Team Update #11

[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.

[Teched3]

Originally Posted by EricH

http://usfirst.org/uploadedFiles/Rob..._Update_11.pdf

Updated manual to follow tomorrow. Burned out Tetrix motor inductors may be replaced, and parts may be repaired (keep the performance the same, though)--though teams are encouraged to use caution when doing to, and assume voided warranties.

It seems the GDC has come up short by allowing us to repair burned out components on the Tetrix motors. How many times can you bend those retaining tabs before they break off? How will they be able to determine if the replacement inductor/capacitor was the exact replacement? What they should've included, IMO, was to allow us to put minifuses on the motor lead(s) to protect the motors. It is just poor safety and engineering practice not to have those motors properly protected. Sort of closing the barn door after the horse has gotten out. Anyone else out there agree?

[Bill_B]

Originally Posted by Teched3

It seems the GDC has come up short by allowing us to repair burned out components on the Tetrix motors. How many times can you bend those retaining tabs before they break off? How will they be able to determine if the replacement inductor/capacitor was the exact replacement? What they should've included, IMO, was to allow us to put minifuses on the motor lead(s) to protect the motors. It is just poor safety and engineering practice not to have those motors properly protected. Sort of closing the barn door after the horse has gotten out. Anyone else out there agree?

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. Can you give us more details about the minifuses? I would put them into my test machinery regardless of competition legality, then remove them for competition.

As far as I can tell the biggest oversight was the failure to include motor leads at all in the first choice parts kit. They ran down the list of needed motor stuff to add to the resource kit but fell short of even the standard connection method. That connector is at least designed for the machine. No visible strain relief in it and no way to secure it to the motor either. I get the idea that it's an afterthought from Tetrix.

[Teched3]

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. Can you give us more details about the minifuses? I would put them into my test machinery regardless of competition legality, then remove them for competition.

As far as I can tell the biggest oversight was the failure to include motor leads at all in the first choice parts kit. They ran down the list of needed motor stuff to add to the resource kit but fell short of even the standard connection method. That connector is at least designed for the machine. No visible strain relief in it and no way to secure it to the motor either. I get the idea that it's an afterthought from Tetrix.

You can pick up minifuse holders and fuses at any car stereo shop or auto parts store. I would suggest you start out with 2 - 2.5 amp fuses, and have spares on hand. They originally had the less expensive motor leads listed, then added the thermal protection leads (at about 4x's the price), which do not react fast enough to protect the motors. Remember, these components are used in robots that run across the floor. That is a whole lot different than using them to climb a 10 ft. vertical pole. In addition, these components are"new" to even experienced FTC teams for the same reason.

[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.