Gravity Vehicle C

[iwonder]

What does

"chase" the threads with a die

mean?

Taps and dies are tools used to create thread patterns. A tap threads a hole(so you can put a screw in it, internal threads) and a die does the opposite(I use one to make the threaded section of our axle, external threads). When you chase over threads, you simply run the die over precut threads, all it does it work off any corroson(we're talking .001" here) and shave a hair off the threads, do this a few times and you'll notice the nut have more and more play. This doesn't effect the consistency of stopping, but it does lessen the friction.

[_HenryHscioly_]

I see..I'll go get die from home depot then :]

Has anyone tested their vehicles from different heights to find optimal release height for different run-distances?
I cant get my stuff down from the garage yet...probably for another week

[illusionist]

On a different topic, what types of metals are you using for the axles? I've been using Zinc threaded rods that I've found at HomeDepot. They also have stainless steel, but it's about 5 times more expensive.

[iwonder]

For the cheaper vehicles I used steel drill rod(local machine shop supply company, it's a really tight toleranced version of the Home Depot steel rod) and made everything out of that(cut my own all thread because I couldn't find straight pieces). This year I'm planning on using 316-stainless and titanium, luckily I don't have to machine the titanium at all... Online Metals(that's the name) has a good supply of all kinda of different alloys and metals, for a pretty good price.(1/8" titanium rod is under $4/foot)

[illusionist]

For the cheaper vehicles I used steel drill rod(local machine shop supply company, it's a really tight toleranced version of the Home Depot steel rod) and made everything out of that(cut my own all thread because I couldn't find straight pieces). This year I'm planning on using 316-stainless and titanium, luckily I don't have to machine the titanium at all... Online Metals(that's the name) has a good supply of all kinda of different alloys and metals, for a pretty good price.(1/8" titanium rod is under $4/foot)

What's the benefit of using titanium? Is it lightweight, stronger, straighter, or smoother?

[chalker7]

What's the benefit of using titanium? Is it lightweight, stronger, straighter, or smoother?

All of the above. It's both lighter and stronger (on a per weight basis) than steel. That means it will stay straighter and hence run more smoothly. Beware that it is incredibly difficult to work with though (in addition to being very expensive.) Since you want to stay pretty close to the maximum mass on the vehicles, regular steel rods should be almost as good. Don't switch over to stainless, in general it's a little less stiff and the corrosion resistance is generally irrelevant for this application.

[iwonder]

Well, it's about the same strength as steel, and twice as strong, so it lets me use a smaller axle(less rotational inertia) yet not worry about the axle bending under the load. The other bennifit is the corrosion resistance(my team doesn't understand that you shouldn't touch raw steel) so I don't have to worry about major rusting. The stainless is just for corrosion resistance(even though its a little weaker than steel), since I don't want the threads to rust.

Oh, as chalker said, both stainless and titanium(especially titanium) are notoriously hard to work with, so my design doesn't require any machining on the titanium rod, and I have access to a well equipped machine shop to turn the stainless down and yes, the steel in my previous vehicle rusted shortly after we started using it(week before states) due to miss handling and if the season hasn't ended we would've had to machine a while new shaft, so I'm slightly paranoid about it this year.

[retired1]

A little silicon spray or WD40 will go a long way to prevent rust. It does not collect that much dust. Candle wax or beeswax might work also.

[iwonder]

That's a perfect idea in theory, but it only goes so far in practice.

[illusionist]

That's a perfect idea in theory, but it only goes so far in practice.

What do you mean it only goes so far? I've used WD40 and have never had issues with rusting.