Hovercraft

The purpose of this project update the Engineering Physics 4A04 Project designed by former students Andrew Jeffery, Dan Ross and Graham Greenland. By updating the project, the project can be cleaned up and can be used in the future provide a representation of the some of the type of work that students in Engineering Physics complete during their time at McMaster.

The task the group was given was to design, construct and complete a robust vehicle with the intention to win a contest. There were specific design criteria to meet, and a distance-cost relationship that was to be minimized.

When work on the project began, several pieces of the hovercraft were missing and on top of this several wires were cut. IT was apparent that the report would be crucial in getting this project fixed. After viewing the schematics many times, the loose wires were soldered in place. The main wire that caused problems was the wire providing 7.2 volts to the voltage regulator of the detection circuit.

The red wire was soldered to the input of the voltage regulator to provide power to the detection portion of the circuit. A servo was added in place of the broken one, but the orientation of the pins was different from the previous servo. To fix this, the connections underneath the breadboard were reversed (the ground and the positive terminal). This meant the wires were properly connected and the servo was in working order.

The detecting LEDs and phototransistors were connected to the front wheel by an adhesive, but it was seemingly loose after 10 years. Silicone sealer was used to put the detectors back in place and properly aligned.

The device was tested and the results showed that both motors and the detection circuit were all working properly. The servo steered when a black line was replaced in front of it and removed. When the detectors detected the stopping signal, the motor turned off and the finished LED turned on. The fan motor provided enough power to cause the craft to hover, while the drive motor spun, though there was a lack of an o-ring to connect it to the actual wheels.

Due to the changes in power consumption by each of the motors, adding a 9 V battery for the detector circuit seemed beneficial so the PIC always received the constant needed voltage. The power source was disconnected from the detection circuit and a 9V battery and a switch were added in place. The 9V goes through the 5V voltage regulator, and as such there is no change in going from the 7.2 V battery to the 9 V battery.

The back wheels were removed so an O-ring could be connected to the drive motor to the wheel axel. Several sizes were tried but none fit well enough. Elastics were tried and eventually one with the right size was found. The drive wheels were put back on the hovercraft.

Each individual part of the hovercraft seemed to be in working order, so the hovercraft as a whole was tested. Black electrical tape was placed in the hallway on the third floor of JHE. The hovercraft began to hover, but the weight of the craft was still too much for the drive motor to spin the wheels to cause movement. The detection system also was not following the line properly. The third problem was the skirt was not connected all the way around the craft. The skirt needed to be secured so that the lift air wasn’t being lost. These issues needed to be addressed in order to get the hovercraft working properly.

In order to get the drive working properly, more lift is needed to alleviate the extra weight. To do this a second 7.2 V battery is added in series with the previous one. These will double the current going to the motors, increasing the lift. The problem with adding a second battery, is the fact that there is no where to place the battery on the hovercraft. Eventually the battery was placed on near the rear wheel adding weight to the wheels so they would drive the craft.

Even though this was supposed to solve the driving problem it didn’t. The wheels still wouldn’t spin enough to make the hovercraft move. On top of this the craft stop working. This turned out to be due to a loose or weak connection in the solder. The breadboards were taken and re-soldered and inspected to make the connections solid again. The hovercraft now works as it did previously.

The second problem encountered in the previous test, was the detection and track following. We were using a typical line following track, but the hovercraft actually follows a novel graded track. With the detectors on each side of the solid black part of the track, analog measurements were used to guide the craft towards the center of the track. This track was not found in the report and one would have to be made to recreate race conditions.

The final change was the changes made to secure the outer skirt. The excess glue was removed so the smooth clean surface underneath was available. Silicon concealer was added to keep the skirt in place. The skirt was left to dry for 24 hours. Silicon concealer was also added to the inner skirt in small areas where it was obvious that the skirt was not connected properly. No air is lost to the skirt now; it solely provides lift.

With these changes, the craft is almost ready to work. However, due to time constrictions this is as far as we came to making the hovercraft operable.

1. Be sure that the rechargeable batteries have been fully drained, and then fully recharge the batteries
2. As the batteries are charging:
   1. Roll out the track to the desired length. In order to activate the stopping program, be sure that there is at least 90cm of black material at the end of the track. (Note: The user can calibrate the length of black at the end of the track so that the craft will stop in a desired position.)
   2. Be sure that all three switches are in the “OFF” position. The drive motor switch, which is mounted on the strainer, should be set to the right when looking at the craft from the rear. The power switch, which exits from the joker playing card, should be set to the right when looking at the craft from the rear. The detector switch located near the front of the craft should be set to the right when looking at the craft from the rear.
3. Once the batteries have finished charging, unplug them from the charger. Plug one in underneath the craft, and the other on the drive wheel axel. Place the craft in the center of the track and point it so that it will travel towards the black materials.
4. Turn on the power switch, which exits from the joker and the detector switch. This should result in the lift fan turning on, as well as the LEDs for the guidance system turning on. Check to make sure both are working. One should notice that the craft will rise on a cushion of air and one can see the red light from the LEDs
5. Now that the craft is turned on, slide it from right to left and then back again across the track and make sure the servo is steering. The steering connections are very minute so watch carefully.
6. Now that everything has been checked the vehicle is ready to race. Place the vehicle in the center of the track and switch the drive motor button to “ON” (button mounted on strainer to the left, when looking from the rear). At this point let go of the vehicle and watch it easily track to the target area where it stops.
7. Notes:
   1. One can increase the speed of the craft by adjusting the blue potentiometer on the rear of the craft with a flat head screwdriver. Note that this is ill advised, because the vehicle has been calibrated to the speed marked with the black marker on the potentiometer. If the craft exceeds this speed, it performs erratically.
   2. If one wanted another PIC could replace the one that is already in place. If anyone got ambitious this craft could be reprogrammed for other tasks.