For quite some time I was considering upgrading my standard EQ6 with better electronics and mechanics.
As any form of commercial upgrade was never an option for me (a matter of principle ) I decided to do it myself..
The first step was Darren's firmware, I did this last year and now I have GoTo functionality.. (with the help of laptop, running CdC)
This time, it was the steppers and gearboxes.
I could not find Konrad gearboxes (most popular choice for many, it seems) so I decided to design my own.
Also, I wanted to end up with such a system that will tolerate much higher slewing speed.
And I wanted to have everything inside existing housing (so external timing belt reduction, an excellent choice from the backlash and PE point of view) was also out of the equation.
The design I adopted is as follows:
1) 200s/rev steppers from 5 1/4" floppy drive
2) Two-stage gearbox (1/4 each, overall reduction 1/16)
3) miniature ball bearings on all shafts
4) re-using the existing gears for worm coupling.
Steppers had only 5 wires, so I opened them and added 6th (so I ended up with two isolated coils with middle terminals).
The gear pairs are all the same:2 x 20 and 80 teeth gears and they all came from my junk-box..
This configuration is also compatible with Bartel's software.. which I know will work perfectly (from the experience with my dobson).
The overall reduction of such motor-gearbox assembly is 66.6666 (the original was 132.8125)
The final resolution (with micro-stepping) is 0.0703 arcsec/step [original was 1.1294arcsec/step, or 0.5647arcsec/ustep (Darren's mod)]
The result (not completed yet) is on the pictures below.
Now the only couple of things remained to do is to assemble the RA gearbox, to mount everything inside the mount and to see how it works :-) .
I will post the results when I do all this. It will not do much for 8min period (worm) but the higher frequency components will be eliminated or sufficiently reduced, as well as backlash.
The next step of this project will involve a software change:
- Darren's code has a problem with 24x slewing speed.
- this is not quite fast enough
and
- it does not support acceleration (not really required for 16x slewing), but absolutely required for anything faster, considering 25kg of telescope and counterweight, loading the mount.
Of course, in a course of things I may decide to stick with Mel Bartels' solution.
In that case, I will have to build the new drivers for motors (to fit inside the mount cavity).
Bojan have you thought about using toothed belts and pulleys. I have them on my EQ6 and there is no discernible backlash. It also gets rid of the 'microjumps' that gearboxes give you. With the side by side, SN10, guidescope, finder system and fridge there is about 70lbs of payload. This guides very well when there is no wind.
You can see the amount of counterweights needed in the last picture.
Bert,
What you have was actually on top of my list of options..
The main reason I went with gears was I had them already :-)
Also, I wanted everything to be packed inside (because of transport.. While I do have a sort of semi-permanent site here in my Mt Waverley front yard, sometimes I go to Daylesford to friend's farm (very dark site).. and anything that protrudes out of mount would be in danger of being damaged.
I even considered internal pulleys (a bit difficult to assemble, but possible) but I could not find right parts for this (thin enough belt or chain was the biggest problem.. I was looking here: https://sdp-si.com/eStore/. BTW, they have gears like I was using in my solution and I think originally they came to my junk box from those guys).
Anyway, this is an interim solution. If it does not work as it should, I will go with timing belts (like you have).
I even considered internal pulleys (a bit difficult to assemble, but possible) but I could not find right parts for this (thin enough belt or chain was the biggest problem..
You mentioned the steppers off a 5 1/4" drive. Did you do any testing to find out if there were better motors. I built a test rig about 12 years ago and tried all sorts of salvaged steppers. The fastest I got comes from a miniscribe 20 MB MFM HDD they were nearly 3 three times as fast as the best 5 1/4" drives I stripped. These were still only half the speed I could get out of the steppers that came with a DOBII drive I had but still quite usefull.
I still have the test sheet I made and will attach it.
Both have reasonably good ranges of small timing belts
and lots of pulley types.
Andrew
Hi Andrew,
Thanks for the links.. I tried them before but they have nothing suitable (actually, it seems most of stuff they have is the same as on the site I mentioned).
The main problem is the thickness of the timing pulley (must be max 4mm to fit into the mount) and available diameters of pulleys (the required reduction ratio is 8 ~ 24, to achieve fine enough resolution without going into too fine microstepping.
This is the reason I went with gears.
