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#61
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Re: Banebots RS-775 Case Short
Using a better ohm meter, although the test leads themselves have a bit of resistance (about 0.1 ohms when shorted).
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#62
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Re: Banebots RS-775 Case Short
Hey Jim,
That is one fine voltmeter ya got there. Have you tried getting it assessed on Antiques Roadshow? Oh, BTW: I think the calibration date is a bit overdue :-) |
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#63
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Re: Banebots RS-775 Case Short
I was just noticing that it was last calibrated when our youngest sons (twins) were still a twinkle in my eye...and they're in college now....
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#64
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Re: Banebots RS-775 Case Short
We got a response when we sent in an RMA request that this was a known issue and that they would not replace the motor. They simply said to apply some voltage across the case and a motor lead to burn off the manufacturing debris.
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#65
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Re: Banebots RS-775 Case Short
Quote:
As far as I'm concerned, this is not a FIRST legal motor if it conducts current to ground. Worst customer support of any FIRST KOP supplier. I hope First thinks twice before using these motors in KOP again. |
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#66
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Re: Banebots RS-775 Case Short
Our kit 775 also had 2.3 Ohms between terminal and the case on BOTH terminals, and we'd been using it off and on for a few days. We shorted the terminals to the case with the battery (one at a time) and now we're seeing 126kOhm between terminal and case on both terminals. Our other 775 that we were "gifted" from 3320 (The M&M's) had 3MOhm between terminals and case.
I was disappointed that there wasn't as much of a fireworks display as others seem to have experienced when we did it. -Danny |
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#67
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Re: Banebots RS-775 Case Short
Quote:
Yes, the BaneBots products have a few flaws. But, it's up to the designer to consider those shortfalls, and design around them. For the price, their products are great. I was quite happy to see the BaneBots motors (especially the 775) in the KOP this year, and I hope they are here to stay. Last edited by sanddrag : 20-02-2011 at 18:04. |
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#68
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Re: Banebots RS-775 Case Short
With the exception of this large design flaw, the 775-18v is a great motor that I hope we get to use again and again. The decision to include the 18v version and to run that at 12 volts was really smart!
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#69
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Re: Banebots RS-775 Case Short
We don't know yet whether it is a design flaw or a manufacturing (quality control) problem.
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#70
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Re: Banebots RS-775 Case Short
Quote:
Quote:
Dan Glenn Mentor, Team Spyder 1622 San Diego, CA |
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#71
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Re: Banebots RS-775 Case Short
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If the design is such that no reasonable (cost effective) manufacturing process would be capable of avoiding unacceptable debris, then it is a design problem. |
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#72
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Re: Banebots RS-775 Case Short
The insides look like countless other motors....but without seeing the complete design documentation, and seeing what the actual problem is, it's guesswork. My guesswork says manufacturing problem, either with the process or materials not meeting spec.
I should unwind the thing and see if there's really any debris, or if the insulation on the wire is damaged. Although it's probably gonna be hard to tell. |
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#73
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Re: Banebots RS-775 Case Short
I cut all the windings at the commutator connections. The first winding (there are 5, overlapping) is the one that is shorted. So I guess I'll take them all off and see what I can find.
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#74
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Re: Banebots RS-775 Case Short
I found the short. The first winding on the motor was touching the amature core, at this corner. I found it by connecting my trusty 77 DMM to one end of the wire and to the shaft, and it beeped until I got this part of the winding loose. It was very difficult to remove the wire here. As soon as I pulled it loose, the beeping stopped.
My take on it: I did not find any "debris" in this motor, but it also had a complete short of winding to armature core. If you have a completely shorted motor (less than 5 ohms resistance from either terminal to case), then I'd suggest you do not use that motor. If the resistance is considerably higher, then you might possibly have a "debris" problem, and if you "fix" it by blowing it with high current from case to winding, the motor might be fine. btw the white stuff is glue that is used to hold the plastic fan in place. I hope this little forensic exercise was helpful! |
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#75
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Re: Banebots RS-775 Case Short
Quote:
Here is my concern based on what you found: If this is in fact the root cause, and common to all the 775 motors showing this fault, then the "fix" is only truly is a poor solution. Here is why I say that. For the "fix" to work, the current path has to be through the terminal(s), through one of the brushes into the commutator, through the short and into the armature then finally through the bushings/bearings to the case. The current that can possibly blow this short open, also has the potential to damage the brush/commutator contact point as well as the bushing/bearing assembly. Yes, the brush/commutator are designed to carry high current, but the bushings/bearings are not. (I use the term "bushing/bearings" because I am not sure of exactly how this motor is actually assembled.) Now, if enough current is passed to open this short, then I can almost assure you that it not passing through the bushing/bearings without having a detrimental effect. How much damage is being done is indeterminable at this point. How long will these motors run without failing is also an unknown. I for one would rather replace the motor with a "known good" one, than risk it failing at the most inopportune time. |
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