Suspension Bush material

So I'm in the process of building a gravity soapbox race car. We have gone for double wishbone suspension. A bit like the screen shot in the picture. This is not my design but have added it to help my description. In the joint where the wishbones are bolted through the brackets I was thinking of adding a couple of 'plastic' washers to help reduce any slop but still allow articulation.

Is this a good idea a what would be the best choice? Nylon 6 or 66 or acetal are all coming up when I Google it. Any tips on turning this sort of material would also be appreciated.

Thanks Colin

Urethane (aka polyurethane) washers are available off the shelf. Widely used in automotive suspensions etc.

But if you make your own, Delrin should work ok. Machines ok with a sharp HSS toolbit. Nylon too, and not so stringy swarf getting caught round the job etc.

Edited By Hopper on 14/03/2022 11:42:59

Material as Hopper has suggested or try glass filled PTFE. I have used glass filled PTFE on motorcycle suspension with good results.

If you want buy try Igus. Plenty of choice of material for both bearings and washers, some at low prices.

The Locost home build cars used "plastic" top hat bushes for the wishbone pivots., although these may be too large for your racer..

It may be worth exploring "Locost cars " on Google, to find a source.

Howard

For the use a soapbox racer will get, is the complication of bushes really necessary?

Hi Colin - sounds fun!!

If it was me, I’d use nylon. Either 6 or 66, not much in it, but 6 if there’s a choice because it’s slightly tougher.

Acetal is a little more brittle and not quite so good wear resistance.

Nylon 6 can absorb moisture (presumably it’s outdoor) which doesn’t cause any issues that should concern you, except they can swell slightly. But we’re talking small dimensional changes, so just don’t make it too tight to start. Nylon 66 absorbs less if high accuracy is an issue.

Cheers Will

I have used Nylatron GS for suspension bushes with good results. It's Nylon with a Molybdenum Disulphide filler. Has better wear resistance than 'ordinary' Nylon in my experience. Machines nicely with a sharp HSS tool.

I would recommend the Nylatron GS that Stueeee has suggested. I have used it for bushes and have also had very good results. Machines without too much trouble.

Neil

You'll find the brackets can deform enough to take out any slop when you tighten the bolts.

Having watched the RedBull soapbox races the major flaws are wheels collapsing under side load and nor enough steering and or brakes.

Oh and doing a rubbish dance at the start.

Thanks for all the input. Give the use I definately dontvghink they are strictly needed and I certainly could just buy them but I'm trying to kearn machining and I'm always looking for opportunities to try something new.

Dave - you are right it's all about the wheels. I'm currently buying all the second hand bmx's I can find (apparently 20 inch bmx wheels are the sweet spot) I've also got the front wheels off mine and my wife's twist and go scooters. They are a bit heavy but definately won't fold. I also like the idea of hydraulic disc brakes as the course is 18 degrees and nearly a kilometre long!!!

How slight are we talking? I had no end of trouble getting the nylon bushes out of a friend's bike's seized headset. They had expanded to the extent that I had to apply extreme force to move anything.

Presumably, for Colin's application longevity won't be such an issue.

George

If you make the spoked wheels slope inwards to the top I think they will resist side loads due to cornering better. This because the outer wheel has higher down load due to the cg being above road level, so the side load at commencement of slip is higher, and the combined is more likely to be in the leaned over plane of the wheel. The optimum will depend on the coeff of friction, and the relative cg height to track.

Edited By duncan webster on 16/03/2022 00:40:51

Thanks for this. I have been learning all about this. What you are referring to I think is called camber. We will be having a bit of this but also some kingpin inclination to reduce the scrub radius (he says hoping he sounds like he knows what he is talking about!!)

I was hopingbthe nylon was going to reduce the possibility of binding. It sounds like this could still be an issue with nylon in the rain!

As per Hopper's post - delrin/acetal was my first thought. Available, inexpensive and machines to a silky finish with a sharp tool.