Hello forum I am building a double four bar and I was unsure what I should gear it. The lift is all aluminum and I am using four motors. I was thinking of gearing it 15:1 but is that enough?

I think it should, but it depends in your robot. As you will be doing compound gearing for that anyways, it shouldn’t be too hard to make it higher if need be.

Also, if you haven’t already, you should consider adding elastics to help the motors.

From my experience, you’re probably going to bend or twist your axles before your motors can even exert the full 15:1 torque. My guess would be a 7:1 torque ratio or a 25:3 torque (two 60 tooth, one 36, and one 12) since you can directly mount those to the system or make them free spin.

or you can just do a torque calculation and make radius the distance of both arms

We have used 15:1 many times…no issues with bending axles ever. We have a 15:1 on one of our eight bar lift bots right now with no issues. If anything with the weight of the cubes this year we might need something bigger than a 15:1.

Interesting. I’m quite skeptical. Either you had slick engineering, didn’t need the 15:1, or my materials just suck. The last competition which “needed” a ratio that high was sack attack. Gateway and Toss up didn’t need those ratios.

14:1 is a good ratio for a reverse 4 bar. 84 tooth gear to a 12 tooth gear that is attached to a 12 tooth sprocket that is driven by a 6 tooth sprocket. 4 motors.

USE RUBBER BANDS. I can’t stress this enough.

15:1 doesn’t seem that extreme to me? It is on our 8 bar lift and the motors still have to work pretty hard to lift with 2 cubes. Definitely no axles bending or anything though. If anything I think we had poor engineering, which is why we had to resort to 15:1…haha. If I have time I can get a picture of our gear setup later…

Are you screwing your arm directly to the 64-tooth gear? I have a 1:21 gear ratio and it’s working out fine…

I will post a pictured the gear box, but I’ll black out everything else. :stuck_out_tongue: