Team Update #11

[pfreivald]

Originally Posted by Al Skierkiewicz

Patrick,
The TU makes repairs replacing defective parts with "identical" parts legal. Adding a replacement in a different location seems to disagree with this ruling.
Thanks for the kind words. I had originally suggested that teams just be allowed to remove the inductor from Tetrix motors, if they were making repairs in order to eliminate the cost of replacing the motor. The GDC felt very generous and allowed teams to make repairs on all components. I have to thank them for that.

Fair enough -- we'll do that for our already-burned-out ones for continued testing, and keep the others as-is.

[diviney]

Al:

Can you please clarify why you feel an identical replacement part that is physically in a slightly different location would not be legal? This seems like a technicality because it is clearly electrically equivalent.

Also, you suggest assembling the brush/endplate to the armature prior to installation... I don't have a motor in front of me, but doesn't that require removal / re-installation of the pinion gear? I would think it easier to drill a couple of retaining holes than to R&R the pinion...

-Tom

[Al Skierkiewicz]

Tom,
The pinion pushes through the motor casing, after you remove the transmission of course. The illegal part is drilling holes in the motor in addition to the external mounting of the inductor. While electrically equivalent, the RF generated by the motor is shielded by the motor casing. Moving the choke to the outside reduces it's effectiveness as a filter, hence not "an identical replacement" repair.

[Rick TYler]

Originally Posted by Bill_B

It is quite possible, likely even, that GDC had no idea how these motors would react to the devil-may-care "design" work done by our enthusiastic high-schoolers.

FTC teams have been burning these motors out since Tetrix replaced VEX. Before abandoning FTC after last season, we had a bag of about 20 dead Tetrix motors -- a combination of motors that had burned out, had broken gear heads, and or had snapped-off power tabs. If FIRST didn't know about it, it's because they never asked FTC teams. I'm not quite so sure it is the GDC's fault.

All you FRC teams should make sure to have plenty of spares. The gear heads are just about as likely to fail as the motors are to burn out during a stall.

[Hjsalom]

Due to the nature of the circuit there is a continuous switching in it, which has a DC transient characteristic repeating every time the brushes leave one rotor coil and get to the next one. The 3.9 µH adds to the rotor inductance and limits the transient current running through the motor. It also limits the current through the motor considering its resistance gets in series with the rotor's resistance. The presence of the capacitor in parallel with the rotor limits the noise due to the switching.

Replacing the inductor with a simple piece of wire , or an inductor with less than 3.9 µH, will allow a higher current through the rotor, which will increase the torque providing an advantage over competitors running with motors which have not been modified at all.

The motor expected life will be reduced with smaller inductors, or without inductor at all.

Hugo J. Salom, P.E.
Engineering Lead Mentor - Team 3337

[billbo911]

Originally Posted by Justin Montois

I understand your desire to keep the discussion in that thread, but due to the fact that this Update specifically says that you can replace the inductor, I feel more people will access the information in this thread.

Below are links that may be an identical part to the inductor that comes stock on the Tetrix motor.

Picture of the Inductor on the motor:
http://www.chiefdelphi.com/forums/sh...62&postcount=1

A PDF listing the specs, also in the upper left hand corner a picture that appears to show a similar inductor as the stock component:
http://www.bourns.com/data/global/pdfs/9310_series.pdf

And a link where you can but the above product:
http://www.mouser.com/ProductDetail/...7kb9bpww%3d%3d

At $0.86, if this is an identical part it sure beats the heck out of having to buy a brand new motor.

Can anyone confirm/deny this part as being identical?

I ordered 10 of the inductors listed on the Mouser site. They are the same value as the one in the motor, BUT, they are not an identical part. They appear to be a bit larger. I will have these with me in St. Louis if anyone needs one (or two). I believe they will be legal to use, but I will get approval first.
Here is a picture of what was delivered.