Can This Motor Be Saved?

VEX V5 Technical Support
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V5 Motor pretty much died and I have no idea why. I took out the cartridge and the actual small white gear driving the cartridge won’t turn at all. Took the whole thing apart and didn’t really see any anomalies, although when I tested the motor via the brain (while exposed) the motor produced a burning smell that probably is unhealthy to inhale.

20201209_205416
20201209_2054163024×2045 2.72 MB

20201209_205403
20201209_2054032320×3269 2.89 MB

20201209_205344
20201209_2053443024×2065 2.69 MB

Although there are visible black marks on the white gear, there is no structural damage to the gear itself; it should be able to drive the cartridge just fine. It does not spin at all when given power from the brain or by hand.
Is it possible to save this motor, or should I just use a new one?

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almost certainly kaput.
when the problem isn’t in the cartridge, there’s very little you can legally do to salvage motors.

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that motor is seized, you won’t be able to save it. the bin or an art project are probably the best place for it now.

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There could still be usable parts in this motor.

First of all, you can disassemble this motor further. Take a look at the hi-res pictures of V5 motor internals: Pictures of Internals of V5 components

4032×3024 1.62 MB

You need to unscrew a couple of more small screws and then remove backplate to get access to motor mounting screws. Once you unscrew them you can disconnect the motor from PCB.

There could be several issues with v5 motors - broken brushes (of the brushed internal motor), overheated and burned out h-bridge chip on PCB, or a smart port burned by static electricity.

If the problem is is with the motor and not the PCB, then you can put it in the spare parts bin and later reuse it by swapping out a PCB zapped by ESD.

If you shake the motor and hear a rattling sounds inside it - then there is definitely a mechanical issue with that motor. Take a look here: Broken V5 Motor... Again - #5 by jack202020

2592×1936 1.92 MB

You should definitely swap this motor with another working one and see if ether motor or PCB still work.

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But note - swapping or modifying any internal components will render the motor illegal for use in VRC.

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Well, you let out the magic smoke…of course it won’t work anymore… :upside_down_face:

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correct, it would be illegal

but who’s going to know? is it really morally wrong to repair it to its initial condition instead of spending another $40?

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“Knowingly violating a rule and hoping no one will notice” is not a great strategy, and it could be construed as violating the code of conduct.

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One definition on “integrity” is to do what is right even if nobody is watching or you can’t get caught. Loosing one’s reputation for integrity will cost you much more than $40 in the long run.

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I think you two are misunderstanding me. I’m not arguing that you should knowingly break the rules, im saying it’s a silly rule in the first place

Modifying motors is unfair, we all agree that that’s wrong. But repairing them to their initial working condition- there’s nothing inherently wrong with that in my eyes, regardless of what the manual says. I’ll still follow that rule, sure- I have enough motors to not have to worry about that- but not everyone does, and I think it’s silly to restrict simple repairs that consequently limit certain teams.

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You aren’t giving yourself any competitive advantage, and in my opinion, the spirit of the rule is not for preventing repair, especially when it is replacing a motor with another motor from VRC. Of course, I’m not a GDC member, or even a competitor at this point.

For some teams, $40 is a big amount, and I don’t think any reasonable person would hold it against a team to replace a legal broken motor with a legal motor from another legal v5 motor.

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Hello!
Still new to this, not an electronics guru, just a “shadetree mechanic” type who got drafted into this from teaching history, because I’m a “shadetree mechanic” type…

Anyway - I’ve got a V5 motor that just quit on us one day during practice. The red LED at the port doesn’t light up, the brain won’t detect it, nothing - tried on different ports and brains - nothing.

No idea what’s really happened, but here’s what I did, and what I noticed: after taking it apart and looking very closely at the circuit board, I noticed something - on the “elevated” part of the circuit board, there are two very small rectangular black components, with silver ends on the narrow ends. On the board, they are labeled “FB1” and “FB2” , Each is just to the left of where each power lead to the motor is soldered to the board. FB2 has some white discoloration on the surface, which can be scratched off with my fingernail. My instincts are telling me that this component has overheated or shorted, and burned out - but I’m not trained in solid-state electronics, so I don’t know for sure.

My questions: does anyone have any idea what happened to my motor, and can it be fixed?
What IS “FB2”, and what does it do?
Is FB2 my problem? If so, where does one get a replacement?
Am I being too anal about trying to save $50 for my school team?

Thanks to all!!

FS

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Old thread I know, but I still don’t understand this. How does mixing up legal, identical parts between legal motors make the motors illegal? It doesn’t modify the motor any more than simply disassembling and reassembling it. There’s no innate, unseen bond between the various components of a motor that differentiates them from any of the thousands of their identical copies, so I don’t see how it could possibly be considered modification.

Google says FB generally stands for “Ferrite Bead”, and that they generally behave similarly to inductors. If I had to guess with the motor light not turning on at all, it’s possible that the DC motor itself is shorted internally. You could try swapping it with a motor form a known good motor (at the slight risk of damaging the good DC motor) and seeing if the board powers up. If it doesn’t, then it’s probably some component on the PCB, which IMO is going to take way more time than its worth to reverse engineer and fix. That is, unless you enjoy such projects, in which case please post your findings here on the forum, I’d love to know more about the motor electronics!

You could try calling up VEX support and explaining the situation to them, if the motor was purchased not too long ago they might be likely to send you a replacement for free. Otherwise, I’m afraid you’ll have to buy another motor.

