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#1
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Re: pic: 2 Speed Switching Module
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Going back to your original problem... A 135 lb robot (120 lb + battery, etc) can only exert a given force on the ground through whatever number of contact points it will have. If you have a good estimate on the coefficient of friction between the wheel and the carpet, you can easily estimate what the ideal gearing should be; no prototyping required. -Brando |
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#2
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Re: pic: 2 Speed Switching Module
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#3
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Re: pic: 2 Speed Switching Module
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CIM normal load = 4320 rpm Torque = 64 in-oz’s Ff= (c.o.f.) * Fnorm T= r * Ff Ratio between high and low gears is approximately 1:2.5 These numbers were calculated using the max weight of a full robot , 150 lbs. 4” Traction Wheel (C.o.f. = 1.25 – 1.5) Low- 1:30 gear ratio, 6000 in-oz’s torque, 2.5 ft/sec, 144 rpm ( before slipping occurs at 6056 oz-inches) High- 1:12 gear ratio, 2500 in-oz’s torque, 6.3ft/sec¸ 360 rpm 6” Omni Wheel (C.o.f. =1) Low- 1:18 gear ratio, 4000 in-oz’s torque, 6.0ft/sec, 230 rpm High- 1:7.4 gear ratio, 1800 in-oz’s torque, 15.25ft/sec, 580 rpm (forward/backward direction only) Slipping occurred at 10.7nM and at 12.7Nm depending on the tread material, so these projected ratios have the torque coming in lower than that value. If the math proves to be grossly off the only true loss is in the traction wheel. So the sprocket ratio from Omni to traction would simply be changed and that should solve any issues with stalling or being too slow and not gaining torque. Any corrections of the math are welcomed, better to fix it now before the pieces are made/ordered. Last edited by crazyStone : 27-09-2011 at 17:24. |
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#4
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Re: pic: 2 Speed Switching Module
No need for physics majors.
I've got to refer to this guy. Just type in gear ratios, it spits out torque, speed, and current draw numbers. It'll also indicate where cut offs for traction limiting is when you play around with the numbers. http://www.chiefdelphi.com/media/papers/2059 You did your numbers with CIM normal load value, this means that the CIM can do this loading all day. Realistically for an FRC application, you should use at minimum the max power numbers (171 oz-in, 2655 rpm, 67.9 amps). While there are other things constraining it (speed controllers, breakers, wiring, efficiencies, etc.), this will give you a better value. When I say FRC application, I mean short pushing matches, two minute matches, etc. Let me just say, we used 4" x 2" roughtop wheels last year at a 10.75:1 ratio and they were still spinning up the wheels. Do yourself a favor, use JVN's calculator. I got to ask, how are you doing your center to center distances on gears? Edit: Forgot to say, while I wrote about the max power numbers up there, the CIMs are capable of putting out 343.4 oz-in at stall current. |
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#5
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Re: pic: 2 Speed Switching Module
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