Buggy BAG Motors

[pfreivald]

Originally Posted by IndySam

The only valid test is to run it for a good while several times.

Right-o. The first thing we did was test the resistance through the windings as we turned the output shaft very slowly, to see if there was a dead spot. The second thing we did was put them on and run them over and over again...

...then we played nine qualifying matches with them with no problems...

...then they exhibited the behavior we saw on our practice robot during autonomous in 2/3 of our quarterfinal games -- including our ability to fire the disks immediately in teleop after giving the robot a bump against the pyramid.

Bad timing, I guess. When we get to Buckeye we're replacing them with other motors, and shipping these ones (as well as the other bad ones) back to IFI for analysis.

[thefro526]

Originally Posted by Kevin Sevcik

Hopefully today. Heh. On account of there's this Lone Star Regional tomorrow and the 3D printer is at work and all...

I could draw it myself, but I don't have the parts available to check fits. Speaking of, what did you guys print this on? A commercial printer, or a Reprap derivative?

Kevin, I hope you were able to download the files successfully.

The spacers were printed on a Fortus FDM 400mc (Large, not that it really maters) from ABS-M30 Material. Technically the machine is 'Production Grade', but I'd imagine just about any printer could knock these out. Worst case would be that the printer doesn't hit the required accuracy - IIRC, the spacers out of the Fortus ran something like +/- .002 - so you might need to sand or tweak the parts a bit for a good fit.

[AdamHeard]

Originally Posted by thefro526

Kevin, I hope you were able to download the files successfully.

The spacers were printed on a Fortus FDM 400mc (Large, not that it really maters) from ABS-M30 Material. Technically the machine is 'Production Grade', but I'd imagine just about any printer could knock these out. Worst case would be that the printer doesn't hit the required accuracy - IIRC, the spacers out of the Fortus ran something like +/- .002 - so you might need to sand or tweak the parts a bit for a good fit.

Not criticisizing you for choosing to 3d print these, but for teams reading wanting to make similar parts, they could easily be turned on a lathe out of plastic really fast.

[thefro526]

Originally Posted by AdamHeard

Not criticisizing you for choosing to 3d print these, but for teams reading wanting to make similar parts, they could easily be turned on a lathe out of plastic really fast.

Adam, you're right. In the white paper post, I mention alternative methods of making the more simple of the two spacers, the most obvious of which being to turn them down on a lathe. I'd imagine that some .75" OD, .5" ID ABS Tubing would do the trick - turn the OD down to .745" (18.9mm) or so and open the ID up to .515" (13.1mm) and you should be good to go. At the time, printing them was both more cost effective (made 7 spacers using $1 dollar or so of ABS) and more time friendly. (~30minutes total)

[Kevin Sevcik]

Originally Posted by thefro526

Kevin, I hope you were able to download the files successfully.

The spacers were printed on a Fortus FDM 400mc (Large, not that it really maters) from ABS-M30 Material. Technically the machine is 'Production Grade', but I'd imagine just about any printer could knock these out. Worst case would be that the printer doesn't hit the required accuracy - IIRC, the spacers out of the Fortus ran something like +/- .002 - so you might need to sand or tweak the parts a bit for a good fit.

Post was up in time, I was late. Working too late to finish up a project so I can play tomorrow, no time to warm up the printer and all that. It's a Stratasys uPrint. We rarely run it, so printing something is the involved process of booting and warming it up and reloading the material* and all that. By the time all that's done, even the smallest of parts takes an hour to print. So no spacers for me at LSR. If it's a problem, I'll print some out for Alamo.

*Thou shalt always unload the support material when not using the printer. And store it in an airtight bag. Otherwise it absorbs moisture and doesn't work worth crap. Some co-worker learned us that one, printing something and leaving the machine loaded. I found out several weeks later and it was already too late.

[sanddrag]

Originally Posted by Kevin Sevcik

*Thou shalt always unload the support material when not using the printer. And store it in an airtight bag. Otherwise it absorbs moisture and doesn't work worth crap. Some co-worker learned us that one, printing something and leaving the machine loaded. I found out several weeks later and it was already too late.

