Prototype Hydrostatic Tractor skidder
Photograph is courtesy and copyright of Forestry Commission, Forest Research, Roslin, and provided with help from Glen Brearley. FR Photo number No B8345 taken by I A Anderson.
Articulated tractor with four hydraulically driven wheels on test at Alice Holt. Concept by a Forestry Commission Research team. Which engineering company was involved? Any history of this development? Photographs taken about 1978.
Mike Turner is the driver and below he has written a short history of the development of this machine.
'I worked on the development of the hydrostatic tractors at the MRO workshops, Alice Holt (Machinery Research Officer) later changed to Gravel Hill workshops and now occupied by JCB Ltd.
I have put together some of the build history but unfortunately memories are fading a little but I believe that I have given a reasonably accurate account of the build.The prototypes were extensively tested in Scotland and were designed mainly for the thinnings there so have an historic place in Scottish Forestry. I believe I am correct in saying that all of the Roadless production units were put into operation in Scotland.
These photographs are of the Hydrostatic forest thinning tractor developed at the MRO workshops, Alice Holt in the late 1960’s early 1970’s. The development team was headed by Roddy Ross MIMechE, assisted by Keith Kernahan MIMechE, Stuart McKenzie, Jim Parker, Mike Turner & Sid Chinnery.
Two prototypes were produced at Alice Holt, the MK1 & MK2 with MK3 being the one that was built and put into production by Roadless Traction in Hounslow, Middx.
MK1 was fitted with an International Harvester 4cylinder engine driving four Caron hydraulic “Ball” motors. These motors were supplied by Caron Hydraulics Ltd, Kirkcaldy, Fife.
MK2 had a Ford three-cylinder engine fitted and driving upgraded Caron Hydraulic “Ball” Motors. The engine change came about because IH could not guarantee supply.
In both prototypes the engine provided power via a splitter box to the transmission, winches & steering. The splitter box provided drive to the three hydraulic pumps and if my memory serves me correctly the transmission was supplied by a Hamworthy pump with the Winches using a Dowty pump and a smaller Dowty pump for the steering.
Drive was obtained by supplying hydraulic fluid to the Caron motors. The motors attached to the chassis and the wheels mounted onto the outer casing of the motor. The ball motor consisted of six cylinders with two pistons in each cylinder, the pistons housed a large hardened ball of approx. 2inch (50mm) diameter. The outer casing had a cam plate mounted at each end with four lobes on them, the hydraulic fluid was supplied to the centre of the cylinder thus pushing the pistons out onto the cam plates causing the casing to rotate. The transmission system is a closed circuit and maximum working pressure on MK1 was 2500psi andMK2 increased to 3500psi. The transmission supply hoses were multispiral hoses with swaged end fittings.
There was a Boughton double drum hydraulic winch which was electric/hydraulically controlled via a radio unit strapped to the operator’s chest, this allowed the operator to walk out with the winch cable and choker a number of poles in one go and walk back to the tractor keeping the poles free of snags it could also be operated from a unit in the cab should the radio fail. Hydraulic fluid for the winch was supplied by the Dowty pump. The radio system was developed by the FC’s radio branch in Chepstow.
The steering circuit was supplied by the third pump which I believe was also a Dowty pump. The tractor is a frame steered unit with the Engine, hydraulic pumps fuel & hydraulic tanks installed in the front half of the tractor. The winch was installed in the rear half of the tractor which is framed steered.
Both steering and transmission was controlled via a “joy stick” with a button on the top of it to operate the “diff lock”. Ie, push the stick forward or pull it back for transmission and side to side for steering.
The main frame and safety cab was made in the MRO workshops but the safety cab was tested for compliance by the Agricultural Institution at Silso, Beds. Should the transmission fail emergency braking was by the rear mudguards dropping onto the rear tyres with the weight of the winches and frame holding it down. Cleats were welded on the underside of the mudguard to match the trye cleats.
A lot of the trials were done with Athol Whayman’s research team at Keilder and also with the training school at Aye. Laurence McClung being one of the instructors.
Mike Turner'
See PDF for more views of test.
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Groups: Forest Research, Timber harvesters, processors, forwarders and cable cranes
4 Comments
There were a surprising number about, with the last one being built by a company in Wales from the remaining parts stocks when Roadless went bust. Comment left on 23 March 2018 at 10:24 by David Shearer
The concept was good but the choice of Caron Hydraulics to supply the wheel motors spoilt it. They were unreliable and service was very poor. You could wait a year for a motor to be repaired. I have vague memories of something like 9 marks /models being produced trying to make improvements. Comment left on 31 October 2019 at 23:17 by John Martin
I believe it is myself who is driving the machine when these photographs were taken' Comment left on 22 February 2022 at 10:52 by Norman Davidson (Website Curator)
I don't think that many were made but a Google search shows one for sale at present. Comment left on 20 February 2018 at 11:59 by Jimmy Thain