Gravity Vehicle C

[Balsa Man]

If you want the description balsaman posted last year concerning the vehicle that'd be here

http://www.scioly.org/phpBB3/viewtopic. ... ch#p203598

Did video of this car ever end up being posted?

Believe a YouTube link was posted- here it is
https://www.youtube.com/watch?v=nHhQAAdUvkg

That video, done by one of our parents notes distance away fm target as 3.5cm- was actually about 1/2 that

[Flavorflav]

The strange thing about that video to me is that at the end of the first run the vehicle showed very little recoil, but on the second run the recoil was quite significant. Was that intentional?

[jacobxc]

The strange thing about that video to me is that at the end of the first run the vehicle showed very little recoil, but on the second run the recoil was quite significant. Was that intentional?

I think they must have used a wing nut brake system, so when it stopped the the recoil was enough to loosen the brake causing it to move further back. To me I think it was a lucky fluck

[iwonder]

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.

[superblackcat]

Wondering if anyone has considered making the ramp out of bending the metal into the curve, because metal bends easier than wood, and cutting wood is hard (IMO)

If someone would give me the pros and cons on that >.>

THanks
SBC

[iwonder]

My ramp's just a piece of sheet metal that's kinda hung between top and bottom. It's definitely easier than wood, but it likes to flex around when the vehicle is launched because it's not very stiff. Other than that, it's nice and smooth and not too hard to work with.

[mrsteven]

My ramp is 2 pieces of 1/2'' square steel tubing bent exactly into a curve with Al bars running between them for supports. The ramp surface lays on top of that bone structure. Very stable no flexing, but requires a great deal of metal working skill/experience.

Edit: ill post pictures soon so you have a visual, im not sure how clear that was. Lots of hammering and bending to get the right curve with two identical pieces

[Flavorflav]

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.

From this description of the design that you kindly reposted, I can only assume that on the second run the anti-recoil ratchet did not engage the pawl. This could have been intentional or fortuitous. The speed and straightness (which are quite impressive) are clearly the result of design and construction, but I'm curious about the recoil.

Wondering if anyone has considered making the ramp out of bending the metal into the curve, because metal bends easier than wood, and cutting wood is hard (IMO)

If someone would give me the pros and cons on that >.>

THanks
SBC

I'm guessing you haven't cut a lot of metal? There isn't much that is easier to cut than wood. Butter, perhaps, but that doesn't make for a very good ramp.

[mrsteven]

http://www.flickr.com/photos/66151628@N ... hotostream

This is a picture of the 'bones' of the ramp with bend 1/2'' squared steel tubing. The cross sections are for support and the bolts running through them double as bolts to hold on the surface to the bones.
The triangle piece in back was a scrap piece that is used to make sure the ramp cannot twist

[Balsa Man]

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.

From this description of the design that you kindly reposted, I can only assume that on the second run the anti-recoil ratchet did not engage the pawl. This could have been intentional or fortuitous. The speed and straightness (which are quite impressive) are clearly the result of design and construction, but I'm curious about the recoil.

Wondering if anyone has considered making the ramp out of bending the metal into the curve, because metal bends easier than wood, and cutting wood is hard (IMO)

If someone would give me the pros and cons on that >.>

THanks
SBC

I'm guessing you haven't cut a lot of metal? There isn't much that is easier to cut than wood. Butter, perhaps, but that doesn't make for a very good ramp.

Well, Flavorflav's right about that 2nd run. The alignment of the pawl slipped. Interestingly, and the fortuitous, real luck piece, was the guys had the start-point for the thread chaser one wheel revolution off. Had the ratchet worked, it would have stopped where the rebound started.
Saying that, of course iwonder's support is appreciated. A lot of good design time, and careful, complicated building went into it. I think I commmented last year on my....coach's frustration over lack of testing time- really getting the dril of running this system down. While it was limited, with everything working right, we were seeing multiple runs with +/- 1cm range accuracy and repeatability (that's both for braking distance, and lateral- lateral is +/- 1cm out to 10 meters). The team 2 vehicle was running a conventional wingnut braking system w/ the same basic chassis. Data suggested that at 7-ish meter range, the drag of the wingnut was costing us btw 0.2 and 0.3 sec.

On the ramp, as also discussed last year, a piece of formica is both EZ to cut, and bend to the desired curve.