My initial design for wheels and tires had many problems. In order to reduce the number of parts, my original plan was to thread the axles themselves and screw the wheels on to the axle. I purchased left hand thread and right hand thread dies to do this.
I practice,, threading the axles tended to bend them, or at a minimum make them less straight. Of course this is a problem. I also had a lot of trouble with marring the axles trying to hold them while putting on the threads. I did get a test car put together this way, but one of the sources of vibration in the car was clearly the bent axle.
The final issue I discovered was that since you are counting on the wheels to help set the gear mesh, the fact that the wheels are getting “tightened” onto the axle while running causes binding.
My initial tire design was based on the tires on Carrera Go cars. The wheel has a “rib” around the middle and the tires have small “flanges” that fill that rib. The intent of this geometry is to keep the tire on the wheel in the turns.
These small side flanges are difficult to cast in a silicone mold. It can be done, but it isn’t as easy as I would like. The undercut in the mold is severe, making filling the flange and removing the tire both difficult. mold life was a bit of an issue.
For a while now, I’ve been working on a project I’ve been calling the Open Slot Car. This project really began as a response to the terrible quality of Carrera Go!!! slot cars. I purchased a Carrera Go set for my son and I to play with a few years ago, and while the track system is quite nice, the cars themselves had many problems. Also, in general, there is much less selection of cars in 1/43 scale than in other scales.
So, I thought it would be fun to design a 3D printable chassis and bodies to enable people to build cars that run better than the Go cars, and be inexpensive to make.
The first car I wanted was a 1974 Dodge Monaco. I found some dimensions and pictures from the internet and set about creating this iconic car.
I learned many things in the design of this car. Number one is that modelling car bodies in regular MCAD is quite difficult. Number two, is that you have to be really careful with how you set up the models so that you can shell them out in order to keep the weight down.
Here is a body off shot. I tested many ideas about flag/pickup design as well as evaluated different options for the front axle. This initial flag design didn’t work very well.
I started off using de-soldering braid I had ordered from McMaster. I ordered braid with no-flux, per the suggestions of others. I thought the little screws pinning them in place was a good idea, but the screws ended up damaging the braid, and I had trouble getting a reliable connection.
For this first iteration, I tried to use as many “commonly available” slot racing parts from other scales as I could. The smallest Parma King Crown Gear I could find was still a bit to tall for what I was trying to do here. That also drove me to use 1/8″ axles, bearings, etc. I had a lot of trouble with the gear “high centering” the car on the track when in motion, causing terrible handling.
You can also see that this car uses a 130 can motor. These are so inexpensive and so common, I really wanted to make these work. However, after trying several different motors, I concluded that for 1/43 scale it is worth the trouble to track down a smaller 030 can motor.
I went into this project with the intent of making my own tires. I wanted a wheel/tire design that would make it easy to change/replace tires (no glue required). I also wanted the tires to be easy to cast. The Wheel/Tire geometry I came up with met those goals to a point. On home track, at relatively low voltages and speeds they work fine. If you take care in the process of mold making, you can produce wheels and tires that don’t require a truer (at least for low speeds and home track use). however, in the end I’ve concluded you really need a tire truer to get any real performance out of these parts. The FDM printed wheels are a little rough, the tires are a little rough, and the truer does a lot to correct these issues. I also tested two different hardness of Urethane, with the softer 20 shore being a clear winner.
If you’ve read this far, you should also be aware that I decided early on that I wanted to be able to run with no-magnet. I did design and test a few different magnets and holders on this chassis. Indeed, adding enough magnet would make it run, but I prefer no-mag racing and wanted to find a way to sort an FEM printed car to the point it could run with no magnet.
This car ended up not running very well for a variety of reasons. However, I used this car to test many different materials/parts/concepts and it served its purpose quite well. I still don’t have a 1974 Dodge Monaco in my fleet, but that day may be coming soon.
