Drill Kart

Lacking a welder, we began sketching a frame made of 2×4 lumber. For the steering, we originally thought of “Frankensteining” a recovered bicycle front fork onto our wooden frame and putting the 2 drive wheels in back. But the more we looked at it, the more it just seemed heavy and inelegant.

So we decided to replace the front fork with a rear caster and bring the 2 paired wheels in front, like on a “tadpole” trike. But they would also be the drive wheels, and you’d steer tankstyle by accelerating one motor or the other! We all liked this idea, as it drastically raised the crazy factor of our kart.

We originally envisioned dropping the drive wheels between wooden forks, but the open wood forks on this “box with wings” just weren’t strong enough. So we decided to box the wheels in.

This design also leaves room to install foot brakes at the kart’s front edge. You can size your kart by test-fitting the seat and its distance to your imagined foot brakes. Once you’ve located the seat, you’ll know roughly where to mount the drills for comfortable driving, and thus how big to make your frame.

Our frame is a big rectangle with internal braces to support the wheels and driver, plus a triangular rear extension to stiffen the long central tailpiece that holds the rear caster.

Cut the 2×4s to length, lay them out, and mark where the wheel axles will go. Use the 3/8" Forstner bit to drill 2 dropout grooves for each axle. Screw the frame together with 2½" wood screws or deck screws.

Flip the frame upside down. Lay an axle in its dropouts, center a bracket over each dropout, mark and drill the bolt holes through the 2×4, then bolt the brackets on. You can unbolt them to remove the wheel.

Bolt the caster to the tail of the frame. You’ll probably have to add wood blocks in between to make it level.

Finally, cut a ½" plywood deck to cover your frame, and screw it down with 1" wood screws.

We settled on simple wooden brakes that rub on the tires, with foot pedals for leverage.

To make the brake pads and foot pedals, use the 1" Forstner bit to drill round grooves in scraps of 2×4, as shown in the first photo. Use the 3/16" machine screws to bolt a brake pad to a length of 1" steel pipe. Bolt a foot pedal at approximately the opposite angle; then mount the pipe in scrap 2×4 supports, so that the brake pad rubs the tire when the driver steps on the pedal.

Repeat for the other wheel.

From an old office chair, we got a comfy seat plus a seat back with a post that mounted easily through the frame. Your mileage may vary.

Liberate the rear hubs and axles from some old bike wheels by cutting the spokes off with a Dremel. You’ll use these as the drive hubs, mounted in the drills.

First, you need to lock the axles to the hubs. The easiest way is to jam the axle bearings mechanically. Unscrew the axle nuts and remove the ball bearings, then overtighten the axle nuts back down as hard as you can. The axle should now be frozen.

If the axle works loose, fix it permanently by drilling and pinning the hub through the axle, using 6-32 machine screws and jam nuts (or nylon insert nuts). We used 3 screws per hub to prevent them shearing off. You could also weld the axle to the hub.

The drills face opposite directions on the kart, but you have your choice of how to align the drive hubs in the drills. If you align both hubs in the same direction, you won’t need to do this next modification.

But we aligned our hubs in opposite directions, because that way the drills line up much better for sitting between them. If you do this, then one of your drive hubs must be drivable backward, so that it doesn’t just “coast” against its drill. This means you’ll need to freeze one freewheel entirely by welding the gears to the hub, making it a fixed hub.

To avoid doing this “fixie” modification, you could also substitute a real fixed rear hub (popular with road racers and bike hipsters), or buy a drive sprocket like we did in the Drill Rod scooter (MAKE Volume 21, page 108) and engineer your own axle to mount it in the drill.

Tip: To prevent the axle from slipping and spinning in the drill chuck, use a file or grinder to create 3 flats on the axle, at equilateral angles. Re-chuck the axle, aligning the flats with the faces of the chuck.

Put the axles in the drill chucks and tighten them well.

The drills drive 2 bike chains that turn the wheels, and the gear clusters of both wheels face the same side of the cart.

Aligning the drills is tricky — you’ve got to fix them securely, within reach of the driver’s hands, and so that the drive hubs line up with the wheel hubs, without the chain twisting or rubbing on anything. To get the most torque, run the chain from a smaller gear on the drive hub to the largest gear on the wheel hub, like downshifting to “granny gear” on a bike.

When you’ve got the alignment and chain tension right, screw down 2×4 blocks to the deck to hold each drill in place. We added straps, threaded through the deck, to tighten down the drills but still allow for easy removal. You could also box the drills in completely, if you don’t want to remove them very often (just remember to leave access to the drill’s battery and vent).

To adjust the chain length, you can add or remove links and rejoin the chain with a master link or half-link. To fine-tune the tension, you could even add an idler or tensioner; this could be as simple as a smooth bolt for the chain to run over, or more complex, like the spring arm from a bike’s rear derailleur.

We painted our kart a bright, MAKE-logo red, and installed cool see-through guards made from acrylic plexiglass over the drive hubs.