mathjax

2013-11-11

Waltz Stepper Drivers: Functional Yet Noisy

After assembling one of the Waltz boards and only screwing up the the tiny driver once the board works!
There were only a few quirks in getting the board to run. A grounding issue between my laptop and the Arduino and the scope which made things flip out whenever the scope connected. Which means something isn't as well grounded as it should be, since half the outlets where I live don't have a ground that might have been the issue... connecting all grounds explicitly in the circuit fixed the grounding issue. From that point out operating the motor was pretty smooth. The board was hooked up to an arduino with modified 'blink' code to step the motor continuously in a given direction. Here's a video of the waltz board driving a stepper:

video

It worked well up to several kHz of step frequency if the step frequency got too fast the motor would just sit there and make a very annoying whining sound. The controllers were tested up to around 10A with no heat sinking or additional cooling. Using the 'will this burn my finger?' test methodology the main power fets remained cool enough up to around 6A that you could continuously keep you finger on them. At 10A they had a temperature of  'owfuckshitthathurts' after around 5s of keeping your finger on a fet, but it wasn't that 'burn on contact' kind of hot. In conclusion I should get some thermocouples/ temp sensors also the boards seem quite capable of being pumped over 10A. Once they are upgraded to D2pak FETs rather than the jankily soldered on Dpak FETs this might improved heat sinking and current capacity.

On the next rev of the stepper driver the caps are going to be swapped out so the motors can run at higher voltage. Hopefully this will push the motor PWM frequency out of the audible range. The way the A4898 does current control is a fixed off time system, this makes the output PWM of the system variable with various operating conditions such as  the voltage supply inductance of the motor and the decay rate settings on the controller. The noise and vibration also seems to vary greatly with the step frequency of the motor and the microstep settings. Motor operation seems much smoother and less noisy at increased speeds, this might be partially due to rotor inertia/velocity matching up with the commutation of the motor. There will have to be some characterization to find optimal operating points.
The motors being used are 27.4kgf*cm (381oz*in), 3.5Arms/phase, NEMA 23 hybrid steppers: data sheet. When stepping the motors vibrate enough on any hard surface to be really obnoxious, that's why the motor is sitting on a cushion in the video. 

Next steps for the millathe project will include measuring up the millathe itself sizing it for a new set of ballscrews and mounting hardware. The next set of boards needs to be designed as well as the motherboard to hold all of the smaller stepper boards.

2013-11-06

Stepper Boards have Arrived: Waltz v0.2

Woooooo the boards arrived like several weeks ago they arrived, but what ever they're getting posted about now so ...woooo stepper boards. They're all pretty n'purple n'stuff.
So far I've only assembled one and there seem to be no fatal errors on the board that will prevent it from functioning. Couple minor package errors and what not but whatever.

here's a pic of the board:
I went with purple because why the hell not?
I've been slightly distracted from the project by work. However there will be more posts soon since there needs to be board testing.

In the mean time pretty boards are pretty, but pretty useless boards are pretty useless until they are tested otherwise.