Summer progress

I've had a full summer, so the bike has plodded along slowly. 

The foam core has been covered with one layer of glass.  This stabilised the foam, and while it still isn't anywhere near strong enough, the foam can now survive the odd knock or two. 

Next, holes were cut in the frame to accept the hard points for the suspension, pedals and steering.  These were aligned carefully and set into place using automotive body filler.  Surplus filler was ground down before another piece of glass was laid around them.

The swingarm is still wooden, but will be reinforced with carbon.  So now I've got something that is actually starting to look like a bike.  Tonight I assembled the major components to see how they look together.

Well the rear end is at the correct height, thanks to the lump of wood shoved in where the shock absorber should live.  The swingarm is still two lumps of wood and relies on the back axle to hold them together.  The swingarm shock mount is next on the list.  The bottom bracket is actually a bb30 bottom bracket adaptor, which was an ebay find.  This was easier than getting a framebuilder to supply me with a tube with the appropriate thread.  The head tube is at the correct angle, although for the purpose of this demonstration I have left out part of the headset assembly. 

More will follow...

Construction begins

in my last post i said I had begin cutting the templates for the chain stays.  The original XR2 design calls for these to be made from aluminium, and while it's possible for me to do this, I had thought about making them out of carbon.  My thought was to make a plywood and balsa former that was to be wrapped in carbon.  But when i started cutting the wood, I realised what a nice bit of wood I had.  It's 6mm modeling plywood, birch I think.  So by way of an experiment I'm going to attempt a wooden swingarm.

I've deviated from the original design again...  The original XR2 has a chain wheel in the middle of the bike, so the right chainstay is set in behind the sprocket, and above the bottom bracket.  As I'm dispensing with this sprocket, I've made the chainstays symetrical.  As a result, I can make a jig and use it to form both sides.

In order to stop the rear wheel rotating and stopping the roller brake from working, I've recessed some lumps of metal into my chainstays.  The epoxy is curing on these just now.  The plan is to add a couple of layers of ply to the chainstays, then join them together in the middle to take the suspension pivot.  I'll be adding a few layers of varnish to lift the colour of the plywood.  This is an experiment, so I'll see how it goes.

Of course, now I have chainstay and frame templates made up, I had to make a mockup using the other components, clamps and imagination.  Ignore the headtube height and angle - that's the angle it wanted to wedge itself in at.

Groundhugger Spotted in the Wild

Newly released spy footage shows a Groundhugger XR2 in it's natural environment.


Thanks to David Wolfe for the video and for the construction tips.  That's him piloting his own XR2 in the video.  His construction diary is here.

In other news, with the assistance of Mrs G, I removed the internals of my Nexus 8 hub, gave them  a spit and a polish and put them back together.  The dropouts on my mountain bike were long enough for me to be able to get the hub in and tested, albeit without a functioning back brake.  The hub appears to work fine, gear selection is painless, and there's no drag from the back end.  I'm now confident in using this in my final bike.

I'm keeping an eye on Ebay for some of the other components I'll require.  I'm also planning a trip to my local bike recycler to have a rummage through their parts bin

Plans arrived.

The plans CD arrived from Robert Q Riley at the weekend, but I've not really had much of a chance to have a look as yet.  What I have seen is a pretty comprehensive set of plans, 3d models and files for the sheet metal parts. 

The manual includes details of how to make the bike solar powered, using a motor under the seat and a set of solar panels that mount either behind the seat, or on a custom disc on the back wheel, transferring the power out using a custom connector.  It's a neat design, but I'm not going to bother with the solar version, because if last summer was anything to go by, I wouldn't have got a lot of charging time. 

I've got plenty of other things to be getting along with at the moment, so progress isn't going to be that quick.

I do have my first component.  I've got a BB30 bottom bracket adaptor with a standard BSA thread that will probably be on the front of the bike.  I'm considering a Sturmey Archer or Sachs 3x7 hub on the rear, with a long cage derailleur to take up the tension in the chain line.  I'll probably fit an idler gear under the seat, in the place of the motor drive to maintain the appropriate chain clearance under the seat.

Other parts will follow from Ebay or my local bike recyclers.

Design considerations

While I'm waiting for the plans to arrive, which are somewhere between the US and UK at the moment, I'm pondering the technical part of the design.

To give myself a benchmark to work from, I'm using my Revolution Pathfinder from Edinburgh Bicycle for reference.  The gearing on that is good for hill climbs, while also allowing me up to 30mph while pedaling like a maniac, downhill with a following wind. 

I am keeping an eye out for a used mountain bike that can be harvested for parts.

The front forks will be purchased rather than made.  I'm not in a position to do that much machining of parts, and besides, why reinvent the wheel...  or fork...

As for the back end, I'm considering a carbon swingarm, rather than the aluminium on the design.

The bike needs mudguards.  This is Scotland.  Dry paths are the exception.

I'd also like somewhere to keep my lunch, so some form of luggage rack to take two standard panniers would be nice.

And I'd also like to make it fit onto a standard Thule bike carrier.  This may mean having the luggage rack detachable for transit, and having the suspension pivot so the rear wheel folds underneath.

And lights are a must.