Overview
Sensors

In order for the computer to make desicions about shifting it needs to know what is going on with the fourwheeler. Many of the older racing fourwheelers do not have speedometers or tachometers, so these are things that will be added.

Measuring engine speed can be done a couple of different ways. First, some type of counter can be attached to the shaft in the motor to count revolutions. This would mean taking the engine apart to install the hardware. A simpler method is to count signals from the spark plug. After these signals are cleaned up using electronics, they can be fed to the card. A routine programmed into the computer card will count the pulses and return an RPM.

To measure wheel speed the rotations of the rear axle need to be counted. This counter can be a magnetic counter on the axle itself, or it can be an idler gear attached to the drive chain with an encoder on it. A hall effect sensor will be mounted in front of the rear chain sprocket. This sensor returns a pulse every time a sprocket tooth passes by the sensor. These pulses will be sent to a computer card and counted using the same routine as the one for counting engine RPM.

Throttle position is measured through a potentiometer mounted on the user's throttle lever. The potentiometer sends a simple analogue single voltage related to the position of the throttle lever. A potentiometer will be placed on the throttle actuator as well to measure the actual position of the throttle.
.The project can be broken down into three different categories - sensors, actuation, and programming.
The platform for our project is a Honda TRX450r. The transmission in the TRX450r is a 5-speed manual transmission.

Actuation

In order for the computer to shift it needs to actuate three things - the clutch, the shifting lever, and the throttle plate. Signals from the computer will be sent to these actuators when it needs to shift.

The actuation for the shift lever is a bit simpler than the clutch lever. The amount of force to actuate the shift lever is only about 10 pounds applied at the end of the lever. Also, the speed of the actuator does not need to be controlled. The actuator will work at its highest speed every time. The full range of motion of the end of the lever is about two to three inches. For such a simple actuation a simple two directional linear solenoid is optimal. This is will provide fast actuation and be easy to control. However, the range of actuation needed is almost an inch and a half in each direction. Solenoids are not optimal for actuation distances of that large. Therefore, a high-speed linear actuator is used.

The actuator chosen  is a tubular high-speed linear actuator PA-15 made by Progressive Automations.​​ The actuator has 3 in stroke length, 11 lbs of force, and a speed of 9.05 in/sec. A linear potentiometer is attached to the actuator to return its position to the computer card.

The throttle plate is actuated normally by a cable attched to the throttle lever on the handlebars. This cable needs to be actuated so that the position of the throttle plate can be controlled by the computer during shifting. The tension in this cable is relatively low, and can be controlled by a small stepper motor.
Programming

The shifting will all be done with a programmed computer card. This card will take all the input from the sensors and decide when it needs to shift and what gear it needs to shift to. When it decides it needs to shift it will send signals to the actuators to start a shifting sequence. Starting from a stop and hard braking are a couple of the special cases that will have to programmed into the card.

The card we will be using for the main program is an Adruino Mega. These cards have there own programming language similar to C++. They can take digital or analogue signal as input, and output as a PWM signal.This card will make up the brain that controls the shifting.

The stepper motor used is 12V, 1.6A, 233 oz-in geared stepper motor. The cable is attached to a pulley that is rotated using the stepper motor. A rotational potentiometer is attached on the end of the shaft to track the position of the pulley and the throttle cable.

The decision as to whether or not to shift is based on the wheel speed and throttle position. A typical driver, as well as an automatic transmission, will shift up at higher speeds with more throttle input for any specific gear. In other words, for greater acceleration or for driving under heavy load (as indicated by higher throttle position) the shift points for each gear will be at higher wheel speeds than for slower accelerations or lighter loads.

To find these shift points, data was collected from multiple test runs. During a test run, a driver accelerates through all five gears and back down through the gears under various loads and acceleration rates​​. The wheel speed and throttle data for each shift point from each run is recorded and plotted on a wheel speed versus throttle graph. One such graph is shown below for shift points recorded from gear 1 to 2.

Curve fits of this data for each shift point are used to acquire equations which the program can use to make decisions on when to shift. If the throttle position and wheel speed approach the curve fit line at any point from below, the fourwheeler shifts up, and similarly for shifting down.

The hardest thing to actuate is the clutch lever. The tension required in the clutch cable to actuate the clutch lever is on the order of 120 pounds force. The full actuation also needs to be as fast as possible to provide optimal shifting. So to actuate the cable a significant amount of power is needed. In addition to high power the speed of the actuation needs to be able to be controlled.

There are several options to consider for this actuation. On a larger vehicle hydraulics would be a very viable option, because they offer a high power output. However, on a smaller vehicle hydraulic actuation creates problems, because it requires a lot of additional components, for example: hydraulic pump, resevoir, valves, etc. Another option is pnuematics. However, controlling the speed of a pnuematic actuator comes with a list of challanges as well. The simplest option on a small vehicle like a fourwheeler is an electric linear actuator. The computer will send its signal to a contoller, which will control the linear actuator.
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