Differential frame bend

I’ve been toying with the differentials lately and I found that in certain scenarios with moderate resistance, the supplied differential frame bends so the spider gear (the center one) stops meshing with the other gears. Has anyone found a way to secure the frame to prevent the bending? A solution could be a custom frame, but I’m looking for something as or at least close to the space-efficiency of the plastic one.

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You could probably create it from a gear and 1 wide metal piece bent into a square or rectangle.

Also what are you trying to achieve the that type of differential?

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I have a few ideas for it so I’m mainly just testing the concept. It started back when my team was planning to make a pretty tall lift for TT. Some of my teammates thought that it would be a good idea to have a differential ‘transmission’ so the lift can be faster with fewer cubes and still be capable of lifting more. I have a tested differential without the frame (using the motor gears and stuff like in the animation everyone throws around), I’m just exploring options.

EDIT: I think some of the turntable pieces fit around the frame, but I can’t imagine securing it there would be easy

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Your wording was a bit vague, but I assume you want a 4 motor differential base powering the drive and lift. In that case the vex differential thing isn’t what you want to use. It is flimsy/weak and it is not designed for this purpose, though it would still work. It is designed to be used like a differential in a car, and not for motor sharing. I would presume you mean this video. It shows how to do it so the mechanism is strong and made of few parts. Those are the basic differential;, some are build other differential design to achieve other things like variable speed/force but those are much more complex.

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I’m not looking to power two different things, rather a transmission for the same mechanism. I think of the differential like a planetary gear set, but it’s kind of hard to explain. I’m powering one bevel gear (I think of it like the sun gear) and then the frame itself, acting like a ring gear. The result is that the final bevel gear has two speeds depending on the direction of the inputs.

To clarify, I’m using differentials in a very unorthodox way in no way representative of how it is used in a car.

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If you want to use a car as an example, you can turn both wheels forward, in which the differential frame will rotate at the same speed as the wheels, or you can turn the wheels opposite directions, where the frame rotates at the difference of speed between the wheels.

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So you are trying to make a differential with changing speed/torque. Something like this?..

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Yep! That’s actually a great example of what I’m going for. I’m only using 2 motors, that video shows two motors powering the same part for some reason. I’m trying to keep it compact, so making a frame like that isn’t really an option.

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have you thought about using ratchets

What do you mean? That would make the mechanism one-directional

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I made a thread about a ratcheting transmission but It only has 2 speed in one direction. The basis of it is that you have 2 gear ratios for example 1 to 2 and 2 to 1 each one has a ratchet so that when the lift has weight the 1 to 2 kicks in but when there is not enough force on the lift the 2 to 1 kicks in. This would take a decent amount of trial and error but could be compact and viable.

Right, but one direction is incredibly limiting and a differential or planetary uses 2 speeds in both directions

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its one directional for 2 speed but it still can move the other direction but is limited to 1 speed

But with a differential if the two motors spin in same direction it is high speed and low torque, but it they spin in opposite directions it is low speed and high torque (or the other way around depending on the design). This way it is in both directions

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Also here is an old reply about the video in an old topic talking about this sort of thing…

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I’ve made several new frames and attached them to a wheel to test, but I’m still having the same problem. Now I’m not sure if the plastic frame was the problem since these ones still aren’t working, but its bend certainly could have helped the gears slipped out. Attached are two slow motion videos. One has two spider gears, that’s where the shafts move the most visibly. The other has a single spider gear with the shaft secured so it wouldn’t slip, but the gears still somehow slip even though it looks like they are still meshing. In the thread that @Codec sent there is a worm gear to prevent back driving but I don’t know if there is a lot of space left for that (and that doesn’t really explain WHY the resistance is able to cause the gears to slip). At this point I have run out of solutions to try, so any help analyzing the problem is appreciated.


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I have come to the conclusion that the standoff screws are the problem. They loosen, allowing the last gear to bend out of place a bit.

Any suggestions to keeping these screws secured in their standoffs? I’ve never had a problem like this before.

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Are the standoff screws locking screws? Last year that was the only thing I could get to keep standoffs in place.

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Loctite
(20 chars is annoying)

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