I think you should look at hoverboard motors as a cheap and powerful motor system, with 2 or 3 board Its more than powerful enough to pull me around the beach and with a 100rpm limit hard coded into the firmware I was confident enough in it to let my kids have a go.
I worked it out, that each motor put out something like 8kg of pull, so 6, was giving 48kg of pulling force so you will loose grip before running out of torque.
with 3d printed wheels it can go just about anywhere.
