A RoboFocus that's cooking its self

[rogerg (Roger)]

Some may remember that my last photo posted, of NGC 3223, was accompanied by concerns that my LX200 was on the way out again. When I entered the observatory that morning there was distinct smell of hot electronics.

I've now narrowed the problem down.

The good news: The LX200 is fine.

The bad news: The RoboFocus motor seems to be cooking its self.

The other good news: Although it heats up over time, when on a fresh the RoboFocus does function normally.

I've sent a support email to RoboFocus to ask them what might be going on and see what I can do to get it fixed. I've had it running flawlessly for 5 odd years now.

The heat seems to be concentrated from the actual motor rather than the gears. After 2 hours of test-run, when I then realised it was the RoboFocus, the motor was too hot to touch, quite literally, extremely hot.

I don't expect anyone out there to have experienced this problem and hence have useful input, but thought I'd mention it in case.

Here's hoping for a speedy fix! (unlikely, considering I'll be dealing with the US and all associated postage delays etc).

Roger.

[Gama]

Stepper motors are always energised when on. And have the maximum current draw when idle/fixed.
For it to draw more current, will occur if :

1) The voltage to the motor phases has increased.

2) The phase winding(s) have shorted out (One maybe, but doubt all of them)

3) The resistor to drop the voltage may have shorted out (Some use this method to increase power to stepper motors without increasing the rated voltage of the phases)

I would check the voltages at the phases, or controller. Plus check your supply is correct. Steppers are normally very low voltage, from around 1.5V up to about 7V for common ones.

Theo

[rogerg (Roger)]

Thank you very much Theo. As it turns out I haven't received any reply from RoboFocus yet so may be needing all the help I can get soon.

While I'm somewhat competent with my multi-meter I'm not familiar with testing stepper motors. I understand their conceptual difference from a servo motor but not how to safely measure the signals going to them. I'm not going to touch the thing before I know I won't fry it, so ... do you have any advice on how to test the output to the motor? I suspect it's somewhat specific to the RoboFocus how it's wired so I may have to rely on information from them.

I have tested the power input to the controller and it's showing a correct 12v power supply.

Roger.

[Gama]

Have a sqiz of this http://www.cs.uiowa.edu/~jones/step/types.html , a little read will guide you a little better on how they work.

But just a quick one, check the supply is correct.

Theo.