Attach the Motor and Battery Box

by Jan Goolsbey
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This string car design employs 1/16-inch nylon cable clamps to mount the motor to the chassis. Your motor must have threaded mounting holes for this mounting technique to work properly.

The motor shown was repurposed from an old DVD drive along with its special M1.7 x 4mm mounting screws. The M2.0 washers were added to keep the screw from damaging the cable clamps.

Do not use motor mounting screws longer than 4mm. Longer screws will protrude too deeply into the motor and could damage it permanently.
  • Snap the 1/16-inch cable clamps on the upper ears of the chassis as shown. The motor will be mounted to the clamps using the 4mm long screws.
  • With your fingers, pinch one of the cable clamps closed. Place the washer and insert the screw through the washer into the motor's threaded mounting hole.
  • Carefully tighten the screw until snug.
  • Test to see if the shaft of the motor turns easily -- if it does not, use a shorter mounting screw.
  • Repeat the process on the opposite threaded mounting hole. 
  • Do not overtighten; the mount only needs to be secure enough to keep the motor from twisting in the chassis.
  • Test the motor shaft to confirm that the second mounting screw is not limiting motor operation.
  • Slide the pulley onto the motor's shaft, keeping about 1/4-inch clearance between the back of the pulley and the face of the motor. 
  • Turn the pulley and verify that it isn't rubbing against a cable clamp.
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  • Cut the battery holder's wire to 4-3/4 inch in length. We won't need the 2.1mm connector, but you may want to put it in your spare parts bin for another project.
  • Split the dual wire pair apart approximately 1-inch.
  • Using wire strippers, remove about 1/8-inch of insulation, exposing the stranded copper conductors. 
  • Twist the exposed copper strands together and put a small amount of solder on the exposed copper of each wire to hold the strands together. This technique of preparing a stranded wire for soldering is called "tinning" the wire.
  • Using needle-nose pliers, bend the exposed portion of each wire into a U-shape.
  • Place the battery box into the cradle with the on/off switch showing face-up and the wire exit on the right-hand side.
  • Wind the wires around the chassis twice as shown.

 
  • Slide the "U" of each wire into the holes of the two motor terminals.
  • With the needle nose pliers, squeeze each "U" to crimp in place.

 

 
  • Solder both wires onto the motor terminals.
  • Insert the 9 volt battery into the box and press it into the snap connections.
  • Close the battery box cover and place it into the chassis cradle.
  • Flip the on/off switch to the ON position and listen for the motor to spin.

 
If the motor doesn't spin, check the soldered connections on the back of the motor. Is the battery fully seated into the snap contacts?
BEND THE WIRE CHASSIS STRING A STRING, BALANCE THE CAR, AND GO!
This guide was first published on Sep 01, 2017. It was last updated on Sep 01, 2017. This page (Attach the Motor and Battery Box) was last updated on Jul 16, 2019.