This Instructable was built in 30 minutes from scratch, using just the items in my pencil case and pockets, in the back of a Geography lesson. It's a really easy, and can draw circles. Anyway...

Parts needed:
2 Elastic Bands
2 Thin felt tip pens
1 Circular pen lid
1 Medium pen barrel
1 Ballpoint pen ink tube+tip
(Not required) 1 Section of a bike grip

Now lets get started!

Step 1: : Main Body

The main body is made out of the highlighter, the 2 felt tip pens and 1 elastic band.
Check out the video on attaching the pens together using the elastic band:
Elastic band fitting
Rules to follow:
1. the pens should be at about 75-90 degrees to the highlighter
2. the pens should be tight on
3. there should be one loop above the highlighter loose for later

Step 2: : Building the Motor(Powered by a Elastic Band)

In this step, it will be easier to describe it by the pictures:
1.You will need an elastic band, a pen lid (ours was from the pink pen), an outer pen barrel (ours was made up of 2 broken ones, one clear and one black-green one), a pen barrel and a section of handlebar grip (this part is completely optional, we had it so that the 2 barrels wouldn't come apart.
2.Push the elastic band through the outer pen barrel, using the inner one as a pushrod
3.Use the inner barrel to stop the band from coming out. meanwhile, hold the other one in your hand.
4/5.Hold the other end of the elastic band using the pen lid
6. Motor is done
7/8/9. place it upon the main body