motor suitabilty

[netwolf]

I was goint to suggest the Littlefoot from Europe, but Rajiva beat me to it.

Rajiva, welcome to the forums in Aus. I have long followed your littlefoot system, i was considering it for my G-11 but the cost of good stepper motors pre fabricated for mounting onto the g-11 was double the cost of G-11 gemini servo motors so i decided to go with the Sitech. The swis escap motors were very nice but the euro to aus conversion is a killer. Also the slew speeds with the exisitng hurst motors would have been to slow for me.

But if you can get surplus stepper motors and have skill for the DIY then the littlefoot, Bartel or even Barry's system are all great options.

A servo alternative is the Sitech, its on Mel's page its a servo controll made by Dan Gray.

[rajiva]

Hi Fahim,

Originally Posted by netwolf

I was goint to suggest the Littlefoot from Europe, but Rajiva beat me to it.

Rajiva, welcome to the forums in Aus.

Thanks!

I have long followed your littlefoot system, i was considering it for my G-11 but the cost of good stepper motors pre fabricated for mounting onto the g-11 was double the cost of G-11 gemini servo motors

Yes, Steppermotors ready made for the G11 are still expensive and with the original hurst motors the goto speed is limited to about 130x at 12V. With the supported 30V you may be able to drive the motors at the double speed (250-300x) but I have no experience with the hurst motors.

I think the main decision that has to be made is what are your goals. If just Goto is the point a servo driven system has advantages over the stepper system. If astrophotography is the goal (this is the main point of all my projects) Goto becomes a totally new importance. When I go out to shoot some pictures I do one or maybe two Gotos per night! The main task of the controller is not Goto. So if your goal is astrophotography you do not go for high slewing speeds, you will like a integrated Robofocus, PulseGuiding, DSLR remote-control with programmable shutter timers, EPEC and other features like this. For the one or two Gotos per night you do not need that high slewing speeds.

But if you can get surplus stepper motors and have skill for the DIY then the littlefoot, Bartel or even Barry's system are all great options.

I do not sell any Hardware any more but I know that a company starting offering affordable motor/gearbox combinations for all kind of mounts is on it's way.

CS
Rajiva

[Kindellism (Rex)]

To all,

I noticed the thread with the reference to my website. It will be moving to Kindellism.webs.com because Yahoo is dropping Geocities.

The gears works well. However, I'm rebuilding the mount. I don't like the motor whine and dragging a laptop out to the field. I designed an unique mount that is polar align and with a clock drive. It is in the construction phase.

Rex

[Kindellism (Rex)]

Sorry that I did not really explain anything about my new mount. The sandman was calling me.

Scope.exe - I build a Dob mount for my ten inch using Mel Bartels stepper motor design. I love the concept but I have a few problems with it. One, I could never get the motors to run smooth. The vibs from the motors were see in the eyepice at 150x. Second, I got tire of dragging the laptop out with it plus the setup time. Last, the whine of the motors. ugh!

Since, I like to star hop to get to objects, I decided what I really want is motor control and a clock drive.

I also decided that I don't like Dob mounts that well is because its polar is directly over head.

My new mount is either a german fork or a split ring mounted on a equaorial table. The fork or split ring will be stepper motor driven and the equartorial will be the clock drive.

I will lilke to have the RA gear to be motor control and the clock drive but I can not figure out how to put two motors on the same gear and have them not to interfere with each other. Any ideas on how to do that?

[bojan]

Use a differential. I found couple of them on scrap yard...parts of old Radio test set

[kinetic (Steve)]

Originally Posted by bojan

Use a differential. I found couple of them on scrap yard...parts of old Radio test set

Bojan's right.

Another way is to clutch the second motor.
I did this with high speed DC motor slews on my old RA spur gearbox.
Steppers for tracking, DC motor for high speed slews.
The clutch was 24v from a photocopier.
I'll post some pics if you're interested.

Steve

[bobson (Bob)]

Steve,

Please post the pics, I follow this topic with great interest.
At present I just read and learn and ones I got enough info I will try to make my 12" Bintel dob computerised.

thanks

[kinetic (Steve)]

Originally Posted by bobson

Steve,

Please post the pics, I follow this topic with great interest.
At present I just read and learn and ones I got enough info I will try to make my 12" Bintel dob computerised.

thanks

Ok, Bob, Rex....here are some pics:
As this old gearbox is now redundant it lies forlorn on the dome floor
at the moment
For the photo, just to demostrate how it worked I have just
bodged up how it all sat together. It's not all bolted together in these
shots...(except for Pic 3, where the DC slew motor is removed)

I draped the old mini chain over the appropriate cogs where it sat,
again, just for the photo.

A description (PIC1):

At the top is the old spur gearbox (an old air-conditioning damper
actuator). It is driven via a small chain and sprocket via a stepper
motor.
Clutched in at the bottom, via a 24V dc clutch is the large DC
slew motor.

PIC2 is a close up of the DC clutch and chain/sprocket.

PIC3 is a very old photo, of the gearbox in it's heyday, all flashy blue
paint and covers on (but DC motor missing)

Obviously a DC high speed slew involved switching in the clutch
on the handpad, and then slewing.
Steppers don't like being spun this way, especially with control wiring
still attached. They tend to feel like a brake adding rotational resistance.
Therefore the slew switching removed the steper control lines via changeover relay.

Retrospectively, this was not ever part of the Bartels GOTO / encoder
setup. (you can't count steps if the stepper is removed!)
The purpose here is just to show mechanically one way to clutch
in two drive systems....there are, of course, many other ways.

Hope this helps.

Steve

[bojan]

Steve, this looks very interesting :-)
I am considering the second modification for my EQ6, using chained gears inside, instead of 47-teeth gears, which are considerably contributing to high-frequency PE on my mount.
Do you know where I can get something like this (sufficiently narrow, to fit inside - that means the chain should not be wider than 4mm)?
The timing belt is also an option but then the problem is pulley: they are significantly wider than belts itself (2mm + or more) and then the whole thing does not fit into available space.

[kinetic (Steve)]

Originally Posted by bojan

I am considering the second modification for my EQ6, using chained gears inside, instead of 47-teeth gears, which are considerably contributing to high-frequency PE on my mount.
Do you know where I can get something like this (sufficiently narrow, to fit inside - that means the chain should not be wider than 4mm)?
The timing belt is also an option but then the problem is pulley: they are significantly wider than belts itself (2mm + or more) and then the whole thing does not fit into available space.

Bojan,

I can't recommend a supplier, only an alternative DIY source:
Look up a place that services industrial photocopiers and printers.
They usually have to dump a trailer load of old photocopier
carcasses every few weeks, and they are probably more than happy
to let you take one or two
Photocopiers , especially the larger ones, are a great source of :

Mini Chains / sprockets
Steppers Bipolar and Unipolar
Toothed belts / pulleys
HV electronics
1st surface mirrors
Lenses / IR filters

I could go on forever....I'm starting to drool just thinking about them.
But be careful, the toner should be handled with care.

BTW Bojan, my father has very successfully in the past made sprockets
to suit any diameter. It's easy to do. Imagine a disk with holes drilled
accurately arround a radius. Then imagine turning the disk in a lathe
and cutting all the metal off until mountains appear around the
disk. He then case hardened the teeth.

Sorry to hijack the thread Rex.

Steve

[bojan]

Excellent, mate, thanks :-)
I will pay them a visit asap :-)