From this image taken from a video it looks like some of the engines have dual motion makers. A gear in the middle and what looks to be a rubber band around the wheels.
https://www.youtube.com/watch?v=pb056gvtSns
https://www.youtube.com/watch?v=pb056gvtSns
![[Image: Untir5tled.jpg]](https://i.postimg.cc/7bGwhvWd/Untir5tled.jpg)