SPoT

The team built this Self Propelled Truck SPoT.

We started with this elevator

and I told the kids they could take the elevator and use parts from the cable stayed bridge and make something new. see photo below

After some brainstorming they laid the elevator down on its side, took the windlass and added a second wheel and mounted this at 1 end- now the back end could roll.

Now for the front end- they took 3 pulley wheels and attached them to the front end.

and presto the "truck" rolled very smoothly.

Well it rolled but only if they pushed it. How to make it self propelled?

They took the 4ft long boom from the cable stayed bridge and attached it at an angle to the front of the SPoT

There's a pulley attached at the tip of the boom so they hung a load (3 bricks) from this line and ran the line over this pulley and down to the axle of the rear wheels.

Now as the load descended, the line pulled on the axle causing the truck to move.

Now as the load descended, the line pulled on the axle of the windlass causing the wheels to turn

The front end of the truck was heavy- what with the boom and the 3 bricks- so we added a counter-weight - a brick

But the truck didn't roll very smoothly- -there must be friction somewhere. Ryan saw that part of the frame was touching the ground- the solution- they taped a piece of smooth wax paper to the frame- that did it.