Gravity Vehicle C

[jacobxc]

My ramp is made of metal with wood sides and our is really good

[EastStroudsburg13]

I was helping score Gravity Vehicle at Conestoga today (thanks, GoldenKnight1!), and the one rules issue that came up the most was in the part in 3b that says the wheels must be on the ramp at the beginning. Several vehicles had their front wheels on the floor when they were set up, and while some teams had space to adjust their ramp and avoid being Tier 3'd, other ramps were too big and didn't have space. So, moral of the story: MAKE SURE that all of the wheels are on the ramp before launch.

[jacobxc]

T1 is running a low friction braking system, with a gear off the axle driving a threaded nylon rod, on which a very low friction "thread-chaser" is run; it trips a spring-loaded braking system trigger that drives a "dog-clutch" into one wheel. A bar inside one wheel that rotates w/ the wheel; a "disc package" that rides on the axle on bearings next to the wheel (3 ~1" diameter discs glued/pinned together), with a "dog" on the wheel side of it; when the brakes trip, the disc package is driven into the wheel; dog engages bar. There is an elastic band attached to the outside/circumference of the middle disc in the package, and then there is a ratchet disc- teeth cut in it, and a carbon fiber strip set so that the end of it gently rides the teeth. When the dog engages, the disc package rotates w/ the wheel, stretching the elastic, the ratchet bar keeps it from rebounding, and braking takes place over about 1/2 of a revolution (essentially no skidding).

I'm interested as to how you think a wingnut braking system could recoil. Please, do explain.

Also, it's a pretty big insult to call that a lucky run... considering the amount of time, money, and effort spent in the design of that vehicle, it wasn't just luck.

The reason I said its was the brake was because you need to watch the video and listen to the clicks. On the first one you hear one click. Then on the next run you hear two distinct clicks, so something that most likey wasn't suppose to happen happened. Also the reason I called it luck was because it doesn't matter the amount of time, money, and effort spent in the design of that vehicle. Sometime you do good because of luck. Such as my team at state when is was on my middle school team doing battery buggy. On the first run they got 7 cm off, then on the next run we adjusted it and then his team mate moved it at the last second without him knowing and they got 0.7 cm off. Which was luck. People got lucky all the time in Science Olympiad no matter how good they are.

[mrsteven]

While I was constructing my new car I became upon a thought, just want to make sure this is correct:

If you glue/epoxy/some way attach the inner ball bearing to the rod such that they spin as one, could I use a threaded rod for both axles without increasing friction?
Having a threaded rod for the other axle would help for attaching wheels and switching them out more easily by loosing nylan lock nuts versus hammering out perminently attached wheels onto a 1/4'' rod

thoughts?

[iwonder]

If they're ball bearings(not bushings or sleeves) it'd work fine.

[mrsteven]

when locking wheels onto a threaded rod, I'm running into the issue that if either side of the nuts holding the wheel on arent straight then the wheel locks in so its not truly perpendicular to the axle so that the car travels straight. The bushings I have on the wheels (1/4'' on a 1/4'' rod) are slightly larger (manufacturing, only so precise) so the wheels can also torque a little bit before tightening so that they aren't straight.

Has anyone had this issue/a solution to these issues?

I tried putting a little piece of paper between the bushing and the rod to make that little space disappear and i was able to tighten on straight, and it worked for one wheel, but not the others. Plus it doesn't solve the nut issue.
I'm thinking there is a better way to mount them than just torquing 2 nuts around it...

[retired1]

Last year we used a 9/32 aluminum tube over the 1/4 all thread and put a piece of 5/16 brass tube over that. Then super glued the two tubes together and cut sections to the needed size. The second tube was to get a nice fit to the bearing inner race. The frame was 1" wood. Bearing holes were done with a Forsner bit then a washer inside of that so that it only touched the outer race of the bearing. One car needed the all thread super glued to the tubing, the other one did not. washers and double nutting worked very well Used small fat wheels that were not ideal but available.

[mrsteven]

So I figured out that problem haha I ended up printing a part the right size so it couldnt torque

but I ran upon another issue, I was using that rubberized CA glue that was suggested to hold the bearings to the axle and it was really really flexing, and today it broke, and messed up alot of stuff on my car... I'm actually back completely to square one.
So what is a better glue for such a joint? ball bearing to threaded rod. I also used it to hold the plastic printed bushings to the threaded rod with even less success

[iwonder]

Didn't realize you had a 3d printer for this... how accurate is it? I'd actually suggest printing parts with threads on the inside for this, then use thread locker... it'd be pretty effective assuming it doesn't react with your plastic. Problem being that it wouldn't work unless you had threads on the inside, thought I guess you could drill and tap it, if it isn't brittle.

[mrsteven]

Didn't realize you had a 3d printer for this... how accurate is it? I'd actually suggest printing parts with threads on the inside for this, then use thread locker... it'd be pretty effective assuming it doesn't react with your plastic. Problem being that it wouldn't work unless you had threads on the inside, thought I guess you could drill and tap it, if it isn't brittle.

my school has one, since I'm in the combat robots program I have access to it, I have to pay for the plastic, but for some smaller parts its worth it.
I mean, its a 3d printer, its pretty darn accurate

I did actually tap one that i made to see if that would work, epic failure. no amount of thread lock will stop it from moving so it has to be glued down anyway, so whats the point of threading it? it just adds a source of human error to guide the hole ever-so off so that the wheel doesnt spin true, which was the issue I had. I find printing just the exact size of the rod so that it cannot torque around and glue from there is better with almost no human-capable error