Let's Make Robots!

Rocket car [Update: New video!!]

Runs fast, measures burnout velocity

The rocket car was build from three RTF model rockets, a cardboard roll, 3 mm stainless steel wire, four 56 mm dia. TAMIYA racing wheels, plastic tubes, a lot of epoxy, aluminum foil and Epoxy Resin Putty.

The rocket car weights around 400 g and will be propelled by two C6 blackpowder model rocket engines. I plan to measure the burnout velocity. The wheel encoder (from an damaged printer) is mounted on one of the front wheels and contains two Hall sensors. The wheel encoder has a resolution of 30°.

The ignition of the rocket motors is remote controlled. After the burnout time is reached, a Picaxe 08M counts the wheel encoder impulses in a defined time intervall and display the value via two CMOS 4026 on a 2-digit-7 segment display. It is then easy to calculate the burnout velocity. I will compare the measured burnout velocity with the calculated burnout velocity by the rocket car equation I have derived.

2010.6.16: New video is up! Have fun and more soon!

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Nice.....

Looks great but I think you might want some airfoils and spoilers like a formula 1 car since this is one rocket you don't want to get off the ground.

As it is I predict the first time the front wheels lift due to a bump in the ground it will become airborn. At this point the weight of the encoder on one side will cause it to roll.

Hope I'm wrong :D

I have some rocket fins left and will add it. It was indeed an idea to make this vehicle also able to fly:

But due to the missing launch rod, the asymmetric rear fins, weight distribution and turbolances cased by the wheels the flight will be not very stable I guess :D

oh thats fine :D as you see I'm new :D but I like this idea of rocket cars too :D verry nice little car here :D

how do you measure distance with precision? :-? at this speed sometimes the wheel shouldn't touch the ground and even spin faster or lower so the wheel encoder isn't the best idea

I don't care about one meter more or less. The short time the wheel maybe not touch the ground, is negligible as it still spin at this short time nearly with the same resolutions. The wheel encoder has a resolution of 12 30° btw.

:D another interesting robot from you, what speeds are you expecting?

Here's one i made a while ago:

http://www.youtube.com/watch?v=4nG_i-G2BPw

Unfortunately the chassis melted after the barrel roll :(

Rocket was KNO3 + sugar, 60/40.

I have derived the rocket car equation (without air drag) a while ago, see here. Air drag neglected and an assumed rolling resistance coefficient of 0.72 I am expecting a burn-out velocity of around 54 m/s (≈194 km/h) if the rocket car is propelled by three C6 motors.