IntroductionThe energy for a mouse-trap powered cars is stored in the mouse trap spring and it drives a wheel by some arrangement such as a string connected from the trap's jaws. There was a competition among the mechanical engineers at my University to build a mouse trap car that could travel the furthest. There were plenty of different designs. The winners had a design that released energy from the spring slowly and had only two wheels! The mouse trap hung from the axle. There are endless variations of designs for mouse-trap cars. The design I describe here is not a record breaker, but it can be made easily at home. If you do want to see some record breakers try Mike Flamino and Kevin McHale's Ultimate Mouse Trap Car Home Page. Actually, I don't think it really is the ultimate mouse trap car but it has a cute animated gif of a hopping mouse.
What You Will Need
One wooden mouse trap or rat trap.
Two lengths of 4 mm metal rod that are each about 15 mm longer than the width of the mouse trap. An engineering firm should be able to give or sell some scraps of steel rod and it can probably be bought at hobby stores too..
Four small eye-hole screws. These are like cup hooks but the hook part makes a circle. The eye must be large enough to put the rod through.
Some pieces of 3-ply plywood for the wheels.
Two rubber bands.
Some string.
A stack of small washers with a 4 mm inside diameter
You will need the following tools:
a drill with a 3.7 mm bit,
a jigsaw or coping saw,
a compass,
a hammer,
a vice,
a hacksaw,
a flat file,
some super glue,
two-part epoxy glue,
a pair of pliers, and
a flat jeweller's file.
How To Build It
With the pliers pull the wire catch that holds the trap open and the bait holder out of the wooden mouse trap. Pull out the wire staples that hold these parts in place, too. Keep the wire catch.
Take one of the eye hooks and screw it into one end of the mouse trap about 8 mm from one of the edges. Leave the eye hook in a position where the eye of the hook looks towards the sides of the mouse trap. Do this gently so that the wood of the mouse trap does not split. If splitting is a problem drill a small hole first.
Screw the other three eye hooks into the other three corners of the mouse trap.
Using a compass, mark out four 75 mm diameter circles on the plywood.
Drill the centres of the four circles with the 3.7 mm drill bit. Make sure that the metal rod will require some force to be inserted into the holes.
Cut out the circles from the plywood with the jigsaw or coping saw.
File the plywood circles smooth with the flat file.
Holding the rods in a vice cut each of them to a length equal to the width of the mouse trap plus two times the thickness of the plywood plus 5 mm.
File the ends of the rods smooth and put a small chamfer on them.
Hold one of the rods in the vice and use the hacksaw to make a small cut across the rod about one-third of its length from the end. The cut should go about half way through the rod.
Using the jeweller's file widen the slot so that the wire catch that you removed in the first step can fit snugly into it.
With the pliers cut a 7 mm piece of the wire catch.
File the ends of the piece of wire so that there are no burrs.
With the two-part epoxy glue, glue the wire piece into the slot in the axle. The wire piece should overhang the rod on one side only. Let the glue dry overnight.
Take the rod with the wire piece in it and put it through the eye hooks at the rear of the mouse trap. The rear is the end where the trap jaws lie when it is set.
Put a number of washers on the axle at either end. There should be enough of the rod left at either side to accomodate the wheels but not too much rod or the wheels will rub against the mouse trap.
With the vice, push a wheel onto each end of the axle.
Assemble the front axle in the same way as the rear axle.
Take the piece of string and tie it to the middle of the mouse-trap jaws.
Tie a small loop in the string so that the tip of the loop ends at the rear axle. Cut the loose ends off the string.
Take the rubber bands and put one around each of the rear wheels. The rubber bands will give the wheels traction on smooth surfaces. Use some drops of super glue to hold the rubber bands in place. The mouse-trap car is complete! To use it start by raising the jaw of the mouse trap slightly. Take the loop at the end of the string and slip it over the wire piece on the rear axle
. Turn the rear wheels in reverse so that the string winds onto the axle. This will pull the trap jaws open. When the trap jaws have been fully opened put the mouse trap car on the ground and release it.
What You Will Need
One wooden mouse trap or rat trap.
Two lengths of 4 mm metal rod that are each about 15 mm longer than the width of the mouse trap. An engineering firm should be able to give or sell some scraps of steel rod and it can probably be bought at hobby stores too..
Four small eye-hole screws. These are like cup hooks but the hook part makes a circle. The eye must be large enough to put the rod through.
Some pieces of 3-ply plywood for the wheels.
Two rubber bands.
Some string.
A stack of small washers with a 4 mm inside diameter
You will need the following tools:
a drill with a 3.7 mm bit,
a jigsaw or coping saw,
a compass,
a hammer,
a vice,
a hacksaw,
a flat file,
some super glue,
two-part epoxy glue,
a pair of pliers, and
a flat jeweller's file.
How To Build It
With the pliers pull the wire catch that holds the trap open and the bait holder out of the wooden mouse trap. Pull out the wire staples that hold these parts in place, too. Keep the wire catch.
Take one of the eye hooks and screw it into one end of the mouse trap about 8 mm from one of the edges. Leave the eye hook in a position where the eye of the hook looks towards the sides of the mouse trap. Do this gently so that the wood of the mouse trap does not split. If splitting is a problem drill a small hole first.
Screw the other three eye hooks into the other three corners of the mouse trap.
Using a compass, mark out four 75 mm diameter circles on the plywood.
Drill the centres of the four circles with the 3.7 mm drill bit. Make sure that the metal rod will require some force to be inserted into the holes.
Cut out the circles from the plywood with the jigsaw or coping saw.
File the plywood circles smooth with the flat file.
Holding the rods in a vice cut each of them to a length equal to the width of the mouse trap plus two times the thickness of the plywood plus 5 mm.
File the ends of the rods smooth and put a small chamfer on them.
Hold one of the rods in the vice and use the hacksaw to make a small cut across the rod about one-third of its length from the end. The cut should go about half way through the rod.
Using the jeweller's file widen the slot so that the wire catch that you removed in the first step can fit snugly into it.
With the pliers cut a 7 mm piece of the wire catch.
File the ends of the piece of wire so that there are no burrs.
With the two-part epoxy glue, glue the wire piece into the slot in the axle. The wire piece should overhang the rod on one side only. Let the glue dry overnight.
Take the rod with the wire piece in it and put it through the eye hooks at the rear of the mouse trap. The rear is the end where the trap jaws lie when it is set.
Put a number of washers on the axle at either end. There should be enough of the rod left at either side to accomodate the wheels but not too much rod or the wheels will rub against the mouse trap.
With the vice, push a wheel onto each end of the axle.
Assemble the front axle in the same way as the rear axle.
Take the piece of string and tie it to the middle of the mouse-trap jaws.
Tie a small loop in the string so that the tip of the loop ends at the rear axle. Cut the loose ends off the string.
Take the rubber bands and put one around each of the rear wheels. The rubber bands will give the wheels traction on smooth surfaces. Use some drops of super glue to hold the rubber bands in place. The mouse-trap car is complete! To use it start by raising the jaw of the mouse trap slightly. Take the loop at the end of the string and slip it over the wire piece on the rear axle
. Turn the rear wheels in reverse so that the string winds onto the axle. This will pull the trap jaws open. When the trap jaws have been fully opened put the mouse trap car on the ground and release it. 
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