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Unread 06-11-2018, 02:26 PM
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Re: Reducing Backlash on FRC Robots

Quote:
Originally Posted by Jared Russell View Post
Make sure that you design your entire mechanism (mechanically, electrically, and software) such that when your feedback controller needs a couple more volts to compensate, they are available.
But how does an inexperienced student design in that headroom? 192 solved it by making students build mechanism prototypes that "must work" off beheaded 12v NiCaD drills. Once the prototypes worked with the small batteries and finger triggers, making them work on the robot was a piece of cake.

So for 841 I picked up 8 of these 12v drills, cut off the heads, and put PowerPoles on them this spring. Looking forward to implementing next season.

Looking back at OP's topic though... this tip definitely falls more under "give your team tools to observe backlash early and often" than "this is how we pull it out of our mechanisms"
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Last edited by s-neff : 06-11-2018 at 02:31 PM.
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Unread 06-11-2018, 03:00 PM
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Re: Reducing Backlash on FRC Robots

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Originally Posted by s-neff View Post
But how does an inexperienced student design in that headroom? 192 solved it by making students build mechanism prototypes that "must work" off beheaded 12v NiCaD drills. Once the prototypes worked with the small batteries and finger triggers, making them work on the robot was a piece of cake.
If you use my calculator to help design your mechanisms, you can set the voltage applied to the motors to 10 or 11 volts. That way if your actual applied load should increase above what you put in the calculator as the expected load, you still have some headroom for the motors to give more power before maxing out.
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Unread 06-11-2018, 03:27 PM
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Re: Reducing Backlash on FRC Robots

That's a sweet calculator.
Quote:
Originally Posted by AriMB View Post
what you put in the calculator as the expected load
And that right there is the roadblock that I'm getting around by asking students to "make it work" at prototype phase with limited power & control dexterity

One we have a functional prototype, we can measure stuff off it, and refine it with a calculator. But I've found that asking for too much math up front can intimidate my students into inaction I'd rather meet them where they are than act as a mathematical gatekeeper.

We're thoroughly off topic now.

Using spring loads to keep backlash in check is my favorite "FRC-ready" method for manipulators (<360 degree motion / single direction). Surgical tubing is magic, just wrap some on there & trust. Your students will need to experimentally determine what the "right amount of magic" is, you'll probably never put a firm number on it for design, and for four hours (1 season) machine operation? I'm OK with that.

Quote:
Originally Posted by Rob Stehlik
I put a hex shaft collar next to the gear, drilled though both of them and inserted a roll pin.
Love this. Could probably do it on a drill press?
I'd want to do it with a miniature VEX collar, but not sure how big a roll pin could fit through the "meat" of that shaft collar. What kind of loads were you putting on this?
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Unread 06-12-2018, 01:36 PM
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Re: Reducing Backlash on FRC Robots

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Originally Posted by s-neff View Post
Love this. Could probably do it on a drill press?
I'd want to do it with a miniature VEX collar, but not sure how big a roll pin could fit through the "meat" of that shaft collar. What kind of loads were you putting on this?
For sure you could do it on a drill press. I think the roll pin was 3/16", but it might have been even smaller. The loads weren't very high since the arm was very well balanced with a gas spring.
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