ProjectVF - November 15, 2009

At right are new pieces at the top of the frame. These will hold the new steering assembly. I made some odd cuts for overlapping the tubing to give it a little more strength but I'm not sure it was worth the effort

Here's huge update, so pop open a cold one, kick back and enjoy. Summer has come and gone, but I made good progress along the way. The frame was heavily modified. New front suspension control arms were built. Further research led to a final design for the steering mechanism. Another Interceptor donor was found. A Magna engine (with the same V4 as the Interceptor) and shaft drive assembly was purchased to replace the original chain drive. Amid all of this I travelled to the Bonneville Salt Flats (the Mecca for Motorheads) to see the World of Speed competitions. I've been busy.

Here's yet-another cheap mockup. I wanted to test the steering geometry to see if it would really work at 1:1, meaning the front wheel would turn at the same angle as the handlebars. I used strips of corrugated cardboard, taped and hot-glued together, and made little indicators to measure the angles. With that I could turn the front wheel from side to side and see if it worked.

My first goal was to lower the seat height to make it easier to get on and off the bike, and at the same time stretch the frame to keep the fuel tank (located beneath the seat) as large as possible. This  frame will never be driven under power, so it's OK to chop and modify and rework it in a rough and crude manner.

After some head scratching and a few drawings, the frame was cut into pieces, as shown at left.

At left is the stretched and lowered frame clamped together and ready for welding. A sheet of particle board atop a table, along with some 1x2 pine scraps helped keep it all square.

It took a lot of prep time to get to this point. Every cut needed to get deburred, then cleaned with a rotary wire brush to make sure the welds would be strong. I figure that for each weld, which takes about a minute to do, I spend about ten minutes to get it ready.

It's like painting a car. You need to spend hours of sanding and cleaning or the paint ends up looking like crap.

And so ends another chapter in the design and construction of ProjectVF. A friend is machining the ball joint adaptors, which means the steering mechanism can be fabricated. After that the inboard shock system will get designed, followed by welding on some folding footpegs and connecting the front brakes.

With all of that accomplished I can start the rolling tests (weather permitting) and see how it all works, hopefully without killing myself. The goal is to that point by Christmas, so keep your fingers crossed and check back then for the next update.

At left is a drawing of the lower control arm and a jig to keep all the pieces aligned for welding. I printed the drawing at full size and taped it to a piece of scrap plywood, then used pieces of 1x2 pine to hold the tubing. At right is how it looked with the parts lightly tacked together.

The jig, with drawing and building, took about two hours to make but was essential to keep everything lined up. Trying to use clamps to hold the pieces together would have been a disaster.

On the other side of the plywood is the jig for the upper control arm. I'm cheap with materials.

At right are the tubing extensions used to stretch the frame and some flat scraps to brace the butt welds. It's pretty ugly but ought to work fine for the prototype.

At this point it's just tacked together. I finally learned not to do the full welds because if I need to change anything else, the cutting and grinding will take a lot less time.

Here are the new control arms with the ball joints connected (crudely) to the triple clamps. The upper arm bolts to the inside of the frame and the lower arm bolts the outside. This provides room for a cam pivot which will connect the lower arm to inboard coilover shocks. I still need to get adaptors machined to properly hold the ball joints, but for now this works to see how the final assembly looks.

I used race-quality heim joints between the control arms and the frame, and the threaded portion allows for side to side and vertical alignment of the forks. I knew my garage fabrication methods would need a fair amount of adjustment and the heim joints work great. All of the parts are sized and rated far above what's really needed . I can optimize and fine tune the final version but right now I want something rock solid.

The fork uppers are just electrical conduit, but for the prototype they work OK. For the final version they'll be replaced by the original steel forks cut down to size.

This is how the revised bike looks. The forks are raked back much further than originally made and ought to work just as well, at least based on the Test Mule experiments. The handlebars are set at a very comfortable angle and at the moment are connected to the frame using a salvaged headstock from a kids bicycle. The wheelbase is approximately 7'-5", the ground clearance is 6" and the seat height is 19", which is about the same height as an office swivel chair. Comfy.

Upper left is the CAD drawing of the new suspension. The radiator and fan I want to use is shown in green. It has to go between the exhaust pipes and the front tire when the suspension moves up and down. It has to be high enough to clear the ground but low enough to not interfere with the upper control arm. Like so many other things, it's a balancing act.

Lower left is how the suspension looks with the radiator wired in place. Once the engine and exhausts are back in place, the radiator can be mounted to the frame with rubber bushings to reduce it from vibrating apart.

Little things like this can take up a lot of design time, but it'll make a big difference when everything's assembled and running.

When I started to design the steering mechanism I needed to know whether long arms or short arms would work better, or could I combine long and short to save room. Would the amount of effort change either way? Once again I turned to a cheap mockup to find out. At right are some pieces of pine to simulate the levers and drag arms, a transfer pivot made from particle board and little nails to hold it all together. I used a bungee cord at the left end to act as the load and at the right end I used a little fish scale to measure how much effort was needed for various combinations. The result showed no differences no matter which way the levers were connected, which meant I could design the mechanism to suit the frame.

Here's what the inboard coilover system might look like. A very strong bar (shown in blue) rotates on the same axis as the control arm, and it's attached at the other end to the shock mount. An adjustable link (shown in green) is attached to the control arm at one end and the shock mount at the other. As the control arm moves up and down, the adjustable link pushes the blue bar back and forth, which in turn compresses the shock. The adjustable link enables the shock's preload to be increased as needed to set the ride height. The coilover itself is located high enough to clear the rider's foot, but low enough to not interfere with the steering mechanism. It's yet-another balancing act.

The results looked good considering the crude materials and methods. Now that I know the basic mechanism will work, I can design the rest to move up and down with the control arms without any binding or bump steer.