Team Update #11

[AllenGregoryIV]

Does anyone know why they changed the rules about the floor protector for the tower? They removed the sentence about it only having a 1/4in ridge in the field but did not replace it with anything else. Does anyone know if this means the bump will be larger or smaller?

[Mr.G]

Originally Posted by AllenGregoryIV

Does anyone know why they changed the rules about the floor protector for the tower? They removed the sentence about it only having a 1/4in ridge in the field but did not replace it with anything else. Does anyone know if this means the bump will be larger or smaller?

Now we are going to get stuck on it and not be able to reach the tower with our 1 inch off the ground bumpers.......j/k

[Al Skierkiewicz]

Guys,
Although the Bourns page is similar it is not nearly the identical part. When I first started research on this a few weeks ago, I found an identical sized inductor with the same conformal package. I believe they were more like 900ma max DC current. The series resistance is much lower than the Bourns above. AT 900 ma used with a motor that stalls at 7.5 amps, you can see why the motors constantly burn open.

BTW, I started the discussion to allow opening Tetrix motors to replace the inductor. My recommendation was based on the purchase cost factor of replacing a motor that had failed simply because an under rated part had failed. I had hoped that teams could cut their losses by replacing the inductor. FIRST and the GDC was overly generous by allowing teams to open and repair other items besides the Tetrix motor and delineating "repairs" from the "modification" rules.

[jskene]

This may be a closer match to the stock inductor:

http://www.mouser.com/ProductDetail/...ZBsTfTG7 Q%3d

It has a maximum current rating of 0.8 amps, still well below what I would have expected the design to require.

There is another Bourns inductor of the same inductance but with a 4 amp capability:

http://www.mouser.com/Search/Product...42-5900-390-RC

I believe this is physically larger than the stock one, although I haven't measured the stock one yet.

[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

[thefro526]

Originally Posted by AllenGregoryIV

Does anyone know why they changed the rules about the floor protector for the tower? They removed the sentence about it only having a 1/4in ridge in the field but did not replace it with anything else. Does anyone know if this means the bump will be larger or smaller?

My understanding is that the ridge will be the height of the 3/16" HPDE Plus the Carpet that covers it. I'd imagine that it would be no more than 3/8" but I cannot be sure. The description is a bit confusing, a drawing would be nice.

[IndySam]

Basically they removed the 1/4" because there is no real way to say exactly how big the bump will be.

A hard number like that will only cause headaches with teams complaining about it being to high when it's not exactly 1/4"

So they are saying "this is how it's constructed plan accordingly YMMV."

[Chris is me]

Originally Posted by IndySam

So they are saying "this is how it's constructed plan accordingly YMMV."

What good will that do a week before ship?

[Teched3]

Originally Posted by Chris is me

What good will that do a week before ship?

You can withhold the minibot and insert fuses in the feed lines from the motor at your liesure. It would take a few dollars for the parts, and about 10 minutes. Hopefully you're prototyping using fuses. Certainly a lot less time and expense than taking a motor apart and replacing an inductor, or the complete motor assembly.