Step #1: Design a framePrevNext
- 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 (see the first picture).
- 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 tank-style 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 (second picture). So we decided to box the wheels in (third picture).
- 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.
Step #2: Build the framePrevNext
- 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 2" Forstner bit to drill 2 dropout grooves for each axle. Screw the frame together with 2½" wood screws or deck screws.
Step #3: Mount the wheels and deckPrevNext
- 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 (as seen in the first picture). 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 (see the second picture).
- Finally, cut a ½" plywood deck to cover your frame, and screw it down with 1" wood screws (as shown in the last picture).
Step #4: Make the brakesPrevNext
- 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 picture. Use the 6" 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 (shown in the second picture).
- Repeat for the other wheel.
Step #5: Add a seatPrevNext
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.
Step #6: Prepare the drive hubsPrevNext
- Liberate the rear hubs and axles from some old bike wheels by cutting the spokes off with a Dremel (seen in the first picture). 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 (second picture), 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 (third picture), 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 and engineer your own axle to mount it in the drill.
- Put the axles in the drill chucks and tighten them well.
Step #7: Mount the drills and chainsPrevNext
- 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 (first picture).
We added straps, threaded through the deck, to tighten down the drills but still allow for easy removal (second picture). 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.
Step #8: Customize (optional)PrevNext
We painted our kart a bright, Make:-logo red, and installed cool see-through guards made from acrylic plexiglass over the drive hubs.
Step #9: Motor!PrevNext
- Take it for a spin — and we do mean spin. The Drill Kart’s crazy 2-trigger tank steering takes some getting used to, and the rear caster loves to spin out. The dual brakes should keep you out of trouble until you get the hang of it, so use them early and often.
- Have fun and be careful. You’re a motorist!