My Tiger 700 goes, stops, and turns, so I have achieved the "GoKart" milestone!
I'm now in to the "Refine and Enhance" phase. In other words, Fix / tweek the car to make it truly roadworthy and robust. Then add the items needed for DOT registration like seat belts, lights, horn, etc. My first step was to order a bunch of new parts. While I wait the parts to arrive, I thought it would be a good time to catch-up on my LoCost forum posts.
To see video #14 on the completion of my chassis ->
Click HereMy CAD design guided the construction of the chassis, but some measurements were adjusted as I went. For example:
- I added 50mm (2"mm) to the wheelbase to ensure I had enough leg room
- The attachment points on the rear subframe had changed, so I adjusted the chassis accordingly
Every pound counts in this vehicle, so most of the chassis is constructed of thinner .065" wall tubing. The FEA-BLE modeling showed that chassis design is inherently strong, so this lighter tubing could be used. In fact the finished chassis is ultra-stiff. I used a variety of tubes and gussets:
- 1.5" x .120" round tubing - This is a typical dimension for a roll-bar tubing. I had a full roll-bar left from an earlier project, so I just cut off one corner of it for the Tiger 700.
- 1" x 1.5" x .065" rectangle tubing - Square or rectangular tubing resists bending better than round tubes. I used the rectangular tube to surround the cockpit to provide greater impact resistance in case of an accident.
- 1" x .065" round tubing - Round tubing is lighter per running foot when compared to square or rectangular tubes. The rest of the chassis structure used the 1" tubing.
[list=]
0.5" x .065" round tubing - Smaller diameter tubes are strong in short lengths. I used the 0.5" tube for short braces, seat frame, etc.
[*].083" x 2" x 2" triangular gussets - Steel plate gussets add considerable strength to tube joints. I used gussets where there wasn't space for a 0.5" round tube brace. [/list]
Now that I have the central chassis in place, you can better see the direction it's heading. Its been difficult to see the big picture until now because I followed a different approach. Most LoCost builders start by building the central chassis and then work out to the suspension. I have always read that good handling starts with the tire patch and then works back to the chassis, so that was the sequence I followed.
- I started by thinking about my spindle, hub adapter, wheel and tire as a single component. This is all un-suspended weight, so wanted it to be a light as possible. I used Miata hollow spoke wheels (10lbs), the lightest 14" tires I could find (12-15lbs), aluminum hub adapters (lathed down to 1/2 their original weight), and the Raptor spindle, hub, brakes are feather weights. The wheels, tires and hub adapters were chosen so they work in concert with the spindle's kingpin angle, to produce almost no scrub radius.
- The combination of the upper control arms, lower control arms, and the rack & pinion were the next component to design all together. Now that the location of the spindle's upper/lower control arm ball joints are known, the length and angle of the control arms can be designed to achieve the proper Roll center and lean camber angles. The inner pivot points of the control arms need to align with the rack & pinion's steering rod universal joints as well.
- The next step is the structure for the upper/lower control arm pivot points and for the spring mounts.
- Then tie the suspension hard points to the rest of the chassis in a way that provides overall torsional and load carrying strength
- Now repeat the steps above for 20+ iterations to evolve your design into a well balanced and build-able plan...Nothin' to it
The engine is a single cylinder 700cc engine, so there will be some vibration. The chassis design incorporates polyurethane isolators to minimize the vibration that the driver feels. There are 6 isolators to the rear subframe and 4 to the front subframe.
Attachment:
Extreme drawings.jpg