had forgotten they also had their own fuses.

I also found a loose wire on one of the cigarette lighter adapters that supplies power to the board. I suspect that may not have helped matters. Motors are fine and the circuit board also appears OK.

Thanks again,

Rod.

[bojan]

No worries, Rod, it is good outcome.
And, I am always happy to help, even if there is no need :-)

[Rod]

I am having problems with the laptop driving my bartelised dob. I wanted some feedback on the solutions I have in mind.

I use small laptops to save weight and bulk. Currently I use a Toshiba Libretto 110ct. It is very compact - about the size of a Video cassette. I have turned off all power management in the BIOS but it will not run the motors smoothly unless I also remove the battery, it then runs the scope perfectly in the workshop. However, when I observed in the cold last night I had the following behaviour:

Tracking was fine. Manual slewing with the handpad was fine. Gotos would start OK but just before completion, the laptop would shut down. So the motors would run together OK at the start but I think the computer crash is occurring when the slew is switching from two motors back to one.

My power supply is 4 x 12 volt, 7AH SLA batteries wired in parallel. This supplies all my power (for laptop, motors serial bluetooth adapter and red LED light). I use a small inverter for the laptop.

I am thinking about doing one of the following:



adding an independent power supply for the laptop - I could add another battery but wondered about just using one of the four I currently have and leaving the other 3 for the motors.
A friend suggested adding a large capacitor in series with the power lead to the battery. He suggested this because I once had a similar problem with another laptop. However, in this case the laptop battery could be used. When the battery was in place the computer did not crash. My friend felt that battery was supplying a little extra current as back up. Any suggestions on the size capacitor required?
This has all left me wondering if my power supply is inadequate?

I should also add that this issue with the laptop seems connected to my use of higher voltage for faster slews. When I run at 12 volts the laptop behaves itself.

Sorry for the long winded description. I would really appreciate any advice.

Thanks,

Rod.

[bojan]

Yep, Rod, your power supply is inadequate.. and capacitor will not help. Only bigger battery...

[Rod]

Thanks Bojan, what size do you recommend? Would adding another SLA in parallel be enough?

[bojan]

Not sure.. but - bigger the better.
Use the biggest you still can consider reasonably practical .

[alistairsam]

Hi Rod,

the Libretto specs show that the adaptor required is 15V, 3A, which is 45W. http://www.batterysupport.com/toshiba-libretto-110ct-adapter-p-38868.html . What is the wattage of the inverter you're using.

you could use two 18AH SLA batteries, but to identify the cause of shutdown, you'd have to measure the voltage at the different points, the battery voltage under full load (DC, should stay close to 12v), voltage at output of the inverter at full load (AC), voltage at output of laptop adaptor (DC, should stay close to 15v).
reason is that if current draw is high from a battery, voltage tends to drop, and if that happens, your inverter won't provide the right voltage for the laptop adaptor to provide 15v at the output even if it is regulated as regulators have input thresholds.

the output of the inverter with your laptop connected should stay at 230v ac or whatever the rating is with load. if that drops, then the output of your laptop adaptor will also drop to below 15v which might be causing your laptop to shut down.

by adding more batteries in parallel, you'd be increasing the current delivering capacity or AH capacity, but the voltage would still remain the same thats 12v.
so you need to measure voltages and you'd know what's causing the problem.

you mentioned a capacitor in series to the battery, not sure if you meant filter caps, the capacitor won't work this way, it has to be across the DC power rail, that way it will provide power during sudden demand, but only momentarily.
the other effect it has is that it will raise the voltage slightly, as rms value of the rectified output increases.

eg, if a 2000mfd cap is connected in parallel to a 12v dc supply at the output, it will raise voltage slightly by 1 or 2 volts.

one option would be to try powering the laptop from the battery directly with sufficient caps in parallel, ensuring the voltage is close to 15v. this would eliminate the inverter and reduce losses as inverters have losses. just an idea.

[Rod]

Thanks for the suggestion and the detailed response. The inverter is a
Powertech can sized inverter (MI-5121):

Output Power (Continuous): 150W
Surge Output Power (Surge): 450W

I used to use a simple dc voltage converter designed to run laptops off a 12 volt battery. This worked for years when the laptop battery still had some life in it in the previous laptop. But the shutdowns began when the battery died. That's when I switched to the Libretto and the inverter. This seemed to resolve things in the workshop - but not when I was out in the cold observing.

I like your suggestion re the capacitors in parallel. It would simplify my equipment. Would this give a small reserve of power too? Can you give me specifications on the capacitors I need to try it - I'm guessing 2 to 3 2000mfd caps? I can make things up OK but I don't understand the theory very well.

Rod.

[alistairsam]

hi,

if you have access to another battery, do try adding that in parallel first and checking if the same behavior is noted.
else, usually one car battery should provide ample power and their chargers are fairly inexpensive.

the capacitors won't give sufficient reserve as they only provide power momentarily depending on the load, so this could be from a few milliseconds to one or two seconds and largely depends on load draw. they're mainly designed to filter rectified dc and ripples in the waveform when used as filter caps.
but like I mentioned, they do increase voltage slightly even with load.
in Audio amps, usually 2000 to 10000mfd capacitors are used in parallel and they provide power during bass notes which require higher power to move the driver.

my suggestion is purely theoretical as I haven't tested this. I would try a load other than the laptop first that's rated at 15v.
measure voltage at battery before applying load, after applying load, and after adding 2 x 2000mfd caps in parallel, but the capacitors need to be rated at least for 50v. I don't remember the formula to calculate voltage rating.
one aspect to be cautious is discharging the capacitors. the higher you go, higher the charge retained. so a simple load like a 15v dc bulb with a 1w resistor and an spst momentary switch would help discharge them.

also try your original configuration with the inverter, but separating the batteries for the laptop/inverter and the motors. that way, if you slew at higher voltages, that won't affect the laptop, and keep observing which battery set drains quicker, and you'll get an idea of what AH rating you'll need and how many batteries in parallel for which.

[Rod]

I don't have another battery but I have a 12 volt 5 amp dc power supply. Could I run that in parallel with the batteries? If it resolves the problem, I could then buy one or two more 7AH batteries.

Thanks,

Rod.

[alistairsam]

not sure what you meant by running in parallel with the batteries. is this an ac to dc adapter?

[Rod]

It's a power supply I bought from Jaycar. You plug it into a wall socket and it supplies 12 volts DC. It is rated at up to 5 amps. I was thinking of adding it to the bank of batteries just like it was another battery - adding its positive lead to the battery positives and the negative lead to the battery negatives.

Hope that makes sense.

Rod.

[bojan]

Wow Rod, that is dangerous.. Power supply you have is not a charger and it should not be connected to battery just like that.

Previously I mis-understood you and/or didn't read your post carefully enough.

If you have a problem with computer when slewing, I suggest you sort this out where the problem is: get a new computer battery or different computer.

[Rod]

Thanks for the warning Bojan. As the laptop's own battery causes it's own problems I might try powering the laptop separately with one or two of my 7AH batteries. What do you think?

Rod.

[bojan]

Yes, this would be much better approach.