Scrambler C

[InfiniCuber]

Our solution for that was to add a track in the launcher that guided the vehicle for the first bit of acceleration, the wheels would still skid but it would at least stay straight. Because of the soft rubber and cleaning the wheels (by the way, the isopropyl evaporates and leaves a much drier surface than possible with water) we didn't have major issues with skidding, even at <1.3 second run times.

Little skidding issues with <1.3 seconds?? We have a car that goes 1.6-1.8 and we have skidding issues...

Ours weighed ~550g(maybe 450? It's been a year since I weighed it) with an egg, and the vast majority of the weight is directly over the braking axle so the front wheels have a ton of traction. Plus they're the softest, smallest ones we could find. We did have issues with the back end skidding out when it accelerated, but we fixed that with a rail on the launcher that held it in line until the string released. We cleaned everything for every run.

Hmm, makes sense. My car also has the great majority of weight over the brake, and the softest wheels, but i believe it is a bit lighter than yours, maybe 250 to 300 grams? I clean the wheels every run also. I'm guessing it is because my car is lighter, not sure.

[iwonder]

Ours weighed ~550g(maybe 450? It's been a year since I weighed it) with an egg, and the vast majority of the weight is directly over the braking axle so the front wheels have a ton of traction. Plus they're the softest, smallest ones we could find. We did have issues with the back end skidding out when it accelerated, but we fixed that with a rail on the launcher that held it in line until the string released. We cleaned everything for every run.

Hmm, makes sense. My car also has the great majority of weight over the brake, and the softest wheels, but i believe it is a bit lighter than yours, maybe 250 to 300 grams? I clean the wheels every run also. I'm guessing it is because my car is lighter, not sure.

Lighter might have something to do with it... The suggestion for solving it is generally rubber washers where the nut hits it's end stop, but it's a but late for major changes now

[InfiniCuber]

Hmm, makes sense. My car also has the great majority of weight over the brake, and the softest wheels, but i believe it is a bit lighter than yours, maybe 250 to 300 grams? I clean the wheels every run also. I'm guessing it is because my car is lighter, not sure.

Lighter might have something to do with it... The suggestion for solving it is generally rubber washers where the nut hits it's end stop, but it's a but late for major changes now

I have a rubber washer

[iwonder]

Hmm, makes sense. My car also has the great majority of weight over the brake, and the softest wheels, but i believe it is a bit lighter than yours, maybe 250 to 300 grams? I clean the wheels every run also. I'm guessing it is because my car is lighter, not sure.

Lighter might have something to do with it... The suggestion for solving it is generally rubber washers where the nut hits it's end stop, but it's a but late for major changes now

I have a rubber washer

I don't know why I assumed you didn't...

[InfiniCuber]

Lighter might have something to do with it... The suggestion for solving it is generally rubber washers where the nut hits it's end stop, but it's a but late for major changes now

I have a rubber washer

I don't know why I assumed you didn't...

It's alright, I just have been trying many things to try and fix it, but it isn't much. It is only about 10 ish cm conistently (which is better than the half a meter it was before lol)
We recently got an increase in speed so just wanted to make sure i could handle the skidding.

[someusername]

How are you guys able to achieve such good times? Are you using a spring launcher?

[InfiniCuber]

How are you guys able to achieve such good times? Are you using a spring launcher?

Yes, or at least I am, and any elastic material works! As long as it is optimized to transfer the maximum amount of energy as possible, times increase dramatically.

[bernard]

How are you guys able to achieve such good times? Are you using a spring launcher?

I was able to get times around 2.4 +/- 0.1 seconds (measured with a stopwatch) with a spring launcher using Tan Super Sport from our Wright Stuff as the elastic. Our vehicle was around 300 grams with the egg attached. If you use a spring launcher, you can maximize how effective the spring is by using rubber that has the highest elastic constant your falling mass (<2.00 kg) can handle, allowing your ETV to experience the launch force for a greater distance (starting at the back of the launcher), and having a light ETV. It's probably late to lighten your ETV unless you for some reason had weights tied to it, but I've heard of teams with ETVs heavier than mine that got times much lower.

[iwonder]

How are you guys able to achieve such good times? Are you using a spring launcher?

Our system used surgical tubing for the spring portion and a pulley on the mass side of the spring. The pulley halved the distance the spring needed to stretch while still allowing the mass to fall almost the full 1 meter. Since the spring was only stretched by 0.5m, it was able to expend all of its energy while still accelerating the vehicle, and it ended the run entirely slack. The 0.5m also meant that we didn't need to angle the spring to fit in the box, which means the weight doesn't have to waste energy lifting the spring.

The big deal for me when designing it was all the little details of how to make the mass fall father, to get just the right energy transfer, get rid of as much friction and other losses, and obviously making the vehicle as light as possible.

[someusername]

How are you guys able to achieve such good times? Are you using a spring launcher?

Our system used surgical tubing for the spring portion and a pulley on the mass side of the spring. The pulley halved the distance the spring needed to stretch while still allowing the mass to fall almost the full 1 meter. Since the spring was only stretched by 0.5m, it was able to expend all of its energy while still accelerating the vehicle, and it ended the run entirely slack. The 0.5m also meant that we didn't need to angle the spring to fit in the box, which means the weight doesn't have to waste energy lifting the spring.

The big deal for me when designing it was all the little details of how to make the mass fall father, to get just the right energy transfer, get rid of as much friction and other losses, and obviously making the vehicle as light as possible.

That's a little different than my spring design. We had a very simple one (had a big pulley and a small pulley and used torque to pull back a relatively stiff spring) but we never had time to build and test it. I'm currently using a simple falling mass and string launcher that shoots the car out kind of like a crossbow without elastic (if that makes any sense) and our time is about 2.2s, which isn't terrible