Shaft getting twisted out of shape

We use a pair of swinging arms to pick up mogos. Each arm is paired by a red motor geared 12:84. The motor velocities are to set 20%. The arms are about 12" long. After a few minutes of run time, the axles with the 84T gears (that are doing the actual lifting) are getting twisted pretty badly. I hope the pictures help. Do we need to switch to those 1/4" high strength shafts? for both 12T and 84T gears or just one?

using high strength shafts, especially on the 84t gears, would solve this problem for sure. It’s probably not needed on the 12t gear, but I would recommend using a metal pinion gear instead of the fragile plastic ones, they tend to shatter under stress.


Thanks. Is this the gear you’re talking about?

On a related note, is there a way to join two high strength shafts to make one longer shaft? We were actually using one of the things in the lower left corner to join the two shafts with 84t gears to keep the arms sort of in sync:

you don’t need to because HS shafts come in 24" lengths.

sadly, they appear to be out of stock at this moment. You might need to find some coupling solution, or rely on good bracing between the sides of the goal lift to keep them in sync. Are both sides of this lift powered by a motor, or is it one motor for the whole thing?


Yes, I’ve been looking at those. The ones in our STEM lab are 12", and the bot is exactly 18" across, so we may have to cut them into shorter pieces. Each arm is powered by its own motor, so the thought was by coupling the shafts, the arms would be at the same angle . We also have some high strength collars, but those are made out of plastic, so that’s why we’re looking for an alternative coupling solution.

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in this case, linking the shafts isn’t that important. You can program the motors to automatically adjust themselves to the same angle, and if you brace the two sides of the lift well, they’ll stay very well in sync. Ideally the shaft would be connected, but it’s entirely possible for it to work just fine without that.

Could you please elaborate on this?

Yes. I’ve seen this been done with a combination of HS shaft collars on either sides of HS gears connected to each other. But beware, this solution will only take you so far.

in your programming, you could have say a toggle that determines if the lift should be raised or lowered. either raised or lowered, both motors could be told to rotate to the same angle, ensuring that they are in sync. And for bracing, just putting a c channel across the two sides should suffice.

Oh, got it, yes, we control both motors as a group. The reason we wanted to couple the shafts is that during practice, one of the arms gets pushed against an obstacle, and as a result, they get out of sync. Same thing happens when one of the kids decides to push/pull an arm for no good reason.

To couple them together, you can take two gears, separate them with some spacers and screw them together. Put the end of each shaft through each of the gears and use shaft collars to lock it together.

Here is my suggestion. Use bar instead of c- channel

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