1 pumpkin (long is preferred to round-use longwise (horizontally)
2 axles (must fit through center of wheels)
4 wheels (lawn mower replacement wheels work well.) Casters are cheaters.
4 washers (sized to axles)
8 nuts (sized to axles)
4 lock nuts or 12 nuts (sized to axles)
Simply put, to build a Derby Racer with a pumpkin or fall gourd, place the axles through it and attach the wheels. The secret to an undefeatable Race Car is having perfectly parallel axels.
Click here to learn about how to build your own pumpkin axle punch jigs.
To drill parallel holes for the axles, place the pumpkin next to the jig. Hold the pumpkin firmly in place and punch the first axle hole by pushing the steel rod or drilling with a long 5/16” bit. Insert a 5/16” rod through the jig into the pumpkin to stabilize it in order to make a second axle hole and repeat the punching and drilling process.
TIP: It is easier to decorate your pumpkin prior to putting the wheels on. Just remember to keep the bottom part of the pumpkin free of any decorations. For example, if you’re making a Mummy Derby Racer, don’t wrap gauze around the part where you will punch the axle holes.
Feed the axles through the path you have just created with the axle punch jig. If the threaded rod gets stuck, poke the steel rod through again to clear the path.
You need to be careful with the threaded rod. The threads can easily bend and then it will be impossible to get a hex nut to go on smoothly. Don’t hammer the threaded rod through the pumpkin or knock it on the ground to help feed it through. If you absolutely have to give the rods a tap, first screw an acorn nut on to the end.
Remember, pumpkins vary greatly in size and shape and will not be perfect in terms of weight distribution or dimensions. Despite your best efforts, it may not go straight. It can be challenging to get the axles on perfectly parallel, but worthwhile in the long run.
After a few trips down the racetrack, you may find that your pumpkin will slip on the axle and become off center. This often happens during some type of crash.
To avoid this problem, thread one fender washer and one hex nut on each axle. The placement of the fender washers should be snug against the pumpkin with the hex nut anchoring the washer in place on the axle as shown in the photo on the right.
While this step is not necessary, it will help to keep your pumpkin centered and keep your axles parallel (although this is discussed at length in Step 8.)
TIP: After repeated use, axles can bend or warp, especially if your racer has crashed. Do a check of the axles to ensure they are straight before each race.
Place nuts and washers on the threaded rod in this order: (does not include hex nut and fender washer described in Step 3)
1: (2) hex nuts
2: (1) flat washer
3: (1) wheel
4: (1) flat washer
5: (2) hex nuts
6: (1) acorn nut
Make sure that the acorn nut has enough room to be fully screwed onto the threaded rod. The purpose for the acorn nut is to protect you from scratches and cuts from the ends of the threaded rods. The sequence of washers, wheels and nuts is depicted in the photo to the right.
Repeat this step for the remaining three wheels. Now that you have all the pieces on the threaded rod, it is time to secure the hex nuts. You will need to create a LOCK NUT. Without a lock nut, the hex nuts will continue to rotate on the threaded rod as your pumpkin goes down the track and possibly cause your wheels to lock up.
To create the LOCK NUT, simply rotate two hex nuts onto each other. This is the step where you will use the two 1/2 inch wrenches. You will have EIGHT points on the four axles where you will need to make LOCK NUTS; one on each side of each wheel.
Place one wrench over one hex nut and the other wrench over the second hex nut. You will essentially be rotating one hex nut to the right and the other to the left. This will give you a tight joint that you will not be able to move by hand. It is important that after the lock nuts are tightened there is enough room for the wheels to rotate freely, but not so much room that they wobble. To avoid this problem, insert a fender washer between the wheel and lock nut as shown in the photo on the right.
Then rotate the two hex nuts back onto the flat washer and make the LOCK NUT joint. When you pull out the fender washer, you will have just enough room for the wheels to move unobstructed and without wobbling.
Make sure you do a test run of your Pumpkin Race Car. This is the only way to see what kind of adjustments you may need to make. A sloped driveway is a great place to practice. The following are common problems:
• RACE CAR RUBS ON THE GROUND: If the pumpkin hangs too low and is rubbing on the ground, you may need to shave some off. Bumps and imperfections in the road may also cause a pumpkin to hit the ground as it races. Make sure you have good clearance.
• RACE CAR RUNS SLOW OR DOES NOT MOVE: Check to make sure all wheels are spinning freely and not wobbling.
• RACE CAR VEERS OFF COURSE: Your Race Car may tend to veer either left or right. This is comparable to a person on a skateboard. Here are a few tips to help you keep your Race Car on a straight course:
o Are all wheels spinning freely? Check to make sure that the wheels are spinning freely and equally. If a left side wheel is stuck, the rotation of the right side wheels will cause the pumpkin to sharply veer to the left.
o Is the pumpkin centered on the axles? If your pumpkin appears to be heavier on one side, you may need to adjust its placement on the axles.
o Are the axles really parallel? The most likely cause of veering is that your axles are not parallel. Stated another way, the distance between the left side wheels or axles is different from the distance between the right side wheels or axles.