# Actual calculations

In past few year I have calculated gear ratios and the torque required to do something, this year we had an arm that had something like 250:1 overall gear ratio that we used to push down and yeet on to have level 2 when we did this we sorta guessed and checked/calculated if it’s possible. What are some things to improve calculations like this? We also had the issue of balls where we ended up not gearing our intake low enough and we were at 30% power and somewhat slow intake and you could feel the slippage. Im not going to be on the team next year but I’d like to learn how to calculate this so I can help the team out next year even when I’m not there or have someone else learn from this.
I remember a guy from 3309 came by and spent a minute tapping away on his calculator and just told us we were not geared down enough. How does your team do this and do you tend to factor in battery percentage or just go a little over when calculating the force required? From what I know stuff we did should theoretically work but issues like this always arise. To the point where when climbing we’d draw so much current the robot wouldn’t send power to the radio and make us disconnect.
Thanks for the help! Sorry for the rambling.

Do you have the calculations you did on hand to share?

While I insist that you/other team members understand the underlying mechanics of things, I would also encourage the use of the couple mechanical design calculators on here that help with that.

Easiest way is to use AMB or JVN calculators found here on CD.
For calculations (and sorry if I’m restating the obvious), you arent able to go all the way up to max torque, or shouldnt. Max torque is achieved at stall, which would end up with too many amps and most likely destroying the motor. There is also a safety factor aspect. You want to give yourself a little wiggle room. When designing for most systems (minus drivetrains), I love to shoot for 10 to 15 amps in operating conditions. That leaves quite a bit of safety factor incase something breaks and additional load is added. For compensating with battery drop, you will want to look at motor curves for the predicted voltage drop. If you want to be able to run a motor at 9 volts, you will need to see how much torque is generated at the ideal location of amperage. I’m not an engineer or anything but these are things I’ve picked up along the years. JVN calculator has been extremely useful in aiding design.

As @Type pointed out, I posted here a handy design spreadsheet calculator to help automate a lot of the calculations you’re doing for designing mechanisms. It also has a bunch of other helpful features for robots design, some that I made myself and some that I borrowed from work other people had done before me. If there’s a useful calculation that isn’t included in there, I’d be happy to hear about it so I can add it.

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