Initial build servo problem?

[bowerandy]

I've just put together my RN1 and I've managed to get the robot to talk successfully to the PC and the RoboBasic program. So far so good.

However, I've found that there is an issue with servo #1 (right leg calf muscle). When the robot stands this moves into the correct home position (as do all the other servos) but it is then possible to gently move the servo clockwise by hand. The anticlockwise direction appears held tight like all the other servos. What this means is that RN1 falls over when any movement is attempted because that lower leg servo only appear to be able to move in one direction.

I've tried to trace the fault by switching the servo to another port on the controller but the effect is the same. To me this implies that it is the servo that's faulty rather than the controller. Also, if I bring up the Direct Motor Control window in RoboBasic the I can use the onscreen dial for Motor #1 to move the servo but only in the clockwise direction. Moving the dial anticlockwise has no effect.

I've double checked the servo horn position for this joint and the connections to the controller. I'm pretty sure these are correct now. I did initially fall foul of the pin reversal problem on the RHS of the board but since I found an up to date manual everything seems okay for the rest of the servos apart from this one.

Does anyone have any ideas? Could it be a gain issue or do you think the servo is faulty?

Thanks in advance

[i-Bot]

I think you are correct in your diagnosis of a faulty servo. Hitec are pretty good at replacing broken servos, so get in touch with your local Hitec office.

[DirtyRoboto]

If you use [F7] real time servo control you are only getting the servo to travel in one direction, It will not return or go in the other direction at all?

You have tried this servo on other ports and it behaves the same!

Have you inspected all connections?

You can open the servo up and put a multimeter between the servo and connector, also inspect the soldering on the servo circuit board.

If it fails on all counts then it is defective. Raise a ticket with Hitec.

Marcus.


Ps. Don't be afraid of opening the servo as they come configurable. When you buy a new servo you have to assemble the casing to the config you need. They come with varios top and bottom plates.

[bowerandy]

If you use [F7] real time servo control you are only getting the servo to travel in one direction, It will not return or go in the other direction at all?

That's right.

You have tried this servo on other ports and it behaves the same!

Yes.

Have you inspected all connections?

Yes.

You can open the servo up and put a multimeter between the servo and connector, also inspect the soldering on the servo circuit board.

I've just opened up the servo and all the contacts look ok. I didn't have a meter to measure the conductivity of the wires but wouldn't a broken wire stop the motor from moving at all? Presumably, if either of the power lines has failed nothing would work and the same for the (PWM?) signal line?

Limor of RoboSavvy (where I purchased the kit) kindly said he would replace the servo if a solution wasn't forthcoming here on the forum.

Many thanks to DirtyRoboto and i-Bot for their help on this.

[DirtyRoboto]

No problem mate!

Did you look at the gears to see if they are seated correctely? (other side of the servo to the board)

Also look at the board with a magnifing glass and inspect the solder tags on the two chips for any sign of shorting.

Marcus.