Did a bit of fine tuning and a few modifications. Had a long hard look at the front end set up and couldn’t work out why it’s pulling slightly to the left. 

Made some adjustments to the drivetrain which should make pedalling easier.

Replaced the spring rod in the rear end with a set up that’s a kilo lighter.

It Lives!

After stashing it for seven years, in January 2022 I dragged the Pospedal out of retirement and made some adjustments.

First off the mark was changing the front wheels from 16” to 20”, to reduce rolling resistance.

 

The smaller wheels had been laced up single crossing front and two crossings behind (see above). The rims had also been offset inwards to get zero offset on the kingpin alignment. This made the steering a bit twitchy and unstable, probably more to do with the tiny contact patch than anything.

I laced up the new rims with two crossings both sides. I also offset the rims to the outside of the hubs instead of the inside. This gave the wheels a positive scrub radius in order to make the steering self-centering and stable.

 

The new wheels fitted. The effect of the Ackerman angle is clearly visible.

 

A new stiffening brace was fitted to the rear of the chassis. Made partly from a tapered bicycle chain stay.

 

A 16mm spring steel rod was fitted to the rear swing arms to increase the stiffness of the suspension. The air shocks were returned to their original positions and reset to 170lbs/sq” (same as the front). I hope to replace this rod with a lighter option in the future.

 

I checked the wheel alignment and found an excessive amount of toe-in that I apparently hadn’t picked up originally. It was corrected to 0.5mm. The old mangled fairing off a previous model was bashed into rough shape and fitted to cut down on drag.

 

Took it for a short test run (I need to get fitter) and all the adjustments seem to have had the desired effect. Steering stable and self-centering, chassis nice and rigid, suspension working well. Topped out at 32 km/h, only halfway through the gears.

 

 

 

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.