A fully functional 12-way snowblade is the dream of every snow cat modeler. Whereas a mechanical solution for the lifting function and also the blade angle function can be realized quite easily, this is getting significantly more difficult for the other functions. Especially if you want to stay true to scale. Therefore we decided to use hydraulics for these functions, just as the original. 

But we could not find any cylinders in 1:12 which would satisfy our request for true scale. That's why we ended up building the hydraulic cylinders by ourselves. But we use commercially available products for the pump and valves.

Pump and Tank

We purchased the hydraulic pump from Modellbau Martin Kampshof and the valve blocks from Modellbau Ulrich Meinhardt. These components have been recommended to us by the pioneer of snow cat model hydraulics Michael Peter. Additionally they permit a much higher operating pressure than the products of other manufacturers.

The pump was delivered with a tank as one unit, but it did just not fit into the tub of the PB400. The whole unit was a few mm's too long. Therefore we had no chance than to built a new tank and place it at the side of the pump.

Fitting of pump and tank in to the PB400 chassis tub

Cylinder

After these first hurdles we started planning the cylinders. Albert (PhD, mechanical engineer) and Eric (metal technician for mechanical engineering) were the perfect team. Albert did the calculations and Eric has the necessary know how for manufacturing. Especially the short tilting cylinders are tricky because every possible mm of lift has to be fought for. The dimensions of cylinder and piston resulted from the available o-rings which are used for seals. We want to use very small hoses with 1 mm inner diameter, so that they are in the correct scale compared to the original. But these yield lower flow rates and also some pressure losses.

After the first tests on our hydraulics test bed (see below) were successful we could start the manufacturing of a first prototype. The parts are really tiny and have to be manufactured very precisely. Therefore a CNC lathe was used. 

WPM Hydraulics Test Bed

To verify our assumptions we built a hydraulics test bed and tested a cylinder by the German manufacturer Robbe with different hoses. Our hydraulics test bed allows to test cylinders under load in both directions. For the load weights are attached with a line to the lever. For pulling force the line is directed over the left arm (in the picture), and for pushing force over the right arm.

Cold Test

Snow cats operate in winter, therefore we immediately performed a cold test. We put the WPM Hydraulics Test Bed into the freezer for a few hours at -19°C (-2°F). The pump showed significant starting problems, the motor first ran jerky, and only after a couple of seconds it started to run smoothly (this can be seen in the video). Unfortunately these are the well known problems with model hydraulics. Also the movements of the cylinder were noticeably slower compared to warm conditions. But at such extreme temperatures we will not be outside anyhow. Therefore we are anxiously waiting for winter to do tests under realistic conditions. So far the hydraulics are working perfectly outside in winter at freezing temperatures.