A passenger car on two wheels

A motorcycle and a car are different machines. First and foremost, in terms of comfort. But can the advantages of two-wheeled transport be combined with the convenience of a passenger car? It turns out they can. Such two-wheeled machines—autorollers or motocars—are sometimes seen on the streets. We suggest you build one of these designs yourself.

This vehicle is a scooter with an engine of about 50 cm³ displacement, which, unlike traditional two-wheelers, has a light plastic body with a folding top, a seat almost like in a car, and two additional small wheels that can be raised and lowered like landing gear on an aircraft.

Let’s get to work. We’ll start with the frame. Obviously, you can’t build it without a welding set. You’ll need steel tubes with an outside diameter of 34 mm and wall thickness of 2.5 mm, tubes 22 mm in diameter (same wall thickness), and a front telescopic fork from any moped or scooter. The frame is designed for wheels from a Riga-built mini-moped, but scooter wheels will work too. You’ll also need sheet steel about 2.5 mm thick.

First, draw the frame full size. This will let you cut the blanks correctly and accurately from the drawing and finally fix the main dimensions of the parts.

As the drawings show, the autoroller frame is backbone-type and consists of a welded two-tube L-shaped spine that also acts as the rear wheel fork. To each tube, 4 mm thick steel plates with longitudinal slots for the axle are welded. We recommend cutting the slots after the plates are fitted—this helps get the work more accurate.

Now join the rear wheel to the frame tubes, tighten the axle nuts firmly, and mark where the bends will be. For a small bend you don’t need to pack the tube with sand—a tube bender is enough. After fitting, the tubes are welded at two or three points.

Next, fit the wheel in the front fork and fix the fork to the floor with wooden battens in the position shown. In the same way, set the frame spine with the rear wheel. Temporarily secure the spine to the steering column with soft copper wire. Check the wheel alignment carefully—they must lie in one plane. If correct, tack the spine to the steering column in two or three places. After final fitting, weld all joints fully. At the front, the spine-to-column joint is reinforced with gussets cut from 2.5 mm steel sheet.

The rear engine mounting bracket is cut and bent from 3 mm sheet steel. Do this in place: first cut a cardboard template and only after fitting make the metal blank. Fit the front bracket the same way.

After machining, attach the bracket to the engine and fix it on the frame with wire. Alignment must be checked again—the cylinder axis must lie in the frame’s plane of symmetry, and the carburetor platform must be level. After tacking the brackets, do a final check and complete the welding with the engine removed.

The frame base is ready. Add the cross tube that serves as the pivot for the extra wheels and small pads for the driver’s seat. The frame is then fully assembled.

For the extra wheels’ axle, choose a tube whose outside diameter allows it to rotate freely in the pivot. If you can’t find one, use a smaller tube or rod and compensate the gap with rings cut from plastic hose—they work well as plain bearings.

The chassis strut is made from 22 mm outside diameter steel tube. Weld a bushing to one end and a turned steel axle to the other. On the left strut, weld a short 10 mm steel rod with a thread for a plastic handle. This is the chassis control lever.

The extra wheels must lock reliably in both extended and retracted positions. The mechanism is straightforward; we suggest designing it yourself.

Chassis wheels can be from a children’s bicycle. Prefer rubber “balloon” or solid-rubber (not plastic) tires up to 200 mm in diameter.

The autoroller fuel tank is a 5 litre plastic or aluminium can. Fit a standard motorcycle fuel tap with sediment bowl and mount it at the rear of the body. Drill a vent hole in the can cap.

The body is plastic. The structure is built from 20×20 mm wooden battens.

The lower part of the body is like a small boat hull. Assemble the transverse frames from battens, then add the longitudinal battens per the drawing. Then skin the frame. Kitchen furniture plastic (sold in hardware stores) is a good option. Use epoxy for gluing the frame and skin. If you can’t find plastic, thin plywood or hardboard up to 3 mm is acceptable, or other options.

The upper part is built similarly. Glazing is transparent film of the kind used for model aircraft. Make window frames from 10×20 mm battens with spacers. Place the frame on the film, cut with a 20 mm margin, fold the film over and glue to the frame with BF-2 adhesive. Iron the joint with the iron set to “silk”. Then screw the frame into the window opening.

The window may not look perfect at first—Mylar is stiff and hard to tension. Use the iron set to “cotton” or “linen” and iron the film; it will tighten and flatten.

Final finishing is simple. With plastic skin, fill joints with epoxy filler (epoxy glue and talc) and paint with nitro primer then nitro enamel. With plywood or hardboard, level with filler, then cover with a layer of glass cloth and epoxy and paint.

Pay special attention to the controls. They are much like a moped’s. On the handlebar (from a Riga mini-moped) fit the throttle, front brake lever (right), and clutch lever (left). If the engine has a manual gear selector, mount it on the left of the handlebar.

The engine starter needs modification. At minimum, reposition the kickstarter lever on the splined shaft so it’s easy to kick from the seat. Better is a cord starter: fit a pulley on the splined shaft with two or three turns of nylon cord, run the free end to a convenient spot for a left-hand pull, and add a T-handle.

The last control is the chassis raise/lower lever—best under the driver’s left hand. The brake pedal for the rear wheel goes under the right foot.

For the first runs, leave the cab (“canopy”) off. Sit comfortably (chassis extended), put the gear in neutral, and start the engine. After warm-up, move off in first, then second. Retract the chassis only when the autoroller feels stable. Operating the extra wheels will feel odd at first but is easy to learn.

When using the autoroller, remember the engine runs cooler than on a moped. Ensure the cylinder cooling opening in the body is in the front wheel well, directly opposite the cylinder, and larger than the cylinder. If cooling is insufficient and the engine overheats, consider forced cooling. It’s not hard: remove the right crankcase cover and fix aluminium blades for a centrifugal fan on the flywheel/generator rotor. Make an air duct from bent aluminium sheet or from cloth and epoxy on a foam former, filled with plasticine or non-hardening putty.

«Modelist-Konstruktor» No. 6’2014, I. YEVSTRATOV, engineer