By Leff
1. The wheel(s) can not rotate freely like the picture shows?

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There are several possible reasons:

2. When I want Vortex to go forward, but it can't, instead, it would always turn left/right. But once I hold up from the table or if I place Vortex upside down on the table, the wheels can run freely as they are supposed to. Reported by dominika.regentova

It is because the wheel is rubbing with the magnet. How to fix: Find a washer to avoid this problem.