Gravity Vehicle C

[fishman100]

We used foam wheels that we found in our school's Mousetrap Vehicle kit from last year. They're squishy and provided a good amount of traction, but I felt like we were losing speed (just a tad) because of the squishiness.

[Balsa Man]

We're using ~2" diameter aluminum- one pair from a RC racer, one pair is aluminum discs with a groove around the circumference we scrounged from the scrap pile of a local mechanical engineering company that does prototype developemnt of instruments and assorted things. Tires are neoprene O-rings that fit slugly in groves/flanges around the circumference.

Quick rundown on the .....trade-offs at play with wheels & tires:
-smaller diameter and lower mass get you lower rotational inertia (than big diameter/higher mass); that means more speed off the bottom of the ramp (less "g" going into spinning up the wheels). We're seeing.....something less than 4 sec to 10m.
-harder/narrower tires lower rolling resistance - less speed loss over the run, less wander off a straight-line run. Foam (typical RC racer tires) and other "squishy" tires, because of deformation will give you significant rolling resistance, hence speed loss. Narrow, relatively hard tend to run straighter (we're seeing ~1cm wander at 10 meters...). Coefficient of friction is the key in - the controlling factor to- skidding. Something that dosn't deform much, but has a high coefficient of friction. When you look at the physics/the equations for friction, area is not a factor, i'e', the thought that you need wide for minimizing skifdding under braking is not correct. Best we've found to balance all these factors is the neoprene O-rings (Ace Hardware, in a wide variety of sizes).

[Half-Blood-Princess]

What type of tires is everyone using? You don't have to say if you want to keep a secret.... Just wondering

I've seen quite a few CDs/mini CDs with balloons wrapped around them.

Yeah, that's what our B team's using for Mouse Trap... I think it works better for them because they have a lighter car

[Half-Blood-Princess]

We used foam wheels that we found in our school's Mousetrap Vehicle kit from last year. They're squishy and provided a good amount of traction, but I felt like we were losing speed (just a tad) because of the squishiness.

Yeah that's what I'm using. And also I'm seeing that we have to clean it a lot, the dust makes it skid

[Half-Blood-Princess]

We're using ~2" diameter aluminum- one pair from a RC racer, one pair is aluminum discs with a groove around the circumference we scrounged from the scrap pile of a local mechanical engineering company that does prototype developemnt of instruments and assorted things. Tires are neoprene O-rings that fit slugly in groves/flanges around the circumference.

Quick rundown on the .....trade-offs at play with wheels & tires:
-smaller diameter and lower mass get you lower rotational inertia (than big diameter/higher mass); that means more speed off the bottom of the ramp (less "g" going into spinning up the wheels). We're seeing.....something less than 4 sec to 10m.
-harder/narrower tires lower rolling resistance - less speed loss over the run, less wander off a straight-line run. Foam (typical RC racer tires) and other "squishy" tires, because of deformation will give you significant rolling resistance, hence speed loss. Narrow, relatively hard tend to run straighter (we're seeing ~1cm wander at 10 meters...). Coefficient of friction is the key in - the controlling factor to- skidding. Something that dosn't deform much, but has a high coefficient of friction. When you look at the physics/the equations for friction, area is not a factor, i'e', the thought that you need wide for minimizing skifdding under braking is not correct. Best we've found to balance all these factors is the neoprene O-rings (Ace Hardware, in a wide variety of sizes).

Wow, thanks for the info! =] Do you mean neoprene O-rings as in like... sort of a roller blade wheel, but softer?

[illusionist]

Wow, thanks for the info! =] Do you mean neoprene O-rings as in like... sort of a roller blade wheel, but softer?

Like this- http://goo.gl/d4Rgu

BalsaMan- How hard do you think it'd be to put a groove on the circumference of a 1/4" thick circle of aluminum on a lathe?

[fishman100]

We used foam wheels that we found in our school's Mousetrap Vehicle kit from last year. They're squishy and provided a good amount of traction, but I felt like we were losing speed (just a tad) because of the squishiness.

Yeah that's what I'm using. And also I'm seeing that we have to clean it a lot, the dust makes it skid

I've had to clean the wheels too when testing. What are you using to clean the wheels? Water and a paper towel?

[Balsa Man]

Wow, thanks for the info! =] Do you mean neoprene O-rings as in like... sort of a roller blade wheel, but softer?

Like this- http://goo.gl/d4Rgu

BalsaMan- How hard do you think it'd be to put a groove on the circumference of a 1/4" thick circle of aluminum on a lathe?

Yup, Illusionist, that's what I'm talking about.
And, If you've got access to a lathe to cut the groove, I'd cut away some of the 1/4" thickness- a lot of rotating mass..

Yes, H-B Princess, they are softer than skateboard ones (which are polyurethane- generally at a Shore hardness of around 80), but because the cross section is quite small, the actual amount of flex/squishiness is very small

[sachleen]

Wow, thanks for the info! =] Do you mean neoprene O-rings as in like... sort of a roller blade wheel, but softer?

Like this- http://goo.gl/d4Rgu

BalsaMan- How hard do you think it'd be to put a groove on the circumference of a 1/4" thick circle of aluminum on a lathe?

Oh wow I didn't know you could get that! I remember one year we used just plastic tubing (http://www.bjwinslow.com/albums/labware ... r_foot.jpg) and hot-glued/melted the ends together and sanded that part down to make it smooth. Still worked pretty well.

[fleet130]

BalsaMan- How hard do you think it'd be to put a groove on the circumference of a 1/4" thick circle of aluminum on a lathe?

If you don't have access to a lathe, you can make the groove using a drill press as an arbor and a round (rat-tail) file to cut the groove. Mount the aluminum disc on an appropriate sized bolt and tighten in place with a nut. If you wish, you can put a washer on each side of the disc to prevent marring it. Put the bolt in the chuck of the drill press and set the drill press to the slowest speed possible. While the disk is turning in the drill press, use the file to cut the groove in the aluminum. Insure the file has an handle to decrease the possibility of getting stabbed by its "tang". If the aluminum is too soft, it may clog the file and render it useless.

Be sure to follow all safety precautions for working with powered machinery/tools. Wear proper eye protection and don't wear loose fitting clothing that can get caught up in the machine. Work slowly and carefully.