er4u - Electronics Blog

{adinserter Internal_left}No electronics lab can go for long without a robot eventually making its way in. Well, in my lab there is approx a dozen. Most are Scorbots by Eshed Robotec (Intelitek, Depco and there may be other names under which they were sold) These robots are usually rather old and by the time you get them they have been through a couple of generations of middle school students. But they were built solid and many survived, even if in need of repair. This is what this post is about So, here is how the drama played out: It took A WHILE to get this guy running. On homing attempt using ER2U controller it would generate Axis 5 homing error. For some reason assumed switched aren't working. Re-checked all switch wiring - all good. Checked homing using Controller-A homing procedure (it shows more info) - showed Axis 5 overload protection. Resettable fuse popped. Checked the motor itself - one of the windings is short. Opened motor - full of metal shavings. What the heck? Threw away (well, into reject bin. I never actually throw away anything electronic) the motor, took a replacement from a sacrificial ERIII. Replacement motor turned out to have a bend rotor axle. Tried to straighten. Sort of worked but makes funny noise, does not look like it will live long. Took another motor from an ERIII. At this point it became clear ERIII is going down - no way to find so many extra GM9413-F motors. Longer axle appears to be a custom order from Pittman. Price list is in $250 range. How would you like a single motor more expensive than the rest of the robot? Anyways, back to repair: put a replacement motor back. Tried homing - same thing! A slight difference - Controller A no longer shows overload. Checked motor #4 reasoning that Axes 4 and 5 are actually moved by synced movement of both motors. Motor OK - runs from a 12V source just fine. Must be encoder then. Checked the wiring, all good. Cross-checked ER4U and ERVPlus wiring diagrams - they show opposite polarities for encoder outputs. What gives? Swapped wires on both encoders for just in case - still no go. Went back to the docs, couple pages further they describe wiring on the 510 encoder PCB. Turns out they swapped wiring assignment twice between these two tables. Two negatives give a positive, in the end both pinouts are the same. Whew! Removed 510 PCBs again to solder the wired back in the original order. During soldering looked VERY closely at the axis 5 510 encoder PCB - one of the pins of one transistor is not soldered! Smacked myself on the head (gently), soldered the pin , closed the encoders and gave it a run. It homed!!! Searching for a problem - approx 10 man hours. Fixing the problem - instant! Oh, BTW, should I mention the robot was sold to me as "working, excellent condotion"?

er4u - Electronics Blog

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