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Muddled Moderator
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Discussion Starter · #1 ·
Has anyone tried to fix a lunging reaper who stopped lunging? I can hear the motor whining, but the arm doesn’t move.

Here’s a thread that shows how the mechanism should work.



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Guess the first step would be a thorough evaluation and possible teardown to see why he's not lunging. Guess it never hurts to try fresh batteries, different power supply, and/or check voltage while the prop is running. If he's down on volts it could lead to a buzzing/whining (but stalled) motor.

Past that, nothing visibly 'hung up' on the outside? Arm not bound up and can move freely if not hooked to the motor? No loose clevises on the rigging? None of the torque arms are broken or stripped out. Does the arm move if you give it a nudge a the right time? Does the motor spin if you remove all mechanical load from it? (unhook all arms and rods from the shaft)

If nothing obvious on the outside, then a deeper teardown would be in order. Anything broken inside the gearbox? Broken /stripped gears? Motor shafts spinning inside the gear hub but not driving the gear? Any stripped shear pins (don't know if they'd be smart enough to use those or not), any slipping clutches (again - smart thing to add, but don't know if they would)
 

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Discussion Starter · #4 ·
Motor still working, and all gears are intact. Band for gear I picture below was removed by me. It tries to move the arm, but the motor just whines. I can move the arm and all gears move manually.
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Good pics - I see the general layout now. That is quite a gear reduction box! Seems like we need to dive a bit deeper and differentiate the points between 'motor still working' and 'motor just whines'. What point does it work OK?

Some pics of the motor would also help. Especially noting - how many wire leads does it have?

If it seems to be working some times and not others, then it would be good to get voltage measurements at those times. I'm sort of guessing, but sounds like maybe the motor can spin/freewheel on its own, but has no torque and just stalls when trying to drive the arm? If that's the case then it points to something back on the power supply side - possibly a bad power supply that can't supply enough power to run the motor, or a bad controller (mosfet?) on a circuit board. (pics of circuit board would also help)
 

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Sounds like the motor is still spinning and when you move the mechanism manually, it seems like all the gears are working. I wonder if that rubber band is not stretched a bit and is just slipping on the pulleys? ...or possibly one of the pulleys is spinning on the shaft? Guess a good next step might be to take a magic marker and put a dot on each pulley to see if either seems like it is slipping with respect to the other.
 

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Discussion Starter · #12 ·
Marked and watched the wheels spin, and all are moving, so I’m guessing the small gear is slipping. So should I give it a little glue.
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Wellllll...... that is going to be a tough one. You need to pull either the gear or the pulley off to get that shaft into the gearbox, correct? So that means you'd be trying to glue the gear in place inside the gearbox and hoping you don't glue the shaft or the pulley to the gearbox. Plus, it would be sort of a 'one time' assembly where you'd then need to break the glue loose to get it apart again.

If the gear comes off now, You might try to take some coarse sand paper and create some scratches along the length of the shaft, then slide the gear back on. Possibly that would make enough friction to hold the gear? If not, it would still be good prep for glue.

If you have to go the glue route, I'd probably start with a water-thin super glue and see if a tiny drop might wick into the joint between the gear and the shaft. The downside is that gear is probably nylon or similar, so not a lot of glue will really stick to it. You might almost have better luck putting a very thin coating of glue on the shaft and letting it dry, then slide the gear back on...the idea being to build up the diameter of the shaft just slightly for a bit more friction with the gear.

If you search various retailers, you can find brass pinion gears which typically come with a set screw. That would be a great fix, but the hard part would be finding one with the right shaft diameter, tooth count and 'module' which refers to the tooth shape.
 

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