WPM


Hydraulics in True Scale 1:12

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.

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.

 

Pump and Tank

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.


Pump tank unit as delivered

Pump with the new side tank


Fitting of pump and tank in to the PB400 chassis tub

Design Phase

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 sealings. 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.

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.


WPM Hydraulics Test Bed

WPM Hydraulics Test Bed with Robbe cylinder

 

Prototype

After these tests where 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.


Cylinder with soldered on nipples

WPM hydraulic cylinder

 

Cold Testing

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.


Cold testing at -19°C (-2°F)

WPM hydraulic cylinder under cold testing

 

Video of the First Tests and the Cold Test



Manufacturing the Hydraulic Cylinders

After a few adaptations based on the tests with the prototype the required cylinders were manufactured on a CNC controlled Proxxon PD230 lathe.


CNC-controlled lathe Proxxon PD230

Making a nipple from 2 mm brass wire


True scale micro hydraulic cylinders for the snow blade

 

Video: CNC-Manufacturing of a Hydraulic Cylinder

 

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