myFocuserPro2 stepper motor choice ( again - sorry !)

[JAS]

26 minutes ago, upahill said:

Nice bracket @JAS Is it homemade? My mounting for the PG was too large and bulky and pushed the motor out too far causing some balancing difficulties.

Something like this could make me reconsider keeping MFP2 instead of getting the ZWO EAF (and save £200)

Thanks Upahill.

 I am a sheet metal fabricator, I made the bracket from stainless steel at work.

[adyj1]

3 hours ago, upahill said:

Nice bracket @JAS Is it homemade? My mounting for the PG was too large and bulky and pushed the motor out too far causing some balancing difficulties.

Something like this could make me reconsider keeping MFP2 instead of getting the ZWO EAF (and save £200)

This is what I find the hardest part of doing the stepper motor focus control - how am I going to mount it? (on an Altair Astro ED-66R) 

Ady

[RolandKol]

in worst case scenario, if you will fail to get the metal one - https://www.thingiverse.com/thing:1406126

Or, you can buy PC sheet sample from ebay and cut it to fit Nema17 bracket. Not sure about PC sheet thickness needed, probably around  10-11mm

https://www.ebay.co.uk/itm/2-3-4-5-6-8-10mm-Clear-Polycarbonate-Lexan-Makrolon-Palsun-Sheet-Cut-To-Size/303204464096?hash=item469864f5e0:m:mQ9df_e9GkOxFQvQ8wHduNg
 

https://www.ebay.co.uk/itm/Mounting-Bracket-for-Nema-17-Stepper-Motor-Geared-Stepper-CNC-Hobby-3D-Printer/392165008194?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

Edited September 22, 2019 by RolandKol

[JAS]

8 hours ago, adyj1 said:

This is what I find the hardest part of doing the stepper motor focus control - how am I going to mount it? (on an Altair Astro ED-66R) 

Ady

Yes the bracket can be a pain.

There is quite a good choice of standard metal L brackets available from B&Q, Screwfix , eBay. I have used different ones in the past and cut and drilled them to suit. I have also used two L brackets bolted together.

The real challenge is working out how to fix it. Google is your friend, search for your scope and things like diy focuser and more often than not you will find several approaches that people have come up with.

Jason

[adyj1]

Thanks  for the tips ☺ 

Ady

[Dr_Ju_ju]

For my ED 80, I printed the motor housing (Nema 17 PG27), which just bolts onto the end of the focuser, replacing the 'normal' knob...

[adyj1]

4 hours ago, Dr_Ju_ju said:

For my ED 80, I printed the motor housing (Nema 17 PG27), which just bolts onto the end of the focuser, replacing the 'normal' knob...

Not sure what you mean - do you have any pics please? 

Thanks 

[Astro-Geek]

My myFocuserPro2 project is almost finished, (pics coming on here soon 🤓).

I've made quite a few mistakes along the way, and my latest one is not thinking about the gauge of cable needed between the controller and the Nema stepping motor.

I've finished my brackets and had my first trial run on my various scopes actually turning the focusers, rather than just running the motors on the bench with no load.

I was disappointed to find that the un-geared Nema needed almost all of the Crayford focuser's tension to be released before it could move it.  I tried adjusting the preset on the motor driver board, but it had little effect, other a certain point giving on/off in actually making the motor step.

The situation with my 27:1 geared Nema 17 was even worse, where it was clicking, but not turning the shaft at all.

I think my problem was my re-purposing an old RS232 extension cable that I used to connect the Nema to my control box.  I cut the female connector off, tapped the 4 pins to be used to find their colours, and cut the others off.  This gave me a nice and neat ready-terminated DB9 male plug, but the fully wired pre-made lead had very thin cores, only intended for rs232 data signals, rather than Nema stepping currents.

On checking the Nema's specified current consumption, it appears to be up to 2 amps. which needs approx 18 awg conductors, a lot meatier than the hair-like conductors in my 232 lead.

To be continued......................................   (when Amazon deliver my 18 awg 4 core flex and DB9 connectors !)  👀

[Dr_Ju_ju]

to connect to the motors, I just use standard RJ11 4 way connectors \ standard flat telephone cable, never had any issues....

[Astro-Geek]

Telephone cable 24 - 26awg is rated at approx half an amp, so as long as it's fairly short, I guess it's sufficient for the motor pulses.

