Re: Banebots RS-775 Case Short
 

You're welcome.

The motor uses oilite type bushings, it looks like they're plenty large enough to conduct a lot of current without damage. I'd be more concerned about the brushes and commutator than the bushings. But I would be even more concerned that "fixing" a shorted winding will melt the wire and open it, so the motor will only be running on 80% of it's windings.

I looked closer at the armature, and I think the issue is that the wire was making contact at a corner of the winding, where it wraps around the core. The green insulating paint is deformed where some of the windings contact it at the corner, and in one spot metal was showing. I think that either the paint was not fully dry, or the wire was pulled too tightly as it was wound on the core.

I've enjoyed taking stuff apart ever since I was a little kid. I think it's part of the engineer mentality.

Re: Banebots RS-775 Case Short
 

This is worth a test.

And if it comes back that that's how the fix works—by severing a winding—then BaneBots should damned well have disclosed that fact. (Not knowing is negligence, not an excuse. I want to give them the benefit of the doubt: maybe their supplier was lying to them about the presence of debris, or maybe this one motor is not representative of the failure mode that they'd encountered. But if BaneBots came up with the fix, it's their responsibility to explain the issue and resolution accurately and completely.)

I don't know the nature of BaneBots supplier arrangement with FIRST;* if they're donating the parts for free, or heavily discounting them, then I understand that we shouldn't ask too much of them. But if FIRST is a paying customer, I think that it would be reasonable to forward BaneBots a summary of the motor rules, with the explanation that all FRC teams are very strictly limited as to what they can and can't do, and that if BaneBots wants to do business, they need to provide somewhat better service. (Aside: actually, I support the idea of being able to repair parts in principle, so the recent team update was a good result. There are too many high-value or high-lead-time items that can fail and seriously disadvantage a team. As long as it's clear the repairs don't rise to the level of a significant functional change, I'm on board.)

This is not to minimize the impact of the corrective actions BaneBots has taken in the past with regard to their products—I'm sure that resolving those issues was stressful and complicated, not to mention costly. But the fundamental flaw those times was misspecification: for example, they hadn't provided accurate information on how to safely use the gearboxes. (Granted, in the case of the bad CIM boxes, if they'd done so, they wouldn't have sold any for drivetrains, because they would have had to publish specs indicating their parts were unlikely to be up to that task.)

In fact, let's consider the problems associated with BaneBots products in FRC applications (am I missing or mischaracterizing anything?):

• 2007: Failures reported on BaneBots high-reduction planetary gearboxes (36 mm & 42 mm sizes); BaneBots has since updated their specifications to warn against high-torque load cases, and released new lines of gearboxes that are apparently more durable
• 2007: BaneBots CIM gearboxes with defective planet carrier plates; BaneBots designed replacement (more durable) carriers
• 2009: Without advising purchasers, BaneBots substituted RS-545/RS-385 motors that didn't match the ones depicted on their website (listed as FIRST-legal), and more importantly, were different from the RS545PH-5125F model in the KOP; never explicitly resolved, but hopefully never happens again (we never found out what the specs on the plastic-endcapped RS-545 motors were)
• 2011: RS-775 motors are frequently defective as supplied
• 2011: Lead times of up to 3 weeks on some gearboxes

So what's the root cause here? Want to bet that it has something to do with not testing their products adequately for FRC applications? And maybe there's some unfamiliarity with just what they're being asked to provide, as an FRC supplier—e.g. have enough stock of the right motors (or be able to get them fast), and communicate with FRC HQ when your supply chain breaks down (instead of trying to pass off non-compliant materiel, or delaying shipments). (It's possible that FRC HQ hasn't communicated these expectations, perhaps because they see things differently; if that's the case, I'm interested in their position on the matter.)

Part of being in business is managing inventory and deliveries—and while it's a company's prerogative to choose to keep low inventory and impose long lead times, it's their customers' prerogative to not choose that company the next time they have a critical project. Similarly, while their low prices are great, I'm certain that the majority of FIRST teams are willing to concede that a little extra cost to ensure quality in a critical component like a motor or gearbox is a good thing. After all, isn't that a big reason why AndyMark products are so popular, despite their often-higher prices? (Along with excellent service and innate familiarity with FRC.) Isn't that why people will pay $25 to $28 for a CIM motor that virtually never fails?

