Page 2 of 2

Re: Pololu Pot Tweaking?

Posted: Fri Jul 06, 2012 2:34 pm
by edwardrford
Higher current will potentially allow your motors to produce more torque. at higher speeds.

In my experience with the Pololu stuff, you need to add some active cooling if you want to get anywhere close to 1.5A -> 2.0A. That means a heat sink+ a small fan to move air through.

I would get the machine running reliable at a lower vref (~0.4), then start tweaking the power on your drivers.

-Edward

Re: Pololu Pot Tweaking?

Posted: Fri Jul 06, 2012 2:50 pm
by atanguay
I would get the machine running reliable at a lower vref (~0.4), then start tweaking the power on your drivers.
So this tweaking is reasonably safe eh?

The Pololi just shut themselves down when they overheat eh? After cooking CPUs in the past, I'm always spooked to push hot chips to do more.

Re: Pololu Pot Tweaking?

Posted: Fri Jul 06, 2012 3:27 pm
by atanguay
I found what Burke says to be exactly right after a first night of playing around with a fully functioning unit ( :D :D )

They can get hot, a fan gently blowing across them alleviates this.

After much digging I think this is normal and just needs to be dealt with. I'm thinking of making something a little more robust and 'thermally efficient' than the aluminum sinks I have on there. Maybe cut up an old copper CPU heat sink or something. I don't want my new babies to burn out.

On another note...it is SO rewarding to see the thing take it's first steps (no pun intended). After about a month of assembling and tweaking, seeing it finally work, quite well even, is really amazing.

Re: Pololu Pot Tweaking?

Posted: Fri Jul 06, 2012 4:24 pm
by levlandau2
I am using these tiny copper heatsinks from Newegg. These seem to be the standard heatsinks used for Pololus. They seem nice and are easy to work with. The copper provides best thermal conductance. They could be bigger however... Fairly cheap as well.

I guess I am going to be adding a fan, but for that to work well I first need a mount/box.

Image

http://www.newegg.com/Product/Product.a ... 6835708011

Re: Pololu Pot Tweaking?

Posted: Fri Jul 06, 2012 7:51 pm
by atanguay
I was wondering where people were getting those little copper factory sinks. :D
Thanks

Re: Pololu Pot Tweaking?

Posted: Mon Jan 21, 2013 7:47 pm
by WillAdams
Newegg is out-of-stock --- is this, from Amazon the same thing?

http://www.amazon.com/Enzotech-MOS-C1-M ... d_add_1_dp

Re: Pololu Pot Tweaking?

Posted: Mon Jan 21, 2013 8:43 pm
by cvoinescu
Yes, it's the same thing. Just a reminder: airflow, especially under the Pololu board if at all possible, is at least as effective as the heatsink.

Re: Pololu Pot Tweaking?

Posted: Sun Mar 17, 2013 5:43 pm
by levlandau2
The enzotech ones are more expensive but nice. Copper is a better thermal conductor than aluminum and the heatsinks have worked out quite nicely for me.

Re: Pololu Pot Tweaking?

Posted: Mon Mar 18, 2013 1:27 am
by ejs
CptanPanic wrote:With max cooling, and what is max you can turn pot up to? All the way?
Nope. Don't do it. One of the odd design choices from Pololu is that if you crank that pot all the way up, the chip will be getting 4 amps pumped in to it. Since the chip is designed to only handle 2.0 amps they will not only smoke, but will go out in a blaze of glory. Literally. I've been amazed at the little jet of sizzling flame that erupts when I've plugged into mains power when the pot was too high.

When you start adjusting the pot it should be turned as low as it will go--that is, fully counterclockwise. Turning it up in very, very small increments and then measuring once the screwdriver is clear. Even a turn too small to discern with the naked eye can sometimes change the voltage measurement by a twentieth or so. Ultimately, you'll never need to turn the pot past about a quarter to a third of the way. Do one driver at a time. Hook up your motor, push the driver in place, power on, tweak, power disconnect, remove driver. Once you measure where you want to be for all of your driver Pololus (0.64v for the recommended 3v NEMA 17s from Sparkfun), disconnect power, plug in all drivers--making sure to orient them correctly--and add your heat sinks. Then you can power on for real and start cutting.

Remember: overdriving motors isn't going to do you any good. There's only so much copper and it's wound with so much resistance to handle only so much wattage. Everything else is just lost as heat. But, you CAN always under drive a stepper motor if they sink is too hot. Without active cooling I've been occasionally worried when the boards were not enclosed and fanned. Dropping the measured voltage down a tenth of a volt or so does wonders and has very little effect on performance.

This little boards are so reliable once properly tuned and with a little protection from the elements. Not sure why the design allows the over-amperage issue to exist.

Source: http://reprap.org/wiki/Pololu_stepper_d ... d#Upgrades and personal experience. The link also shows corrective action that can be taken.