Programming Servos For AndyMark Transmission

[de_]

We just received our new AndyMark transmissions and have yet to find any posts on the following question.

Will we risk burning out the servos if we request the servos to shift but the motors are not turning and the transmission dogs are in a position where they cannot engage and hence the servos go to full stall torque and current perhaps for an extended period. My experience with servos is you are asking for a broken gear case or burnt out servo motor if the servo is left in a stall state for very long (never mind drained batteries)

Should the code say something like ...

Initialization code
{
// set shift servos to 1/2 way as you don't know what gear you are in and
// the failsafe action is to go to 1/2 way (ie neither slow nor fast)
transServo = notHighNotSlowSpeedValue;
}

Main Loop code
{

// only attempt to shift if the transmission is moving. The simplest
// estimate of this is if the motors have been requested to turn (don't
// care what direction) ie value sent to motor pwms is != 128
// The only flaw is if the robot is not moving even though power is being
// applied (ie robot is stalled against an obstacle or a blocking robot).

if (motors are not off)
{
if (user requested high speed)
transServo = highSpeedValue;
else
transServo = lowLowSpeedValue;
{
}

or do we know the servos are rugged enough so we don't have to worry about it ?

Also, is it true that the servos are actually powered via the backup battery (via the RC somehow) ? If thats true, running the servos at stall currents might lead to prematurely drained backup batterys.

Anyone know what the stall currents of the servo might be ?

[robind]

If you setup the IFI provided recharging circuit you shouldn't have any issues with drained back up batteries.

[haroony341]

has anyone had the chance you test how long the backup battery would last when your only servos are used for shifting?

also, if the shifting was programmed to stay in high gear only when the trigger is held, does that mean that the servo would constanly use power to stay in that position?

[Jared Russell]

The servo only uses power to get to a position, not to stay there.

Also, if your dog gear is getting stuck then I suggest greasing the gearbox.

[team222badbrad]

Originally Posted by Abwehr

The servo only uses power to get to a position, not to stay there.

Also, if your dog gear is getting stuck then I suggest greasing the gearbox.

If it can't get to that position then it is always under power.

We tried servos way back in the day of Drill Transmissions.

For the past 4 years we have stuck with pneumatics. Faster, more powerful, and reliable, only downside is weight if you don't have plans for pneumatics.

[JohnC]

Originally Posted by Abwehr

The servo only uses power to get to a position, not to stay there.

Our robot initializes the camera in regular drive mode but doesn't search until autonomous is activated. So, in regular drive mode, the servos have power but are told to sit still. They will fight you if you try to turn the camera mount with your hand, so it seems like they do use power to stay there. Maybe we're talking about different kinds of servos?

[Alan Anderson]

Originally Posted by JohnC

...regular drive mode, the servos have power but are told to sit still. They will fight you if you try to turn the camera mount with your hand, so it seems like they do use power to stay there.

If you force the servos out of position, they use power to try to get back to where they are being commanded. Once they get to where they want to be, they don't use (much) power.

When used to shift a gearbox, it's possible that they will be physically unable to get quite to the spot they're being told to be, so they will constantly draw power as they keep pushing against the stop. I'd want to calibrate the commanded position so it does not do this.