This is one of the more intricate projects in my Laser Cut Advent Calendar series.
It’s a small three wheeled toy vehicle, propelled by a rubber band.
It is also one of the projects I did when I was Artist in Residence at Instructables/Pier 9 in July 2013 and that I am finally posting as an Instructable.
It Is not the ultimate rubber band car, but shows the principle. Winding the rubber band is limited to a couple of turns of the rear wheel or it will get stuck. Actually, to my experience it is best to attach a piece of string to the rubberband and wind that on the axle, but I wanted to stick to the materials I choose for my laser cut Advent Calendar series: 3mm acrylic sheet, rubber bands, M3 x 20 mm machine screws and M3 nuts.
The video shows how it launches (sorry for the low lighting conditions). See the last step for more on that.
Step 1: Materials, Parts and Tools:
The design is made for 3 mm sheet material, taking in account the thickness can vary 15% plus or minus.
Three M3 x 20 mm machine screws
Two M3 nuts
One rubber band 1” x 1/8
One rubber band 2.5” x 1/16
I made the design in Inkscape and included a zip file with the design in .pdf and .svg format.
The parts were cut out of transparent amber acrylic sheet on a 120W Epilog laser cutter in the workshop at Pier 9, were the Instructables HQ is. The speed was set to 50% and the power to 70%.
Step 2: Building:
Start by putting the 1” x 1/8 rubber band on the notched wheel as a tyre. This proved to be necessary to get enough traction. As you will see further on, the notch still retains its function.
This wheel is sandwiched between the two vertical panels, with a machine screw as axle. Keep an eye one the orientation of the notch. No nuts are needed. Actually, tests showed it works best when both the wheel as the axle can spin freely.
Mounting the wheel and panels on the chassis plate takes a bit of fiddling, first putting in the front side and then sliding the back parts into place.
wheel gets a machine screw as axle. A nut is mounted, but kept at the very end. The nut is brought in the cut out (again, can take some fiddling) and only when it is well in, the screw is tightened.
The band 2.5” x 1/16 is attached to the front, keeping the loop open as shown.
It proved importand to keep the rubber band loop open to postpone it getting stuck to the sides of the wheel wen winding. Actually, compared to the prototype shown, I changed the design slightly. I made so that the rubber band loop sides are closer together than the side of the vertical panels. This to avoid the rubber band to get stuck to the side panels when winding.
Step 3: Playing:
To start winding the rubber band, first bring its end to the notch in the back wheel. Actually the “tire” can keep it in place without the underlying notch, but it is a bit trickier to start winding.
Put the toy on a flat surface and pull it back, but no more than a couple of vehicle lengths (only a couple of windings).
Let go to see it launch forwards. As is, it travels about 1 to 1.5 m. So there is certainly room for improvement. Try doing the actual winding around the axle with a string attached to a shorter, doubled rubber band.