Another EQ3 stepper mod

[furrysocks2]

I've just acquired an EQ3 with single axis drive and am looking to convert to DIY goto/track. I've flicked through a few threads here and elsewhere, so I know there's plenty of prior.

 

I understand the RA and DEC worm ratios are both 1:130. If the supplied RA motor has 48 steps/revolution and a further 1:120 reduction, then single stepping would give 1.73"/step, less if microstepping. But I can't backdrive the 1:120 gearing with the slow-mo handle, so it's out.

For RA, If I used a directly coupled 400 step motor with 16x microstepping I can squeeze out a comparable 1.56"/ustep, less if I used gearhead or belt/pinion reduction, and (presumably) still be able to backdrive it when unpowered. I'd prefer something more compact than a directly coupled gearhead stepper, so my choice is either a directly coupled stepper with no reduction, or an offset stepper, preferring belt to pinion I think.

I have the Easy Driver and Big Easy Driver stepper boards, various Arduinos and a collection of GT2 pulley wheels.

I've seen AstroEQ and OnStep as possible platforms. OnStep gives the ability to use bluetooth from a smartphone as well as ASCOM, while AstroEQ and EQMOD seem to be more commonly used. I also like the idea of a simple standalone controller with a Wii nunchuck or similar and on-the-fly alt-az to eq conversion, for the kids.

 

The simplest mechanical solution for RA would be a directly coupled 0.9deg stepper, 16x ustepping. At 15"/sec tracking rate and 1.56"/ustep, that's a ustep frequency of ~9.6Hz? Seems ok, particularly for wider fields of view? I assume I can be less concerned with step resolution on the DEC axis, though the simplest mechanical solution here looks like either pinion or belt drive.

 

Those who have thought about this or done similar before, do you have any advice or comparisons? Any particular thread suggestions?

[furrysocks2]

Couple of favourites so far:

http://www.tanstaafl.co.uk/2014/08/astro-eq-conversion-of-eq3-2/ (parts 2, 3, 4 and 5).

http://www.forumastronomiczne.pl/index.php?/topic/9214-astroeq-na-cg4-eq3-2/

 

First uses belt reduction for both, second uses a 5:1 NEMA14 directly coupled to RA, and belt driven on DEC.

I had originally thought NEMA17, but NEMA14 looks good enough.

[John78]

AstroEQ is bluetooth also, if you DIY or buy the new ones I believe were going to be ready to go - its simple as adding a HC06 BT dongle in there on RX0 TX0 pins, it also has standalone mode - but I think that is just tracking.

 

If you already have stepper drivers - building a DIY astroEQ is supported and easy and very very cheap - just need an arduino mega.

[furrysocks2]

54 minutes ago, John78 said:

AstroEQ is bluetooth also, if you DIY or buy the new ones I believe were going to be ready to go - its simple as adding a HC06 BT dongle in there on RX0 TX0 pins, it also has standalone mode - but I think that is just tracking.

 

If you already have stepper drivers - building a DIY astroEQ is supported and easy and very very cheap - just need an arduino mega.

Thanks, John.

HC06, stepper drivers and Mega1280 sitting under the bench.

I hadn't realised the AstroEQ was bluetooth capable. A benefit of OnStep may be its Android app unless a similar solution exists for AstroEQ, but regardless I may begin with the latter.

 

DEC: I've just threaded a hole in a NEMA17 bracked and mounted a 1.8 degree stepper to the DEC axis and drilled out a 5mm bore pulley to attach to the worm - 1:1, so no reduction. They line up well but need a 126-GT2 belt - may try splicing a temporary one while waiting for shipping. I should be able to tension the belt and prevent rotation by shimming underneath the bracket slightly.

RA: I'll look at making a quick mount and coupling for a 27:1 geared NEMA17 I have already and check for clearance. 

[furrysocks2]

I discovered today that you can wire a 6-wire unipolar stepper as 4-wire bipolar by leaving the common center taps disconnected.

 

I mounted a 6-wire NEMA17 stepper (5mm shaft) to the DEC axis that I found in one of many boxes of bits and bored out a pulley to 6mm for the worm shaft. I then decided to mount a 4-wire NEMA17 27:1 gear head stepper (8mm shaft) to the RA axis - one which I had bought recently. The flexible coupling from the stepper that came with the scope (5mm motor to 6mm worm) was bored out to 8mm - it looked a as ugly as I knew it would.

I then remembered having more than one 6-wire NEMA17 stepper and picked another one out (5mm shaft). It was slightly smaller, so I decided to substitute it for the one mounted to DEC, which I would mount to the RA axis instead of the 27:1. Either way round, two NEMA17 steppers, both 200 step and both with 5mm shafts. Great, I'm rocking!

 

I need a new flexible coupling.

[John78]

On 1/6/2017 at 16:13, furrysocks2 said:

Thanks, John.

HC06, stepper drivers and Mega1280 sitting under the bench.