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According to the VRC Q&A, it doesn’t matter if you modify the motor or not, simply disassembling it past its “user-serviceable” stage (the cartridge) is actually illegal, apparently. Basically, the motors aren’t supposed to be disassembled that far.

Screenshot_20210429-184836_Chrome

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The quote is

Any further disassembly, modification, replacement, removal, or re-purposing of the V5 Smart Motor is neither an intended design of the motor, nor an intended design challenge in the VEX Robotics Competition, and would not be legal.
What parts of the motor and motor cartridge can VRC teams modify? : Robot Events

The question is asking whether it is legal to use a motor in such a disassembled or modified state on a robot, not if it has been disassembled at any point in its lifetime. The GDC’s point was that they don’t want people removing, modifying, or using elsewhere random parts of the motor on their robots, not that it is illegal to loosen a few screws then put them back in.

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However, it also states that “The intent of points “c” and “d” exist to point out that certain parts of VEX motors were designed to be user-serviceable, and servicing those parts is legal.”

More importantly, “servicing those parts is legal”. Servicing implies any sort of handling, meaning if you were to replace the internal gearing at all (even if it’s identical) then it would theoretically be illegal.

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There is a dual context present. First yes, the GDC is saying that it is legal to replace the cap and standoffs of the motor with identical replacements, as it always was, even before the rule clarification.
The second context is that they also say that since the cap is designed to be user serviceable, it is permissible for VEXU teams to actually fully remove it and manufacture their own.
https://www.robotevents.com/VEXU/2020-2021/QA/611

Finally, take a look at the last sentence in the above answer:

Modifying, removing, or custom-fabricating (such as via 3D printing) V5 Smart Motor Caps would not be legal in VRC.

By your own interpretation, this answer would mean that it is illegal for VRC teams to at any point remove any cap from any of their smart motors if they wish them to remain legal. This cannot possibly be what the GDC meant, so the only logical explanation is that the GDC’s wording is meant to apply to the state of motors that are on robots in matches, not to the entire lifetime of the motor.

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I definitely agree that in terms of its functionality and performance, a motor cobbled from the ‘good’ parts of various broken motors should be no different than a never-broken, unambiguously legal motor (assuming that the cobbled-together motor was reassembled correctly, etc.).

That said, the test isn’t whether a motor is functionally identical to a new one - the test for R22 is whether the motor has been “altered from [its] original state in ANY way”. R22d spells out pretty clearly what this means for V5 smart motors:

(emphasis mine)

Swapping out internal electrical or mechanical components of a V5 motor (other than the cartridge) is clearly not any of those things. Additionally, if you have a motor that’s not working due to some broken internal components, and you swap out those components such that the motor now works, I think it’s pretty clear that you’ve made a “modification” to that motor, even if the replacement parts are identical to the parts they replaced before they were broken.

I do think there’s a reasonable case to be made that assembling motors from the functional components of various broken motors should be allowed. But in terms of the rule as currently written I don’t think it is.

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I would like to disagree that it is illegal or unethical to open up V5 motors for servicing (like lubrication) or swapping out identical, VEX legal, parts between two defunct motors to make one working unit.

We could guess with high confidence that the reason GDC put that text in the Game Manual was to address the issue of some teams cheating by shoring out overcurrent protection PTCs in the old 393 motors. And that they issued a blanket “no modification” rule because they didn’t want to go into a rabbit hole of interpreting “no modification that gives you unfair competitive advantage” language.

As they like to say VRC ethos is about learning STEM without cheating. And the fair repair, by swapping out VRC legal components, perfectly fits such mission of learning, without violating the spirit of no cheating.

The only advantage you gain by repairing your own motors and learning how they work and fail would be that you will become a better engineer.

I guess, you are talking about the components in the top left part of the motor PCB:

V5motorBoardRTs
V5motorBoardRTs2384×1852 1.1 MB

And, as @sazrocks said, those are likely ferrite beads connected like in this diagram (source) to supress EMI noise from the brush/commutator contact bounce of the DC motor.

ferrite-bead-motor-protection

If you suspect that FB2 acted more like a “Fuse Block” than a “Ferrite Bead” you can, first, unplug the DC motor from PCB and then try to spin it by hand.

If it spins easily and doesn’t feel like something rattles or is broken inside, then you can measure resistance between its terminals and, if there is no obvious short, try to connect it to a 9V battery, and see if it runs.

Then you can measure resistance of the FB1, FB2, and FB3 components on the board. If the theory that FB2 is burnt out is correct, than resistance of FB1 and FB2 should read close to zero, while FB2 reads open circuit.

If the motor is still under warranty, you can always ask VEX support about replacement options, otherwise…

VEX is unlikely to give us any specs on the unmarked parts, so if your school is planning to compete in VRC and you believe in right to repair, then I would save this motor in a special box to be used later for harvesting any usable parts to repair other motors in the future.

If this is for classroom use only, your school is tight on budget, and you are not afraid of soldering, then…

No light of any sort may be an indication that something else got damaged during a short circuit event (i.e. crushed motor brushes).

After disconnecting the DC motor from PCB you can open up another working motor, connect them both to a V5 brain and start measuring and comparing voltages (vs ground wire) at various points on the PCB.

This could lead you to discover if any diode, resistor, or voltage regulator along power route is damaged.

Burnt ferrite bead, diode, resistor, or capacitor would be relatively easy to replace, rather than other more complex active elements in the absence of schematics.

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It probably sounds silly but I’m assuming you tried using a different wire.