Rubber band on rollers breaking

RPM, or, revolutions per minute, is a measure of angular velocity, ω. If I was feeling a little snarky today, I would tell you that the equation for RPM was revolutions/minutes.

Alas, angular velocity is defined by the equation P=τω and ω=v/r, where P is power in watts, τ is torque in newton-meters, v is velocity in meters per second, and r is radius of the rotating body in meters. As you can see in the τω expression, torque is inversely proportional to angular velocity, when considering a system sustained with a constant power P. With a little bit of algebra, you can also note that P=τv/r, which implies that as radius increases, the torque must as well for the same unit of power and linear velocity.

The implications of the inverse relationship between ω and τ are found pretty often in vex with gears. As you increase the radius of one input gear relative to its meshed, driven partner, the angular velocity of the output increases by the ratio of the sizes of the gears- while the torque decreases by that same factor.

So, simply put, the formula for rpm in vex is i can’t do this anymore
rpm = revolutions/minutes you’re welcome


Thank you for the lesson in regretting my existence. I already knew what rpm stood for. I think I’ll just stick to slo mo --> pixel measurements for fun —>mph —> rpm.

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that is possibly the worst way to measure rpm lol.

if you know your motor rpm and your gear ratio, you can figure out the output rpm pretty easily. just multiply the motor’s rpm with the gear ratio.

for example, if you’re gearing a 100 rpm motor 1:7 for torque, you would multiply 100 by 1/7. which is roughly 14.3. so your output rpm would be 14.3


Yeah but it’s fun. ButI’ve been told that it looks nice when properly explained and demonstrated in a notebook. It’s not efficient but it works.


I’m not exactly sure but I feel that wouldn’t be enough room to get enough compression on the ball thst you would want.

Explaining and doing the math is probably faster and more impressive on a notebook than using a bad and inconsistent method.

Calculate the rpm by multiplying motor output by gear ratio. If you want to know the tangential velocity, convert rpm to radians per second, then multiply by the radius in meters.

To convert rpm to radians per second, multiply the rpm by pi then divide by 30. This can be some good content if you can prove the math on notebook.

For example, if I want to calculate the linear (tangential) velocity of my drive, which is 257 rpm on 4” wheels, I’ll do the following:

257 rpm * pi / 30 = 26.91 radians/s
2” radius = 0.05080m
linear velocity = (26.91)*(0.05080) = 1.367m/s


You are missing an easy way to attach bands, one that yields the same tension in ALL bands. Shove some screws through the sprockets. Hook the bands over the screws. Easier, faster, and more consistent.

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This solution has already been presented (by yours truly lol). Also, I’m pretty sure after 2 months, they probably figured it out. Please don’t revive dead threads.