Gravicar develops

Have now built a Gravicar, and several things have needed changing. The width didn't quite give enough room for the wheels to fix. If you were careful they worked well, but any slight difference in building and they fell off! So now the whole thing is 10mm narrower as well as having extra marks on the cardboard sheets of joiners to show which way is up when assembling the three main frames.
The 10Th of February is a big day because I am running a whole day event for 150 students in 6 classrooms, simultaneously building them as part of a STEM day I am running at a clients. This means getting all parts ordered and in stock, card pieces laser cut, info and building sheets copied and staff briefed. As with all my projects, I am going to base the building around a PowerPoint using Sketchup graphics and photos to show the stages. Backed up with a Students building sheet to build 'ON' and a diary sheet to record 'ABOUT' the day, that should be enough to keep them all going.
The one featured here rolls about 5 metres using the 500ml bottle of water. Replacing the wide wheels with CD's would give a very low rolling resistance and with string that unwound completely from the axle, should travel about 30 metres on a good flat floor indoors.
I am going to use very slight ramps to start it off as some built will be a bit 'sticky' with too much friction. Probably a sheet of polypropylene about 50mm high
This is not a new project, but I hope I have streamlined it enough that all the students can build it without too many problems, and that the non-specialist staff can assist them