Drive a skid-steer excavator
Suggested exercises and observations
Enter your username, complete the exercises below then post to your LRS using the email button.
Driving screen
♦ Drive between a path of boxes, hitting as few as possible. The number of boxes hit is counted on the right-hand side of the screen.
1. Enter your username into the edit box on the menu page.
2. Select screen 1 (Drive a skid-steer excavator)
♦ Click on and drag the black levers to operate the controls.
♦ Click on and drag the red button to operate the left and right track drives together.
♦ Practice operating the drive, slew, and boom arm control.
♦ Drive through the line of boxes hitting as few cases as possible.
♦ Note your score on the right hand side.
Experiment 1: Hydraulic systems control the drive, slew, and boom movement either gradually by the position of the lever, or ON/OFF at either zero of full power.
Question 1: What might be the advantages and disadvantages of proportional and ON/OFF control?
Experiment 2: Wheel drives and cab slew use hydraulic motors. Boom extensions use hydraulic cylinders.
Question 2: What actuators are the crane winch and arm extension system likely to use?
System operation screen
3. Select dropdown 2 (Explore how the electro-hydraulic control systems work) to move to screen 2.
♦ Move the mouse-over or click on the left hand group of components to select the hydrostatic drive system.
♦ Move the mouse-over or click on each component to see a description for what they are.
♦ Click on and drag the black lever to see how one side of the hydrostatic drive system works
♦ Observe how the control signal (volt/amp) changes as the lever is moved.
♦ Observe how the pump swashplate moves +ve and -ve for different flow directions.
♦ Observe how the flow rate and motor speed change, proportional to the lever position.
4. Move the mouse-over or click on the middle group of components to select the slew system.
♦ Move the mouse-over or click on each component to see a description for what they are.
♦ Click on and drag the black lever to see how the slew system operates
♦ Observe how the control signal (volt/amp) only switches between zero and maximum as the lever is moved.
♦ Observe how the pump swashplate only moves in one direction as the flow starts.
♦ Observe how the spool valve position controls the direction of flow and therefore the direction of motor rotation.
♦ Observe how the flow rate and motor speed is either zero or maximum.
♦ Observe how the shuttle valves feed the motor supply line pressure back to the pump control valves.
5. Move the mouse-over or click on the right hand group of components to select the boom arm extend and retract system.
♦ Move the mouse-over or click on each component to see a description for what they are.
♦ Click on and drag the black lever to see how the boom control works.
♦ Observe how the control signal (volt/amp) gradually changes between zero and maximum as the lever is moved.
♦ Observe how the pilot line pressure changes with lever position and this pressure controls the position of the spool valve.
♦ Observe how the spool valve position controls the direction and speed of flow.
♦ Observe how the flow rate controls the cylinder and therefore arm speed.
Experiment 1: Hydrostatic drive systems are efficient because there are no control valves with high-pressure drops across them so, therefore, fewer energy losses.
Question 1: Why aren't all systems run as closed-circuit designs?
Experiment 2: Shuttle valves are used to feed the highest load pressure back to the pump's load-sensing control.
Question 2: Why is it important to sense what the highest load is?
Experiment 3: Pilot pressure reducing valves are used to control the pressure on the end of the boom control spool valve, and therefore control the spool position.
Question 3: Why don't we just control the spool position by an electrical solenoid?
Circuit diagram screen
6. Click the Home (house) button to return to the menu page.
7. Select screen 3 (How hydrostatic drive circuits work)
♦ Move the mouse-over or click on each component to see a description for what they are.
8. Select dropdown 2 (Identify all pressure control valves).
♦ Click on and drag the pressure gauge triangle to each pressure control valve.
♦ Your score is shown on the right hand side.
♦ The nodding or shaking head will indicate if you are correct or incorrect.
9. Select dropdown 3 (Identify all flow control valves).
♦ Click on and drag the flow control triangle to each flow control valve.
10. Select dropdown 4 (Identify all air and fluid filters).
♦ Click on and drag the dirty fluid triangle to each filter element.
11. Select dropdown 6 (Build a hydrostatic closed-circuit system).
♦ Click on and drag each component to rebuild the circuit in the shortest time.
12. When finished click the mail icon to post your results to your Learning Results Store (LRS or LMS).
Experiment 1: The main pump/motor circuit does not link directly with the fluid reservoir but has a separate pump that delivers a small flow into the system.
Question 1: Why do we need additional flow in the main motor/pump circuit?
Experiment 2: Shuttle valves are used to feed the make-up fluid into the low-pressure line of the main circuit.
Question 2: Why is the fluid not supplied to the high-pressure line?
Experiment 3: When the engine is turned off the pump will not produce any flow or pressure. In this situation the vehicle could start to roll if it did not have a parking brake.
Question 3: How is the parking brake applied and removed?