We've only experienced this problem on our Dimension SST 768 with a VERY old cartridge. We've had cartridges in for 6 months and been fine. Should we be really be removing it and sealing it in a bag every time? I feel like that's too often.

[Kevin Sevcik]

Originally Posted by sanddrag

We've only experienced this problem on our Dimension SST 768 with a VERY old cartridge. We've had cartridges in for 6 months and been fine. Should we be really be removing it and sealing it in a bag every time? I feel like that's too often.

Depends on the cartridge, I'm sure. I don't think the Stratasys uPrint ones seal very well. Also, I live in Houston, a highly urbanized swamp. I just know a reel of support material was sitting in the machine for close to a month, and the next time I tried printing with it, all I got was bubbles.

[wilsonmw04]

Greetings,
Our team decided to use a bag motor for our shooter connected through a versa gear box modified to a 1:1 ratio. It experienced the same issues mentioned previously in the thread: one would not start up when required and another would run a varied RPM's. It is rather frustrating, honestly. We will be removing all bag motors from our robot until the reliability improves. I now think that all vex motors are suspect. Has anyone experiences these issues with the "mini cims?"

[Dale]

Has anyone experienced problems with the recently shipped BAG motors? In other words was this just a bad batch? If I get replacements from VexPro is that likely to solve the problem?

[sdcantrell56]

We just had the last of ours fail at peachtree this past weekend. Fun times. Especially trying to center a 550 in the mounting plate with as much slop as it has. Vexpro should look at including a centering ring similar to what dustin designed. Even a temporary thing just to align them.

[wilsonmw04]

Originally Posted by Dale

Has anyone experienced problems with the recently shipped BAG motors? In other words was this just a bad batch? If I get replacements from VexPro is that likely to solve the problem?

These bags were from two different orders. One from the KOP and the other from an order shipped 2 weeks ago.

[CalTran]

Team 2410 competed with three BAG motors that we ordered somewhere around week 3 or 4 and, as far as I could tell, we did not experience the symptoms of a buggy bag motor.

[Richard Wallace]

Our robot has three BAG motors: two that drive lead-screws that power our chin-up arms, through 20:1 VersaPlanetary gearboxes; and one that drives our scoop-store-shoot mechanism's tilt control, through a 100:1 VersaPlanetary gearbox and 3.6:1 VEX 20dp gearset, for 360:1 overall ratio. The tilt is back-driveable, and the leadscrews are not.

So far we have not seen any of the failures described in this thread. I have spoken and emailed with Paul a few times about the issue, and believe that his team is diligently pursuing a solution.

BTW, several other things on our robot have been stressed to failure already. The BAG motors have gotten very hot several times, even emitting smoke once or twice, but are still working well. After the drive team reported seeing smoke I took the motors off and measured free Amperes, still normal.

I like the BAG motor design for power and thermal robustness -- my personal theory is that the root cause of the failure mode reported here will ultimately be found to be an armature production process, either winding tension or commutator tang crimping, that is not properly controlled.

[AllenGregoryIV]

We finally had two fell this past week, after running one through the entire lone star regional and a lot of practice before that with out problems and it's replacement. It's only been our back shooter motor in the 3:1 VP that has failed, the front motor that is in the 1:1 setup has not had an issue. The initial replacement motor failed rather quickly after less than 100 shots. We replaced it with another and it has been running fine through two days of heavy practice.

[Dale]

We finally had two fell this past week, after running one through the entire lone star regional and a lot of practice before that with out problems and it's replacement. It's only been our back shooter motor in the 3:1 VP that has failed, the front motor that is in the 1:1 setup has not had an issue. The initial replacement motor failed rather quickly after less than 100 shots. We replaced it with another and it has been running fine through two days of heavy practice.

Was the replacement motor thaqt failed after 100 shots a recent one from VexPro or one from an earlier batch? We're trying to decide if we can trust BAG motors fresh from VexPro or go though the pain of swapping them out.

Like you, our initial shooter wheel was going through a 3:1 transmission and failed. We replaced it with a MiniCIM which works fine but, of course, weights a lot more.