Wheels, suspension components

25 Dec 2012, 11.30am

Since the last blog I’ve done some work on the suspension and wheels.I did a bit of work on the foam cores for the bottom bracket mounts, then my Canondale Lefty front hubs finally turned up and I diverted to lacing up the front wheels. I’ve used a single cross pattern on the outside and two cross on the inside. The wheel centre is offset 7mm to the inside, a standard setup for Canondale hubs. The rims are 16” Velocity Triple V’s.

I had second thoughts when I fitted the discs to the Cannondale hubs. The Magura Big setup that I bought from Greenspeed was alarmingly massive and I had pictures of the front end shattering under panic braking, so decided I had to set them up on the back wheels. I cobbled a setup together, seems to work OK.

First off, I made a mount that screws onto the freewheel thread and is fixed with three 6mm grubscrews (the hub thread is going the wrong way to lock under braking).

The brake calliper frame looks like this -

Swiss Cheese inner mount and knuckle joint (similar to a bicycle handlebar mount) -

Swing arm Teflon bushes have been recycled from the Mk IV –

The steel frame is 5/8” chrome moly, recycled by chopping up the old Mk IV driveshaft. The knuckle joint is set up so that, in the event of a flat, the calliper mount is swung out of the way by loosening the axle nut and the knuckle joint and sliding the tube back, then swinging it up out of the way, passenger’s role changing to a jack. The wheel doesn’t need to be removed to attend to the tyre. Took a couple of hours work to shim the calliper up properly. Just needs a lick of paint. The calliper mount was deliberately set up with a small gap to the calliper, allowing me to shim it accurately. The weld pulled it out of shape quite a bit and it needed to be tapped back into place.

I also finished off the second lower wishbone by gluing the chassis mounts in place with epoxy reinforced with nanotubes. That’s plasticene used as a funnel and mould.

Here’s an upper wishbone ready for the rod end mount. Rod ends need to have brass linings, the one's I used on Mk IV had plastic linings and wore very quickly.

The jig to align the mount, made from a piece of scrap that’s been in my shed for 25 years -

The resin setting in the jig -

Trimming the wishbone with a router -

Trimming down the mount with a saw fitted with an aluminium cutting blade

The finished wishbone, just needs a coat of paint and maybe a couple of rivets for extra security

For those wondering how the Elderflower champagne went, here’s the result. Pity that, it tasted pretty good, sort of a cross between cider and ginger beer.

Merry Xmas.

Infusing front wishbones

Sunday 16 Dec 2012, 10am

Been doing a bit more Carbon Sequestration. This blog details the infusion of the second lower wishbone.

Firstly I cut the 19 layers of carbon cloth using a cloth cutter and cutting mat –

These are the stacked 19 sheets

Then I put the four layers of carbon tube (two diameters) over the primed aluminium tube, which has a piece of dowel inside it and the ends plugged with plasticene. Cean cloth used to handle it to prevent oil contamination from my hands. It has been washed with prepsol.

Here’s the prepared mould. Since it’s been used once already, it only needs one application of release wax and has been coated with mould release PVA. Note I’ve drilled a hole in the centre of the mould so I can infuse from the back to ensure complete penetration of the resin from both sides (it worked).

Then a layer of breather fabric and peel ply

Then the mat layers

Then the tube and unidirectional bundles

And two layers of unidirectional tape across the tube

Followed by peel ply and breather fabric

Then the bag is sealed with mastic and vacuum checked (14.2 lbs/sq. inch) and we’re ready to go

Infusing from the mould side

Then from the left

And the right

Infusion finished, vacuum applied to all four ports

As it came out of the mould the next day

After removing the peel ply and breather fabric. Penetration excellent.

Rough trimming with a router. Note alloy plate to prevent dust dropping into the router. Carbon fibre would destroy it. A fan off to the side helps. Wear a mask. Finished off with a file.

The next infusion was much simpler, making the two upper wishbones in one hit. I used 15 layers (much less stress on this member than the lower wishbone) of cloth and wrapped it around the plugged aluminium tube. It was held in place with tacks of superglue.

Infusing, with breather and peel ply underneath as before

As it came out of the mould this morning

Excellent penetration. Might all be a bit pointless if the world ends on Friday.

Rear swingarm, front wishbone

Thursday 13 Dec 2012, 6.30am

I haven’t been able to update this blog for a while because I haven’t had a camera. I’ve gotten quite a bit done over the last week, finishing the second swingarm and making my first lower wishbone for the front end.

The second swingarm caused some problems, as the resin didn’t penetrate into the inner layers of carbon, as I found when I drilled into it afterwards. So I had to do a second infusion, running resin through it underneath the outer skin. That seems to have fixed it. This is a pic of the completed swingarm before I cleaned it up and a pic of the finished swingarms –

I’ve sprayed them with gloss white enamel to protect the plastic from UV. I didn’t bog the surface and fair it, it just adds weight.

At the top are the axle mounts, in the middle is a mount for an idler cog to keep the chain tensioned. The tubes are the swingarm pivots, which ride on the rear axle bearing support tube on Teflon bushes, and at the bottom is the shocker mount. My original intention was to cut a hole in the carbon and mount the end of the shocker inside the arm, but I realised this wasn’t going to leave much carbon where it was most needed, so I’ve decided to mount it to the side instead.

