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Unread 06-11-2003, 09:19 AM
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Victor problem

Our TechnoKat robot does not want to cooperate. I'll try to explain the situation and maybe there is someone out there who has seen similar happenings with their robot.

Our team's electrical guys have not been able to check out the problem yet, so I thought I would let you guys chew on it and give me your opinion.

We recently had a demo in Chicago where I personally blew three Victors within 90 minutes... it was pretty frustrating. It was more like a demo on how to blow a Victor (ok, kids... here comes the magic smoke!). There is a root electrical problem that I cannot find.

Here is what has happened (with some history):

1. The left side drill Victor blew at a previous demo.
2. I replaced the left side Victor, and all was well (this happened before the Chicago demo).
3. Once it started driving in Chicago, the right side drill Victor blew.
4. I replaced that Victor with one that was already on the robot (in a different spot) but not being used.
5. The newly added right side drill Victor blew. This was after it was operated successfully by itself, but it blew when the whole drivetrain was operated.
6. I replaced the right side drill Victor again (this time, stealing from one of the Globe motor Victors).
7. This newly added right side drill Victor blew again, just like the previous Victor.

So... I blew 3 Victors, all in the same place (the right side drill). With that info, you would think that the motor may be bad... but read on, it gets better.

Keep in mind that not only I was working on this, but also Darrel Noble, lead electrical guy from 71 was helping me. We both confirmed each time that we had the wires right before it was turned on.

There are a couple of things that are odd about when this failure happened:

1. When I ONLY drove the right side, by itself, it worked fine.
2. The Victor would blow when I drove both the left and right sides together.
3. When I pulled all of the 40A breakers, except for the 1 that had the blown Victor, I would push the right joystick forward and backward. The robot would not move (since the right Victor was blown, of course), but the far left Victor's light would light up. Darrel thought that it was from the motor acting as a generator, but the motor wasn't moving!
4. Looking back to the last time that the far right Victor blew, it happened when I had the right joystick about 1/2 way and the left at full throttle.

I seriously think that there is some odd electrical leakage between the far right victor and the far left victor. The far left victor is getting some sort of power or signal when the right victor is being told to move. This could lead to the cause of this problem.

My first suspicion is that there is some sort of short in the 40A breaker bar. Somehow, voltage is being leaked between these two Victors. When only one is actuated, they both work fine... but when both are being driven, one of the Victors is fried.

I have not taken a voltmeter to the 40A breaker bar... that is probably my next step.

I'm tired of wasting $115 Victors. We blew 2 at Championships, 1 at a previous demo, and now 3 more, for a grand total of $690. Something is seriously wrong. Help!

Andy B.

Last edited by Andy Baker : 06-11-2003 at 09:22 AM.
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Unread 06-11-2003, 09:34 AM
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Jeff Waegelin Jeff Waegelin is offline
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Your suspicion of the 40A breaker box sounds like a good place to start. It looks like you've covered most of the rest of the electrical system, and that block is one of the few parts that can't be easily visually inspected. It's possible that there's a defect in your 40A block. I would definitely look at that first, Andy.
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Unread 06-11-2003, 09:37 AM
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*Ouch.

If you have checked your wires for any "extra" grounding and everything seems fine - you proally should break out the Mulitmeter. Try to check the PWMs too - see if the computer is freaking out too?

Sorry - I don't know what to make of this problem. When we fry something it's b/c of an "extra" ground that the robot thought it should have.

Hope this can start a huge help thread!
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Unread 06-11-2003, 11:23 AM
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Warren Boudreau Warren Boudreau is offline
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If you want to rule out the 40amp breaker bar, re-wire the speed controllers to the 30 amp breakers on the other breaker panel. The motors will run with the 30 amp breakers, they'll just trip more often.

Your note about the left controller lighting up when no breaker was present is strange. Have you considered swapping out the motors? Or disconnecting the PWM inputs?
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Unread 06-11-2003, 11:29 AM
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Just for more data, what was the robot doing when the Victors blew? Driving along in a straight line? Turning? Is dynamic breaking on? Perhaps sudden speed reversals from one victor cause some huge voltage spike and it's leaking back to the right one, perhaps in reverse polarity? I don't know if thats even possible.

Perhaps replacing the other Victor that's lighting up could solve it.

This is just odd, Victors seem pretty sturdy. So its probably a big voltage spike or some how it's getting reverse polarity.

Do you plan on contacting IF? I suspect they would be very interested to hear about this...

-Andy A.
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Unread 06-11-2003, 11:49 AM
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Andy,

One or both of your motors may be shorting to frame internally. It's also possible that a motor has a shorted winding. In either case, this would cause momentary shorts as the motor is rotating which would cause high voltage spikes when the rotor moves past the short.

High voltage spikes will certainly kill the IGBT drive in the victors but not right away (it's cumulative damage to the silicon substrate). If so, it's hard to "logically" tell which side is causing the problem.

High voltage and current spikes will also create EMI noise which you also seem to be seeing.

I have never seen this on a FIRST system but I have seen it on larger motor drives we use at work.

I would replace both of the motors.

That's my best scenario...

The only other idea I have is that a wire's dielectric insulation is breaking down (either to chassis or to another wire) between one of the Victors and the motors. However, this is not very likely (we use 300V wire).

Good luck!
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Unread 06-11-2003, 12:49 PM
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My best guess is your MaxiBlock (40A) is defective. Maybe file shavings in there or something. That would easily create the problems you are having. Did you try replacing it at all? Either that or try opening it up.

