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Gearing for 20 FPS?
As hard as it would be to control, would it be possible to gear a normal 120lb FRC robot to travel at 20 feet per second while still having decent acceleration? It wouldn't be practical but it sure would be a fun driving experience.
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So, yes, it is theoretically possible. Now comes the fun part: calculating the gearing. I would suggest having a 2+ speed gearbox, one for starting motion and one for flying. |
Re: Gearing for 20 FPS?
I think you also want at least 6 motors in the drive. That should help quite a bit with acceleration in addition to a multiple speed gearbox. 254 routinely gears for about 17.5 fps in their high speed but they are also usually underweight and have their west coast drive down to a science.
As an actual competetive robot it would be pretty crazy for most games, but just as a offseason project it could be pretty cool. |
Re: Gearing for 20 FPS?
It is definitely possible. I can't quite remember where I read it (it may have been on their website), but I believe Slipstream (Team 254's 2011 robot) had a max speed of 20fps in one of their gears. I believe CD-Media has a few pictures of their gearbox around it. You may be interested in looking around for those and see if you can't get a good look at their gearing. When watching 254, I rarely saw them use it aside from the moments when they had to make quick runs across the field, and with 5 other robots on the field, that was not often. But it it would still be a nice feature to have in case of emergencies.
It is definitely possible. Hope this helps! -Leeland Edit: Okay, 19.8. This robot also weighs only 100lbs, but it should still be possible. |
Re: Gearing for 20 FPS?
This looks like a job for the JVN calculator!
...which I haven't spent enough time studying to learn what all the numbers mean. :\ |
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Now, COULD you build an FRC-legal drivetrain? It's plausible with the right math (I echo the endorsements of JVN's mechanical design spreadsheet) and from parts available on AndyMark's website. As an exercise, try to figure it out before you hit the spoiler: Spoiler for How I reached it:
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Sidenote: 148 in 2008 was originaly designed for 30fps, but later reduced because it was too uncontrolable. |
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Someone want to channel their inner Mark Leon and do the math? |
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Our drive this year was geared for 18.5 ft/s in high gear after accounting for losses. Before losses, the theoretical free speed was something like 22+ft/s. I discussed this in another thread, but controlling the robot at that high rate of speed is not something to take lightly. Here is the other thread- Post #s 8, 10 and 12 were my comments on driving at that speed: http://www.chiefdelphi.com/forums/sh...42#post1085342 Some teams routinely can handle the high speed, but it is certainly not for everyone. My main point is don't assume you can drive that quickly and be able to just control it like you could a slower robot. Make sure you have good reasons to go for it, you've done the math, have a solid design and a good strategy for control and you will be ok. -Brando |
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Now as I'm remembering back, I do vaguely recall that. That would have been something to see that little nine-sided robot cranking around the field at 30 ft/s. -Brando |
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Considering how that swerve was driven (RC Car controller) if any robot was going to do 30FPS well it would've been 148... But with John saying that it would've been foolish, it makes me believe that 30FPS is just too fast to be successful on an FRC field. I remember seeing a few 25fps-ish robots in 2008 and most of them seemed to be under driven or barely controllable. (Though, at 30 FPS, they'd have been running laps in what? 5 seconds?) |
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-Brando |
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