Dragster Design, Part 1

We had an extended sixth grade class today.  Students were challenged to design and build the fastest robot car they could.  Last week, the measured the velocity of the standard robot car built from the LEGO directions.  Those went about 1 foot/second at 75% power and about 1.25 ft/sec at 100% power.  We discussed ways to make faster cars especially since we can’t get a faster motor. Ideas they had were to make lighter, to change the tire size, and to use gears.  The latter had to be strongly emphasized by me and reviewed.  This class has only 2 years of robotics experience and did not experience gears and gear ratios like the current kids coming up.  I hope this will not need as much direct instruction in future years.

I was excited to give them the LEGO NXT Resource Kits this year, which have tons of extra parts including many interesting gears, tires, and wheels.  There was a lot of rebuilding, which is normal, as kids discovered how to build a car without directions.  Many teams made cool cars but did not really pay enough attention to the goal, to make a faster car.  Some thought a bigger wheel would make the car go faster.  I’m not sure but I think it’s the same if the speed of the motor is the same.  Smaller wheels will turn faster but also not cover as much ground.    You can make a faster car by having the motor drive a large gear, which then drives a smaller gear, which then drives the wheel.


Two teams were able to have a testable prototype today.  The first car went at 1.43 ft/second and did NOT use gears to make the car faster.

The second team successfully used gears to increase the speed.  Their car is called Lightning.  The team was so proud when I announced to the class that they now held the speed record of 2.5 feet/second!  It really booked right along.  Made me feel really good to see them so happy.  I was also pleased that I seemed to have finally gotten the open-ended challenge for grade 6 right.  The one I had last year had some problems (too hard, took too long).

Can’t wait to see what next week will bring!


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2 Responses to Dragster Design, Part 1

  1. Wayne Burnett says:

    John, my experience is like yours – students like to build and re-build but not always focus on the challenge, like speed. And, same, it seems that gears need to be explicitly taught. Good experience! Thanks, Wayne

  2. Interesting. A lot of this seems to be universal.

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