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Stepper motor driver

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Peter Bell16/10/2017 12:53:36
264 forum posts
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I'm driving a Nema 17 stepper motor driver with pulses from a voltage controlled oscillator. The motor runs fine at high speeds but when I run at slow speeds ie,20rpm the black driver keeps flashing the alarm light and the motor sounds rough, the open frame one sounds better but at slow speeds the motor makes a ticking noise.

stepper-2 .jpg

stepper-1 .jpg

Tried various switch settings for pulses/rev and current and adjusting the input frequency to maintain a low speed but no real difference in the noises.

Is this a characteristic of these cheapo drivers, am I expecting too much or are there smoother alternatives?

Peter

John Haine16/10/2017 15:58:37
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20 rpm is pretty fast for a stepper! That's 4000 Hz step rate. Or do you mean 20 Hz? Steppers do have resonances where the inertia of the motor and the reluctance torque of the magnetic circuit are close to the drive frequency, and it may be better just to avoid these speeds.

What main supply voltage are you using - and microstep ratio?

Neil Wyatt16/10/2017 16:09:36
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20 rpm is 66Hz without microstepping.

A typical NEMA 17 will run up to about 1800rpm at about 1/5 full torque.

Microstepping will be smoother BUT try changing the decay mode, at low speeds they become 'lumpy' as the inductance causes the small signals to current limit before the motor actually moves so many of the microsteps don't register. Changing decay mode should help this.

Neil

John Haine16/10/2017 16:19:07
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132 photos

Oops! Minutes, not seconds. I should engage brain...

Peter Bell16/10/2017 17:25:55
264 forum posts
123 photos

I'm on 1/8th step with 25v supply.

Thanks for the explanation about smoothing, never heard of that. Its on 100% smoothing, if I reduce it in stages the movement becomes progressivly more jerky.

It cycling between 73 and 2350hz under the control of a picaxe to the vco (4046) but that might have changed as I've twiddled!

When I set it for 1/16th steps the speed increases so still wonder if the driver is faulty?

As its a very cheap driver do they become smoother with price, notice some have 4 dip switches to set the step rate?

Neil Wyatt16/10/2017 17:59:24
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Confused - you have two different drivers in the photo, which ones are you using and can you show a photo of the dip switch settings?

A Pololu will work a Nema 17 and costs pence, but you will need to short a resistor on the board for smooth low speed operation.

Neil

Peter Bell16/10/2017 18:05:25
264 forum posts
123 photos

Sorry--the black one is the very odd noisy one and the open frame (2nd pic) ticks and seems to increase the step rate to 1/16.

Just glanced and see plenty of Pololu---like to give one a try--any particular reccomendations?

Peter

SillyOldDuffer16/10/2017 18:12:38
3977 forum posts
808 photos

Odd noises from stepper motors aren't unusual, but the alarm light is worrying.

Some possibilities:

  • Incorrect current switch setting
  • Power Supply isn't man enough, or it's a Regulated PSU that doesn't like pulsing.
  • The control pulses are mishaped or mistimed.

That type of driver is well known and I've not noticed many complaints about it on the web. I don't think it's faulty.

There are a lot of variables and it might be a combination. Can you provide more details of your set up? Circuit diagram, identity of the VCO, PSU and all the switch settings.

Dave

Muzzer16/10/2017 20:05:07
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Bit of a strange mix of technologies - digital stepper driver and (digital) micro - with an analog VCO in between. Can't you simply generate the pulses directly? It may be that the Picaxe isn't up to the job but there are so many microcontrollers about these days such as 32 bit Arduino compatibles that you shouldn't struggle to manage it.

There's a pretty good roundup of potential options on the Mickmake Youtube channel if you want some ideas.

Murray

Peter Bell16/10/2017 22:00:49
264 forum posts
123 photos

Thanks for the replies. PSU is easily coping with the current which is around 0.2-0.5a as it cycles through its sequence, pulses look good as well on the scope. Tried various current settings without much effect on the sound

Agree its a mix of technologies but a magnetic sensor clocks the shaft movement, (its a belt driven linear actuator), the picaxe counts the sensor pulses so fairly low speed and closes the loop

Its been performing quite nicely with repeatable numbers from the movement for days so dont really want to change too much, was unsure if I had faulty drivers.

Going to follow Neil's suggestion so ordered some Polou drivers to play with--is the low speed mod detailed anywhere?

Thanks

Peter

Neil Wyatt16/10/2017 22:23:43
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Posted by Peter Bell on 16/10/2017 22:00:49:

Thanks for the replies. PSU is easily coping with the current which is around 0.2-0.5a as it cycles through its sequence, pulses look good as well on the scope. Tried various current settings without much effect on the sound

Going to follow Neil's suggestion so ordered some Polou drivers to play with--is the low speed mod detailed anywhere?

0.2-0.5A is quite modest.

0.2A is about right for a Nema 17 on a 3D printer, a rotary table is a bigger load.

OK for the steppers to run warm.

Here:

stargazerslounge.com/topic/268438-pololu-uneven-microstepping-solution/?tab=comments#comment-2938666

<edit> the answer for you should be to set the decay to 0%

Edited By Neil Wyatt on 16/10/2017 22:25:50

Peter Bell17/10/2017 07:44:44
264 forum posts
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Thanks Neil, thats really good info and things to try I would never have found!

Peter

Neil Wyatt17/10/2017 08:52:49
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To be honest it took me ages to find out the solution, it made a big difference to the smoothness of my scope drive.

Neil

Peter Bell22/10/2017 08:23:44
264 forum posts
123 photos

Ordered some parts and now at the waiting stage.

Its just occurred to me that with my present arrangement the controller I use to drive the stepper motor has opto isolators for clock, dir and enable which I feed with 5v at the appropriate time and also a 5v pulse for clock.

The 3D drivers (DRV8825, TMC2100) I intend trying have no opto isolation. Does anyone have the signal levels that a 3D printer runs these drivers on especially the clock? Has anyone put a scope on these?

I'd like to avoid frying too many before I get something working!

Thanks Peter

John Haine22/10/2017 08:44:12
2414 forum posts
132 photos

The data sheet here indicates rather indirectly that the TMC2100 chip is intended to run with 5V logic levels.

Peter Bell22/10/2017 10:58:15
264 forum posts
123 photos

Thanks John, Read the data sheet a few times previously but couldnt really find any figures that applied apart from the blandish statement below

"The STEP and DIR inputs provide a simple, standard interface compatible with many existing motion
controllers".

Peter

John Haine22/10/2017 11:09:55
2414 forum posts
132 photos

Section 14 absolute max ratings: I/O supply voltage max is 5.5 volts; logic input voltage level is V I/O max +0.5 volts.

Peter Bell28/10/2017 21:38:19
264 forum posts
123 photos

Now got my TMC 2100 but I'm not having any success in making it go using the simple pulse generator I used previously. Connected as a standalone driver for one stepper motor as per the pic feeding a nice buffered 5v 274Hz square wave.

From the data sheet info below I naively hoped that all I had to do was hold dir negative, apply a pulse and it would go but dont think it as simple as that! Looks like I've got timing issues at least?

Has anyone used a driver like this as a standalone stepper driver and not on a 3D printer with all the other driver grubbins?

Thanks Peter

tmc2100 simple 28-10-17.jpg

step dir data.jpg

Neil Wyatt28/10/2017 22:18:53
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You need to make sure the 'enable' pin is held low/high as appropriate.

Neil Wyatt28/10/2017 22:20:03
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Have you got the enable pin wired up to the right signal level. left unconnected it will probably default to 'not enabled'

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