Team Update #11

[Justin Montois]

Does anyone have a supplier for the inductors?

This opens up a situation where gracious professionalism is going to be paramount. Even in an instance where a team makes an honest mistake an thinks they have replaced the inductor with an identical part, the performance difference can be huge.

[Trying to Help]

Thank you for posting this. How does FIRST know that today I ordered both mini-bot and pneumatic parts?

[Mike Betts]

I would hope that FIRST publishes the recommended inductive component part number so that teams with limited technical resources can take advantage of this change.

[martin417]

Originally Posted by 340x4xLife

Does anyone have a supplier for the inductors?

This opens up a situation where gracious professionalism is going to be paramount. Even in an instance where a team makes an honest mistake an thinks they have replaced the inductor with an identical part, the performance difference can be huge.

My Electric Circuits theory is a bit rusty, but I am pretty sure that an inductor appears the same as a wire to a DC current. I don't think there can be any advantage gained by using different components in place of the inductor. The purpose of the inductor is to work with the shunt capacitor to make the motor less electrically "noisy". Unless the inductor has a resistive component as well (more than an equivalent length of wire) the only effect of substituting the component will be more electrical noise in your system.

___pause to check the specs____

I just looked at the specs for the 3.9 microhenry inductor listed, and it shows a 2.3 ohm DC resistance. It also lists a max current of 280 mA. at the max listed current, the inductor would drop 0.65 volts. I doubt that .65 volt drop would account for a "significant" difference in pole climb time, but it could make a small difference.

[martin417]

Originally Posted by martin417

My Electric Circuits theory is a bit rusty, but I am pretty sure that an inductor appears the same as a wire to a DC current. I don't think there can be any advantage gained by using different components in place of the inductor. The purpose of the inductor is to work with the shunt capacitor to make the motor less electrically "noisy". Unless the inductor has a resistive component as well (more than an equivalent length of wire) the only effect of substituting the component will be more electrical noise in your system.

___pause to check the specs____

I just looked at the specs for the 3.9 microhenry inductor listed, and it shows a 2.3 ohm DC resistance. It also lists a max current of 280 mA. at the max listed current, the inductor would drop 0.65 volts. I doubt that .65 volt drop would account for a "significant" difference in pole climb time, but it could make a small difference.

After talking with an EE, I have been informed that there COULD be significant gains by replacing the inductor with a wire. Possibly as much as a 10% power boost. has anyone tried this? An easy test for this is a resistance check across the motor windings. The motor winding resistance is normally quite low, so a quick check could show that someone has "mistakenly" replaced the inductor with a non-complying part.

[Justin Montois]

Originally Posted by martin417

After talking with an EE, I have been informed that there COULD be significant gains by replacing the inductor with a wire. Possibly as much as a 10% power boost. has anyone tried this? An easy test for this is a resistance check across the motor windings. The motor winding resistance is normally quite low, so a quick check could show that someone has "mistakenly" replaced the inductor with a non-complying part.

We found around 20ohms of resistant across the windings with a stock motor and 6 ohms with just a wire in place of the inductor. Pretty big difference.

Does anyone know if the inductor I listed earlier in this thread an identical part?

[Bill_B]

Originally Posted by 340x4xLife

We found around 20ohms of resistant across the windings with a stock motor and 6 ohms with just a wire in place of the inductor. Pretty big difference.

Does anyone know if the inductor I listed earlier in this thread an identical part?

That's a big help in telling whether a motor is repairable. My armature coils measured much less than 20 ohms. That is further support for my presumption that there is invisible damage to my coils internally.

I'm confused about your 6 ohm measure though. Why would shorting the inductor cause less than the coil winding resistance?

So, my advice now about trying to repair a motor is to measure your coils first, across all three pairs of commutator contacts. If you find a coil pair that is significantly less than 20 (or 6?) ohms, don't bother trying to replace the inductor. Even if you were to get an operating motor going, its work and power characteristics will be different than a stock motor. That would make the repaired motor questionable to use for prototyping. It might still be useful as an arm mover on an FTC robot though.

[GaryVoshol]

Has anyone seen the rules files with the Team Update 11 changes in them? The said they would be published on Wednesday; it's now Friday and a new Update should be appearing.

[Al Skierkiewicz]

Jerry,
You might want to check out the data sheet. That 4 amp Mouser inductor is almost 1/2" in diameter.

[vamfun]

Originally Posted by Bill_B

That's a big help in telling whether a motor is repairable. My armature coils measured much less than 20 ohms. That is further support for my presumption that there is invisible damage to my coils internally.

I'm confused about your 6 ohm measure though. Why would shorting the inductor cause less than the coil winding resistance?

So, my advice now about trying to repair a motor is to measure your coils first, across all three pairs of commutator contacts. If you find a coil pair that is significantly less than 20 (or 6?) ohms, don't bother trying to replace the inductor. Even if you were to get an operating motor going, its work and power characteristics will be different than a stock motor. That would make the repaired motor questionable to use for prototyping. It might still be useful as an arm mover on an FTC robot though.

Thats a good idea... I was wondering about the possible failure modes of the choke. If it fails open, the motor should be a brick which I suspect most people see that can revive the motor by replacing that. If the choke can have a partial failure mode and still allow current to flow then we should see a partial power motor... like all three of the ones we smoked. But if the choke can typically only fail open, then likely the windings are shorted and should be tested like you propose.


What confuses me is the motor R should be 12v/Imax = 12/7.5 = 8/5 ohm.
So I suspect that the shunt capacitor may be interacting with the ohm meters to corrupt the reading.

[Al Skierkiewicz]

Chris,
The stall current should occur when two windings are in contact with the brush at the same time. If you happen to measure when only one winding is contacted, you will see a higher reading. The failure mode on the inductor is open if stall occurs often or for an extended period, accompanied with a little smoke and possible debris. Partial short with smoke if running extended over several amps. The cap is so small that you likely can't measure any resistance even if it was outside and not connected. The choke is so small that high heat causes the coating to crack and the in some cases the core cracks as well.

[Justin Montois]

So does anyone have a distributor for the stock inductor?

[pfreivald]

Justin, one of my people found the exact inductors today -- but I don't know the URL to order them. I texted him and will let you know where to get them. If you don't hear from me by, say, 11am tomorrow, have Rees call me!

[Justin Montois]

Originally Posted by pfreivald

Justin, one of my people found the exact inductors today -- but I don't know the URL to order them. I texted him and will let you know where to get them. If you don't hear from me by, say, 11am tomorrow, have Rees call me!

Sounds good! Thanks!

[pfreivald]

Sorry so late:

http://www.mouser.com/Search/Product...lkey434-22-3R9