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Subject: Skid steer calculations

Date: 09/10/99
Posted by: Gary Harper
E-mail: gharper(at)pcilightingcontrols(dot)com(no spam)
URL: http://


I have been trying to work out a skid steer system of two motors, valves and pumps. The problem I have is that my calculations leave me needing more torque than a small block Chevy can even produce. I must have missed something!!! I have included a copy of what I have done. It is an excel program that I have written to do the calculations, but I sure could use some help. I would be glad to send it to anyone that would like it and would be willing to help me find my error! Thanks Gary Harper gharper@pcilightingcontrols.com Hydro Drive Calculator Input fields highlighted in YELLOW SPECIFICATIONS CONVERSIONS Vehicle Weight 575 lbs lbs 1000 453.5927 kg Vehicle Capacity 500 lbs kg 453 998.694048 lbs Total Weight 1075 lbs VEHICLE DRIVE CALCULATIONS Surface Resistance: (per 1000 lbs vehicle wt Sand: 60-300lbs Mud:37-150lbs Snow: 25 -37lbs Dirt: 25 -37lbs Select surface resistance 300 lbs/1000lbs vehicle wt. Target Max Speed 20 mph converts to 29.2 feet/sec Time to accel. to Max Speed 20 sec. Tire Diameter 22 inches Percent Grade Capability 40 % Force needed to overcome Surface Resistance Force Equals 322.5 lbs Force needed to climb grade Force Equals 430.0 lbs Force needed to accelerate vehicle Force Equals 48.9 lbs Force needed to overcome air resistance is negligible TOTAL FORCE NEEDED TO DRIVE VEHICLE 801.4 lbs TORQUE CALCULATIONS Total Axle Torque 8815.3 in.lbs. 734.6 ft. lbs. Number of Axles Driven 6 Torque required per Axle 1469.2 in. lbs./axle 122.4 ft. lbs./axle HARDWARE SPECIFICATIONS System working pressure: 1350 psi Axle RPM required to reach target speed 305 rpm Nunber of motors to be used 2 Torque required per motor 4408 in. lbs 367.3 ft. lbs/motor Component size requirements (min.) Motor requirements 20.50 Cu. in/rev Motor/Pump flow requirements 27.11 GPM Select pump/engine RPM 3000 rpm Pump volume(@ selected RPM) 2.09 Cu. in/rev Selected pump efficiency (from manf..) 100 % efficiency Engine requirement (@ 85% typ. pump efficiency) 50.25 HP (@ selected efficiency) 42.71 HP

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