110ft/s (75mph) robot design

[Aaron Ng]

Originally Posted by nuclearnerd

They work with friction wheels that turn in a toroidal cylinder (some car CVTs work in a similar method). They're also really wasteful

loosing so much efficiency for a shifting mechanism doesn't seem like a worthy trade off, but i will look into it.

On the surface, if you could shave another 10lbs off of it (no shifting, carbon fiber frame, only 4 wheels so it's a straight line, belts) then your time & current are MUCH lower.

hmmm. getting rid of 4 cims would shave off a little over 11lbs. so if i can design a lightweight shifter...

i was thinking of using carbon fiber, but was hesitant because our shop doesnt have the capability to work with material like that. and i wanted the design to be feasible irl.

so it takes 16 seconds to accelerate? lets say it draws 300 amps. that means, at best, the breaker lasts 17 seconds before popping. it can still work! though it is pretty clear to me at this point that this design definitely needs a few major changes to have any feasibility.

on another note, how did you create those graphs and spreadsheet?! they are amazing. did you calculate by hand and make a nice spreadsheet, or is there an actual program that generates it?

As you have limited your acceleration by only driving two wheels anyway

wait... 4 wheels are on the ground at once, and all 6 are powered. shouldn't i not loose acceleration because all the wheels are powered? or has my life been a lie for the past two years?

If you're only driving two wheels, drive them together (perhaps with a solid shaft), and have one shifting gearbox that drives it. Hopefully you can get away without a differential.

wouldn't that mean that the outside wheel will scrub a lot when you turn?

steering two unpowered wheels is not terribly complex.

uh...no, it's very easy to design an build.

i was thinking of powered ackermann as being difficult, because my gut tells me that unless most of the weight is in the front, when you turn the wheels, they will just slide and create friction, acting like a brake instead of actually turning. of course, cars do this, and they are fine, and this is my gut, and my gut is often wrong.

Finally, I agree that more shifting range would be better than more CIMs in trying to get an intentionally light robot from zero to 75 using a single FRC battery. I would use cascaded shifters

cascaded shifters? is that a shifter driving another shifter? (that was my idea for a easy solution) im afraid i cant picture what you are saying.

Could I get a picture of the gearboxes (and cims) only. I'm very intrigued.

i dont have a render of that, but i can describe it.
its three cims that are chained together, and that drives the output of a ball shifter. and the ball shifter gears drive the hex shaft for the center wheel. and the center wheel is chained to the wheels on both ends.

[philso]

Originally Posted by Aaron Ng

loosing so much efficiency for a shifting mechanism doesn't seem like a worthy trade off, but i will look into it.

Often, the "lost energy" becomes heat in one way or another. Be ready to deal with it if you do choose to go this route.

[GeeTwo]

Originally Posted by philso

Often, the "lost energy" becomes heat in one way or another. Be ready to deal with it if you do choose to go this route.

I would say that "in general' the lost energy becomes heat. OBTW, for a physicist (e.g. me), "in general" is a code word for "always".