VREF / Changing Stepper Voltage

Software / Firmware
1

Hello team, math question here. My motors are getting stupid hot and Im afraid I will burn them out. This is partially due to the enclosure I built, but ui am positive my voltage is outta whack.

now, now, before everyone jumps at me for this … Ive tried … Im confused … and need a sanity check. Maybe this will help another noobie out there.

So, this is what I have so far:
Control Board: RaMBO 1.4 direct from Ultimachine (Ryan was out when I first looked)
Stepper Motor: StepperOnline
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Driver: A4298SETTR-T (RaMBO 1.4
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Ive done the basic math for (Itripmax = VRef / (8 * Rs)):
Itripmax (@70%): 2.0A * 70% = 1.4A
VRef = 1.4A * (8 * 1.4ohms)
VRef = 15.68

Is 15.68 supposed to be what I change in Marlin?

2

I don’t think you want to use the motor per-phase resistance in that formula. The driver board manufacturer puts a known sized “sense resistor” in the test circuit which informs what measured voltage matches up with the desired current - that’s the value to use for Rs. I’m not running the Rambo board so I don’t have the right value in my brain, but I know it has been discussed on the forums and that the value that @vicious1 has put in the firmware is working for most folks.

3

https://docs.v1engineering.com/electronics/ultimachine/#driver-math_1

I’m getting 1600 for you, but I would see if 1300 works. You want the steppers warm, not hot. More often than not the manufacture’s spec sheet for cheapie steppers is not even close.

1 Like
4

Basically our firmware should work out of the box for you. From there you can turn it up a tiny bit if needed from the LCD if you ever experience a skipped step. You gain nothing driving them at as hot as possible. You just need them to not skip which is easier than you think.

5

16 is way too high. I think something is wrong with the Vref. (0.1 is a common one).

But at the end of the day, you just want it to be tuned for your motors and machine. You will not reach the spec limit.

If you measure the temp, keep them under 50C. That seems to avoid the plastic bending (which will fail before the motors). A little warm is ok.

6

Is the heat most likely from the enclosure then? Also, does the tube (DOM) tend to get warm also during a carve? Is there a time limit we should run the DW 660 before giving it a rest?

The firmware does work out of the box … was finally cutting chips

I will realign my center carriage and see whats up.

7

FWIW, while I’ve noticed the collet nut gets quite warm on my DW660, any where else on its body is quite cool to the touch even after running 45-60 minutes.

8

dang, might be the enclosure then… looks like Im going to have to buy a power supply unit and hook up some old PC fans to blow air in. Probably too much to try and pull from the Kastar PS unit huh?

Ill start digging into the forums. Any thoughts/advice appreciated

9

Surprised me the first time I made a fairly lengthy cut, being a plastic body I wasn’t expecting the warmth metal might have but it was surprisingly cool.