We've been looking for some large wheels around 250mm diameter for Dangly Too. But all the ones we've found are quite heavy and would cause problems in driving around due to the unusual centre of gravity and the gyroscopic effects of heavy wheels.
What do we do? Create our own custom lightweight wheels, of course!
This is what we made
How did we do this?
Step 1 - Make the wheel body
We decided to laser cut some 5mm acrylic using a simple 6-spoke design. This should be strong enough and we happen to have a lot of this acrylic freely available. Thanks to Hitchin Hackspace, we can use their laser cutter to make the wheels 👍
We're also using Pololu wheel hubs, bought from the PiHut to attach it to an 8mm stainless steel axle. These require 6 x m3 screws to hold in place.
The design was produced using OnShape, our preferred 3D design package, but it can also do 2D designs suitable for laser cutting. Simply create a single "sketch" and export that as an STL file.
Assembled using the Pololu hub with 6 screws and another smaller laser-cut hub for strength, we have a basic wheel. Then repeat for another.
Step 2 - Create a tyre
When we built the original Dangle, we 3D-printed tyres using TPU flexible filament, but found it was not very grippy. This time, we're going to try making tyres made from some silicone tubing attached to the rim of the wheel. First, we bought some 5mm internal diameter tubing, blue is nice we thought!
Cut to slightly smaller than the circumference of the wheel
In order to fit the tubing, we needed to slice it open so it fits tightly around the rim. This required a bit of improvisation and we ended up using a Stanley-knife blade attached to a split pin, which we then drew through the tube to cut it. Worked a dream!
Quick test fit seems to work. Maybe a bit loose, but we can stretch it to fit tightly
Step 3 - Fit the tyre
Stretch the tubing around the wheel and and glue in place. Seems to be a good solution, but time will tell how durable it is.
Step 4 - Attach to Dangly Too
Once we fit the two wheels, we start to see how Dangly Too will look and behave. We have a moving robot!
Next Steps
We now need to put him through some tests to ensure he can move and have enough grip to climb obstacles that we may encounter in the Temple of Doom!
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