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Using the AX2550 to Remote or
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Important Warning and Disclaimer
Remote controlling or operating semi/fully autonomous full-size gasoline powered automotive vehicle is EXTREMELY DANGEROUS. Such a vehicle should only be operated on a secure test track and never be used to carry passengers.
This information is provided for reference only with no warranty. Users of this information shall do so assuming their own responsibility and liability
The Challenge
With the proper hardware it is not much more difficult to remote or computer control a full size car than it would a small model-car. In either case, all that is require is to attach servo motors to the following elements:
- Accelerator,
- Brake
- Steering
- Transmission
The challenge with a large gas-powered vehicle is the force with which to activate some of these elements which far exceeds this of the heaviest-duty RC servos. This is particularly the case of the brake and steering activation.
When operated in the position mode, the AX2550 can be used to create very high-power servos capable of such operation.
Closed-Loop Theory of Operation
In the closed-loop position mode, the axle of a geared down motor is coupled to a potentiometer that is used to compare the angular position of the axle versus a desired position.
If the potentiometer senses that the motor has not reached the desired position, power will be applied to the motor until that difference becomes zero. A PID filter is incorporated inside the controller to ensure that the motor moves as quickly as possible to the end destination without overshoot and/or oscillation
Steering Assembly
The steering assembly can be as simple as connecting the motor+potentiometer in place of the steering wheel.
An alternate method would be to use a chain or timing belt to connect the steering to the motor.
In both cases, the motor must be geared down so that the steering will move from full left to full right in 50 to 100 motor turns.
The potentiometer can be placed in any location that will provide an accurate position reading. For best results is should be placed near the motor and there should be minimal mechanical slack between the motor and pot.
The pot should turn from the min to max position as the wheels are in the full left to full right position. Depending on where the pot is placed, this may require a multi-turn potentiometer.
Brake Assembly
Activating the brake is a little more complex as the motion is linear and because the braking is set by the pressure that is applied on the brake pedal rather than the pedal's travel distance.
The diagram on the left proposes one possible method for activating the brake using the AX2550. The motor and screw assembly form a linear actuator. A linear pot captures the actual distance and is used to close the position loop.
The pedal is connected to the linear actuator using a spring. The result is a variable amount of pressure applied to the brake as the the actuator is extended or retracted.
Throttle and Transmission Control
Throttle control can be achieved by simply connecting a heavy duty R/C servo directly to the engine's carburator. It may be necessary to disconnect the accelerator pedal and its springs so that the servo has sufficient power to activate the throttle on the carburator.
The mechanism described above for the brake could also be used to activate the accelerator pedal if there is not easy way to mount a servo in the engine
The activation of an automatic transmission can be done with a linear actuator as well. In this case, the actuator should be connected to the trasmission stick without a spring.
Electrical Wiring
The diagram below shows how to wire the AX2550 to two motors in position mode.
Operating the Vehicle
If using an R/C remote control radio, the vehicle's operation is as simple as driving a toy car, with the added risk of significant rist to people and property should something go wrong or the operator fail to drive properly or responsibly.
As seen in the diagram, the controller may also be connected to a computer for a semi-autonomous or fully-autonomous operation. This is the mode used for experimental, self-guided vehicle applications such as the DARPA Grand Challenge contest.
For further inquires
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