Hello did you never have enough money to buy a proper Lego technic motor?
well have no fear because you can make one very easily and it's cheap

Step 1: Get the Materials and Bricks

1.a dc motor (I hacked mine from a toy fan)
2.double sided tape
3.blue tak
4.a AA battery
5. an 8 tooth Lego technic gear
6. 4 4x2 bricks
7. 1 8x2 plate
8. 1 8x4 plate
9. 1 16x8 plate
10. 2 2x4 plates
11. 1 1x4 brick
12. 12 2x1 bricks
13. A pair of scissors (not in the picture)

Step 2: Preparing the Base

step 1: get the stuff in th picture
step 2:attach the 8X4 and 8X2 on the 16X8 (as in picture 2)
step 3:attach the 2X4 plates in the middle of the yellow plate (as in picture three)

Step 3: Attaching the Motor

step 1:cut a strip of double sided tape and stick it in the middle of the 2X4 plates (as in picture two)
step 2: attach the bricks to the plates (each layer shown in picture 3,4 and 5)

Step 4: Attaching the Battery and Making It Technic Compatible

step 1:cut out another strip of double sided tape and stick it on the 16X8 plate (were you place it depends on the lent of your wire)
step 2:take one wire and connect it on the negative side of the battery with blue tak
step 3: shove some blue tak in the gear like in picture 4
step 4:attach the gear to the shaft like in picture 5

Step 5: DONE!!!

If you want to turn it on attach the other wire to the positive
if you are having problems with the wires battery and blue tak you can switch it with tape
hope you enjoyed this instructable