How can I determine the gear ratio I need on a lift to lift a certain mass?

I am doing a CAD Model of a robot that my team wants to design. Ideally, we want a robot that has a 4-bar and tray, but I don’t know how to determine the gear ratio of the lift. What can I do?

First, you could try finding a solution online. There are multiple pictures of 4 bar lifts online you could check out. If that doesn’t work, you could mess around with something just a little more than a constant ratio, such as an 84:64 ratio.

Calculate the ma of your lift. I don’t remember how many N metres a v5 motor has, but if you know it then all you need to do is calculate the amount of extra force needed. The extra force comes from gear ratios. Don’t forget about friction though.

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you could do math to find out, but the physics is a lot more complicated than you would think because of inefficiencies in the system. with rubber banding, anywhere from 1:5 200 rpm or stronger should be safe. go for 1:7 200 rpm at the fastest if you’re unsure of your build quality. And use bands.

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ok thanks
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1:5 200 rpm would be faster or slower than 1:7 200 rpm? because people never say it correctly

It doesn’t matter whether they say it correctly or not in this instance. Those are gear reductions which mean that the larger the driven gear the slower it will rotate.

test it irl. that’s how you determine it accurately

unless you know exactly how much friction and load you’re going to be dealing with it’s pointless for anything more than a super rough estimate

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1:5 200 rpm is the fastest you could probably get away with on a lift.

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this is entirely dependent on how much power you have allotted for the system. for a 1m system this is usually pretty accurate though

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I mean yeah if your lift is heavier than 1:5 200 rpm isn’t going to cut it. You may just be able to get away with 1:3 100 rpm for a really really light lift, but I don’t think any sort of lift could go faster than that. and ye, this is in terms of a 1m lift. With 2 motors you can push it a bit faster, but you really shouldn’t be using a 2 motor lift for change up.

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NXS ran 1 motor 100rpm 3:7 lift which is faster than 100 rpm 1:3

ofc
but the original question didn’t provide any context about what the lift was for so i think what i added in about power is fair

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Yeah it’s definitely power dependent. Still though it really depends on your build quality, design, and banding too. Faster than 100 rpm 1:3 is clearly possible as evidenced by NXS, and it can certainly get faster than that

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the speed and torque of the arm is also dependent on the length of the arm itself, not just the weight. haven’t seen anyone mention that here but that’s just as important of a factor as gear ratio. smaller arm has higher acceleration and more torque etc etc

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Clarification:
1:3 100 rpm is 33rpm effectively.
1:5 200 rpm is 40rpm
3:7 100 rpm is 43rpm

1:5 200 rpm is faster than 1:3 100 rpm. @Xenon27

A third thing to about lifting is power efficiency. When its too fast, the motor is spinning slower than it should(lower efficiency) and at worst will stall(0% efficiency). On the opposite end of the spectrum, if the motor has far more torque than it needs, the lift will be powerful but slow, with nothing to push the motor to its limit, it is not using its full potential. For a given load, the motor has an optimal range to work at. I don’t quite know what it is for v5 so you will have to experiment with it. I think the brain has built in stuff to check motor efficiency.

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im pretty sure xenon was just saying it the other way around; there’s a discrepancy between vex and the rest of engineering where we tend to say ratios backwards (i.e., some people will say 1:3 is a speed ratio and 3:1 is torque, and others will say 1:3 is torque and 3:1 is speed. it’s pretty silly lol, but there’s decent justification for both)

(everything else you said sounds right though)

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nah I just had a brain fart and thought 1:3 100 rpm was faster than 1:5 200 rpm for some reason.

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The length of the four-bar multiplied by the weight on the end of it will give you the required torque(excluding friction and other stuff like that) then have the ratio of teeth on the input gear(connected to motor) to the teeth of the output gear(connected to lift) be greater than or equal to the ratio of required torque to the motor torque.

In case your curious, the correct answer is both to an extent. We should state our gear ratios as the driving gear to the driven gear eg. 3:1 for a geared down lift, however the torque ratio is the opposite, 1:3.

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