After intensive use of the ElektorWheelie it appears that the carrying bolts (see lower photo) can bend, warp or even break off either through intensive use or because of excessive oscillation. To prevent this I have come up with the following modification.
Take four brass or aluminium tubes with an internal diameter of 5 mm (0.2 inch) and an outside diameter of 6 mm (0.25 inch). These tubes can be cut from a longer tube and have to be 25 mm (1 inch) long. These will then fit exactly in the holes in synthetic wheels of the ElektorWheelie. Brass or aluminium tubes that could be used for this can be obtained from various model-building shops and perhaps also from building supply stores. Conrad Electronics www.conrad.com also has a suitable tube available. Search for part number 297321.
The intention is for these brass or aluminium tubes to be glued into these holes (see upper photo). Use two-component epoxy for this and apply it to the outside of the tubes. Use the wheel driver plate as a jig, so that the tubes will be in the correct place in the wheel and position the entire assembly into the holes in the wheel. Make sure that the bolts and driver plate are not glued to the wheel — you still have to be able to take it apart in a tidy way.
Allow sufficient time for the glue to set (overnight) and then remove the driver plate with the bolts from the wheel. The tubes are now held rigidly and in the correct place in the wheel. To make the entire assembly even more rigid, fill the remaining gaps in the holes in the plastic with more glue. You could use either two-component epoxy or hot-glue for this.
Once the glue has hardened sufficiently, you can reattach the wheels to the ElektorWheelie. Do not forget to use Loctite again on the centre nut (which attaches the driver plate to the shaft) to prevent it from coming loose.
With this simple modification you reduce the forces on the wheel carrying bolts and the shocks they experience during oscillation. The wheel is picked up immediately and in this way you prevent the bolts from warping or even breaking off.