LOL. Blasted thing... Will just upload it raw...
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Thanks to Aaron, I now have a weight for every major part in Scissorhands and up to 900 grams spare . That's bound to come down but its a handy buffer so that I don't have to worry about getting parts made and then having to cut them down to weight.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Before moving furniture for the inlaws today, I opened an account at RS Components ( the most over-priced store in the universe). Their trade counter is like a candy store for tech heads, the standout toolbox bling was undoubtedly this Fluke thermal imager:



Of course the price tag could buy me two Shrederators, so I put it down and bought a year's worth of crimp terminals, 5 litres of isopropyl alcohol and a trial pack of urethane casting compound.

The important thing is the urethane; I found that reducing Scissorhand's wheel diameter is a Really Good Thing; less gearbox shock damage, smaller target, more torque and more tolerance of motor over-volting. The plan is to make moulds from the spare UMHW around the workshop and use the TWR15 wheel hubs. If that works, I will make my own wider hubs from Delrin for extra traction. Wheel design one is 25mm wide by 52mm diameter, with a polyester and kevlar mat for strength and tear resistance.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Double post time: I drew up a basic design for the wheel moulds:



Imagine that all bolted together with some locating pins to keep it straight and that's what I am making tomorrow. The wheels can't be moulded until I get some strenghening mesh; the idea is to use some stiff polyester mesh with kevlar thread woven into it as a belt like a car tyre. Research suggests that wax will be an OK sealing and mould release agent and it looks like everything will be in place for the first run in two weeks.

PS This is uncharted territory for me: any advice will be greatly appreciated!
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

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Originally posted by Nick:

PS This is uncharted territory for me: any advice will be greatly appreciated!

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why not just solid rubber?

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mmm, well the urethane is still going to get cut up. What about replaceable tyres that interlock onto a titanium hub
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Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.
Albert Einstein.

A mesh would really increase the chances of getting gaps and air bubbles in the moulding which would weaken the wheels. Ypu also need to know if the urethane will bond to the mesh.
I like silicone spray as a mould release.
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The mesh is a bit experimental, however Jake has been very happy about embedding kevlar in urethane - it's a multi-strand fibre so there is plenty of surface area for mechanical locking. Bubbles are certainly a concern - I was going to try wetting the mesh and the mould walls with a brush or sponge dipped in urethane before pouring. I'm not sure how viscous the urethane is yet; if it is thin enough I might just drop the mesh in after the pour. If it doesn't work on the first few wheels, I will just wind kevlar around the hub to help the tread stay on.

I did some research on hub material; I was going to use delrin but after comparing specifications, glass filled polycarbonate has the same tensile strength and twice the impact resistance, which makes it a better choice. It is also less slippery, which will help the urethane to stick to the hub.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

i think the idea of urethane in jakes wheels was to stop the urethane tearing off the hub on account of the huge diameter of urethane. dont think he used it on plan b wheels??

id think dimpling or grooving the hub would be better than the mesh
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Russel seemed pretty keen on both grooving and kevler. The urethane I am using is softer than theirs and I have one near-new Whyachi wheel (which has a deep groove in the hub) where the urethane has completely seperated from the hub and spins around on the hub. I plan to mill extra grooves across the hub to help prevent that and also etch the hubs in acid.

The idea behind the mesh is just to hold the top 5mm or so of the tread together as it starts to get shredded. The urethane is much cheaper than buying new wheels so I am happy to improve the reusable hubs and keep replacing the tread.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

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a trial pack of urethane casting compound.

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Originally posted by TDT:

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a trial pack of urethane casting compound.

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The 500 gram urethane pack was $90 - like I said, RS is expensive! It is called Flexane 60 (Google it) and larger quantities can be had for less. Unfortunately, it goes off quickly and buying more than you need means the rest is wasted. One can should do 6 to 8 of my small wheels.

Ti wheels? Perhaps its just an armour disk for the outside edges...
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Actually, I ebay-whored two bits of titanium stock for $15 each They are 60mm diameter and around 50mm long. Thought they would make some puurdy wheels, or maybe some pullies. Impulse spending, and probably the only Titanium I'll buy

$90 is spensive, might look at a bulk pack, can make plenty of other things out of urathane besides bot parts... My S13 needs some suspension bushes replaced anyway
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