Replacing steering linkage

Sunday 30 November 2014, noon

I decided to replace the trick steering linkage with a simple ungeared linkage, for more leverage in the steering. It will probably result in twitchier steering, but will be more direct.

Swivelling bush on other side of M board –

Bush made from polypropylene, pivots from Teflon. I also removed the length adjustment from the rods connecting the handlebars to the linkage. They are now a set length, meaning the ‘driver’ seat can’t be moved without changing them. The adjustment clamps were prone to slip. Might work out a better way to set up adjustment one day, possibly with a screw thread.

On the Road Again

Friday, 31 January 2014, 9am

Took the beast out for its first test run yesterday. Had to do quite a bit of work before that momentous occasion. First up was building a geared steering mechanism –

The radius of the fulcrum slides along the bolt, increasing from 41mm to 56mm radius and increasing the turning gearing by about 2.5 times at full lock. This enables fine control at small amounts of steering and maximal turning near full lock. The spring, which was installed to assist return from full lock, was later removed, as the gravitational return provided by the wheels themselves proved an adequate assist. Steering at centre –

Left turn –

Right turn –

Not that the pivots are set up to mirror the movement of the steering arm, resulting in very little rotation in the rod end link.

Handlebar arrangement, as in a tracked vehicle, handlebars made from a piece of a walking frame –

One handlebar rotates back as the other moves forward. Both are linked to the same mounting point via two adjustable track rods –

Mounting detail –

The mount holes are ‘twisted’ about 30 degrees, so that I could get the mounts as close to the outside of the seat frame as possible, maximising rigidity. Handlebar bearings are made from polypropylene chopping board.

A mount for the speedo sender was fitted to the chain tensioner mounting –

This was a bit tricky. You’d think the magnet would be set up to run between the cable ties, allowing you to get it as close to the sender as possible. It wasn’t, and I finally found it worked when running next to the top tie.

A full-length chain guard was installed between the seats, made from a half section of that wonderful hang glider tubing of Eddie’s.

The last problem I had to overcome was that the leverage on the back shocks was too great. The shocks were compressing too much, even at the maximum pressure of 300psi. So I bodged up some steel mounts to move the shock fulcrum further away from the centre of the swing arm pivot. I also took the opportunity to move the shock mount directly under the swing arm. This brought the shock pressure down to a more reasonable 200psi, though it had the unfortunate side effect of reducing the travel from 4” to 3”. A project for the distant future will be to tidy up this end of the swing arm with some carbon. Two views of the mount –

It’s a bit messy, and I haven’t painted it, but at least it works. The lower shock mounts were reversed and trimmed down to keep the shock ends working in as direct a line as possible.

The test run went well, only attempted a short run (1km), with no passenger to assist, but still managed to get it up to 35kph on the flat. Then I bought it home and checked it over, but there was no need to adjust or tighten anything up.

As it looks at the moment, still a bit blunt at the front end without any fairing –

Note drink bottle holders at the rear, mirror and horn. It’s a bit on the chunky side, weighing in at 47kg. Magura ‘Big’ disc brakes are awesome, chassis is very rigid and ride is nice and smooth, as is the gear shifting. As is usual with cycle gearing, reverse is engaged Flintstone style. Hope to post a video of it in action sometime soon.

Fitting the Seats

Friday 10 January 2014, 4pm

Had a short burst of activity for a couple of weeks and finished off the seat mounts. This is how the front mounts finished up –

And here’s the rear mounts, made from a modification of the mounts supplied with the seats –

Allowing for adjustment -

The seats are GT seats from Greenspeed (Taiwanese) and weigh 4kg each. The overall effect –

All that is left to do is make the controls and fairing.

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.