Hello CD so I’ve been working on some wheel driven rc cars aimed at going, well hopefully really fast and I’m running into something that could be quite the potential issue. I plan to do my final drive stage with belts but depending on what wheel size I go with I can be expecting these pulleys to be spinning anywhere from 17k rpm to 30k rpm. I was somewhat hoping to use vex parts including vex belts and pulleys but I’m not entirely sure how to know if they would be able to withstand this kind of treatment.
Some my questions are:
Would the vex pulleys be able to withstand this kind of treatment (More looking at the higher end of the rpm range)? If not is there anything I should be looking for out of a pulley to handle this rpm?
Would the vex timing belts themselves be able to handle this kind of strain? If not should I remain looking at other timing belt options or if I should use a different kind of belt what properties should I be looking for?
EDIT: Just for clarification this cars intended goal is to run in a straight line, it will not be turning at all other than minor adjustments achieved via a servo driven rudder. This car is being built to specifications put forth by ROSSA (Radio operated scale speed association) and will fit in the Electric Open class and is being built as not necessarily an attempt at the current record but as a personal goal to reach 180mph and then to be retired to allow the production of a new vehicle incorporating all that I have learned from the 1st iteration.
I sorta didn’t want to include what my intention was with the car because let’s be honest, it sounds ridicules and it’s likely that I will not achieve my personal goal but it’s worth a try.
I don’t know much about the pulleys and belts at this speed (though I’m pretty doubtful about them at this speed), but just the idea of running **wheels **at up to 30kRPM is disturbing. On FRC robots, CIMS run free at a bit above 5kRPM, and teams typically **reduce **their speed by a factor of at least 4:1 and more commonly 12:1 before applying it to a wheel. My car’s tires are (trip to garage) on the high side of 27" in diameter, which means that at 70 mph (1232 ips), they’re spinning at a bit under 900rpm (about the same as a CIM at 6:1 reduction). At the speeds you’re considering, check everything - bearings, wheels, and transmission methods, because those are definitely high-performance speeds.
Yea, in this car the wheels are going to be among the most difficult parts to design just due to what they are going to be put through. It’s a tight balance of a wheel softness between grip and being able to hold from exploding. The wheels are probably going to be the biggest challenge in this build other than maybe the body shell. You can be sure I’m not going to use any colson wheels though, last thing I want is one of those thing exploding at 25k rpm, that could be very dangerous.
Paper towel math (Bounty of course) has me thinking you’re trying to go over very fast with this design. 3" diameter wheels hit 100mph at around 11k RPM for reference. I don’t like this idea. Lots of crazy things with vibrations happen when you start to get to really high RPMs especially for things that aren’t professionally built. Bad!
Also, unless you drive these things all the time, I’d be worried about actually controlling it safely as well.
P.S. Excess buffalo chicken sauce works for doing math!
Wowsers. 30k RPM is fast. Really really fast. With a 1" wheel, you’re already going ~90mph. Gus is right; you’ll have to rethink everything. The vast majority of FRC parts just aren’t designed for that. If you do use hex shaft, you’ll have to stay away from the hex bearings and use round bearings with high speed certification. You can check the Gates Design Manual for information about max speeds for belts. As for the timing pulleys specifically, I’m honestly not sure. My gut says that you should be good with the aluminum timing pulleys, but I’d stay away from the multi-piece plastic pulleys.