I hadn't realised the AstroEQ was bluetooth capable. A benefit of OnStep may be its Android app unless a similar solution exists for AstroEQ, but regardless I may begin with the latter.

 

DEC: I've just threaded a hole in a NEMA17 bracked and mounted a 1.8 degree stepper to the DEC axis and drilled out a 5mm bore pulley to attach to the worm - 1:1, so no reduction. They line up well but need a 126-GT2 belt - may try splicing a temporary one while waiting for shipping. I should be able to tension the belt and prevent rotation by shimming underneath the bracket slightly.

RA: I'll look at making a quick mount and coupling for a 27:1 geared NEMA17 I have already and check for clearance. 

All arduino devices are 'bluetooth' you just put a HC06 on the TX and RX pins (even for programming using the IDE) - but - once you've done that though you can't power the arduino using a USB data cable or use the USB port as serial as its on the same comms lines.

[furrysocks2]

Another mounting solution: https://www.youtube.com/watch?v=TQEURmXOibg

[furrysocks2]

For reference, GT2 belt length calculator: http://www.bbman.com/belt-length-calculator/

Mounting brackets, couplers, belts, pulleys on order - enough to cover two designs.

[furrysocks2]

All parts now received (though little thought yet to wiring/connectors).

Current plan is that Dec will be GT2/belt driven 1:1 from a 200 step NEMA17. For RA, I have two choices - either belt driven 5:4 (same length of belt as DEC) from a 200 step NEMA17 with option to later change pulley/belt length, or directly driven from a 200 step NEMA17 with ~27:1 planetary gearbox. The latter will protrude further and I have yet to check clearances.

Just a matter of finding time to spend on it.

 

[hughgilhespie]

Hi Furrysocks,

"The simplest mechanical solution for RA would be a directly coupled 0.9deg stepper, 16x ustepping. At 15"/sec tracking rate and 1.56"/ustep, that's a ustep frequency of ~9.6Hz? Seems ok, particularly for wider fields of view? I assume I can be less concerned with step resolution on the DEC axis, though the simplest mechanical solution here looks like either pinion or belt drive."

I think 9.6 Hz is a bit low. I think the visual image will be a bit jerky. As I recall, for cine film, a frame rate of about 20 Hz was the minimum for smooth motion. If you can, use a driver that has a larger range of microstepping. This one

SparkFun AutoDriver - Stepper Motor Driver (v13)
would probably be OK although it says some worrying stuff " Please keep in mind that the L6470 requires a great deal more configuration and adds software complexity to your system. "

It's also more expensive. Still, what's expense in this wionderful world of astronomy!

Regards, Hugh

 

 

[Stub Mandrel]

I don't know if this spreadsheet will be any use to you; it may be too chaotic for someone other than me to follow it!

RA and DEC.xlsx

[furrysocks2]

Thanks, Hugh.

I only have 200 step NEMA17s, with and without gearhead, and drivers up to 16x - will attempt something with this kit first before purchasing anything else. A bit of trial and error and learning, perhaps, but thinking again on this before I start...

My starting point is 16x (max) microstepping with a 200 step NEMA17, either with a combination of 16T/20T or a 27:1 gearhead, but could upgrade the non-gearhead option either to a 400 step motor, a 16T/60T pulley combination, or both.

It's been suggested to me on the OnStep yahoo group to aim for something like 1 to 0.5"/ustep, which I believe equates to 15-30Hz, so your proposed 20Hz makes perfect sense in that respect.

Based on all that, the gearhead stepper at 4x or 8x microstepping could be the winner, being the least complicated, mechanically. Provided there is enough clearance.

Time to have a fiddle...

[furrysocks2]

4 minutes ago, Stub Mandrel said:

I don't know if this spreadsheet will be any use to you; it may be too chaotic for someone other than me to follow it!

RA and DEC.xlsx

Thanks for that - much improved layout compared with my own! And my own maths seems to tie up, which is reassuring.  

[Stub Mandrel]

1 hour ago, hughgilhespie said:

I think 9.6 Hz is a bit low. I think the visual image will be a bit jerky. As I recall, for cine film, a frame rate of about 20 Hz was the minimum for smooth motion. If you can, use a driver that has a larger range of microstepping

My rate is 17Hz and was chosen to minimise problems for astrophotography.

In practice the rate of movement is so slow that I think you could go down to a few pulses a second for visual without problems.

5 minutes ago, furrysocks2 said:

Thanks for that - much improved layout compared with my own!

I don't believe that for a moment!

[furrysocks2]

6 minutes ago, Stub Mandrel said:

I don't believe that for a moment!

You've got headings and units and everything! Don't take my screenshot above as anything like representative of the rest of it!

 

6 minutes ago, Stub Mandrel said:

My rate is 17Hz and was chosen to minimise problems for astrophotography.

In practice the rate of movement is so slow that I think you could go down to a few pulses a second for visual without problems.

RA is obviously the most important for me to begin with but I'd like to image and play around with guiding so should probably be conscious of the DEC axis at some point.

