Gravity Vehicle C

[Balsa Man]

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.

YES.
Thanks both for the good, detailed description and the very appropriate safety precautions!
Only a couple thoughts to add-
Aluminum comes in various alloys, and their properties vary considerably. There is a system of numbering & lettering- see Wikipedia. The stuff you can get at Home Depot/Lowes (not sure which alloy it is) is easily worked, but fairly soft. T6061-T6 (any decent metal/alumuminum supplier) is a good upgrade- still workable with wood shop tools (table saw w/ carbide tooth blade, circle/hole cutters) significantly stronger & stiffer than hardware store stuff.

Washers when turning in a drill press are a very good idea- they help prevent wobble which will affect both the trueness of the groove you're putting in, and wallowing of the center hole.

Since you're putting side pressure on the edge of the disc, 1) put the holding bolt as far up in the chuck-as close to the chuck jaws as you can, 2) consider clamping a backing block on the drill press table- a block of a hard wood positioned so it is just in contact with one side of the disc, and you bring the rat tail in on the opposite side.

Set up a way to brace your hands and the rat tail against something solid

Leather gloves provide hand protection without interfering much in hand sensitivity.

Have fun

[illusionist]

I should have asked this earlier, but how do you cut a precise circle from a sheet of aluminum? Just use a hacksaw and then sand the edges smooth?

[chalker7]

I should have asked this earlier, but how do you cut a precise circle from a sheet of aluminum? Just use a hacksaw and then sand the edges smooth?

That depends on the tools you have and the size of your aluminum sheet/wheels. Probably the easiest thing to do is to cut them out with a hole saw (basically a large round saw that plugs into a drill like a drill bit).
Hand cutting them with a hacksaw is incredibly difficult and I wouldn't recommend doing that. You are very unlikely to get a perfect circle and will likely end up with some sort of a wobble.
If you have access to any computer controlled machines (CNC, Laser, plasma or water cutters), those are definitely the best way to do it.

[illusionist]

Thanks everyone for the info. I should be able to go down to our robotics room later next week. I think it'd be easier to use some sort of plastic rather than aluminum, not only for making the part, but also because plastic would be lighter and if I recall correctly, lighter wheels allow for greater speeds.

[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

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

Yeah water and a paper towel, I can't think of anything else that might work better =/

[Half-Blood-Princess]

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

Huh... awesome. Seems fast What times are you getting? I'm getting around 2.1 sec for 5.0 meters

[Half-Blood-Princess]

Thanks everyone for the info. I should be able to go down to our robotics room later next week. I think it'd be easier to use some sort of plastic rather than aluminum, not only for making the part, but also because plastic would be lighter and if I recall correctly, lighter wheels allow for greater speeds.

Hahahahahah you think its hard for you and your ' robotics room'!? I'm homeschooled, we built our car in my partner's garage

[chalker7]

Thanks everyone for the info. I should be able to go down to our robotics room later next week. I think it'd be easier to use some sort of plastic rather than aluminum, not only for making the part, but also because plastic would be lighter and if I recall correctly, lighter wheels allow for greater speeds.

Hahahahahah you think its hard for you and your ' robotics room'!? I'm homeschooled, we built our car in my partner's garage

Please stop posting replies to each post separately, it makes it very difficult to read and spams those of us who are subscribed via email. Instead, just copy each person's text that you want to reply to and do it all in a single post.

[Half-Blood-Princess]

Fine then, if you can't scroll down....

[Balsa Man]

H-B-P,
You asked about time.
Posted at 10m on the previous page ("under 4").
At 5m, just under 1.9. I was pleasantly surprised how little speed is getting lost from 5 to 10