I’ve also laced up both of the back wheels –

The wheel is 48 spoke 20”, with Velocity Triple V 1” rims (Queensland made) laced to Joytec BMX flip-flop hubs, allowing me to fit a left hand threaded sprocket on the right hand side and a right hand threaded sprocket on the left hand side. Having single speed freewheels on each side provides the differential for cornering – only the inside wheel drives. Pattern is triple cross. Tyres are Greenspeed Scorchers. Here’s where it mounts to the swingarm –

The wheel has been laced up with a 10mm offset to the inside, minimising the moment on the axle under load.

Now to the lower front wishbone. First I had to make a mould. I bent up this sheet of 3mm thick gal steel using the tray of my ute as an anvil.

The vacuum bag from the infusion is still attached, I’ll re-use it on the second wishbone. That yellow mastic is super sticky stuff, you have to cut it with a knife to separate it. The mould was polished four times with mould release wax, then coated with mould release PVA. The wishbone separated easily using wooden wedges. I’ll detail the manufacture process when I make the second wishbone. I also had to make another jig to ensure that the mounts were accurately located -

The two verticals hold tubes that locate the chassis pivots. Top centre is the shock mount and the nut at the bottom locates the rod end that attaches to the bottom of the kingpin. This is the finished piece –

For this part I used 19 layers of twill woven carbon cloth, in total about 1m x 1.5m, with a fillet of unidirectional fibres (preventing cavitation and adding strength) down each side of the central 16mm aluminium tube (primed with etch primer to prevent contact with the carbon and ensure good adhesion to the epoxy) and two layers of unidirectional tape across the tube to ensure a good bond to the main member. The tube was sheathed with 4 layers of tubular carbon, of two diameters. It’s massively rigid and only 4mm thick. This was the member that failed on Pospedal Mk IV, I don’t think it will be a problem again. Also shown are the shock and mounting bolt, as well as one of the stainless steel pivot bolts riding in a phosphor bronze bushing that will be mounted to the chassis. The locknut has been machined down to save weight.

You can see that the rod end is angled at 12 degrees. This is the castor angle. The shock mounts have stainless steel inserts and the chassis pivots are threaded to take the 10mm bolts. All metal parts were fixed with epoxy. The small gaps left around the edges of the chassis pivots after gluing were filled with epoxy thickened with talcum powder.

This is how the wishbone fits in the jig –

I had the same resin penetration problems with this part as I had with the second swingarm, and had to do a second infusion to finish a large dry patch on the part against the mould. It was OK after that, but next time I will be infusing it from the mould side as well to prevent this problem recurring. It was complicated trying to work out an angle of attack –

Next time – infusing the second lower wishbone.

Making carbon swingarm

Tuesday 4 Dec 2012, 5pm

I’ve been a bit busy since my last blog.

Friday was a learning experience. I wanted to preform mounts for the swingarm components, which are seen here after spraying with etch primer. The tubes were later sheathed with a layer of fibreglass and the smaller aluminium components were coated with epoxy, to prevent contact of this metal with carbon fibre and consequent galvanic reactions.

 and after an all day effort arrived at this mess

  

Which I realised was going to be inordinately complicated to cast with the components in situ, and decided that night that it would be rather easier to fit the components after casting the swingarm.

On the weekend I took a couple of days off and drove up into the forest at the end of our road with Chris and David for the purpose of arting. Much fun was had by all. Here’s the result (all pastel and Charcoal) –

Sylvester’s (Saturday)

Mt Walker (Sunday)

In the Creek (Sunday)

My first artistic efforts in three years. Not much to do with engineering, but this is my blog after all.

Yesterday I got stated on the carbon fibre (that’s ‘fiber’ to any Americans reading this) components. I started by making two new cores for the swingarms from surfboard foam.

Then I started wrapping them in carbon socks

This shows the materials used in the wrap. Unidirectional at top and two diameters of sleeves below. The smaller sleeve (32mm) is stretched and consequently the weave is more across the component than the 64mm tube, thereby giving a couple of different directions of weave to combat twisting. The unidirectional gives strength along the spar. Thirteen layers in all, giving about 6mm walls to the tube. A bit over the top, really.

About ten layers at this stage.

This is the final tube assembly with the materials for the layup, firstly peel ply (which I stitched in place), then breather fabric (allows the resin to flow around the outside of the component) and finally the transparent bagging plastic. All materials came from playwithcarbon.com

This is the part ‘in the bag’. Mastic used to seal the edges and inlet and outlet ports fitted with extra breather under them (unnecessary, as I discovered).

This is the vacuum pump and catch pot (for excess resin drawn off the casting) in action

And this is the layup with vacuum applied (14 pounds per sq inch, or one atmosphere), no resin introduced as yet

And here we go with the resin. The tube between the inlet and outlet is clamped during infusion, then opened to apply suction to both ends of the layup. Carbon nanotubes mixed in the resin give it its black colour (Americans read 'color'). Fingers crossed.

Unwrapping at 9 last night –

Needs a bit more force –

Finally naked –

Today I put the second arm in the bag and proceeded to clean up the first arm (has a note of cast iron when you bang it on the fireplace) and ready it for it’s metal components. Apologies for the quality of the next few pics, didn’t realise the camera was on the wrong setting until much later. Clamp the arm in the jig –

Drill out a couple of holes and then bolt the arm through these to drill the rest of the holes.

Preparing the jig, sealing with plasticene and bagging plastic. It leaked. You can see the aluminium tube has a layer of fibreglass on it.

Finally woke up to the camera setting -

Pouring resin mixed with nanotubes into the swingarm to anchor the metal components. That’s it for today, hope you’ve enjoyed my first foray into resin infusion. I’m nackered. Bottling elderflower champagne in the morning for a change.