The lift’s gearing is compounded 21:1. It is four x-s tall, about 60something inches. I’m using the old metal sliders but I’m sure that’s not causing a problem.
The small metal pinion gear skips against the big plastic gear, but only when the lift is fully lowered. Other than that it’s completely fine.
I tried solving the problem by: moving the bearings in as close to the gears as possible but since I want the lift to be able to lower alot, and have the middle c-channel fit in between the outer ones, (see pics) the distance is still quite great. I also made a bearing out of lexan that spans between the pinion gear and the big plastic gear and keeps them together (that you can see in the pictures) but it doesn’t seem to be enough. I will also put a gear in back of the pinion gear on the existing shaft to help brace it against the big gear/sandwich it between the two.
I cannot put a pinion gear on the other side of the big gear because when the lift is fully lowered, the c-channel is oriented so that it would get in the way…
Any Advice???
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notes: looking at the 5th picture you can see that the lexan bearing thingy I made is actually bent when the gears aren’t skipping, showing that perhaps the distance between the two holes is too great by a tiny bit making it have no effect in keeping the two gears together…
Also, the shaft locks in the pictures are not in place correctly, I realise.
It seems like the plastic gears are pretty badly damaged in the spots where it was skipping. This will make it very hard to fix the skipping because the teeth look rounded out and bent. Maybe try rotating the gears to a fresh part and try it with the fixes you already have.
In one of the pictures, the pinion gear is not lined up with the plastic ones so you definitely want to line those up. Try filling up the extra space on the axle with white spacers and leave as little wiggle room as possible.
A 21:1 ratio has a ridiculous amount of torque so shredding gears could be a regular thing.
On scissors lifts often the solution is far away from the actual problem. I’d check alignment especially at the extreme ends. We had a similar issue and the problem was our scissors axis mount was on the top 18th hole on a 35 hole piece of c-channel but the scissor’s base had been mounted at the bottom first hole to allow for clearance as it arced on raising. Moving it up solved the problem and created a new one which was remedied with a spacer between the mounting bracket and supporting cross member.
And if using custom lexan cuts for support make sure you drill holes with it mounted on a vex piece for an exact pattern.
-I’ll replace the stripped big gear.
-I was thinking about using high-strength shaft for the big gear. This would get rid of bending basically completely for the big gear’s shaft…
-And for the small gear’s shaft, I’ll put a gear against it on the other side to sandwich it between that gear and the big gear.
-Before I put the motors on the lift I could push it up and down (in the same direction the motors do) with very little effort so I doubt friction in the structure is a cause.
Other pointers?
the only area where it was skipping was pinion against planetary so thats the only place ill have to repair damage.
from the images is there anything you’d advise to do differently? I’m sure there are other improvements to be made. Feel free
i think your problem lies in your 2nd picture i think that your lowest point is actually lower then what is should theoretically be. when looking at your second picture your first and last stage has a fairly large gap compared to your middle stages it might not be your fault with the amount of give that square holes allow.
I could be wrong, but I think it’s the axle holding the 84-tooth gear that’s causing the gears to skip, rather than the 12-tooth gear. Have you tried adding a pinion gear behind the 84-tooth gear to keep that axle from bending?
- Replace the marred plastic gears. They are shot. The surface area a gear actually meshes is pretty small as it is. So when you get plastic deformation on the gear teeth, you might as well replace it.
2)The length of shaft from the driven 36 tooth across gear to the 12 tooth gear is pretty long and that allows for bending outward which leads to gear skips. I can’t remember off hand if this will work, but would a 36 tooth gear where there is a shaft collar on the drive motor shaft work?
- The plastic piece is tight because the holes are smaller, but the material is weaker than steel or aluminum. Is there another way to do that?
Personally, I think that you should use more elastics lower on your lift. Your robot and my robot are remarkably similar in design, but I have rubber bands on every section.
problem fixed. For the shaft of the big gear, I used high-strength shaft so I have virtually no flex there. I backed the pinion up against a 36-tooth gear, sandwiching it between the two gears, effectively, reinforcing it. There’s no gear skippage now.