Beefing up the Seat Mounts

Saturday 31^st August, 2013, noon

A quick update on beefing up the seat mounts. Tried something simple and dodgy, but it seemed to work OK. First up just laid four new layers of mat, brushing on the resin between layers into the old mould to hold it all in place and covered with some plastic bagging –

Then laid in a bicycle tube inside it –

Put the lid back on and blew up the tube to hold the mat in place –

It did an OK job, with a bit of extra wrinkly resin. Nice and strong now –

Time for a break.

Front seat mounts in carbon

Back into the carbon fibre, making the front seat mounts. I firstly made a mould from a piece of the frame tubing and a couple of bits of melamine screwed together with a bit of wood at the bottom. Fillets were made with plasticene –

I later pulled this apart and sealed between the pipe and melamine with mastic before redoing the fillets (plasticene is not airtight). This is the lay-up during infusion –

It was necessary to add the blocks at the top and the clamps below to prevent the pull of the vacuum distorting the mould. Here’s the trimmed piece, sitting on top of the clamps that will eventually anchor it in place-

The piece is a bit too flimsy for my tastes (used 6 layers of carbon) and I’ll be adding a few more layers to the inside surface later. I’ve made two, one for each side.

Chains and Derailleurs

Thursday, 22 August 2013, 9am

First off I made two dropouts for the first two derailleurs –

Which were fitted thus –

With both derailleurs –

Then the centre front derailleur –

And the rear derailleur –

Mounts for the tensioners for the back wheel chains –

Fitted in place –

The finished setup –

Fitting the seats next.

P.S. If you’re interested in seeing some of my more recent artwork you can find it at

http://posp-art.blogspot.com.au/

Fitting the Drive Shafts

Wednesday, 14^th August 2013, 2pm

Before leaving the front end, I fitted travel stops to the steering arms and fixed the slop in the shocker mounts. Fox shocks come with 8mm diameter bushes, but they are more like 8.1mm, and the resultant slack is quite pronounced at the wheel. To remedy this, I turned down 10mm stainless bolts to 8.1mm –

On to the drive shafts. For the right hand end of the front drive shaft, I machined down another rear wheel hub, fitted an internal sleeve and bolted it to the end of the shaft I had previously fitted a cassette to the left hand end of –

I then bolted the centre sprockets in place –

This is what the final assembly of the front drive shaft looks like –

Ten sprockets at each end and two in the centre. And so to the rear shaft. I made inserts for the ends of the shaft, which extended it a little (unfortunately when I bought the tube I wasn’t sure of the final length and had it cut slightly short) and welded the end of a bottom bracket axle into each end –

You can also see here the 16 tooth sprockets I made to fit onto the ends of the shaft. These were made from the centre bosses of right hand pedal cranks with 16 tooth freewheel sprockets welded on, offset by 10mm. This is the shaft fitted in place –

I then had to fit a cassette to the middle of this shaft. To do this I had to fix a freehub shell (from which I had previously removed the bearings) to the shaft. I machined up a sleeve which was an interference fit on the ratchet teeth, bashed it into place, tack welded the end internally and then machined the internal hole. Final act was to fit it to the shaft with a grub screw –

To the right can be seen the derailleur dropout, in it’s approximate final position. With the cassette fitted it looks like this –

And the fitted shaft looks like this –

Next job is to fit the chains and derailleurs.

Steering linkages

Sunday, 11^th August 2013, noon

Managed to get a bit of work done and my skin’s holding up well. Connected the two front wheels, a tricky job involving a bit of 3D trigonometry.

These are the components for the steering linkages –

One end of the arms with the rod ends connects to the kingpins, the other end connects to the square section brackets which mount to the chassis. The arms are made from some more bits of that hang-glider and I have used some tiny 16x6x8mm ball bearings that I had lying around.

These are the templates I used to mount the brackets –

Getting the rod ends positioned accurately is critical, otherwise the toe-in will alter as the suspension compresses. The motion of the inner rod end must parallel the movement of the outer rod end precisely. It’s axis of rotation has to be the same as the kingpin, with the inclination and caster the same as the kingpin. As well as that, both the inner and outer rod ends have to be centred between the inner and outer wishbone pivots.

