Step 1: Gather Files
Go to Thingiverse.com and download the Rubber Band Powered Car files:
Drag a downloaded file into the model window of MakerBot's ReplicatorG software.
If you don't have a 3d printer, you can still have the files printed at a commercial 3d printer.
Select "Generate GCode" from the right hand menu.
Mostly, I leave this alone--except that I check "Use Raft/Support." A raft is a web of plastic printed on the base under your 3d object.
Note that if you have two extruders (the more expensive model), you can choose to use the left extruder (drop down menu item on first check box) if you so desire.
Select "Generate Gcode."
Step 4: Picky Stuff
It has been my experience that the bed of the Replicator needs to be 115 degrees instead of 100 for reliable adhesion of the raft.
About the 20th line down in the Gcode list is a line "M109 S100 T0" Change the "S100" to "S115". Choose "File, Save."
Keep the "gcode" tab selected.
Make sure the "gcode" tab is selected. If the "model" tab is selected, you will generate gcode (a sometimes slow process) again.
Start the print by selecting the "arrow into the peanut" icon.
It can take up to three hours to print even the fairly simple parts.
Step 6: Leveling the Build Plate
If the raft does not look like this image (smooth flat lines), then the build plate is probably too low. Squiggly lines indicate a low build plate.
How to level the build plate . . . . here's what I do. Go to "utilities, level build plate" (on the Replicator, not the computer). Tighten the four screws and start the process. Instead of using a sheet of paper, I "eyeball" the extruders and get them where there is barely daylight between the extruder and the plate. The mistake I made many times was not turning two screws at the same time (the instructions say to turn two screws, not one). For example, I would start in the first position raising the plate and the right extruder would touch. I would quit turning the right screw and adjust with the left--which usually didn't have enough play to work. My mistake. When the right extruder touches and there is air on the left, reverse direction on the right screw--lowering the right while raising the left. Always keep turning both screws while adjusting--not necessarily in the same direction. This seems to work better for me.
Step 7: Cool Air, Raft Release, Curling
I read about this in the forums and it works for me. Block off the side openings (I used paper and masking tape). Don't allow breezes from cooling or doors to enter the chamber while in operation. This helped solve my problem of curling and separation from the raft.
Note the hollow spaces inside the wheel--the solid structures are not solid.
This is one of the side plates on the raft. I pull the raft loose and pull any loose "strings" from the main part.
Once you have a complete set of parts, you are ready to assemble.
Snap a side plate onto the base.
Add the other side plate--they should be snug but not difficult to assemble.
Insert a pencil (round, not one with flat edges) into a wheel and push the axle assembly through one of the axle holes.
Add the other wheel and repeat the process for the front axle.
Attach a rubber band to the rear axle.
Secure the other end of the rubber band to the V in the front of the base.
The rubber band should look like this.
Wind it up and see what kind of distance you can get.
Changing the rubber band, weight in the car and connection to the rear axle (if the rubber band is finger held instead of secured to the rear axle, the car can free wheel when the band is exhausted) can impact the distance traveled.