[FTC]: Common failures with TETRIX

[PhilBot]

Since, this is the first time the NXT/TETRIX kit has been used, I think it shows great potential, but it's still got a long way to go before I'd call it a great system.

The only way to improve, is to identify and correct problems, so I thought I'd compile a list of common problems we had/saw during this FTC season. I will pass these on to NI/LEGO Education/PITSCO/Hitechnic to see if improvements can be made in future designs.

See if you agree with these, or have any additional suggestions.

1) Wobly Brass Bushings.
These seem reasonably snug when first installed, but after several hours of driving, most of our gears and wheels seem to wobble quite a bit. We used the propper wheel mounts, and two points of support, but they are still getting looser. Not sure that they are reusable for another season.

2) Bending Axles.
To aggravate the problem above, any time an axle has any length that's unsupported, they seem to bend when they take a hit. Perhaps they could be made with a better grade of Aluminum.

3) Encoder cables.
The thin wire used to connect the encoders to the Motor controller are incredibly brittle, especially where they are crimped into the encoder connector. These need a higher strand count, and a different grade of plastic to be able to withstand even a single season.

4) Motor burn out.
With the problems associated with glitches in the Motor controllers, it's common for a motor to drive for several seconds when it's not meant to. If the motor cannot rotate, this often leads to burned up motors. There is meant to be some overload protection, but it's clearly not enough to prevent letting the magic smoke out. These motors are TOO expensive to let a software glitch destroy them.

5) Motor drive shaft bearings coming loose or free.
All of my encoder housings now spin freely on the motor shaft, despite the set screw being fully tighened. It appears that the brass bushing that they are attached to eventually comes loose. In one instance, the bushing has actually broken free of the gearbox. This motor was driving a 40 tooth gear which was driving an 80 tooth gear. The setup had no latteral load (except due to normal gear-gear interaction). This sort of catastrophic failure needs to be prevented.

6) The comunications between the NXT and Motor Controller needs to be made MUCH more robust. Many of the supposed field/bluetooth issues are really related to this interface, since they can be "corrected" simply by cycling the 12V motor power. I will tollerate many things in a robot, but I won't be at the mercy of random software glitches (and neither will my S/W team). As far as I'm concerned, getting a good Auto mode is the real goal for any of these games, so the closed loop control needs to be bullet-proof. This interface glitch MUST be fixed WELL before the next season.

Phil.