You mentioned the steppers off a 5 1/4" drive. Did you do any testing to find out if there were better motors. I built a test rig about 12 years ago and tried all sorts of salvaged steppers. The fastest I got comes from a miniscribe 20 MB MFM HDD they were nearly 3 three times as fast as the best 5 1/4" drives I stripped. These were still only half the speed I could get out of the steppers that came with a DOBII drive I had but still quite usefull.
I still have the test sheet I made and will attach it.
Barry
Hi Barry,
Thank you for the list, it is a great compilation
I did some tests with those motors I have and the speeds I achieved are not great (~400steps/sec @ 12V), however, those motors will do with current Darren's firmware (and 16x slew rate) and with existing drivers.
To achieve faster slews, I will need different drivers (higher current-limited sources, to overcome coils inductance) anyway.
You have stirred up a little interest for me. I still have the motors (I will need to make some sort of a gearbox to attach them) and I have a cheap equatorial head (something like an EQ3). It has a RA drive. The standard type Sid, X2 and x8.
I also have the black box I built to drive them and a Qbasic program I wrote that controls all with a two star alignment, planet calculator, alignment star data base, M, ngc and IC data bases etc. I used to sit with it connected to a computer and watch it go through its antics while the motors drove a couple of threaded rods with pointers on them as I did not have an equatorial head at the time. At a I arcsecond per pulse gearing I got a slew rate of about 1 degree/second.
About this time I got an LX200 classic and did not do any further development.
Well, time has come to test the new gearboxes..
And now I have mixed feelings about the whole project and all the noise on the internet about Synta products.. at least the noise concerning the recent Synta products (my mount is one year old now).
When planning the upgrade, my main goal was to reduce high frequency components from PE spectrum, allegedly generated by horrible gears and even worse grease used in original Synta gearboxes.. I was quite aware that there is not much that can be done about PE intruduced by worm gears pair.
But, what I ended up with was the situation not much better..
Yes, the PE amplitude is almost halved, from 24 arcsec what was before now I have ~16 arcsec. I am attributing this improvement to much smaller backlash, because I spend considerable time adjusting the meshing on the mount before assembly of the RA shaft. Also, some of it may be due to different phases between worm gear and gearbox.. I should do the proper PE analysis by FFT (I do not have autoguider yet so this must be done by careful measurement on the images, pixel-by-pixel.. the awful job I do not want to do really)
But the high-pitch PE components are still there, in almost the same amount, something I did not expect to see on the test shots.
My gearboxes also introduced its own PE components, this is quite visible on the attached images (the second one is with original, the first image is with new gearboxes) as "wave" with 1/4 period compared to the main one (corresponding to one rotation of the worm shaft). This is due to the second stage of my gearbox (I am using two stages, identical gear pairs - 20/80).
The original Synta gearbox has the last gear pair reduction ratio 1/3, and this is also visible on the second image as wave with 1/3 period.. and surprisingly, the amplitude appears to be somewhat smaller)
Also, my gearboxes are very loud, and I can even "feel" the stepping vibrations by placing my hand over DEC shaft housing (this is only when slewing with 16x speed of course.. Darren's mod uses microstepping for tracking, so this is not the issue at all).
I opened one of original Synta gearboxes and found out that:
- the first pair of gears (on the motor shaft) is helicoidal and plastic, that is why they are so silent.
- the grease used appeared to me to be of very reasonable quality (judging by the smell and touch)
All this is in direct contradiction with dreadful reports found on some webpages which promote installation of Conrad gearboxes (mentioning "un-defined material used for gears" and goo-like stuff used for lubrication)
So, what happens now?
What was left of original mount (in terms of tracking) is as follows:
- Bearings on the RA shaft (replaceable.. maybe I will try this later)
- worm gear pair (not that i can do much about it..)
- transfer gears (47 teeth, they can eventually be replaced with timing belts.. to be tried later when I find something suitable).
I'd suggest trying first to get a better graph of the PE.
It's not hard to do. Many programs chart the PE , I use K3CCDTools
Drift Explorer then put the chart into an Excel spreadsheet.
Just use a webcam / imager, find a medium power, turn on the
charting process and let it run for a complete cycle of the 2nd
from last gear in the gearbox , if possible.
A better chart will let you identify the main component of your problem.
There is not much point trying to reduce the PE of a gear 3 or 4
orders back in the reduction anyway, depending on your ratios of
course.
As for steps being visible, is it Microstepped of half steps?
If micro, then as you well know, Mel B suggests a reduction of
at least 4000:1 to have a compromise between good high speed slews
and no visible steps at the eyepiece.