Maybe BaneBots needs to concentrate on being a little more like AndyMark or IFI, or else consider taking a step back from their current role as a critical FRC supplier?

*Why don't I know this? Is there really any harm in disclosing this fact? After all, the benefit of disclosure is that it calibrates the community's expectations.

Re: Banebots RS-775 Case Short
 

Another bright side: They don't sell airplanes :-/

BTW - the one's we used the ZAP fix on do not perform as well as the ones that tested OK. Anyone else notice a performance hit?

Re: Banebots RS-775 Case Short
 

Yes, our programmers have commented on that fact as well.

Re: Banebots RS-775 Case Short
 

Do you have any quantitative data, or is this mostly a perception ?

Re: Banebots RS-775 Case Short
 

Is there anyone who has access to a function generator or an oscilloscope who would be willing to test the locked-rotor inductance (and resistance) of a few "fixed" and non-defective RS775's ?

http://www.chiefdelphi.com/forums/sh...ad.php?t=90246

Re: Banebots RS-775 Case Short
 

A picture of what I suspect is the problem with the motor I disassembled.

Notice the "dents" in the green insulating paint at the corner of the armature core, where the wire wraps around it. There are two places where the metal is showing through. The wire is insulated with a thin coat of some type of paint also (in the old days, it was varnish, I don't know what these ones use). It doesn't take much to scrape the insulation off the wire, and have it short.

Re: Banebots RS-775 Case Short
 

Jim,
Thanks for all the CIS on this motor. As Jack pointed out, my next question (assuming all of the motors have a winding to core short) is does the fix burn open one of the winding? In his case it seems as if it does. In your original photo, I also noticed a solder blob buried in the windings. That is a pretty bad job no matter what. Every student on my electrical team can do a better job than that.

Re: Banebots RS-775 Case Short
 

Al, I expect that motors with a low resistance short have the problem I encountered, and it's likely that applying a lot of current will melt a wire. But I have no idea if there are other things wrong with other motors. I only had one to take apart. There are a lot of things that can go wrong when building an electric motor within strict cost constraints.

Re: Banebots RS-775 Case Short
 

2 out of 3 bad for us...any chance the company actually tests their motors before they ship them out now??? Not comfortable with the "fix" if it reduces the performance as has been seen with some cases.

Re: Banebots RS-775 Case Short
 

IDK - Why test? They don't care what they sell us. I ordered two for spares and specifically asked for two that tested infinite resistance between leads and case. They sent two that tested 56k and 32k.

I will NEVER do business with them again!!

Re: Banebots RS-775 Case Short
 

Jack, et al,

There is not a motor in the world which will pass that criteria.

Most of us spec out motors to a specific criteria form a recognized approval agengy (such as UL) called a Dielectric Withstand Test. The parameters for such a test would be that the device withstand a voltage (such as 2 times the rated maximum voltage plus 1000V) with less than a specified current (such as 1 mA) for a specified time (such as at least 60 seconds).

But we aren't buying UL listed motors, are we? We are using motors that are factory seconds or discontinued items that have been donated (or sold at a deep discount) to FIRST.

I'm not defending Banebots. This case shorting issue is not acceptable. However, you get what you pay for.

BTW, please check with your electrical lead mentor before attempting a DWT as you need specific test equipment and the test degrades the insulation being tested.

JMHO,

Mike

Re: Banebots RS-775 Case Short
 

I realize you get what you pay for. The problem is we really have no choice when FIRST limits the brand/model and number of motors and the brand with the most choices has such poor quality product. We don't mind paying more for better product...just wish we had the choice to do so.

Re: Banebots RS-775 Case Short
 

Just as long as paying more doesn't involve $30 tetrix motors that are even worse...

Re: Banebots RS-775 Case Short
 

Well, we paid $5000+++ to enter a competition that limits us on what we use to certain items. I'd prefer it if those items weren't faulty. Just sayin'