After our previous failed attempt, we were determined to make it work this time. We bolted the crankcase cover on to provide more structural support for the block and heated it to 250 F. With the sleeve in the dry ice again, we set up a smaller hydraulic press with a more controlled pressing capability than the hand press. To our surprise, the sleeve actually slipped right into the cylinder without pressing. Luckily the relief chamfers lined up with the connecting rod path and that was it, the sleeve was in the cylinder. As they always say, third time's a charm.
Once the sleeve was in, we drilled and tapped holes to match the bolt pattern of the Honda OHC head. Dan pressed the lower timing gear on the crankshaft and a timing shaft extension on the camshaft. With the timing chain tensioner in place, we were one step closer to getting the engine running. Next on the list: intake and exhaust systems.

Unmodified 3.5HP Briggs and Stratton block

Modified B&S block with cast iron sleeve

Sleeve with silicon putty on the piston to check for valve clearance

Honda head mounted to B&S block with external timing gears and chain tensioner

Just a quick video of us pushing the car around the shop floor at Central Roller.

Dan machined a sleeve out of a 4" cast iron stock and cut two relief chamfers on the inside diameter on the lower end for connecting rod clearance. Then we put the sleeve in dry ice to shrink it for an easier press fit. When we tried it on the hand press, we placed the sleeve on top of the cylinder and starting cranking, but there was one major problem: the sleeve wall did not line up perfectly with the cylinder wall. Result: the block began to flex and a wall of the crank case actually shattered.

Cast iron stock

Machined sleeve with relief chamfer

Sleeve dropped halfway into cylinder, broken crankcase wall

With the prototype frame fully rolling with brakes and all, I was able to go ahead and start framing up the body. Back in December I ordered 60ft of 0.5" OD steel tubing with 0.035" thick wall (very light stuff), that I planned to use as the space frame for the body. The next question was what to cover it with. After debating fiberglass, balsa, and remote control aircraft covering, I ended up deciding to try out PVC boat shrink wrap. I went to Hern Marine in Fairfield and discussed the project with them, and ended up leaving with plenty of shrink wrap to experiment with in three colors! Thanks to the guys at Hern for their support.

We didn't waste any time experimenting with the shrink wrap on the prototype frame. The first thing we did just to try it out was boxing in the front sides of the frame. Some tape around the edges, some patience with the heat gun, and the result was a drum tight, smooth surface!

Taping a piece on the side

Hitting it with the heat

After Shrinking

Feeling confident from the first try, we covered the other side. But we didn't stop there. We went ahead and used the small steel tubing to create a rear "lower cage" and then shrink wrapped that. We then formed the rear "upper cage," which is removable.

Checking the canopy with the prototype sides

The rear "upper cage" prior to covering

Covered and ready for shrinking

Rear "lower cage" covered and shrunk

Car with prototype tail put together

Check out the LED taillight

Jason has finished up one set of his new steering bracket configuration (see previous post). Big thanks to FKI logistics for helping us burn these parts out with the laser and using the brake to get the initial bend in for us! Jason had to mill a hole for what we call the "axle shoulder," which ended up being an interesting exercise in finding centers of holes on the mill. Jason also had to bore the axle shoulders for a snug fit with our 20mm aluminum axles from KMX Karts.

Milling for the Axle Shoulder

Boring the Axle Shoulder

With the milling completed, we hand cut small gussets to sit on either side of the brackets and welded the whole assembly together. The next challenge was to cut the old brackets off of the prototype frame and weld in the new downtubes with just a touch of leading caster in them. Jason decided that 2 degrees of leading caster would help the car track true, and so we put together a quick fixture with the tubing notcher to accurately notch each frame tube for the desired caster. Jason then used some aluminum rod which we threaded (one side right hand, the other left hand) for custom tie rods. The whole assembly looks and works great.