Steve,
Thank you for you comments :-)
Will try it on first opportunity..
Actually what is visible are not individual steps, but PE introduced by last (second) gear stage (1/4) of my gearbox (as well as Synta's last stage, 1/3).
The tracking used microstepping (32 /usteps).
The audiable vibrations are introduced by half-stepping (while slewing).
You are right, for presentation purposes the better graph would be helpful, but I am already aware what in fact are the problems: last stage in gearbox (both gearboxes actually) and something which is more noise-like and erratic, sudden 3-5 arcsec jumps (bearings?) which has period (?) close to 3 sec. This may be due to bearing.. or dirt in worm gear. Or most likely transfer gears (47 teeth.. and it appears there are that many jumps per main period.. in that case the belt drive would help here)
The attached images have scale 1.07 "/pixel.
However, all that has been done so far was actually an improvement..
Before, only 30% of my 30sec shots (with MTO100A) were usable.. Now I have 60-70% shots that can be used for stacking.
Would anyone know if you can use the synscan eq5 upgrade kit on a heq5 standard mount non goto. Particularly do the stepper motors have enough torque. I know there is some modification needed on the mounting plate for the motors.
I have also sent a email to skywatcher with no reply yet asking is the eq5 upgrade the same as the heq5 upgrade kit.
Finally, I put together another set of gear boxes for my EQ6.
As I described earlier in this thread, previous modification almost halved the PE, introduced by original gearboxes.
However, what bothered me was the residual 3-5arc-sec pp component, caused by transfer gears (47 teeth gears, they are different, with smaller modulus, and it seems of better quality in newer mounts with Synscan).
So, I decided to go for timing belt coupling as my next attempt to further reduce PE, or at least to have it smoother, so the future auto-guider can do its job properly.
The belts and pulleys came from Small Parts & Bearings, and overall reduction is 1:16, same as in previous version [20:80 spur gears pair (I wish they were helical) and 12:48 timing belt pulleys].
This gives 1:2880 at motor axle, and resolution is 2.2500 arcsec/step or 0.0703 arsec/u_step (at 32 /u steps as per Darren's firmware)
The details of the gearbox design are visible on the attached photo.
I expect the installation of those gearboxes may prove to be quite challenging job.. and if all goes well, my EQ6 should be as close to the perfection as it can be...
3-5 P/P arcsecs bothers you?, sheesh, Id wouldve been happy with that, what portion of that was seeing (what were the guide exposures used whilst determining PE)?.
I admire your persitance, will be interesting to see what diff belt drive makes
3-5 P/P arcsecs bothers you?, sheesh, Id wouldve been happy with that, what portion of that was seeing (what were the guide exposures used whilst determining PE)?.
I admire your persitance, will be interesting to see what diff belt drive makes
Well, it is erratic and rather sudden jitter (and there are ~47 or so of them for worm period so I strongly believe this is due to transfer gears, and this should not be present with belt reduction, according to people who install it.. and this can not be smoothed by auto-guider (which is still on my drawing board).
Otherwise the total PE is of course larger, ~32 arcsec p/p (and it is not going to be much smaller with belt, but I expect it to be smoother)
OK, I get it, but gee, total 32 arcsec is not good, but as you say, as long as you can get it smoother with belts, you can guide it out.
Your fairly locked into tight sub 2 sec guiding with no backlash (and at short FL imaging though), could be tricky, I hope your on the right track overall.
OK, I get it, but gee, total 32 arcsec is not good, but as you say, as long as you can get it smoother with belts, you can guide it out.
Your fairly locked into tight sub 2 sec guiding with no backlash (and at short FL imaging though), could be tricky, I hope your on the right track overall.
I believe I am...
As my prime interest is photometry and (as a next step) spectroscopy, a relatively short FL (up to 1000mm) is quite OK for the purpose [I am already using MTO1100-A (Maksutov cassegrain) for this, and 30 sec sub-exposures without guiding are quite possible even as the things are at the moment (with ~30% reject, due to aforementioned jitter].
The belts and pulleys came from Small Parts & Bearings, and overall reduction is 1:16, same as in previous version [20:80 spur gears pair (I wish they were helical) and 12:48 timing belt pulleys].
