Author Topic: Ward indexer - Pololu DRV8825 Stepper Motor Driver  (Read 1114 times)

Offline PekkaNF

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Ward indexer - Pololu DRV8825 Stepper Motor Driver
« on: February 11, 2018, 01:41:19 PM »
This indexer:
http://www.worldofward.com/rotarycontroller

Bought some years ago and finally got to order keypad and other parts.

Took a little time to fiqure out how to konnect the keypad. Layout was correct, but rows are inverted.

My problem is that the rotary controller seems to be working right and I can measure that all pulses comes out fine from it but the stepper motor does not rotate.

The stepper driver and motor are small, but I want to test the indexer completely, before I comit building the mechanics and rest of the system.

Pololu DRV8825 Stepper Motor Driver Carrier:
https://www.pololu.com/product/2133

This circuit:
https://a.pololu-files.com/picture/0J4232.600.png?f2f6269e0a80c41f0a5147915106aa55

The Ward rotary controller seemst to work fine. PSU for it is 12VDC galvanically separated switched mode powersupply. The linear regulator makes +5VDC. GND is connected to stepper controller GND.

The Pololu stepper controller receives +5V to RESET ja SLEEP pins.
FAULT-signaali is +5V all the time.

Motor current is adjusted to 1A:


PSU to stepper controller is repurposed laptop brick (16VDC/n.7A). Bulk capacitor is 100uF.

I haven't connected or disconnected anytjing with power on.

Nothing heats up, but the stepper bridge is floating, it does not feed the stepper, no matter what I do.

Am I doing something fundamenttaly wrong?

Pekka

Offline John Swift

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #1 on: February 11, 2018, 03:10:46 PM »
this is what I would do for my initial tests

once its working the stepper driver enable can be connected to Steves indexer
and the mode inputs M0 to M2 re wired to set the desired micro step


John


Offline PekkaNF

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #2 on: February 11, 2018, 04:49:40 PM »
Thank you. Enable et.al. have pull-downs, but when I scoped them, I found some HF-componenet.

I ditched ungrounded PSU (12 volt one, that was feeding rotab indexer) and supply both of them from single 16V lap top PSU. That solved the problem.

Stepper is working now and I can shift my interest on mechanics. I need a bigger stepper and some bits to hook stepper on harmonic gear.

Pekka
« Last Edit: February 18, 2018, 04:31:59 AM by PekkaNF »

Offline chipenter

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #3 on: February 12, 2018, 02:55:16 AM »
Insted of a larger motor you could gear down the drive , I have 100 steps per degree with a small motor .
Jeff

Offline PekkaNF

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #4 on: February 12, 2018, 03:47:48 AM »
That looks pretty nice.

The gear I have is 1:50 harmonic drive. It has a coupling for 8 mm shaft, therefore I'm very much inclined to buy a stepper motor with 8 mm shaft and then stepper motor drive to suit.

I don't have a worm gear, but if I could find a worm wheel that clears 40 mm shaft and fitting screw I would fit that into lathe. I can think many ocasions that lathe chuck index would have been really nice to have.

Pekka

Offline philf

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #5 on: February 12, 2018, 04:02:15 AM »
That looks pretty nice.

The gear I have is 1:50 harmonic drive. It has a coupling for 8 mm shaft, therefore I'm very much inclined to buy a stepper motor with 8 mm shaft and then stepper motor drive to suit..............

Pekka

Pekka,

I'm jealous of your 1:50 Harmonic Drive. My 4th axis uses a 1:200 Drive so, however fast I try to drive the stepper, it moves very slowly. With 1/8 microstepping it does give me 0.001125 degree resolution!

Phil.
Phil Fern
Location: Marple, Cheshire

Offline chipenter

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #6 on: February 12, 2018, 04:11:30 AM »
Made the worm and wheel , it's only ER16 collet chuck driven by Pllolu shield and Arduino .
Jeff

Offline PekkaNF

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #7 on: February 12, 2018, 08:22:45 AM »
Those brass gears are pretty!

There is a small difference on fouth axis and indexer. Speed is a secondary consideration to me.

