[FTC]: De-energizing a Hitech Servo

Does anyone know how to de-energize a Hitech servo so it will “go limp” and NOT hold their position while the robot is powered. We’re using a couple servos that we would like to “float” (coining a motor command from NXT-G) to give them a little extra protection from accidental contact while they’re not in use.

We’re programming with RobotC 3.X

Thanks!

All servos on a controller may be disabled at once:

Address Type Contents
48H byte PWM enable

The PWM enable field is used to control the PWM output. If it is set to zero (00H), it will enable the PWM outputs, causing the servos to be active, and start a ten second timeout running. If it is set to 255 (0FFH), it will disable the PWM outputs, causing the servos to be inactive. If no I2C communication is received during the ten second timeout period, the PWM enable field will automatically revert to 255 (0FFH), disabling the servos. If the PWM enable field is set to 170 (0AAH), it will enable the PWM outputs, causing the servos to be active, and disable the ten second timeout. The PWM enable field is set to 255 (0FFH) during power up and after the timeout has elapsed.

There are 6 outputs, so the bit pattern 10101010 (0xAA) doesn’t seem to map to each output and a timer disable for each output.

Hope it helps!

On the opposite note, does anyone know how to have a servo STAY energized after a match is over? We have our servos on a crate and if they turn off, the crate will drop.

Is it possible? Thanks!

I’m almost positive unless you turn the 12Volt off it will stay energized and hold position.

I think that’s only if the program continues to run. In a match, if the FTA’s “stop program” won’t the servos return to their orginal state?

The default template code turns OFF all the motors and powers down the servos when a “Disable” state is issued from the FCS.

If the Teleop program is halted before receiving a “Disable” the Servos will hold their position until the internal watchdog kicks in (2.5 seconds I think), but if the “Disable” is sent first (which it should be for safety reasons) then the servos will go limp immediately at the end of the match.

You may need to install some sort of mechanical latch to hold the crate in it’s upper most position.

Phil.

The watchdog actually only exists for the DC motors, not servos.

NI is planning a patch to address the current behavior that forces servos to go limp when the FCS issues a disable signal. This will help robots hold up crates after the match ends. It will also help certain robots that require energized servos to stay within the size constraints at the start of the match.

Is there an ETA for when this patch will be available?