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I Need More Motor Torque

Posted by martinprice2004 
I Need More Motor Torque
April 03, 2010 03:36PM
I am having trouble driving my work platform on my home made CNC/rapid prototype machine.

I'm using an Arduino Mega, EasyDriver 4.2 and stepper motors from Zapp automation. The axes tend to stutter and stall even when turned up to the maximum. I run them froma 12v motor supply.

Are the Easy Drivers limiting my motor torque as I believe they are rated to only 0.75A? would the Pololu drivers give me more power at my motors? The motors are rated to 1.68 Amps (I believe they may work best at 2.8 Volts). They don't get hot at all leading me to believe they are not recieving enough power.

Motor Specification Here

Would lowering the voltage make a difference?

Anything else I could try.
Re: I Need More Motor Torque
April 03, 2010 06:16PM
you need more current. try the pololu drivers IF you're prepared to heatsink them properly- see my blog for a way that works.

lowering voltage won't do anything at all with current-limited drivers except reduce your top speed

Wooden Mendel
Teacup Firmware
Re: I Need More Motor Torque
April 03, 2010 07:16PM
Here's a web page post by the guy who designed the board:


He mentions a adjustment pot, did you turn up the current?
Re: I Need More Motor Torque
April 03, 2010 07:33PM
Of note: Someone has successfully built a Mendel with those same Stepper Motors, so it definitely points to the electronics.
Re: I Need More Motor Torque
April 03, 2010 07:41PM
my motors have almost identical specifications, and mine get quite hot when being driven by my pololu controllers. they have heaps of torque, although I don't have enough of the mechanics built to see what they're like doing actual printing work.

Wooden Mendel
Teacup Firmware
Re: I Need More Motor Torque
April 04, 2010 07:46AM
I have turned the pots up to maximum and they still were not giving enough torque.

My machine does use lead screws and plain bushes, so is not exactly the same as a reprap, but the mechanism is quite free running.

Late last night I rewired my electronics to supply 5 volts as opposed to the 12V and to my surprise the motors seemed to work much better and didnt miss a beat until I put the axis feed right up.

I agree with Triffid Hunter that this shouldn't work in theory but it did for some reason. I'm a little confused as to why. Perhaps the current limiter on the board is affected by the higher 12V supply.

There is a 3.3V on a PC power supply (On the floppy disk connector) so I may try that one to see if it improves things further. I don't really need this now though as the torque with the 5V supply now is quite acceptable for my needs.

The trouble with the EasyDriver boards is that there is only one + voltage pin. This supplies the board electronics and the power to the stepper.

Edited 1 time(s). Last edit at 04/04/2010 07:51AM by martinprice2004.
Re: I Need More Motor Torque
April 04, 2010 08:05AM
The torque required is determined by the mass and static/rolling friction of the system.

Might want to try starting and stopping your machine at different points, could be that certain elements of the machine are not square and as a result the machine is effectively jamming.
Re: I Need More Motor Torque
April 04, 2010 09:40PM
Are you running the steppers all off the same +12V supply?

It could be that you're drawing too much current for your power supply at +12V, and you have more current available on the +5V rail. That said, if you draw too much current, the PSU should really shut down, but not all PSU's have decent over-current protection.

Note: A lot of PC power supplies have multiple +12V and +5V rails (2 or 3 usually for +12V in your average PSU, though sometimes more), and each can provide a set maximum current. Usually, the combined current rating of each rail is what is listed as the total current for the +12V output, which can be misleading, as you can't simply draw all that current out of the one rail.
Re: I Need More Motor Torque
April 19, 2010 07:56AM
I have my machine more complete now and got the software fully installed. The axes are fairly free running, but not ideal. The torque supplied by the motors and easydriver boards is still proving to be a problem however.

The easy driver boards are Micro8 stepping, which is also I believe may reducing the torque.

My power supply is only an old 250 watt supply, but the problem occurs even if I drive just one motor.. I'll try a different 400 watt power supply and report back if there is any improvement. The motors are still stone cold when running, but the driver chips do get hot.
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