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penguino88
09-07-2013, 06:14 PM
I'm running into an interesting issue with a new MX-64, and wondering if anyone has any ideas as to what's going on.

I am able to communicate with the motor for about 10 seconds and then it just drops off and goes completely unresponsive. It doesn't respond again until I do a power cycle, which gives me another 10 seconds.

I'm using USB2Dynamixel and have tried with both the Dynamixel Wizard and my own code (which both work fine with other Dynamixels). I've tried different USB2Dynamixels and restoring the firmware a few times, but nothing seems to change the behavior.

Any ideas?

tician
09-07-2013, 06:35 PM
How big is the power supply you are using? I have had serious problems with AX-12 responding unreliably (or not at all) using a 12V 0.4A SMPS during a bit of 'quick and dirty' testing a while back (did not have access to the usual 12V 5A SMPS).

penguino88
09-07-2013, 07:20 PM
Currently I'm using a 12V 12.5A Mean Well power supply. I was running some other Dynamixels on the same supply, but removed them once I needed to troubleshoot this.... so it's just the MX-64 on the supply now.

jwatte
09-07-2013, 08:48 PM
Do you have an oscilloscope? Are you seeing any drop in voltage on the TTL bus after the 10 seconds?
It may be a damaged input buffer on the Dynamixel TTL bus, lowering the hold-up voltage and input impedance, to the point where it doesn't work.

penguino88
09-08-2013, 08:22 AM
I was thinking it might be something like this. I'll have to wait until I'm back in the lab tomorrow to check with a scope.

A quick question: I am using the 4-pin version, over RS-485, should I check both data lines at the same time or does that matter?

And then the final question, if it is a damaged input buffer am I going to need to send it back to Robotis for repair?

Thanks so much for your responses, I really appreciate it!

jwatte
09-08-2013, 02:29 PM
I don't have experience with the RS-485 on the Dynamixels, but measuring both lines would be the right thing to do. When idling, they should have a small bias offset; while communicating, the signals should be clearly differentiated by 5 Volts. Given the necessary pull-ups and terminations of the RS-485, more things could be wrong than with the TTL bus, but when working, RS-485 is more robust.

If it is a damaged buffer chip, yes, Robotis will be able to replace the PCB for you. It may be covered under warranty if conditions are met; else there will be some cost (but not nearly as much as the cost of replacing a motor!)
I know that Tyberius used a hot-air rework gun to de-solder and replace his buffer chips when they died (they are SMD parts) so if you have that level of equipment and training, that could be an alternative.