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Gear ratios for launcher
Has anyone found that magic gear ratio that works best for the launcher?
Our team tried doing a direct drive with the CIM motor but the ball did not go very far. I remember reading that a 2.7 to 1 gear ratio works best but I can't be sure. Any ideas? |
Re: Gear ratios for launcher
We've been running 2 BaneBot 550s with 20:1's and they work beautifully. We may just be able to pull off our master strategy after all :D
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OP, care to provide any details? My team's experiments show that you should find the exit speed you need for your range, assume the ball will go 60%-70% of your theoretical tangential free speed, and gear accordingly. |
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This post may be of interest: http://www.chiefdelphi.com/forums/sh...5&postcount=20 |
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We were just worried that a high gear ratio wouldn't have enough force to launch several balls and it would be hard to get back up to speed. |
Re: Gear ratios for launcher
The new kit wheels tend to tear up the balls, according to a couple of reports from teams who tried them. We're using a single 8" kit wheel from a year or two ago, driven by last year's FP motor with it's 19 tooth pinion, which drives an older FP plastic first stage gear from the FP gearbox. The ratio is 19:72, I believe. This gives us a pretty good range....
http://www.youtube.com/watch?v=81vOT2KY2ig But the gear ratio you want will depend on a lot of factors, as others have mentioned. |
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Other than the fact that the tread pattern on the 2012 KOP wheels chews up the foam basketballs, any single-wheeled shooter with six inch wheels (when directly driven from a CIM) should easily be able to shoot the balls a more than adequate distance. Simply changing the gear ratio won't solve this problem; the real problem is probably related to ball compression, shooter hood design, and/or misalignment/binding/friction in the moving parts of the shooter. FYI: The 2.7:1 gear ratio is what is inside the CIMulator from Banebots. There will likely be a fair amount of teams using this gearbox this year, as this gearbox makes a 775 or 500-series motor "emulate" the output characteristics of a CIM motor. This allows teams without a lot of machining resources to keep their CIM motors in their drive train and use "emulated" CIM motors elsewhere on their robot. |
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With a 6" wheel you could be looking for 2,000-5,000rpm axle speed, depending on what range you want. the actual ratio will depend on what motor(s) you're using. |
Re: Gear ratios for launcher
Has anybody posted test data anywhere that includes wheel rpm, wheel diameter, squeeze, launch angle, and distance? [edit] and wheel moment of inertia, if available? (yeah, I know: dream on) [/edit] I've been keeping an eye out, but haven't seen anything yet. It would be most useful as a sanity check for some of the calculations. |
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The trick is to find a balance between not enough compression (not enough energy from the wheel gets transferred to the ball, leading to wimpy shooting range) and too much compression (too much energy is taken from the shooter wheel without any shooter range improvements). If you do some experimenting, you'll find an a good balance between the two. Once you find the ideal level of compression, then you can look into substituting other motors, gear ratios, and wheel sizes. |
Re: Gear ratios for launcher
FIRST Team 1296 is trying 2 FP 801 motors at 6:1 and 2 AM motors at 4.64:1 driving 2 8" wheels (both under the ball) - have not got it running yet, a proof of concept with a CIM at 3:2 worked nicely compressing the ball 1-1/2"
HTH |
Re: Gear ratios for launcher
Team 166 is direct driving 2 axels with 2 8" wheels each. Each axel has a cimulator with 2 rs-550 motors each. We have not clocked its top rpm yet but the wheels spin quite fast as you can see in this video: http://www.youtube.com/watch?v=YtiK87pE_9U
We don't know the range of the final shooter yet, but the prototype could shoot 46-50 feet, the prototype was direct drive cims instead of cimulators. |
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We're making very consistent shots from key range with AM motors and planetary gearboxes, though the spin-up time between shots is too long. We're working on that problem now!
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