Prepare For a Ground Assault

Pedals are mounted. Freewheels have been coupled to the Hyperdrive. Chains are connected. The Falcon can finally travel without being pushed. Huzzah! 

It took some effort to get this far. After basking in the afterglow of mounting all the wheels, I got to work attaching the frames for the pedals. We are going to pedal recumbently but we are using regular mountain bike frames. I mounted them at an angle like they are “popping wheelies,” so that the pedals can be cranked from a seated position. The freewheels they turn are located under the drivers’ seats and line up with the input shaft of the Hyperdrive.

The bike frames had to be secured to the truss but the support structure also had to clear the path of the pedals. At first I thought I’d have to weld some tubing together at eccentric angles and drill holes in the bike frame to attach, but after staring at it for a while an easier solution presented itself that didn’t require any welding or virtual development. Who needs Fusion 360 to engineer parts? I do, but in this case I was able to make all the modifications IRL.

I bolted a single aluminum tube with 1/4 inch thick walls across the truss, much like the support tubes for the seats. Then, I bolted 1/2 inch threaded rod between the support tube and the kickstand bracket(!) on the bike frame. Only one of the frames had a kickstand bracket, so I used fender washers as a makeshift bracket for the other one.

Not only was welding not necessary, but the height of the pedals are now adjustable. The rear forks were secured to the front seat support tube using hose clamps.

I then mounted all the bike hardware onto the bike frames. This was the easiest way to see what was missing and what needed to be replaced.  The pedals rubbed up against one of the bike frames, so we had to get a slightly wider bottom crank. We also needed a different front derailleur and a new set of gear shifters.

Alternative Freewheel Support

Normally, the rear hub of a bicycle spins independently of the axle bolt that attaches the wheel to the bike. However, the Falcon needs the freewheels to do the opposite, to actually turn the axles. They make adapters that do this, but a spinning axle meant we had to mount bearings somewhere to support them. And the bearings also needed to be close enough to the freewheels’ original location so that we could still run bike chain from the hub and derailleur to the pedals. To accomplish this I had to design a new part that sits the the elbow of the rear fork. 

I designed it so it can be bolted to the rear forks using the original hub location’s bracket holes. Before making this part in metal, I 3D printed it in plastic. Good thing, too, because the initial design fit on one bike frame but not the other. I figured out that I could make it work by stretching the mounting hole into a slot (see image above).

Once I updated the part virtually, I made the brackets on the Tormach CNC mill.

The new location of the freewheel works great! The only issue is we can’t go down to its smallest gear or the chain rubs against the bolt securing the bracket. I just set the limits on rear derailleur to avoid that gear.

Universal joints compensate for any misalignment between the freewheel shafts and the Hyperdrive input shaft. Of course, I could not find joints with 1/2″ holes. I bought 12mm bore joints and drilled them out for the slightly larger 1/2 inch shafts on the Hyperdrive. 

Drive Sprockets

The sprockets on the Hyperdrive were another small headache to install. Apparently, the sprocket sizes we need are not made with 1/2 inch mounting holes. I can get them in 3/4, 1 inch, inch and a half, but not 1/2 inch. After finally accepting this, I bought weld-on sprockets. 

This type of sprocket lets me mix and match different hubs with different sprocket bodies. The only downside is that the hubs are solid steel and quite heavy.  I bought the sprockets and 1/2 inch hubs and welded them together.

Then I mounted the front sprocket on the Hyperdrive and layed out the chain connecting the front wheels. The tensioners both tighten up the chain path and redirect the chains around obstacles.

I tested the mud gear once everything was together. This mode has larger forces going through it than the road gear, so it is a better test. The last belt on the Hyperdrive started slipping because it was under tensioned.

I worried for a brief moment. “Oh nooo. Wait. Okay.” The belt is on a slider, secured by 4 screws through a slot. It was maxed out. I thought I couldn’t stretch it more, but then realized I could just take the bottom to screws out to get the tension I needed.

With that problem solved, I ran into the next issue. The pulleys and sprocket on the front sprocket axle slipped under load. They had only been secured with set screws, so I expected this might happen. But I hoped it wouldn’t.

To fix this, I took apart the front of the Hyperdrive to get the shaft out. I then drilled divots into it for the pulleys and milled a slot in the shaft for a keyway. The sprocket has a corresponding key way. Dropping a square bit of steel, the key, into the slot and then sliding the sprocket over it locked them together.

I put the Hyperdrive back together and tried the pedals a third time.

It’s working pretty well. As soon as I hit an obstacle, other pulleys started to slip, so I added divots to the other six shafts on the Hyperdrive.

We still have to mount the rear drive sprocket and chain, work out the rest of the steering mechanism, make a brake lever, run the brake lines to the lever, add flotation and turn the front wheels into paddlewheels. No sweat (i.e., multiple long days of sweat).

Time is ever ticking, but we continue to move forward. You see what I did there?