Bantam Menace Pot Racer Propeller Drive


The above figure shows the highly detailed and dimensioned blueprints I used in designing and building the prop drive for the Bantam Menace Pot Racer.

The picture above shows the crankset (upper) end of the drive unit. Simple flanged cartridge bearings are inserted into an aluminum tube that has been welded onto a hollow aluminum strut. The metal bracket next to the "bottom bracket" is used to clamp the cartridge bearings into place.

The picture above shows the bottom end cog and propeller shaft assembly. The two aluminum cylinders hold the two flanged cartridge bearings in place on either side of the cog. The cog is threaded onto the remnants of a steel bicycle hub that has been welded to a 3/4" steel tube. This way the gearing can be easily changed, and worn gears replaced.

The two halves of the bearing mounts are clamped around the aluminum strut with a hose clamp. This enables the bicycle chain tension to be fairly easily adjusted.

This picture shows the propeller mount. I took a nut, welded it to a small washer which fits inside a 7/8" tube (which was almost exactly the diameter of the circular groove inside the APC propeller hub), welded a bit of metal on opposite sides of the washer on the side away from the nut to create two keys, welded the nut in the center of the tube (using some holes in the side of the tube for access) to create a propeller mount with a threaded insert. There are probably easier ways to do this, but this worked well. Anyway, the APC prop was modified slightly with a Moto-tool to create keyways on either side to mate with the keys on the shaft. A 5/32" bolt was used to secure the prop to the shaft.

This picture shows the propeller mounted on the shaft, and the lower cog and bearing assembly in place around the strut. The hose clamp has not been attached yet.

This shot more or less shows the plan of the drive unit, sans mounting brackets and chain.

This shows the linkage between the "normal" gear reduction jack shaft on the bike, which is a normal bike crankset and spindle assembly, and the prop drive "add-on" jack shaft, which uses a cartridge bearing style crank spindle and some cheap 3/4" flanged cartridge bearings to make an equivalent bottom bracket assembly.

To link the spindles together I took some 3/4" tubing, drilled four small holes about 1/2" from the end equally spaced from each other. I then welded some small blobs of steel inside the holes. This created four keys that aligned with the four flats of the spindle. Next, I cut the tubing, leaving about an inch of it (with the holes/blobs), and welded it inside a 7/8" tube that was about the length of my Allen socket key wrench. I found some Allen socket spindle bolts at my local bike shop that happen to fit perfectly inside the 7/8" tube, and the edges of the bolt are about 3/4" diameter, so they work well in securing the tubing to the spindle.

The larger tube is used to join the two spindle tubes. Using pins through holes arranged at 90 degrees to the other pins seems to work pretty well as a semi-universal joint.

The spindle bearing clamp is also seen here. Friction is all that seems to be needed to hold it in place.

This picture shows the chain angles as it enters and exits the lower cog area. I found it necessary to add chain guides to ensure that the chain does not derail when the prop is spun in a forward or a reverse (yes!) direction. This might be augmented in the future with steel fittings of some sort as salt water and chain abrasion seems to eat the aluminum somewhat. I might also find a chain with smoother sides. The pin securing the prop mounting shaft to the 3/4" axle shaft is also quite visible here.

This picture shows a front view of the propeller

The above three pictures show the prop drive in the raised position. With the 16x16 prop or the 14x14 prop there is interference with the wheel or the bike frame, so I have been careful not to spin the prop in this position. I have been stowing the prop mount shaft on the prop drive jack shaft behind the bike seat for safe keeping.

This picture shows the prop drive in the deployed position.

Darth Sanders and his apprentice Darth Chicken, who enjoys sitting between the handlebars of the Bantam Menace Pot Racer.

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