There must be a short in the system for that to happen.
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Last edited by Jnadke : 06-11-2003 at 12:52 PM.
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Unread 06-11-2003, 03:33 PM
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I would look to the motors myself. Not sure how a short in the fuse holder wouldn't either trip the 120A breaker or the 40A itself, and only cause a problem when you are applying a signal to the motor, and the same motor for 3 victors.
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Unread 06-11-2003, 09:13 PM
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Is this possible?

I know this does not exactly fit all the facts, but it may explain some of them and you may think back and revise your telling of the story after you think about this possibility.

Could you possibly have the motors wires such that you have the M- sides of the motors flip-flop (M- from the right Victor is hooked to the wire from the LEFT moto lead and M- from the left Victor is hooked to the wire from the RIGHT motor lead?

How about haveing the M+'s flip-flopped?

In either of these cases you may get some strange results that could blow your Victors depending on the phase of the two chopped motor pulses.

The H-bridge has some diodes to dump the current from the motor when the motor is acting like a generator (say when you let off the joysticks rapidly).

I am thinking that if you have the H bridges confused you may be bypassing some of the protective diodes.

As to why always the right side, could it be that you always were turning the same way during your demo?

I don't know if I am just making this up or if I am on to something, but it you can check it out in any case.

Joe J.
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Unread 06-11-2003, 11:24 PM
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We've had odd shorts on occasion. Don't know if this is what your problem is. But, this is what I would check.

Shorts from the Victor to case (in this case the robot). We've had shorts from the Victor mounting screws to the M+ lead. We now use plastic mounting screws.

We've had shorts from the drill motor drive wires to our cooling shroud and thence to our case.

So, I would recommend to perform an insulation resistance test between M+ and robot case and M- and robot case. I would do this for all speed controllers and relays, just in case you have a really weird ground path.

If you're getting shorted windings in your motors, you can check the no-load current. If that has gotten really big (10 Amps), I would replace the motors. It could be that your motors are drawing a lot more current than they did at the beginning of the season. I doubt if this would cause the problem you're observing. But, it might aggravate another problem which has been present all along but hasn't manifested til now.

You should be able to check for shorts between the ports on the 40A breaker.

Since you've already blown a bunch of speed controllers, I would recommend against swapping parts out before finding the problem. It might be worthwhile to pull the offending motors, speed controllers, etc off the robot and try only those bits. This would remove the possibilty of sneaky ground paths.
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Unread 06-14-2003, 10:57 PM
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Andy,
Sorry I didn't make it to the Sensor Expo, work and union business has kept me busy the last two weeks.
As you have stated, it is not uncommon for the lights on a Victor to come on when the motor is driven particularly when selected for braking mode. (This occurs even if the breaker is pulled.) Since that is one of the conditions and you are sure that the motor is not being turned then the other motor is the one that is back feeding. I will bet that the motors are cross wired, possibly in the M- leads or there is a high resistance connection from the two Victors back to battery common. I know that there was a lot of gear crud coming out of the transmissions at Nationals and that may have made it's way into anywhere as well.
Did the Victors fail as they were in Houston? i.e. one or more of the 12 power transistors exploding? My feeling is if only one blows it's case off or if three side by side are destroyed, there was something conductive in the controller. If transistors on opposite sides of the controller blow, then there may be short in the wiring or a defective brush assembly. (Remember that the new drills have notoriously bad brush parts and I have seen some where the brush holder(s) move out of alignment and touch the body of the motor bearing housing. If a wiring error caused something to come in on the motor leads, i.e. +12 volts to M- when the motor is directed to drive forward, you might find one or two transistors in a string fail and it would always be the same string.
As a last resort, check the +5 volt line at the RC. It may have failed and is high, causing failure of the PWM input. This is pretty unlikely though, unless a 12 volt source was backfeeding through the PWM cable to the RC. I wish I could have got a look when you were here.
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Unread 06-23-2003, 09:02 AM
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I'm not the electrical guy for my team but, I think I might know the problem that you are having. I would first change all of your pwm inputs to the speed controlers. Then I heard our electrical engineer talking about puting spikes after the speed controlers to prevent large voltage spikes.I would then try that and if that doesn't work just rewire the whole darn thing. P.S. if you wold like to pm our electrical team leader his address is ark 1230
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Unread 06-23-2003, 02:16 PM
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Um as far as I know, spikes, or relays are used simply to turn things on or off, such as the compressor or rotating light, not to control voltage spikes... But I know little about electronics, so I could be wrong

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Unread 06-23-2003, 02:29 PM
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Quote:
Originally posted by dddriveman
I'm not the electrical guy for my team but, I think I might know the problem that you are having. I would first change all of your pwm inputs to the speed controlers. Then I heard our electrical engineer talking about puting spikes after the speed controlers to prevent large voltage spikes.I would then try that and if that doesn't work just rewire the whole darn thing. P.S. if you wold like to pm our electrical team leader his address is ark 1230
I'm not sure that this would be legal under FIRST's rules, particularly with respect to wiring a spike after a speed controller.

I'm otherwise useless to this thread, but I have to say that it's probably among the best I've read in a long time. I've never seen all the "Really Smart People" get together at once like this.
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Unread 06-23-2003, 03:37 PM
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like i said i'm not the elwectrical guy. I just heard our electrical engineer argueing about it with our electrical team leader. Sorry about that.
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