Banebots RS-775 Case Short

[Al Skierkiewicz]

OK,
Now I am really confused. I haven't taken a 775 apart. I wonder if there is winding terminations at both ends of the armature.

[ChuckDickerson]

For what it's worth, 3 of our 8 775s had a short to case. I had marked them as "bad" and was going to pitch them in the trash. After reading here about the zaping procedure I figured what the heck and gave it a try. The zaping procedure seemed to fix all three of our motors, however, we will still not be using them in competition and are considering not using any 775s at all and changing our plan to use 550s and the FP. I am pretty disappointed in BaneBots over the years and this just adds insult to injury.

Of the 3:

The first 2 sparked somewhat spectacularly both apparently from the larger holes near the back/terminal end.

The last 1 produced almost no spark at all and was only visable as a tiny (~1/16") arc when the wire touched the case. No sparks apparent coming from inside the motor.

The first one we zapped with the lights on and sparks were clearly visable even in a well lit area. For "effect" we cut the lights off on the last 2 and the first one sparked nicely and the last one was the one with almost no spark which probably wouldn't have even been visable if the lights were on. On all three it only took one zap to fix the motor. The procedure was about as simple as it gets. I took a robot battery plugged in an Anderson connector with bare wires, held the red to the red terminal on the motor and touched the black to the case. No breaker involved. For as strange of a "recomended fix" as this is it seemed to work. The second motor we did does have a slight burned black line on the case where the wire touched. Other than that no other obvious signs on the outside other than where I wrote on them with a Sharpie.

[Ether]

Originally Posted by DeepWater

The procedure was about as simple as it gets. I took a robot battery plugged in an Anderson connector with bare wires, held the red to the red terminal on the motor and touched the black to the case.

You left out the most important step:

I checked to make sure everyone in the room was wearing their safety glasses.

[ChuckDickerson]

Originally Posted by Ether

You left out the most important step:

I checked to make sure everyone in the room was wearing their safety glasses.

Yeah, and we made sure there were no flamable liquids ar vapors nearby as well.

[sanddrag]

I'm super curious as to what exactly is shorted in the first place, and is blowing apart inside during this procedure. Can someone who has some 775 spares sacrafice one for curiosity's sake?

[Nick Lawrence]

2 of our 6 RS-775s had case shorts as well. We tried the case-to-lead zapping procedure recommended by BaneBots, and it remedied the problem on both. We did have to zap one of them twice after we spun it a few times after the first attempt. I wish there was a safer way to fix this without taking them apart.

-Nick

[MrForbes]

I keep forgetting to measure ours, we just have the one that came in the kit. If it's shorted, I'll take it apart. If I remember. We happen to be kind of busy building a robot, so I'm sort of distracted when I'm at the school.

[falconmaster]

We just two more yesterday and checked them. They are both good! We have to earlier and they are good two.. I guess we got lucky

[Chris is me]

Our kit motor and one of the three we ordered had the case short. Luckily the decision was made to use a Window motor on our arm instead. The other two motors were installed on CIMulators and will be put on our drivetrain once we find some CIM keys...

I'm really hesitant to do the battery pulse fix on these motors. We'll see.

[Al Skierkiewicz]

Hey Jim, You have used that excuse in the past.

[MrForbes]

Thanks for reminding me to make a reminder for myself....hopefully I'll see it when I write some other reminder on my hand today.

[Al Skierkiewicz]

Ah, the signs of spring are in the air, preship craziness. I am off to playing field and shop for a day of fun and fluorescent light.

[MrForbes]

We got lucky, our kit 775 has less than two ohms resistance between the case and terminals. Good thing we didn't try to use it. We did not try to clear the debris with the battery trick, but did take it apart, and aside from slightly chipping the brushes while removing the end cap, did not see any debris. The windings are almost a dead short to the motor shaft (measured between shaft and commutator). Any suggestions for what to do now? Maybe we could unwind the windings? the soldering job doesn't look very good, but it also doesn't look like it would be causing problems. I took some pics but don't have means to get the pics off my camera here at school.

[sandiegodan]

I pulled our Banebot 775 apart before I read about the fix. The connection to the case is through the rotor assembly to the rotor shaft. A direct short can be read between the commutator and the shaft.

There is no obvious debris. I could speculate what happens during the "manufacturing process," but until Banebots is more forthcoming with specifics, I don't think we will really know. The rotor assembly is pressed then varnished, without extensive forensics, I would say the exact problem will be hard to get at. There are some balance holes machined out of the stack, so maybe that is the source of the issue.

After I reassembled, I applied the battery current across the terminal and case. There was a minor spark and now the motor is fine. We can't use it in competition since it has been disassembled, but it will be perfectly acceptable for practice.

If anyone knows if Banebots is replacing these it would be nice to know.

Dan Glenn
Mentor
Team 1622 Spyder, Poway High School, California

[MrForbes]

picture of armature.