Cutting off the old steering brackets

Notching for the Kinpin Tube (2 degrees leading caster)

New Kingpin tubes welded with 2 degrees leading caster

The new assembly with custom Tie Rods

We were able to get out and test the two steering systems Jason has been designing: one with a "Pitman Triangle" as we call (like most go-karts and many four-wheelers), and the other using a junior dragster rack and pinion box. We predicted that the triangle would steer much quicker, which is not necessarily what we are looking for when running a 1.6 mile oval track. Stability is key, and the rack and pinion we suspected may give us an edge.

We modified the prototype frame (the tank) so that we could use both systems, and did some light experimentation with the two (the weather was cooperating back then). Rusty, our driver, confirmed our predictions that the rack and pinion steered slower and smoother. Our concern, however, was that it did not steer quickly enough to be able to maneuver through the slalom section of the steering test. A couple trips around the shop floor at Central Roller, however proved it to be enough. An official steering and tip test is soon to follow now that the snow is melting.

The Pitman Triangle setup

The Rack and Pinion setup

No winter coats back then!

While Rusty was cutting and welding the Tank frame, Jason was busy fabricating his first prototype steering configuration for the Tank rolling chassis. His set-up was similar to go-kart style steering, using a custom assembly of M20 bolts (cut and drilled for axles), water-jetted steering arms, and custom turned kingping tubes:

David running the waterjet at DieCraft Engineering, one of our team sponsors

After having prototyped the steering assemblies, and verifying our component layout, Jason entered the next phase of his design: optimization. He also used COSMOS to weight-save his steering configurations.

After having fabricated the first set of steering components, Jason suggested and we all agreed that a change in the design would offer a number of design improvements. Rather than having spindle brackets (the c-channel) welded to the frame, and the axle and control arms welded to the kingpin tube, he decided to weld the kingpin tube to the frame, and attach the axle to to the spindle bracket. I know, sounds confusing, but the pictures should explain.

Using COSMOS, Jason analyzed an aluminum and steel versions of his newest design. He found that by using 1/8" steel plate and small gussets, the new configuration could be within 0.25lbs of its aluminum counterpart--which will be much easier to weld and manufacture than the aluminum version. The following are pictures of the latest configuration with bearing loads and braking loads applied to the brake brackets.

Jason is currently underway making the newest steering design a reality.

While we all have much love for "The Tank," we knew that we could save a good bit of weight on the frame through optimization. To accomplish this we turned to the COSMOS analysis software inside the SolidWorks suite. It took a couple of days to learn, but it wasn't long before Rusty was running multiple loading conditions on various frame configurations, cutting weight every time.

The two main loading scenarios he has been analyzing are the static 250lb roll bar load (per competition rules), and a composite load of his distributed weight and hitting a 0.5" bump on one front tire. We have made loading assumptions around this scenario as our "worst case".

The following are pictures showing the latest frame iteration, which saves 9lbs--approximately a 30% reduction in total weight! This leaves the frame at a predicted 22lbs. This was achieved primarily by experimenting with various combinations of tube size and wall thickness.

We just picked up the steel to make the new frame and fabrication will be under way shortly.

Rusty had come to his latest frame configuration in late November, and we were all eager to see it come alive. We wanted to go ahead and cut and weld the frame for prototype purposes. Jason had designed a first-run steering configuration, and we wanted something that Rusty could actually sit in and steer. We also planned to use this prototype frame for design and construction of the first body trial.

We laid out the frame and canopy full-scale with our first set of dimensions. This way, we could get a realistic feel for how components would actually stack up before we started welding. After some minor adjustments and a few updated drawings, we were ready to start fabrication on the prototype frame.

This first rolling chassis came to be known as "The Tank" in that it was not optimized for weight, but built for dimensional accuracy and component layout. After making some tricky cuts and notching lots of tubes, the tank came together quite well:

A couple "jump on the roll bar" tests and we were confident the tank was plenty robust. Ok, so it was really more scientific than that...but you get the point. The tank continues to serve as our primary guinea pig for dry-running our components.

It's time to update our blog! Late November, December, and early January have been extremely busy for us with design, prototype fabrication, and the holidays. We are basically in a stage of part optimization; primarily for weightsaving purposes. The following blogs will detail progress being made in key areas.