Over here in Blighty the schools have just broken up, no more homework, no more exams. So what do the darling offspring do . . . Facebook, Minecraft and anything on the iPads because "they don't embarrass us like dad does".
Well regardless of what they think, they need to get out and away from the electronics so I'm forcing them to have some good old bone breaking fun by making a downhill racer.
So we want something simple, quick to build and capable of transporting anybody in the family downhill at break-neck speed . . . oh and I don't want to have to go out and buy anything for it.
We used the following materials:
- 16mm plywood
- oak boards
- old rope
- M8 threaded bar
- M16 threaded bar with washers and nuts
- 10" wheels for garden trolley
Step 1: Wheels and Axles
We want to get out and racing so everything about this build wants to be quick.
First thought was to utilise the various bike wheels that are currently unused but as soon as we considered how to attach them to the main structure we found that we would have to fabricate new axles so they could be side mounted instead of fixed both side as when used on a bike. So they were struck off the list.
Then junior offspring dug out some unused trolley wheels from the back of the shed and immediately I knew we had found our answer. A very simple setup, pneumatic tyres with a central bearing that fits a 16mm threaded rod.
So next question is "how do we attach the wheels?" . . . we settled on making triangular blocks that would be attached to the frame with glue/screws and a central hole would hold the axel. The result looked good but the moment somebody sat on them, the torsional pressures just broke the blocks apart and sheared them off.
Back to the drawing board, quite literally, and what we really wanted to do was drill a hole right through a solid block of wood that would withstand all the forces. Ever tried drilling a 500mm hole down precisely vertical? It is not going to happen here so we needed another solution and then it struck, if we could not put the axel through the wood, we would put the wood round the axel.
The axel is 16mm and I had some plywood approximately the same thickness so it was a simple case of screwing a strip of ply to a wider piece, place the threaded rod next to it and screw down a second strip of ply to create a ply/rod/ply sandwich. A fourth and final piece of ply completes the surround. For added strength the screws went through all pieces of wood. These were not going to bend or stretch or split this time . . .
Only thing now was to reduce the length of the threaded rods. Lots of options here, bandsaw, chopsaw but realistically it is just as easy to grab the hacksaw and do it sans-electric.
Step 2: Frame
A single central oak board screwed to the axel surround creates the main frame structure. Two additional boards are placed either side, screwed once more to the axel surround as well as to a baton at the other end. This creates a very solid seating area.
If you wanted to be tidier you could screw from the back but I wanted to use the longest screws possible and this was only possible by screwing from the top.
The offcut of threaded bar now becomes the steering fulcrum. So a hole drilled through the central frame board and through the second axel surround, a bit of bashing and we have the steering fixed in place. Simple controls, put your feet on the wood, push left and you go left, push right and you go right. A couple of nuts holds the whole thing in place.
Step 3: Brakes
As soon as we had all four wheels attached together and started taking journeys on the racer, it became blatantly obvious that we had missed something important . . . .brakes!!!!!!!!!!!!!
What you see here is my attempt to fashion a spring loaded friction brake that pushes against the wheel tyre.
We have a surround similar to the axel surrounds that encapsulates the brake. There is limited vertical movement and lots of horizontal movement. The surround is screwed to the back of the frame and the brake bar inserted. A piece of elastic is then looped around everything to keep the brake pulled away from the wheels. Although I do not have a picture of the brake cable, you can see the two holes drilled into the brake. A piece of rope was looped through each and flows over the main central board in front of the rider.
The idea was that by pulling on the rope they would be able to pull the brake onto the wheels and because it is a single piece of rope, it would apply equal pressure to each wheel.
How good was the stopping power? The answer is "what stopping power?". I think unless there was some form of pulley system you would never be able to apply enough force to actually cause you to stop . . . never mind!!!!
Step 4: Brakes - 2nd Attempt
Back to the drawing board again . . .
This time we are back to old school braking there the brake drags on the ground to slow the racer down.
A bar is mounted in a frame and screwed behind the back wheel. Two paddles are then created with a hole corresponding to the bar drilled in them. Once mounted they lie flat by default but if you grab them and yank up you will push the other end onto the ground and slow yourself down.
Step 5: Final Details
Just time to add a steering rope. All we had was some skinny nylon rope but luckily number 1 daughter plats her hair so she knocks up a metre or so of 3 ply plat.
A couple of plates with a hole are screwed to the front moveable axel and the plat rope knotted at the back.
We're done and a few thrills and we'll be back with an Instructable covering how to apply leg casts using resin instead of plaster of Paris.