Remote Control Lawn Mower

Transcription

1 Remote Control Lawn Mower ECE 791 Senior Project Progress report

2 Team members: -Hajrush Aliu -Neeraj Gill Faculty Advisor: -Professor Wayne Smith Courses Involved: ECE 541, ECE 543, ECE 649, ECE 651, ECE 617, ECE 618 Introduction: The purpose of this project is to design and build a remote controlled lawn mower. This would be beneficial because man power is not required in mowing the lawn on those hot summer days, where you would prefer not to be out in the sun. The remote will allow the user to control the speed and direction of the lawn mower by moving the joy sticks. For safety purposes, the engine of the lawn mower can be turned off via remote. Design specifications: The main objective of this project is to turn a push lawn mower into a remote control lawn mower, where pushing is eliminated by battery power. The battery will be used to power the dc motors, which will turn the gears and cause the wheels to turn with greater torque then what the dc motor can produce. The steering of the lawn mower will be done in a skid steer fashion by having the wheels turn in the opposite direction causing the lawn mower to turn either left or right, with swivel wheels in the front.

3 H-Bridges: Two H-Bridges will be designed to control the direction of the DC motors; turning the dc motors clock-wise or anti-clock-wise. This will make the lawn mower go forward or backward, and in either direction, left or right. The lawn mower will be turned left or right by turning the wheels in the opposite direction. Microcontroller: A microcontroller will be used to interface the receiver of the remote control to the H- Bridge. The pulse width modulation is used to control the speed of the DC motors. The microcontroller will be used to switch the direction of the current flow in the H-Bridge; which will change the direction of the motor. Wireless remote and receiver: A 2.4 GHz remote and an AR500 receiver will be used to control the operations of the lawn mower, such as: speed, direction, and safety shut off. The remote will send pulse width modulation signals to the receiver; which then will be used by the microcontroller to control the operations of the DC motors. Testing and Implementation: The H-Bridges was built and tested under different loads. We also tested the speed control by varying the PWN signal (0.1% to 99.9%) of the signal generator. The speed control test showed us that the motor stalls at below 8%. After the project is completed, a series of tests will be performed to see how the lawn mower performs at different landscapes (hills and flat areas). The safety shut off switch will be tested by using the remote. Additionally, the lawn

4 mower engine will automatically shut off if the remote signal is lost. After testing is completed, certain things might have to be re-implemented to meet the project s goals. Progress: In mid October, we decided to build H-Bridges using P channel Mosfets on the high side and N channel Mosfets on the low side. It was really difficult to find P channel Mosfet that can take high current. The ones we found were surface mount transistors (30A), we thought we can work with them but it was very difficult to solder wires to the pins. New P channel 19 Amp Mosfets were ordered and we decided to put two in parallel with heat sinks to meet our stall current requirement of 43 Amps. The H-Bridge was built using the new transistors and when we tested it, we found out the motor was not spinning fast enough. The reason was the two P-channel mosfet on the High side were not turning on and off completely. After testing each pin, it was found out that the driver circuit was not working as expected. Based on the specifications from the data sheet, P-channel mosfet needs 0v to turn on and about 12v to turn off due to the Vgs voltage. The driver we used provided 4v and 9v, as a result the transistor was not turning on and off properly which caused the transistor to overheat. The h-bridge and driver circuit once again were redesigned and rebuilt. The results were far better than the previous H-Bridges we built. The Mosfets were no longer heating and the speed of the motor improved which means there is no current loss in the circuit. Now that the H- Bridge is working as expected, an identical H-Bridge will be built to control the second motor. Now the next step is to interface the receiver with the microcontroller because the receiver outputs a PPM signal which we need to convert it into PWM signal in order to control the speed of the motor. We decided to order an Arduino Mega 2560 because it uses C language and can be

5 easily programmed. Once we receive the microcontroller, we will interface the microcontroller with the receiver and program it to control the H-bridges. If everything goes as planned, the project will be completed by the end of January. Estimated Budget: Category Parts Price Lawn mower $ Drive system Wireless Controls Circuitry -Motors -Gears -Wheels -Swivel wheels -Remote -Receiver -Wires -Circuit board -Microcontroller -Circuit Components Used from an old Power wheels HUMMER $ $ $ 8.00 $ $ Others Miscellaneous $ TOTAL $ Actual Budget (spent) Category Parts Price Lawn mower $ Drive system Wireless Controls Circuitry -Motors -Gears -Wheels -Swivel wheels -Remote -Receiver -Wires -Circuit board -Microcontroller -Circuit comp. Used from an old Power wheels HUMMER $ $ $ $ $ Others Miscellaneous $ 20 TOTAL $

6 Timeline (Updated): May 12, Decided to design a remote control lawn mower. June 4, Met and decided on the design specifications and goals of this project. June 20, Worked on how to implement our goals. - Gathered ideas on what design procedure to use. July 20, Bought a used push lawn mower. July 28, Decided to us parts from an old powered wheels hummer -Took the lawn mowers handle and rear wheels off. August 15, Installed a switch to turn the engine off because the handle was removed and there was no way of turning the lawn mower off. August 25, Installed the battery powered rear wheels on the lawn mower. -Installed the battery holder. September 10, Bought the remote control and receiver. September 20, Tested the output of the receiver and decided to use a microcontroller to interface the receiver and H-Bridge. October 8, Ordered transistors from On Semiconductors. October 18, Received the transistors and built the H-Bridge using N channel and P channel Mosfets but did not work. Redesigned and simulated the H-Bridge. October 20, Rebuilt the redesigned H-bridges but had a heating problem and motor running slow. The P Channel transistors on the high side were overheating and burning. October 22, Decided to use driver circuits for the H-bridge to eliminated the overheating problem. November 10, Built the H-bridge with drivers but motor was running at low speed then expected. November 16, Ordered New P channel mosfets. November 29, Built the H-Bridge with the new P channel Mosfets and driver circuit. The H- Bridge worked perfectly. December 2, Found heat sinks will go on the P channel Mosfets.

7 December 6, Ordered Arduino MEGA 2560 December 9, Designed H-Bridge with new driver cicuit.