Hi. I am creating an elevetor for cad training but i dont how to calculate gear ratio. Can anyone help? I am doing so that by kickoff we have a working elevator that can carry 10-15kg maybe using an elevator will be our choice. thanks in advance.
ReCalc is a popular mechanism calculator for FRC. You can open the linear system calculator and play around with the gear ratios to find which is best. You can also use the gear ratio finder to find a suitable gear box.
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Another amazing calculator is:
https://ambcalc.com/mechanism?=
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Use the new startup calculator, it currently is the only non-custom calculator that properly supports deceleration dynamics which are significant.
https://ambcalc.com/startup?=&stop-type=Stopped
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The calculators are great but it is good to understand the choice you are making with your elevator drive ratio (and this same choice reappears all throughout FRC mechanisms.
A given motor produces a certain maximum amount of twisting force called torque. And motors have a maximum speed at which they rotate called free speed. The maximum torque (and therefore maximum current draw) occurs at 0 rpms. So for ever motor you will find a chart of these variables. Somewhere in the middle of this chart is a range of rpms where you are getting near peak efficiency (that is the most mechanical power output for the amount of electrical power consumed. Ideally your design runs your motor somewhere in this range (esp if it is a mechanism used throughout a match).
But you have a constraint. You must produce at least enough power to move your mechanism. For a vertical elevator this power required is simply its weight (ie mass times gravity). It is highly likely that direct (ie 1:1) output from an FRC motor is going to be up to the task, so this is where a gearbox comes in. A gearbox trades speed for torque (or vice versa). If you have a 6:1 gearbox, its output speed is 1/6th of its input speed, the output torque is 6x its input speed.
Once you have computed the ratio needed to move your mechanism (with some margin for error), you can compute how quickly the elevator will move. If the movement is too fast, you are in luck. You can either increase your gear ratio or drive your motors less hard. If the movement is too slow for your liking, choices might be more difficult—use a stronger motor if available, use multiple motors, redesign your mechanism to need less power to move (eg lighten it, or counterbalance it with springs, etc)
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I don’t think you understand what the calculators are doing, as to correctly solve the dynamics problem that mechanism design creates, you need to use a simulator.
This is a bad way to look at mechanisms, because dynamic loads are significantly higher than gravity or anything else. 40lbs might seem like a lot until you are trying to accelerate it at several Gs. Mechanism design is inherit a dynamics problem. Solving the dynamics problems by hand is hard, which is why these calculators exist which numerically solve the dynamics problem. The ideal ratio for every mechanism is significantly higher than the ratio needed to maintain steady-state, because acceleration is that important.
Motors operate throughout almost all of their dynamic range in correctly geared mechanisms. Designing fast mechanisms involve balancing the free speed of the mechanism with its acceleration, such that the mechnism has the highest average speed. Peak efficiency is a strong function friction, which causes it to heavily get skewed based on how much friction your mechanism has, which is hard to measure.
I was trying to keep it at a high school physics level rather than 3rd year Mechanical Engineering.
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FYI AMBcalc has documentation for all calculations:
All documentation file (“All Docs”) located at the top-right corner in this link (where you choose which option you want to use from the calculator):
In addition, each calculator (e.g. Mechanism Ratio, Mechanism Startup…) has specific documentation at its top-right corner “Docs”
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the most important issue with calculators of all types is that students often use them blindly, which is worse than guessing, pedagogically. you can read about how they work, but there’s almost no benefit to that. if we wanted students to just read about robotics, the whole program would be a lot simpler. 
Instead, use John Wheeler’s principle: never calculate until you estimate. do a simple estimate using a simple model (e.g. gravity and gears). then do another, with a bit more complexity (e.g. energy or acceleration). then use a numeric solver when the model gets too hairy (e.g. friction).
there’s a place for simulators, but it’s not step one.
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Quoted for emphasis.
When you see a simulation result your first question should be Is That Answer Reasonable? (ITAR™). If you don’t know, then the simulation was done too soon.
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I wouldn’t say to use only the steady-state mechanism calculator (ambcalc.com/mechanism) or the startup mechanism simulator (ambcalc.com/startup). Each one leaves out some important information that the other includes. Which one you want to start with depends on the specific design case (how much time the mechanism spends accelerating vs at top speed), as well as design philosophy (aggressive vs safe).
Regardless, I do recommend using both calculators as sanity checks for the other. If one says the elevator will lift the weight in 0.5s and the other says it will take 10s (or not succeed at all), either there’s something wrong with your inputs or you’ve found a bug in the calculator.
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