Power Functions Servo Motor

darthdc

I'm having problems with the servo motor in my Volvo digger/front loader. After noticing that the vehicle wasn't entirely straightening up when switched on, I broke it apart to look at the motor. I seemed to have solved the problem, with the dots realligning, and rebuilt it.

But now, the vehicle will not steer left. It will steer right, but when I try to steer left, it remains straight.

Paperballpark

Is it possible you did something wrong when rebuilding it? If the servo motor was working fine before you started putting it back together...

CCC

How far right can you go with just something simple attached? Often servos will go -180 (left) to 0 (centre) to +180 (right). But it may be that you have reassembled it off centre and now go from 0 to 360 (right) but nothing left. Obviously anything past 180 is really left in this situation, but you have to go through right to get there.

darthdc

It steers about 45 degrees right, but thats due to the vehicle's restrictions

CCC

Can you take it out of the vehicle and run it with just an axle in (maybe add a bar to act as a pointer for the angle)?

darthdc

You'll have to wait for an answer - it takes hours to break apart, due to the way it's built.

CCC

Ok. Did you take the motor apart in situ?

darthdc

I've never actually taken the motor apart. I was actually referring to the digger - it's built like a tank.

CCC

Sorry, my mistake. I thought you had dismantled the motor and rebuilt it!

I'd try taking the motor out and checking it with no load (or a very light load). It does seem surprising as servo motors typically have three cables - two for power and one for signal, so if you can steer right and return to centre, then all three must be working OK. Which possible means something inside the motor is jammed to prevent turning past a certain angle.

PS. I've just had a look at mine, it is only a -90 to +90 degree range, not the full -180 to +180 like some other servo motors. Also if you look really closely there are two small dots on the orange axle connector from which you can tell if it is rotating correctly, even if you don't add an axle with a bar attached. I had never noticed them before.

darthdc

the instruction manual highlights this, and prior to the actual build, it tells you to connect the motor to the battery box, with an IR receiver inbetween. Switching the power on should cause the dots to align. However, it doesn't give any info on what to do if they don't.

But I've realised that if you don't put the IR receiver between them, the dots misalign.

willobee498

If you put the battery box direction switch right in the middle, which is a bit finicky to do, the servo will center itself.

Cyberdragon

darthdc said:

the instruction manual highlights this, and prior to the actual build, it tells you to connect the motor to the battery box, with an IR receiver inbetween. Switching the power on should cause the dots to align. However, it doesn't give any info on what to do if they don't.

But I've realised that if you don't put the IR receiver between them, the dots misalign.

Yes, it probably just needs calibrating. I would think the dots would be aligned at center though. If it doesn't align at all, it's either mechanical or something wrong with the potentiometer inside. It might be fixable if it's mechanical, but if it's the pot, it's actually part of a circuit board and not replacable (unless the wiper is just bent or something).

willobee498

Also, contact Lego about it. I heard they are very good at replacing motors, even if they are a few years old.