Gravity Vehicle C

[aim4me26]

HEY CHALKER! THAT WASN'T NICE! I TOTALLY RAN THE EVENT! I SAT ON 6 VEHICLES, BROKE 3, AND I USED 8 OF THE RAMPS AS SLIDES. THAT TOTALLY COUNTS AS RUNNING THE EVENT.

Seems legit.

[chalker]

I thought that the rules of this site called for being nice or politically correct. I think that response could have been phrased a bit kinder. Granted, the truth is not always nice.

It was a joke (as indicated by the wink at the end)... Bear and I have exchanged similar threads here on SciOly in the past if you follow enough of the threads going way back. All of the various National Event Supervisors I know that are active on this site are extremely dedicated to Science Olympiad and amongst the best of the best.

[bearasauras]

I thought that the rules of this site called for being nice or politically correct. I think that response could have been phrased a bit kinder. Granted, the truth is not always nice.

It was a joke (as indicated by the wink at the end)... Bear and I have exchanged similar threads here on SciOly in the past if you follow enough of the threads going way back. All of the various National Event Supervisors I know that are active on this site are extremely dedicated to Science Olympiad and amongst the best of the best.

[retired1]

Ok, so I am old school. I do not text, so had no clue that was supposed to be a wink. The fact that two out of a couple dozen national folks chose to joke, in a less than polite manner, does not make it correct. There are hundreds if not thousands of young impressionable teenagers that visit sioly. You are setting the standards for this site a bit lower than I was led to believe was the DESIRED.
That said, I very much appreciate the technical answers that you post. So do my students.

[_HenryHscioly_]

Has anyone used balsa for the vehicle's frame? Would it be too weak..?
Is it beneficial to spray a wing-nut braking axle with wd-40, or graphite powder?

[iwonder]

Balsaman's team last year used a balsa wood and carbon fiber lamination that was pretty strong, more details are in last year's topic. And yes, it would probably be beneficial to put graphite on a leadscrew type system.

[Balsa Man]

Balsaman's team last year used a balsa wood and carbon fiber lamination that was pretty strong, more details are in last year's topic. And yes, it would probably be beneficial to put graphite on a leadscrew type system.

Yup, we did, and it worked like a charm.
Sandwich construction. The core was from 3"x1/2" low density balsa; 3 pieces edge-glued together. Upper and lower skins were, as I recall, 0.014" CF sheet. Edges were 0.030"x1/2" strips. CF skin epoxied to the core. Really light, and really stiff, and that's what you want for the chassis plate. Stiffness was comparable to a 3/4" oak board, and weight was ~100gr.
Why?. Two main reasons. 1) The stiffer the chassis plate, the less everything mounted to the plate can move around. Flexing, in the plate and things mounted to it, absorbs energy. Speed score is all about minimizing the rate at which energy is lost. 2) The lighter the chassis plate, the more ....options you have for managing the rest of the weight. You want vehicle weight up at the max limit, to maximize momentum. The lighter the chassis (plate, plus everything else mounted to it), the more mass you can creatively manage to maximize your initial velocity off the ramp.

As to lubricating the threaded rod in a wingnut braking system, absolutely. The lower the friction loss, the more slowly you loose velocity, and the better your speed score. You can also, by the way, reduce friction in such a system by "polishing down" both rod and nut to open up the clearances

There was a LOT of good discussion of all the various design considerations last year. Lots of really good tips and ideas. Very much worth anyone's time to go back and read thru.

[illusionist]

How do you mount the bearings to the chassis? My thought is to use a block that is mounted underneath the chassis, with a hole large enough for the OD of the bearing to fit in. With this method though, I'd imagine that the bearing would fall out of the block when braking occurs.

After looking through last year's thread, I found this response from Balsa Man about the topic:
"You set up bearing holders so that that the outside diameter of the bearings fits snugly into them, and the inside diameter of the bearings fits snugly on the axle. A way to do bearing carriers is use a piece of some kind of bar- aluminum, plexi, or lexan. For instance, we are using 1/8th axles, with ¼” o.d. bearings, 1/8th” wide. Bearing holders are ½” x 1/8th lexan bar, with slots filed in ¼” wide x ¼” deep. The tricky part with a live axle is getting/making sure the axle is straight; if its not, you will get wobble, which will cause vibration at speed, and movement of the bearings (or if the bearings are tightly held, binding)."

You say that the bearings are 1/8" wide, and that the bearing holder is 1/8", yet you drill a hole that is 1/4" deep in a 1/8" wide bar? I might be misunderstanding it. Can you please clarify?

[iwonder]

Hmm... I've always just bought mounted bearings, is there any bennifit to building your own mounting blocks? I assume it'd be cheaper, but unless you have access to some nice tools you'd also loose some percision(ie. the bearing might have a small amount of play relative to the body) right?

Illusionist, if the bearings keep falling out, there are two solutions I see... The easiest is to drill your hole slightly smaller than the bearing's od, and either simply press the bearing into the block using a press or vice, or you could(with a metal block) hear up the block and get a thermal fit to tennesring(that is probably permenant). Or, you could use set screws to hold the bearing in place(but it'd be difficult to drill and tap holes that small).

[illusionist]

Hmm... I've always just bought mounted bearings, is there any bennifit to building your own mounting blocks? I assume it'd be cheaper, but unless you have access to some nice tools you'd also loose some percision(ie. the bearing might have a small amount of play relative to the body) right?

Illusionist, if the bearings keep falling out, there are two solutions I see... The easiest is to drill your hole slightly smaller than the bearing's od, and either simply press the bearing into the block using a press or vice, or you could(with a metal block) hear up the block and get a thermal fit to tennesring(that is probably permenant). Or, you could use set screws to hold the bearing in place(but it'd be difficult to drill and tap holes that small).

Thanks for the suggestions. What do you mean you've bought mounted bearings? As in pillow blocks?