A. H. McDonald & Co.

The company management had heard of Bottrill's "Pedrail" wheel system for tractors, and decided that a specially designed tractor and trailer fitted with Pedrails would help to solve their problem of getting supplies to the mine site and delivering the ore product to Port Augusta. They called for tenders and in due course awarded the contract to Austral Otis, a Melbourne engineering company. McDonalds were only just becoming interested in Bottrill's invention, so probably did not tender for the whole contract, however, they undoubtedly worked with Austral Otis on the project, for they were chosen to supply the engine.

McDonalds' standard production engine then would have been a 40 HP four cylinder D type but this was not used. Instead, they adapted new gas engine design for use with petrol/kerosene fuels. This twin cylinder engine was rated at 45 HP and occupied a smaller base area than the D type although it stood much higher.

After field tests on the swampy flats behind the Austral Otis works, the tractor was shipped to Hummock Hill (Whyalla) in 200 separate packages. On arrival it was assembled by Frank and Reuben Bottrill and driven to Port Augusta where it was loaded with fuel, oil and mine supplies. The rig carried 35 tons, 10 on the tractor and 25 on the trailer.

The trip to the mine took 109 hours of which 50 were lost due to "stoppages necessary to adjust the shortcomings of the plant and engine." Engine problems arose as a result of the hot conditions with temperatures up to 116 Deg (Far) in the shade. It had a heated inlet manifold which was not required in these conditions so it was disconnected. The return trip took seven days, with no further problems.