The 9 core shielded RS232 cable that I was using was way thinner than that, and about 6 feet long.  I would guess that its current carrying capacity was about a 20th of an amp.

I thought about using RJ11 connectors myself, rather than the DB9 (rs232 style) 9 way connectors that Robert specified.  Meade used them on my 10 inch fork mount, to connect the Dec motor, so they must have quite a good current capacity.

[RolandKol]

11 hours ago, Astro-Geek said:

The situation with my 27:1 geared Nema 17 was even worse, where it was clicking, but not turning the shaft at all.

Just some thoughts/comments which may be completely irrelevant.

Presumably if all wiring was done correctly, usually, it is caused by the incorrect current value on the driver, or maybe you were on 1/32+ steps mode.

For  steps modes 1/16 and higher, you will also need a TL Smoother module, - I have installed it to check how it works on 1/64, - and all works fine, but in this case, yes, it is ACTUALLY VERY SLOW, - steps are almost in nanometer values!!!!  

[Dr_Ju_ju]

15 hours ago, adyj1 said:

Not sure what you mean - do you have any pics please? 

Thanks 

This is what I mean :

 

And for completeness, the full drive controller  (Note that the PCB layout is my own design, using Robert Browns circuit):

 

 

[Astro-Geek]

7 hours ago, RolandKol said:

Just some thoughts/comments which may be completely irrelevant.

Presumably if all wiring was done correctly, usually, it is caused by the incorrect current value on the driver, or maybe you were on 1/32+ steps mode.

For  steps modes 1/16 and higher, you will also need a TL Smoother module, - I have installed it to check how it works on 1/64, - and all works fine, but in this case, yes, it is ACTUALLY VERY SLOW, - steps are almost in nanometer values!!!!  

All thoughts/comments gratefully accepted !! 👍

I've checked the wiring several times, and everything else on there seems to be working correctly, (LEDs, LCD, manual stepping, beeping etc..)

Amazon have now delivered the DB9 connectors and the 18 AWG 4 core wire and I've made up the "2.5 amp" capacity connecting lead.

The non-geared Nema 17 now works ok, stepping the focuser at a reasonable speed and without faltering.

I'm still having problems with the 27:1 geared Nema 17 though.  When I disconnect it from the gearbox, it is turning at about the same speed as the non-geared Nema (as expected), but with the gearbox connected, it's incredibly slow, even at "full steps" and "fast".  I haven't had the patience to time it, but it would take several minutes to complete one revolution.  It seems far too slow to be a practical speed to turn the focuser knob.

************************

After today's mods and tests, I've just re-read Robert's comprehensive documentation and I'm now confused about the wiring of Nema 17 motors. 

The various documents and drawings of the myFocuserPro2 seem to vary in the red and green connections between the motor and the motor controller board.

They also show variations between the non-geared Nema17 and the Geared Nema17.

I've attached  a composite image of the various references to highlight the differences.

So now I'm wondering if my veryyyyy slow stepping of the geared Nema is due to the fact that it should be wired differently ?

 

 

 

[upahill]

You can check the coil pairs with a multimeter, its possible that they are wired with incorrect or just different colouring, I know the ones for my CNC were.

Could it be a step size issue in the settings, I dont have mine set up to check but I know in APT i was having to set a much larger step size so that each time I pressed the movement button it would actually do something. Just throwing ideas around though as I cant check anything and its been a while

Also the DRV8825 to have a adjustment pot on them which needs to be checked/adjusted to suit the motor.

Edited September 23, 2019 by upahill

[RolandKol]

my experience, was hit and miss with PG27 wiring, even official scheme from supplier was wrong, - as Upahill mentioned, I was made to check resistance per each coil to find the pairs and experiment, to get them right.

[Astro-Geek]

I've just tapped out the connections, and I'm even more confused now.  🙄

The 27:1 geared Nema has 29 ohms resistance between black and green, and 29 ohms resistance between red and blue.

The non-geared Nema has 2.5 ohms resistence between black and green, and 2.5 ohms resistance between red and blue.

So the coils appear to be the same colours on both motors, contrary to the diagram on page 129, (albeit for a different controller).

Also, I'm confused at the big difference in resistance, a factor of ten to one.

