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Help needed finding stepper driver
« on: June 18, 2007, 11:19:27 AM »
I have two Step-Syn 2.5V 2.1A and two Step-Syn 4.5V 1.8A
All of them is unipolar (6 wires)

It will only be a 3-axis but if it's a 4 axis driver it won't be a bad thing unless it costs a lot.
I want the driver to be as cheap as possible but better expensive than crap.
I have a driver that goes from 5v and up but it's whole step only and won't work for the other two.
I would like atleast half-step to get better accuracy and faster travel.

The rest of the table will be made from bits and peaces in a scrapheap sort of way. Nothing professional. Will be mostly for wood but also for metal.
As it looks now it will be able to work on a 80*80 cm area. It will be screw based on all 3 axis, that is if I can find some. It will be interesting none the less.
And you can expect it to be fully documented in realtime. (aka SLOOOOW)  ;)

Offline Chaoticone

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Re: Help needed finding stepper driver
« Reply #1 on: June 19, 2007, 09:37:19 AM »
Lots of stepper drivers to choose from. Maybe someone will give you some suggestions.

Brett
;D If you could see the things I have in my head, you would be laughing too. ;D

My guard dog is not what you need to worry about!

Offline stirling

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Re: Help needed finding stepper driver
« Reply #2 on: June 20, 2007, 04:29:50 AM »
Apologies if I'm teaching granny to suck eggs but note also that your six wire unipolars can be wired as 4 wire bipolars if that helps your search. I use Geckos.

cheers

Stirling
Re: Help needed finding stepper driver
« Reply #3 on: June 25, 2007, 08:54:40 AM »
Thanks.
I asked HobbyCNC if their driver would work with these stepper and they said it would.
http://www.hobbycnc.com/hcncpro.php

I feel the extra money put into the pro would be justefied by the idle current reduction and extra protection. Am I right on this?

Are their any other drivers that I should choose instead?

Should a ATX PSU suffice as powersource? I have pleny of those.
I have quite a few capacitors as well so it can be buffered with about 1 farad. Not that I think it would need that much tho.
I can also make something around 24V if that's better.

Offline stirling

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Re: Help needed finding stepper driver
« Reply #4 on: June 25, 2007, 11:00:49 AM »
well I've never used these so I wouldn't like to comment on them specifically.

These are unipolar drivers, i.e. only half of each phase of your motors will be powered at any given time. Given that your motors are not the most powerful anyway - you'll get more power out of them driving them as bipolars with a bipolar driver.

Idle current reduction is a moot point. A lot of drivers offer this facility. Upside - you pay less to the electricimy man. Downside - your motors could be forced to "freewheel" (dependent on your screw pitch). i.e. not as much power holding them steady - chances are this would really only be of use when the machine is idle or for the Z axis when cutting 2.5D but you could find your Z axis wandering - ouch nasty.

An ATX power supply in my view would be no use at all - particularly with your 4.5V 1.8A motors. you'll need to give them much more than 12V for any sort of real power at speed. Taking your 2.5V motors into account I'd be looking to experiment somewhere around 50 to 60V. Unregulated supplies are the mutt’s nuts for stepper motors.

1 Farad - wow...
Re: Help needed finding stepper driver
« Reply #5 on: June 25, 2007, 11:36:20 AM »
I have test run one motor at slow speed using a cheap full-step driver (one coil at the time) and at about 10 Hz and lower I have no chance in the world stopping it. (this was with the 4.5V 1.8A) And that is with slightly lower current than rated. I don't think that i could load it that much that it starts to move at 50% current. I thought that Z would be slower anyway so that would not be a problem.

Are you saying that the motor will need a lot higher voltage than rated to get the current the same as low speed when running higher speed?
The driver has the input of 42V maximum and 12V minimum. I thought I would need to go as low as possible so that the steppers would not take harm.
The steppers are 9.5cm wide(round) and 6cm long so they are not small.

I know. I have a bunch of capacitors. Most big ones ony go up to 15V tho.

Offline stirling

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Re: Help needed finding stepper driver
« Reply #6 on: June 25, 2007, 12:48:13 PM »
Not sure what you mean by "one coil at a time" but anyway, I'm sure your motors appear fine at low revs (do you mean 10 revs/sec or 10 steps/sec by the way?).

Steppers develop torque in inverse proportion to their speed. I only ever use bipolar chopper drives and with these at least, anything around 20 times a motors rated voltage is normal - nay required (with LR drives this may not be the case - I don't actually know). When I first started building these things I remember experimenting with 2.1A 6V unipolars using an LR type driver and an AT power supply and at any useful speed the torque was useless.

regarding your Z moving slower, well maybe - depends how you choose to  gear it and whether you're cutting 2.5D or 3D.
Re: Help needed finding stepper driver
« Reply #7 on: June 25, 2007, 01:30:56 PM »
It's 10 steps/sec

With unipolar steppers you can use one coil or two coils at the time.
the HCNC pro board is 114$ including SH for a 4 axis driver.
Do you know of any orker driver in that range.
Unipolar motors can be run as bipolar wich is about the same as running the unilpolar with two coils at the time. The only difference is that you connect the coil in parralel when using two coils and in series when using it as bipolar.

I don't expect great speed out of it.
I can't get a lot of speed out of it with that driver as the current drops rapidly when running fast. But with these drivers it might work. I have read that the steppers should be good for around 2kHz (2000 steps/sec) If it gets that high sped will no longer be an issue. If it does half that I would be happy.
The 2.5V id 1.8*step and i think the 4.5V is 2.2*step. Not sure about the last one.

If you know any relativly cheap bipolar driver, I have a few more steppers that was used in a printer to move the printerhead back and forth. As far as I know they are pretty strong and might work for something else.

Offline stirling

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Re: Help needed finding stepper driver
« Reply #8 on: June 25, 2007, 02:59:41 PM »
thanks for the lesson on unipolar/bipolar... ;D

I guess I've come to the end of what I can say. I havn't come accross any other driver for that price so maybe it's worth a go.

Re: Help needed finding stepper driver
« Reply #9 on: June 27, 2007, 04:42:54 PM »
I have spent the last few days reaserching for my CNC project and found this thread about a bipolar driver.
http://cnczone.com/forums/showthread.php?t=33756
I will put the HCNC driver on hold as this looks far more interesting.
HCNC seems like a less and less good alternative due to some posts I have read.
Gecko seems like the way to go for quality but they are pretty expensive.

http://pminmo.com/ Has a lot of info about this sort of stuff.