Scissor Lift Bent Axles

My Lift is a 1:21 4 stage scissor lift, and the axles that connect my 36 tooth gear and 12 tooth gears keep on bending. All the gears are between 2 c channels. Is there a way to solve the bending?


Pictures would definitely help a lot. Whenever I have a compound reduction with a 1:3 involved, I usually put one of the metal lock bars between the two axles to hold them together and eliminate skipping. This might or might not help depending on your situation.

With pictures the forum can help a lot more.:smiley:

Here’s a photo of the 1:3 part of the gearing. I also forgot to mention in extreme cases the axles twist also.

On any lift where you have a really high-torque gear ratio (compounding, 15:1, 21:1, etc.) the axles are under a lot of stress. There’s bound to be some bending, especially if the places where the axle is supported are far apart. It looks like you have almost 2 inches of space (I calculated 1.875") between the two c-channels, which almost definitely will result in bending. Try cutting that down (putting shaft collars and bearing flats on the outside, taking out spacers, etc.). You can also switch to high strength shafts, which are made for high torque applications.

Perhaps you just need more rubberbands assisting your lift upward? The rubberbands should be doing the majority of the lifting…not the motors.

Thanks for all the ideas and help on this thread. I have one more question, and its that I’ve seen teams have a another set of gears spread to another side to reduce stress. Is this method reliable?


By the other side, do you mean left/right side of the lift? Because I can see in your photo that you have motors powering both sides of the 84 tooth gear.

I dont know what you mean by opposite sides.

scissors are hard in this way because they take a lot of power to power up for the first few inches. (sometimes I wish we could weld in vex).
I would personally just change the power reduction ratio. instead of the 1:3 section. chain a 1:2 and keep your 1:7. the extra power dosnt do you much good if it is being put into candy caning an axle. you will also be faster.

hope this helps

A 21:1 should not twist axles unless something is wrong. Are you using elastics to counteract the weight of the lift and intake? I don’t mean a few, our scissor uses around 50 #64 rubber bands through out the tiers of the lift.

A larger picture of the robot might give some more context and let us look for more issues.

Although the intent is good, I would never put a chain on any type of lifting system. Chains snap a whole lot easier than gears skip and chains add absurd amounts of slop. you can get pretty close to just about any (reasonable) ratio you want through some combination of compound gearing and changing internal motor gears. 21:1, 15:1, 13.125:1, 9.375:1, 9:1, 8.75:1, and 7:1 are the options I can list off the top of my head with only gears.

Hmm, I thought it was the other way around. A higher gear ratio should in fact be more prone to twisting than a lower gear ratio.

Yes it will. Seen twisting with a 5:1 ratio. So more torque equals more ability to turn an axle into a drill bit.

The two biggest culprits of shaft twist are the distance the load has to travel on the shaft and the size of the shaft itself. If you want the true math and formulas behind it just ask.

But you have two options to fix it:

  1. Reduce the shaft distance from the force input part to the driven part. The shaft has to try and not twist over this distance.

  2. Go with a bigger shaft. This is new this year but it is sometimes not feasible like when dealing with a 12 tooth shaft. Another way of dealing with it is putting more 12 tooth gears along the shaft to not allow them to twist. This almost effectively increases the diameter of the shaft. The shaft profile has a larger contribution than the distance. So changes to this have a greater impact.

The third option is not legal in the game which is change materials to something stronger.

For bending, the amount of support points and how much clear distance between supports are your culprits. More bearing blocks and building out little support structures in the middle help a ton. Don’t let that shaft bounce about.

I might have been somewhat vague in my recent post and didn’t correctly convey what I was trying to say.:smiley:

What I meant, was that I’ve seen plenty 21:1 scissor lifts that haven’t had this problem(have counteracted it so it wasnt an issue). I dont think 21:1 on a scissor lift is a faulty design that will always twist shafts, so I figured it must be something wrong with this specific implementation, which led me asking for more pictures. What we’ve seen so far is relatively solid and of high-build quality, so assume for the problem to persist there could be a problem somewhere else. I wasnt saying 21:1 is less prone than a 15:1 or a 7:1, but it still shouldn’t twist if done correctly.

Until OP says I’m wrong, I’m strongly leaning towards them not using enough elastics and lifting a whole lot more load than a usual scissor.

I can provide more detailed pictures when I work in the robotics lab tommorrow, but I have a youtube video showing me doing skyrises before the axles started messing up. I will add more elastics (thanks 400X) and I’ll see how it goes tommorow.

Thanks, AlphaPixel

P.S the robot when we took the video wasn’t finished yet and alot of stuff like the cube manipulator was still loose and in prototype phase.