The geared motor had an amperage of 0.4, and the non-geared was 2 amps. So iw ould have expected a differnce in resistance of only five to one.

The specs for the two motors are:

---------------------------------------------------------
Nema 17 Stepper Geared Motor 27:1 Planetary Gearbox 0.4A

MPN:     17HS130404SPG27
Full Step Angle:     0.067 deg     
4-Wire Bipolar
Nominal Rated Input Voltage:     12 V, 24 V     
Resistance per Phase:     30ohms
Actual Rated Input Voltage:     12-24VDC

Holding Torque     3Nm
Rated Current/phase     0.4A
Inductance     34mH±20%(1KHz)
Gearbox Type     Planetary
Gear Ratio(Exact Gear Ratio)     26 + 103/121
Efficiency     81%
Backlash at No-load     <=1°
Max.Permissible Torque     3Nm(425oz-in)
Moment Permissible Torque     5Nm(708oz-in)
Shaft Maximum Axial Load     50N
Shaft Maximum Radial Load     100N

 

-----------------------------------------------------------------
Nema 17 Stepper Motor, Longruner Stepper Motor Bipolar 2A

38mm Body 1.8 degree with 1M 4-pin Cable.

 1.8 degree step angle (200 steps/rev.)

 64 oz.in (45Ncm) Holding Torque.

5mm shaft

[RolandKol]

your resistance measurements are equal to the datasheet.

as you noticed, - your wiring is not yet correct, so spend some time to connect coils properly and I am sure you will be happy with the speed and holding torque.

keep in mind, once you will be adjusting current on the driver, - do not give too much, go with minimal current which allows motor to move properly, - otherwise motor will start heating very fast... same with drivers, - they tend to heat a lot also. Overheated driver will send incorrect signals and motor will start skipping steps.

[Astro-Geek]

Thanks for the responses on this, much appreciated.

I've been tinkering with it since and as far as I can see, the connections are correct, with the same wiring as the non-geared, the coil pair colours appear to be identical.

I tried reversing the red and green, but nothing moved, so I've now wired it back the same as the non-geared, and it is stepping correctly, though still with the same very slow revs on the PG27.

The non-geared Nema works perfectly, all of the stepping modes, coil power on, coil off etc..

The PG27 also steps correctly, (stepping modes etc..) but one rev in 90 seconds.

The only thing I've noticed is that the steeping speed (slow/medium/fast) has no effect with either motor, so does that mean I may be stuck in slow mode ?

Also, the step size is not enabled on the controller, and it is currently set at 50.00.

[Astro-Geek]

Here's my testing setup... 🤓

[RolandKol]

why don't you adjust step size properly on the controller? 50 vs 5000 is a huge difference....

[RolandKol]

P.S.

just checked my app settings. not sure which settings you been talking about...
the below, are mine for PG27

 

P.S. not sure what may cause unresponsive speed setting... It should work if all correctly set up

Edited September 23, 2019 by RolandKol

[upahill]

Am I right in thinking that if you are testing with the same step size on each motor, then for every movement the geared motor will be turning 3.35 degrees, whereas the regular one will be moving 90 degrees. That would make it appear an awful lot slower.

As RolandKol mentioned those drivers are very sensitive to over-current, and can get quite erratic when overheating. They also have a tendency to let out magic smoke if even slightly overpowered.

[Astro-Geek]

My "Extra Settings" is a drop down menu, and the step size seems to be fixed at 50.00, and is "not enabled"  ??

[RolandKol]

1 minute ago, Astro-Geek said:

My "Extra Settings" is a drop down menu, and the step size seems to be fixed at 50.00, and is "not enabled"  ??

Extra settings work once motor is disconnected

[Astro-Geek]

1 minute ago, upahill said:

Am I right in thinking that if you are testing with the same step size on each motor, then for every movement the geared motor will be turning 3.35 degrees, whereas the regular one will be moving 90 degrees. That would make it appear an awful lot slower.

As RolandKol mentioned those drivers are very sensitive to over-current, and can get quite erratic when overheating. They also have a tendency to let out magic smoke if even slightly overpowered.

I've been mindful of the overpower/overheat warnings, and I keep feeling the motor and the heatsink in the drv8825, and neither are getting warm, let alone hot.