This is the bracket riveted in place, showing the linkages attached –

To find the length of the connecting rod between the two sets of linkages, I set up a makeshift trammel for the front wheels, setting the toe-in to zero for minimum drag and clamping the wheels in place –

I was then able to make the rod (chromed shower curtain rail) incorporating two bushes at the ends to allow a bit of vertical travel, install it and connect the linkages–

These pix show the effect of the Ackerman angle on the front wheels as the machine corners –

As can be seen, the inside wheels are turning much tighter than the outside wheels. The turning centres of both front wheels pivot about the same point on the projected axis of the rear wheels, ensuring that the wheels travel without scrubbing or drag. The inner wheel is also leaning into the corner more than the outer wheel, due to caster and kingpin inclination.

Glad to have that out of the way, it was a bitch of a job to get right.

What's Happening?

Just a short note to let anyone that's interested know why nothing's happened for a while.

My hands have been problematic and I'm waiting for the skin to get tough enough to continue. I'll be back at it as soon as they can take the punishment. Stay tuned.....

Front shock mounts

Tuesday 23 April 2013, 9.30am

Just a short blog to document the installation of the front shocks. This is a pic of the bracket I made to mount the shocks –

As you can see, I’ve used polypropylene again to mount the end of the shocks, and this is what it looks like mounted in position –

Action is nice and smooth, set the front pressures to 90lb and the rear to 150lb as a starting point.

Fitting the rear wheels

Sunday, 14 April 2013, 9am

I’m still alive and back in the blobisphere, haven’t been working on the Pospedal for a while to give my contact dermatitis (from the epoxy) time to heal, seems OK now.

I’ve built the rear shocker mounts using some bits of polypropylene cutting board –

The square aluminium insert is the threaded nut for the shocker pivot bolt. The aluminium brackets were later rivetted to the chassis. This is the swing arm fitted –

There is a clamp (nearest the camera) fitted to the swingarm pivot tube to hold the swingarm in place. I had to relieve the fit between the swingarm and shocker by putting a small dent in the swingarm tube. I also glued a small piece of neoprene to the chassis to cushion the swingarm under zero load, in the unlikely event that the rear wheel leaves the ground. This is a pic of both of the back wheels fully installed –

The only other thing I’ve done is fit the central bearing mount for the front cross-shaft –

It was a bit tricky fitting the brackets, had to make them twice as long as they needed to be in order to clamp them in place to get the holes drilled, then trimmed them afterward.

Building the arse end

Friday, 8 March 2013, 3pm

Another long break since the last blog. Putting the back end together involved a lot of machining and a lot of waiting for epoxy to harden around threaded inserts.

First off the rank was making the frame to hold the rear cross-shaft/swing arm pivot from a few bits of M-board –

I riveted the outer bearing brackets in place, clamping them back-to-back with a bit of tube through the bearings to make sure they would line up. Fancy bit of clamping –

After fitting the frame tube mounts similar to the front ones, these members were clamped in place on the floor panel and bolt mounting holes drilled in the ends of the tubes. The rear cross-shaft has been fitted to check the alignment of the bearings –

Next up I machined the threaded inserts to connect the supports to the floor –

The lugs are to ensure positive location of all the brackets. Gluing the outer mounts in place –

The large alloy plates are to spread the load -

Threaded inserts are fitted to the inner mounts -

Note I have started drilling 2mm holes either side of the inserts, the epoxy being introduced on one side until it starts to exude from the breather hole on the opposite side. And here are the brackets that they mount into riveted to the M-board -

I’ve been using large ¼” rivets, drilled out to 3/16” and then riveted from the other end with 3/16” rivets, thereby making double-walled and double-headed rivets. These are the inner mounts fitted in place and bolted to the floor –

Note I’ve also added a couple of small brackets to the inside of the outer bearing mounts to stiffen them up.

These are the forward floor brackets, made from one big chunk of high tensile aluminium -

The thicker band at the top of the circular holes will later have slots filed in them to house the carbon fibre seat mounts. This is where they fit –

The right hand tube extends inward beyond the mount to support the derailleur dropout. And this is what it all looks like bolted together –

So that’s most of the chassis finished and most of what’s left to do is fiddly stuff. I’ll probably be finishing off the drive train next.