This gives 1:2880 at motor axle, and resolution is 2.2500 arcsec/step or 0.0703 arsec/u_step (at 32 /u steps as per Darren's firmware)
Hi Bojan,
can you please clarify how you get the 1:2880 reduction ratio from 1:16,
is it after the worm and tooth reduction on the EQ6?
is it detrimental to use v belts and pulleys rather than timing belts? its just that I need a total reduction of around 800:1 for a step clock of 33Hz, and I can't get the matching timing pulleys or pulleys with tooth on the OD and Hub to make a gearbox with timing pulleys to reduce backlash.
i've been thinking of planetary gearboxes, i pulled out one from a cordless drill, reduction ratio is quite high, but not sure of backlash.
had a look at the stepper gearheads from various suppliers, they're quite expensive.
It is easy:
EQ6 has 180 teeth worm, so 16*180 = 2880.
No, you cant use conventional or V belts, because their reduction ratio will depend on pulley's diameters.. and there will be also some un-controlled amount of slippage in such pulley-belt system, so you have to use timing belt and pulleys.
Planetary gearboxes from tools are good idea, however the backlash will definitely be there - those gearboxes are not designed with precision in mind.
All depends of what you want to do:
- If you are using Bartels' system, reduction ratio is not critical (because it is parameter, entered into config.dat file).
- If you want to use existing driving circuit, then you must maintain the existing reduction ratio (because you can't change that parameter in existing synscan and so on units.. The exception here is Darren's mod, which I am using and it accepts wide range of reduction ratios.
Give me some more details of the design (what motor, how many steps and so on) so that I can be more specific.
But, one thing is certain: the simpler, the better.
That means, 200-step motor (with micro-stepping) driving timing pulley reduction 1:4 (this one can be fitted inside EQ6) or 1:8, which is then coupled to EQ6 worm-gear.. Bartels' program does that easily (but requires DOS on PC, 33MHz old laptop works OK.. faster the better of course).
If you have just a stepper driver, and need specific frequency to drive it, you have to calculate what it should be (based on available reduction) this can be generated by micro controller easily.. and here you go..
Now, you've got me thinking about V-belts... if you have auto-guider, actually, in principle, you CAN use v-belts.. because the guider will take care of reduction ratio variations.
The only thing that will not work is GoTo.. But, even this could be made to work (in Bartels system) provided you have encoders coupled to controller.
Hmm.. something to think about
However, I would still use timing belts and pulleys. They are not so much more expensive but they provide non-slipping reduction for PicGoTo or Bartels or Darren's or whatever driving system you choose...
Quote:
Originally Posted by alistairsam
Hi Bojan,
can you please clarify how you get the 1:2880 reduction ratio from 1:16,
is it after the worm and tooth reduction on the EQ6?
is it detrimental to use v belts and pulleys rather than timing belts? its just that I need a total reduction of around 800:1 for a step clock of 33Hz, and I can't get the matching timing pulleys or pulleys with tooth on the OD and Hub to make a gearbox with timing pulleys to reduce backlash.
i've been thinking of planetary gearboxes, i pulled out one from a cordless drill, reduction ratio is quite high, but not sure of backlash.
had a look at the stepper gearheads from various suppliers, they're quite expensive.
Hi,
I'm using a 1.8deg nema 23 motor. also have a nema17.
I got a 130 tooth T2 timing pulley from small parts as my nema17 motor has a 20tooth T2 pulley on the shaft. This shaft is 5mm.
I found a site that shows how to fabricate a gear puller from a steel square pipe, a screw and two nuts. so thats very handy in case I'm changing the gear or pulley on the motor shaft.
I also found a couple of timing pulleys from printers, and have achieved a reduction of 83:1 so far. just need another stage to reduce it further.
maxonmotor have some precision gearheads but they don't have steppers. they have something called EC motors and they're coupled with their sensors and gearheads some of which are low backlash. not sure how it works though. some of their gearheads with high ratios are quite affordable.
i'm looking at an autonomous system that can be interfaced with a pc if required.
have also been looking for microcontroller code for the PIC or the picaxe (easier to program), that incorporates acceleration and deceleration, this will result in high rpm needed for a high ratio gear.
other option i thought of was to use electromagnetic clutches found on most printers.
if what i understood is correct, they can engage a motors shaft to the drive train when energized, so that way a DC motor can be used for slew and a stepper for tracking.
i've seen a similar design on these forums but he used a relay to cut the stepper in and out of the train.
all this is not on any existing mount, its one i'm building from scratch, so i can vary things quite a bit.
i thought i'd keep away from worms as i think you'd need the precision ones if you want to minimize backlash.
) I decided to do it myself.. 