I am torn between ER32 collet for the stepper (need to build the whole taper part) and small three jaw chuck. I need to consider that tightening of the ER32 collet to nominal torque might be more than that harmonic drive is designed, on the other hand, ER collet would most likely produce goog enough centering for most of the time.

I am inclined to use full step mode (200 steps per revolution) together with 1:50 gear. That should do most of the time.

Pekka
« Last Edit: February 12, 2018, 11:01:34 AM by PekkaNF »

Offline chipenter

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #8 on: February 12, 2018, 08:33:33 AM »
On a small stepper motor less than full step dropes a lot of the power , and droped steps are still counted giving some strange resultes . 
Jeff

Offline PekkaNF

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #9 on: February 12, 2018, 11:04:37 AM »
Made the worm and wheel , it's only ER16 collet chuck driven by Pllolu shield and Arduino .

Can you elaborate bit more arduino/program and that Pololu hardware?

Pekka

Offline philf

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #10 on: February 12, 2018, 12:08:08 PM »
Those brass gears are pretty!

I am torn between ER32 collet for the stepper (need to build the whole taper part) and small three jaw chuck. I need to consider that tightening of the ER32 collet to nominal torque might be more than that harmonic drive is designed, on the other hand, ER collet would most likely produce good enough centering for most of the time.

Pekka

Pekka,

My 4th axis has a Myford spindle nose to take 2MT collets or a chuck or a faceplate. The spindle takes a c-spanner to counteract the tightening torque but there's still a risk of damaging the harmonic drive. What I should have done (and it probably won't be too difficult to retrofit) would be to fit a split clamp to prevent the spindle rotating whilst tightening or undoing any attachments.



Phil.

Phil Fern
Location: Marple, Cheshire

Offline PekkaNF

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #11 on: February 18, 2018, 04:45:41 AM »
Thank you Phil.

That is a problem I have to consider too.

I got a Chinese driver from the mail and proceed to test that one.

Tehnical spesification claims it's perfect:
https://www.banggood.com/TB6600-Upgraded-Version-32-Segments-4A-42V-5786-Stepper-Motor-Driver-p-981997.html?rmmds=search&cur_warehouse=CN

But when I cross referenced the spesicication and TB67S109AFTG data sheet I noticed that word "upgrade" is very missleading and they have kept overly optimistic TB6600 numbers there to attract noob buyers. I don't even go trough the mistakes, it's all lies.

Anyway I got it, hookes it up to 16VDC/7A PSU and signal generator. Motor is NEMA 17 1,7A 200 step model.

Motor sound sick, moved erratically and hardly any moment on any mode. Also the motor current was all over the wall.

The front cover DIP settings have something wrong, I don't think same settings produce differet current limit.

Also motor connection differes on PCB and cover.

Found that current sense resistors had cold solder on the other end and unsoldered from the other end. Also the capacitors were pretty much unsoldered.

Pretty sure it was completely untested.

Offline chipenter

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #12 on: February 18, 2018, 11:17:02 AM »
Ive bought two TB6600 from Bangood no problems , but had a problem with Arduino megga board complained and they sent me a new one , just had to wait tree weeks for it .
Jeff

Offline JHovel

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Re: Ward indexer - Pololu DRV8825 Stepper Motor Driver
« Reply #13 on: February 19, 2018, 10:44:41 AM »
.....
Pretty sure it was completely untested.

There is no Chinese word for testing....

Actually, it is more complicated and sad than that: when Chinese workers find a fault on the production line, they are indeed required to report it so that things can be done to fix the problem. However, that means invariably 'dobbing in' a person up the line - maybe your best friend working next to you. The person who made the mistake then gets their pay cut to pay for the amount of their labour on the dud parts. So everyone keeps their mouths shut and passes the dud parts along the line as if nothing was wrong.
Until there is a change in attitudes of making people responsible for removing dud parts from the production line without either incriminating someone or the person who made the mistake being trained better instead of losing pay, there will be no reliability in quality of Chinese products... That will take another generation I'm afraid.
What would you do if you were working on the production line in China today????
Cheers,
Joe