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FRC 2015 Best Gear Ratio?

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  • FRC 2015 Best Gear Ratio?

    Hi, everybody. We're Team 835 from Michigan and this is out first post. We wanted to ask a question about gear ratios. Our robot's drive train is powered by CIM motors. We are planning on tank drive, but might use Mecanum wheels. What do you guys think is the best gear ratio for this year's competition? Thanks!
    Last edited by dcds835vp; 01-08-2015, 07:22 PM.

  • #2
    Re: FRC 2015 Best Gear Ratio?

    Originally posted by dcds835vp View Post
    Hi, everybody. We're Team 835 from Michigan and this is out first post. We wanted to ask a question about gear ratios. Our robot's drive train is powered by CIM motors. We are planning on tank drive, but might use Mecanum wheels. What do you guys think is the best gear ratio for this year's competition? Thanks!
    I just signed up for this forum myself, and I hope you found some advice elsewhere before now!!!

    If you haven't discovered it yet, chiefdelphi.com is a great forum for these sorts of questions. It's hosted by one of the founding FIRST teams, and you can usually find answers to questions like these by searching the forums. For what it's worth at this late date, wheel type is not primary, and maybe not even secondary in determining a good gear ratio (or ratios, if you use a shifting gearbox). The things to consider are:
    • What do I want my top speed to be?
    • How much acceleration do I need?
    • What is the diameter of my wheels?


    From these bits of info, you can figure out things like whether or not you need 1 or 2 (or perhaps 3) CIMs on each gearbox, and what the high/low gear ratios should be. For the record, our robot this year has an 8.45:1 gear ratio (we built a KoP drivetrain and made some mods from there) and 4" wheels. If anything, we feel this will be too fast for this game, as speed in alignment and pickup are more critical than speed to cross a long distance. Also, going too fast increases your chances of knocking over a stack, removing points that you or your alliance partners thought you had already scored. If we had not already had these gears ready to go, we probably would have selected a lower gear ratio, somewhere around 12:1. As you have probably already figured out, FIRST is definitely a forum in which "perfect is the enemy of good enough". That is, if you can do something "good enough" today, don't waste very much time and effort on "perfect". Instead, find the places where you aren't good enough and work on them.

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