Looks like the gearhead stepper should fit ok, provided I don't venture too far north.

[hughgilhespie]

The geared steppers are a good solution. Bags of torque at reasonable drive voltages.

Have a look at the Accelstepper library. You can ramp the speed up and down so you get nice, jerk free starts and stops. Also makes it very easy to changes motor speeds and, as it uses floats for speed setting, you can set the step frequency to exactly what's needed for sidereal rate tracking.

Regards, Hugh

[furrysocks2]

5 minutes ago, hughgilhespie said:

The geared steppers are a good solution. Bags of torque at reasonable drive voltages.

Have a look at the Accelstepper library. You can ramp the speed up and down so you get nice, jerk free starts and stops. Also makes it very easy to changes motor speeds and, as it uses floats for speed setting, you can set the step frequency to exactly what's needed for sidereal rate tracking.

Regards, Hugh

Thanks for the pointer - I'll likely be using either OnStep or AstroEQ in the first instance, but have a tendency to get creative/destructive. I'll definitely take a look though - I'm hoping to drive an eq platform for the dob and put a motorised focuser on at least one of the scopes.

[furrysocks2]

3 hours ago, furrysocks2 said:

Looks like the gearhead stepper should fit ok, provided I don't venture too far north.

Arg.... but I can't backdrive it - I knew there was reason I was shying away from this...

Unless I can replace one of the grub screws on the coupling with a thumbscrew...

 

[Edit: scratch that, it does backdrive - just... good enough in a pinch but may see about thumbscrews at some point]

[hughgilhespie]

I have just been looking at Howard Dutton's OnStep Arduino software. Wow!!!

It's like a Good Practice Guide for Writing Really Clear Software. After seeing his code, I am embarrassed about my own efforts and feel an urgent need to rewrite everything!

Regards, Hugh

[furrysocks2]

I am embarrassed about the state of my workshop - unable to locate my flexible shaft couplers. I feel an urgent need to clear my feet and restore order.

[Edit: found]

[furrysocks2]

Thinking about how to connect my steppers, Big Easy Drivers and Arduino together.

The controllers each require 7 wires from the Arduino - direction, step, microsteppingx3, enable and gnd - and a 12V+ supply. The steppers each take four wires from a controller.

I've decided to go with RJ45 as I have a box load of patch cables and a crimp tool. I've ordered a few of these off eBay for about 50p each:

Roughly scaling the jack off the image, I think they should measure about 50x60mm or so. I expect I'll velcro them to the mount - could have gone with smaller inline sockets and started soldering wires, but these should be ok and handy for other projects and can always dremel and heatshrink them if I wanted to.
 

Having chosen my cabling and connectors, the next design choice is either:

• co-mount the controllers with the steppers;
• or co-mount the controllers with the Arduino.

If I co-mount the controllers with the steppers, I could use active power over ethernet, or could carry power separately. Active power over ethernet would require a few extra bits but would be tidy - passive power over ethernet dedicates 4 cores, so I'd have to hardwire the microstepping to reduce the number of signals between Arduino and controllers.

While the active power over ethernet idea sounds neat, if I co-mount the controllers with the Arduino, I can run the four wires to the steppers in pairs by doubling up the RJ45 cores and I've less bulk to mount on the scope itself and could replace controllers more readily if I needed to.

 

Based on all that, co-mounting the controllers with the Arduino seems like the best option - I wasn't sure when I started writing this post. Whether the housing gets attached to the tripod or a box of tricks under it I'm yet to decide, but within limits, I can extend the patch cables to the steppers to suit.

[furrysocks2]

On 07/02/2017 at 10:16, furrysocks2 said:

Roughly scaling the jack off the image, I think they should measure about 50x60mm or so.

50x57mm, quality feel, 26AWG connections internally. Should mount up on the steppers/brackets nicely.

 

Edit: shame they're beige...

[hughgilhespie]

Useful looking connectors - any chance of a link to them on Ebay. I have looked but failed miserably!

Regards, Hugh

[furrysocks2]

1 hour ago, hughgilhespie said:

Useful looking connectors - any chance of a link to them on Ebay. I have looked but failed miserably!

Regards, Hugh

PM sent.

[furrysocks2]

Stole a wee hour tonight to push this on a bit.

I should have looked out the green screw terminals before starting to solder - they have the same pitch as the outer row of holes on the drivers, would have been perfect for the motor side. As it stands, the boards are on 0.1" pitch pins to a project board, then I've patched in the screw terminals (minus center pin which is bent out the way) and then splayed slightly to match the 0.1" holes. Terminals are facing inwards because I thought I could route the 4-wire bundles slightly more neatly that way. Broke my symmetry on the blue/yellow wires by starting the whole thing one pin too far up. Soldering's not terrible, but should have cleaned the copper side of the project board off first. It's going to be a right pain if a driver pops. Bit of a dog's mess, tbh - hope it tests up ok.