the cart (from above)

pull test

the cart (on side)

pull test

I performed two pull tests with this model. One was to pull a weighted cart and the other was to determine the maximum tractive effort.

The model was able to pull a cart weighing 94.5 lb (42.9 kg). It moved very slowly, but it moved!

The tractive effort was determined by pulling a hanging weight connected by rope. This weight was suspended over the side of my desk by using a large plastic wheel. The maximum weight pulled in this set up was 6.5 pounds (2.95 kilograms). The gears strained and after just a bit, one of the 12-tooth bevel gears in the power gear train broke.

gear shift

gear box

I built this simple transmission for a number of reasons. I didn't have the new (at the time) shifting parts - the ones that engage the dark gray 16-toothed gears. I wanted a transmission that could be shifted by a motor and remotely controlled. And I wanted a robust gear train capable of transmitting power from four geared 9V motors (and that's a lot of torque).

This transmission worked but was tricky to operate. Getting it to shift properly took some tweaking and operator finesse. In the end, it was too much trouble and took too much fiddling to keep it shifting properly.

This transmission also took up a lot of room inside the model. That's why there's a big, tan "lump" in the cab instead of a proper seat :-)

I modeled my tractor after Case IH tractors. Their current line of large articulcated tractors is the STX Steiger 4WD series (on the left). My model is actually closer to the older series of tractors (on the right).