Sept 10

Sept 10, 2004

Almost there...

Today I fabricated a couple of disc brake calliper mounts and installed one of the disc brakes - I realized I only received one brake with my parts order, so I'll have to go out and pick up a brake for the right side.

Then I took it out for a 15 minute test ride and here are my thoughts:

1. Frame flex. I noticed quite a bit of frame flex when I jammed on one break. I'm a little concerned about metal fatigue after a million flexes like that. I need to look closer at it to see exactly where the frame is giving and then possibly add a gusset to strengthen the area.

2. Poor turning radius. I need to re string the cable for the steering system again. The turn buckles I added to tension the cables stop the steering bar about 2 inches short of it's full turn. There is enough turn for general riding, but not enough for slow speed maneuvering - like I can't do a U-turn on our super wide cul-de-sac. I need to invent some other way of tensioning the cables where they connect to the steering bar.

3. Nervous about tipping. I really need to become more comfortable with this trikes limitations with high speed turns. It seems like slight turns at high speed feel more tippy than very sharp turns. I know that doesn't sound right but during a deep turn, the riders weight is shifted to the far inside of the turn and away from the outside which is where centrifugal force wants to toss the whole thing in the opposite direction of the turn. During a high speed slight steer, there is almost no weight shift at all, so while the bike wants to continue to move forward, it's now pointing in a different direction, and the result is forces that want to tip the triangle forward and over. Like this:

The solution would be to move the rear wheels forward more, or further out to the right and left. However - this may not be a problem. I think I might need to actually cause the thing to flip over at some reasonable speed - then I would know for sure what the limitations are, and they may indeed be within an acceptable range.

Here's the frame to do list:

1. Buy and install right brake
2. Invent new cable tensioner to allow more steering bar turn radius
3. Add front derailleur
4. Order 20mm axle bolts for the rear wheels (I'm using 1/2 inch now which isn't right)
5. Design and machine 2 seat mounts out of aluminum to replace current steel ones.
6. Order a new front wheel! (Helen is kind of upset that I am user her Zipp race wheel!)
7. Start work on the first fairing

There's a totally cool web site called emachineshop.com You use the on-line 3D modelling application to design a part, then actually order the part! They mill it with their CAD CAM machines and send it to you. I'm going to test out this service by re-designing the seat clamps out of lighter weight aluminum. The clamps I made to hold the seat to the frame actually serve a couple of purposes. The front clamp holds the front of the seat down, but it also includes a bracket that the steering cable sheaves fit into. The rear clamp holds the top of the seat to the frame and also a bar that the cables 'grab' onto to pivot the frame. The steel versions are heavy and ugly with welds and gussets, etc. I'd really like to replace them with some pro looking, light weight milled aluminum parts. Once I figure out a better way of tensioning the cables from the steering bar, I'll probably have those made by emachineshop.com also.



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