2011 Cars

[Silver Surfer]

Finally finished all of the cars. Cubs car is the one covered in chrome monokote. His sisters for the sibling race is the green and gold, same design but her's turned out so smooth we decided not to monokote it. Mine is the pirate car, I am going to have to cheat to have the fastest car this year.

[DenDadBob]

Nice work. They are similar to our cars this year. What kind of fan is that and what is powering it? Good luck at the derby. Let us know how they do.

[Silver Surfer]

I beleive it is this one http://www3.towerhobbies.com/cgi-bin/wt ... XHHP1&P=FR.

Puts out almost 2 oz. of thrust. Car only weighs 3.5 oz., we will see how it does on friday!

Maximum velocity just had an article on fan cars. The are using capacitors to get the fans spinning up really quickly. Very neat ideas to take to rediculous levels next year!

[DenDadBob]

That is pretty light. Mine was about 6.5 oz and might have done better if it was lighter.

What type of battery are you using? Is there a kill switch on the back?

I wired mine just like the MaxV article with the capacitors. It provides an initial burst then tapers off quickly and it was nice that it automaticlly shut down. I don't think I am getting everything out of the motor since the capacitors are only being charged with 9 volts. Still with no other powered cars to compete against it didn't matter. I think I may have competition next year so I will have to make some improvements.

I got the fan from MaxV and don't know what the specs are, but it looks smaller than yours.

I'm looking forward to hearing how yours does.

http://www.derbytalk.com/viewtopic.php?f=19&t=6130" target="_blank

[Silver Surfer]

Radio Shack 4 AAA box. It has an on off switch built into it. I wish I would have had more time to work on this. I decided to do it 2 weeks ago, so I could not test many configurations and I had to keep the electronics conservative. I would not have had time to get new parts if I burned up the motor.

[Silver Surfer]

Whoops weighed it again. It is 5 oz. not 3.5. Still 40% thrust to weight.

[Silver Surfer]

Thinking about it somemore, I doubt the AAA batteries re putting out enough amps to fully power the motor. Tried having it push a scale up against a wall and only got 1.15 oz.. I do not know if that is acurate or not, probably close.

[DenDadBob]

I just tried measuring the thrust on mine. I ran a string from a weight on a scale over a pully to the back of the car. When I started the fan it lifted up on the weight and the scale read less. I used a wind tunnel that I built following the example in a MaxV newsletter article on wind tunnel testing from a few years back. The reading on the scale dropped from 3.6 oz to about 2.0 oz, but went back so quickly I could not get a good reading. So it looks like I may only be getting 1.6 oz of thrust for a very brief time out of mine. Of course this is probably far from accurate. If you are getting 1.15 oz of thrust continuously, you may get more speed than I did.

[Silver Surfer]

I bought a force sensor from sparkfun.com a week or so ago. I wonder if I could use it and my arduino to graph thrust through 2 seconds. Will have to see how accurate it is.

But first I am going to have to back up and get the kids more involved with this car. They are missing some learning opportunities.

[Silver Surfer]

fan car did 2.5 on 42' Best Track
Green car did 2.91
silver surfer did 2.96