Intro: How to Build a PUMPKIN RACER With Two Parallel Independent Axles
Here is a fun thing to do this Halloween, Pumpkin Racing. For our race, the use of a solid base with affixed wheels is illegal. No skateboards. No rollerskates. No Tonka trucks. The pumpkin itself must be the support of the pumpkin racer. The challenge is to build the fastest racing pumpkin with two independent axles.
And here is the secret to an undefeatable winner: For the pumpkin racer to go straight down the track, the axles have to be perfectly parallel.
For this Instructable I am using five inch soft rubber wheels with a 5/16 axle opening. These instructions are easily adapted to any size wheel.
Don't forget: Being creative is just as important as speed.
(1) medium pumpkin
(2) eighteen inch long peices of 5/16 threaded rod
(4) five inch soft rubber wheels, plain bearing
(20) hex nuts 5/16
(8) flat washers 5/16
(4) fender washers 5/16
(4) acorn nuts 5/16
(2) wrenches 1/2 inch
PUMPKIN AXLE PUNCH - check out the Instructable on how to make this.
Step 1: PUNCHING AXLE HOLES
Place your pumpkin next to the Punch. Hold the pumpkin firmly in place and punch the first axle hole by pushing the steel rod through the pumpkin. Do the same for the second axle.
I prefer to insert the end of one steel rod into a drill and drill the axle paths. It is a whole lot less work.
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 materials. For example, if you do a mummy pumpkin, don't wrap gauze around the part where you will punch the axle holes.
Step 2: INSERTING AXLES
Feed the axles through the path you have just created with the PUMPKIN AXLE PUNCH. If the threaded rod gets stuck, you can poke the screwdriver through again to clear the path.
You really want 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. It might seem like a good idea at the time, but you will regret it later. If you absolutely have to give the rods a tap, make sure you screw on an acorn nut first.
Thankfully if you do bend the threads, there is a simple solution: a tap and die. I always make sure to have one on hand for race day, just in case.
NOTE: After repeat use, axles can bend or warp. Especially if your racer has sustained a crash. Do a check of the axles to ensure they are straight.
Step 3: CENTERING THE PUMPKIN
After a few trips down the race track, you may find that your pumpkin will slip on the axle and become off center. This can happen during a crash, either with another pumpkin racer, someone's legs or the curb.
I would charachterize this step as not being absolutely necessary, but it will help to keep your pumpkin centered and it can help get or keep your axles parallel. This is discussed at length in step 8.
After reading this Instructable, you can decide for yourself if you want to add fender washers.
On each axle, thread one fender washer and one hex nut. The placement of the fender washers should be snug up against the pumpkin with the hex nut anchoring the washer in place.
Step 4: ATTACHING WHEELS
Here is the order in which to place nuts and washers on the threaded rod: (2) hex nuts, (1) flat washer, (1) wheel, (1) flat washer, (2) hex nuts, (1) acorn nut.
You want to make sure that the acorn nut has enough room to be fully screwed onto the threaded rod. The only purpose for the acorn nut is to protect you from scratches and cuts.
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. If you skip this part, the hex nuts will continue to rotate on the threaded rod as your pumpkin goes down the track. This will cause your wheels to lock up, your racer won't move, and you will lose.
Step 5: LOCK NUT
To create the LOCK NUT, you are simply going to rotate two hex nuts onto each other. This is the step where you will use the two 1/2 inch wreches.
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.
You will have EIGHT points on the four axles where you will need to make a LOCK NUT.
Step 6: IMPORTANT TIP
You need to make sure that there is enough room for the wheels to rotate freely, but not enough room for them to wooble. Here is a simple suggestion.
I like to insert a fender washer between the wheel and the flat washer. The picture will explain this step. 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.
Step 7: TEST RUN & TROUBLESHOOTING
Do a test run of your racer. This is the best way to see what kind of adjustments you may need to make. A sloped driveway is a great place for practice.
PUMPKIN RUBBING ON THE GROUND: If the pumpkin hangs too low and is rubbing on the ground, you will 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.
RUNNING SLOW OR NOT MOVING: Check to make sure all wheels are spinning and not woobling. They may also be spinning but just a bit tight.
VEERING LEFT OR RIGHT: Your pumpkin may tend to veer either left or right. I like to compare this to a person on a skateboard. A person is able to tell where their center of gravity is to go straight and can lean left or right for a path correction. No such luck with a pumpkin. You are going to have to make these adjustments for your racer by observation.
Lets use the example of a pumpkin that veers to the left. First 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.
If your pumpkin appears to be heavier on one side, you may need to adjust the placement of it on the axles.
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 than the distance between the right side wheels or axles. If your axles are off by even 1/8 of an inch, your pumpkin may not go straight.
In step 8, SPECIALITY HARDWARE, there are some more ideas for getting your axles parallel, but when it comes to this problem, don't underestimate the value of a strategically placed piece of Duct tape to pull your axles in slightly or push them out slightly :-)
WARNING: When you get all the bugs worked out, your PUMPKIN RACER will really pick up speed as it goes down the hill. Depending on how steep your track is, you may want someone at the other end to put on the brakes.
Step 8: SPECIALITY HARDWARE and CUSTOM ADJUSTMENTS
Take a spin up to your local hardware store and you will find specialty nuts and washers. Two of my favorites are as follows:
I really like an item called a FREE-SPINNING WASHERED NUT. This little item has the washer attached to the nut already. The washer is free-spinning. This particular nut may save you from many of these step. Try it out and see how it works.
My second favorite is called a TEE NUTS PRONGED. This little nut has teeth to it and could be used to help stabilize an axle or keep an axle in parallel. Once you find the perfect position, just jam it in the pumpkin.
There was also a nut called a MILLED EDGE COUPLING NUT. It is like a wedge.
I also found washers with holes in them, however, it would be easy to recreate this for less money by simply drilling a hole through a fender washer. You could use a screw through one of the holes to bring an axle into parallel.
I drilled through a fender washer to make my own. A picture of this is attached. I used my enhanced washer to fine-tune axles into parallel and found it to work well. First I secured the front axle with my custom fender washer. Then I measured for parallel on both sides. I was 1/8 inch off. I then adjusted the back axle by pulling slightly forward. Measured both sides until parallel and secured the fender washer in place. Perfect. Then I yanked and pulled on the screw as a test and found it held nicely.
Step 9: FINAL THOUGHTS
REMEMBER: This is a pumpkin and it is made in nature. Despite your best efforts, it may not go straight.
Yes, it is challenging to get the axles on parallel, and it is precisely that fact that makes the race fun. On race day, pumpkins will zig and zag across the track. Some will end up on the curb. Some will never get off the starting line. Some will zoom through the finish leaving everyone else in the dust. But for everyone, it is a unique and creative way to spend time with your family and friends.
GOOD LUCK AND SEE YOU AT THE RACES.