[FTC]: Common failures with TETRIX

[basicxman]

I actually have a few unopened packages of bearings i haven't tried yet. So it could really well be an isolated incident. For clarification, the screw went through the bearing and metal but wasn't able to make it through the servo bracket. I'll post a picture perhaps (lol if I kept the "mismanufactured" bearing set)

[Abra Cadabra IV]

The pivot bearings are useless for everything EXCEPT what they're used for in the manual. Most metal is just way too thick for the length of the screw; it only really works with the really thin stuff. It's sad, because there's so much we could have done with it...

[alan4cast]

add these two to the list:

12) motors (with encoders and PID turned on) don't brake consistently (if at all). If a motor has pressure against it and you set the speed to zero it will brake and actually stop (depending on the settings in place at the time) (this is for raising an arm for instance). If, however, the motor has been acting to slow the item down (think of lowering an arm under control) then when you set the speed to zero, you just remove power - you don't stop it (most of the time). I haven't looked into it to see if this is a symptom of the connection to the NXT, but I don't believe that it is.

13) more servo options, or some way to not reset the encoder position in both lego and drive motors when the program starts running.

[PhilBot]

Originally Posted by alan4cast

13) more servo options, or some way to not reset the encoder position in both lego and drive motors when the program starts running.

Yes, Both the Lego and DC motors use pulse counting encoders, so they don't have any absolute way of detecting their starting position.

You either need to have some way to "home" them, or some external absolute sensing device.

One idea to Home a motor is to add a touch sensor, and run the motor at low power until it hits the sensor (or some other hard stop). The you can reset the encoder. Remeber... use low power !!!! Or, you can reset the encoder every time the arm moves past a light senor.

The other thing to consider is that it IS legal to add the Hitechnic soldered prototyping board, with external sensors ..... like a potentiometer. In theory you could add a feedback pot to an arm to sense the actual position, and just use the encoders for fine speed control.

Servos are great, but unfortunately you can't read their starting position, so your first action has to be to move them to some safe position. If you can always physically place your servo arm in a known position (eg: all the way up or down), then if you can figure out the servo values that correspond to this starting position, that can be your first servo command.... eg: Go to where I know you should be starting.

I do like that you can send the servo to position "0" which means "stay where I last sent you". why? If you don't continually send servo commands, they will droop down after about 2 seconds... so, to prevent this, you can have a loop that runs in the background sending "0" comands, which will keep them wherever they were last commanded. Unfortunately you can't start out by sending "0" commands because there is no "history" and the servo will go to the center.

[Mushrooshi]

For us, it was that we had 2 of the C-clamps actually crack on us.

[Buzz2001]

I think I saw the answer already, so forgive me for asking directly -- will the servo burn out if stalled? We are using it to run our claw & depending on how the ring nests it may not close entirely, stalling the servo. I am thinking we will need a spring relief for this. What do you all think?