Trouble getting servo to work

[mitchklong]

We have successfully programmed with the servos that came with the KOP, but recently purchased a different one for slightly more toruque.

We cant get them to work. Its a hitec HS-5485HB. Its digital, unlike the analog KOP servos, but the specs suggest they should program the same.

The servo powers up but wont respond to position requests by the code.

ideas ??

[Whippet]

It would help us a lot if you could tell us whether you're programming an FTC or FRC robot, along with the programming language you're using and your current hardware setup.

[GeeTwo]

I agree with whippet that more info on both HW and SW use is needed.

One thing that strikes me as I look at the specs for this servo is the high current draw (500mA no load at 6V, presumably much higher when there's a load, much less at stall). You may want to check the voltage supply to the servo while you're trying to drive it; you may be pulling that voltage below the 4.8V required for reliable operation.

[DaveL]

Originally Posted by mitchklong

We have successfully programmed with the servos that came with the KOP, but recently purchased a different one for slightly more toruque.

We cant get them to work. Its a hitec HS-5485HB. Its digital, unlike the analog KOP servos, but the specs suggest they should program the same.

The servo powers up but wont respond to position requests by the code.

ideas ??

Where are you connecting the servo motor?

[mitchklong]

We are in FRC using java.

The servo is plugged directly to a PWM port of the roborio. We are using the servo class.

I dont think its a current draw problem. When we are testing the servo and it first gets power, it repositions itself to 0 degrees. The toruqe and movement look fine. If you turn it it repositions back to 0. So it seems to function normally, we just cant control it with the rio like we can with other servos.

[randantor]

Does the servo stop trying to move when the robot is disabled? What about when it is plugged into an unused PWM port?

[BitTwiddler]

Originally Posted by GeeTwo

I agree with whippet that more info on both HW and SW use is needed.

One thing that strikes me as I look at the specs for this servo is the high current draw (500mA no load at 6V, presumably much higher when there's a load, much less at stall). You may want to check the voltage supply to the servo while you're trying to drive it; you may be pulling that voltage below the 4.8V required for reliable operation.

Just for reference the roboRio spec for the 6VDC power is rated at 2.2 Amp total.

[GeeTwo]

Originally Posted by BitTwiddler

Just for reference the roboRio spec for the 6VDC power is rated at 2.2 Amp total.

Again, note that the 500mA spec is for no-load operation. This is just to produce enough torque to overcome the internal friction. If there is a load resisting the servo's attempted travel, the current use for each servo could easily be several amps.

[mitchklong]

I dont think we tried plugging into a different PWM port. It returns to zero even when disabled.

[seg9585]

Originally Posted by mitchklong

I dont think we tried plugging into a different PWM port. It returns to zero even when disabled.

Is the PWM wire plugged in with the correct orientation? When the roboRio is disabled, the servo should be getting no PWM signal to go to any position including zero.