TechZone Stepper Controller Trimpots

Does anyone know a good way to adjust the trimpot on the techzone remix stepper controllers without connecting up a motor? The pot doesn't seem to have an end (i.e. I can turn it endlessly in either direction), and I'd like to determine the minimum current setting without potentially frying anything.

I've read elsewhere in the forum that you can hook up a multimeter and check the voltage as you adjust the pot. I tried this, and ended up with the same voltage no matter the adjustment (didn't actually send any signals to the board when I tried this). Should I be attempting to measure current instead? I was afraid to do this without the motor attached. Can I read the value of the thing from the software without connecting a load?

Is there a way to tell where the endpoints of the pot are by looking at it?

Thanks.

D'oh, I haven't seen, touched or bought the electronics, but I'd guess from here it looks like you might have a bad pot. Sometime the little itty-bitty parts are rated for only a few cycles. (Toggle switches on a circuit board are something else that comes to mind. They're pretty scarce nowadays because jumpers blocks have got to be cheaper and more reliable)

Do you have any soldering skills? Is there a warranty?

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My blog's Reprap feed: [blog.markbova.com]
I'm currently working on a stock Mendel build with a Seeeduino Mega and four Pololu A4983 stepper controllers.

Yeah, these pots are a bit of a pain to use. As far as I can understand, they don't have any mechanical start or end location. I haven't searched much more about how these types of pots work, so someone who knows this stuff should probably be talking about that part.

As far as I can tell on my steppers, the pots work almost like this. (Of course the values could be upside down and mirrored, but it won't matter).



The green dot in the picture marks the part I use to determine where to turn the pot. It's a bit difficult to see, but the pot is slightly sloped, and the green dot point to the highest part of the slope. Also, there are some small notches on that side. The position in the picture is what the boards came like from tech zone electronics, and I use this as a "base" for future adjustments. Turn to the left you decrease the voltage, turn to the right, you increase.

It's very sensitive though, so do only tiny adjustments of about 5-10 degrees at a time.

Did this make any sense at all?

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-Nudel
Blog with RepRap Comic

Yes, that made perfect sense - thank you very much. Did you adjust yours as suggested on the wiki (start from low position and adjust until the motor moves), or did you use some other method?

Glad to help I started out with the position like in the image I posted, which I interpret as 50% or middle position. The extruder motor needed to be turned down a bit to turn at all. The different axis worked fine, but they struggled now and then so I turned them up a bit to ensure smoother flow.
If the motor gets very hot or make funny sounds, you might want to turn it down a bit.

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-Nudel
Blog with RepRap Comic

What's the "middle" position is heavily depends on the motor you have. The lower the motor's resistance, the lower you want to adjust the trimpot. Mine have 1.53 ohms and run best at 15 to 20 degrees measured from the low point. If I'd put the trimpot at where the picture shows "50%", the stepper motor driver would already overheat.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

The position of the pot sets the current, so it depends on the current rating of the motor, not its resistance. I.e. if you set it to give say 1A it will give 1A regardless of the motor's resistance.

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[www.hydraraptor.blogspot.com]