I am building a simple electric vehicle which will carry my gear and follow close behind me as I walk long distances day after day after…… (I like taking things with me but I don't like carrying them all on my back.) I will not pull the vehicle and it will not push me either. I don't want to concern myself with control of the vehicle. What I have come up with is a tricycle with the front wheel powered by a electric motor. Presently the motor drives the wheel through a freewheel clutch - just like most bicycles.
concept sketch http://www.flickr.com/photos/charleschandler/10470195316/
The vehicle is tethered to the walker with a telescopic tiller tube (like a kid's wagon handle) which accomplishes steering. The forward tube of the tiller is fastened to the operators waist strap. The rear tiller tube is linked to the front fork of the tricycle. The two telescopic tubes permit the trailer to wander a fair amount along the axis of travel without bumping into the forward or aft stop of the forward tube and giving a jolt to the operator. I guess this would be around plus or minus 300mm travel from the midpoint position. The control system modulates the the power of the vehicle drive motor to maintain the vehicle at the midpoint position. I guess this would be accomplished with a PID control loop.
The vehicle also has a simple mechanical brake on the left side of the front wheel. I'm thinking, follow the KISS rule for now and don't get into regenerative braking. When the vehicle is descending a hill the controller will reduce the motor power to zero. The controller must then operate the brake to control the position of the vehicle. I am not sure about the details of how this will work. I am thinking the system would be structured in one or two ways. Option 1. Operate a linear actuator which would be linked to a 5K potentiometer which provides the command voltage to the control built into the motor. The actuator would start to close the brake pads as the output voltage from the potentiometer goes to zero. Perhaps there would be a bit of overlap.This way one actuator would have control of the motor and the brake. Option 2: The motor could be controlled by outputting a 0-5 volt signal directly to the motor controller that is built into the motor and an actuator could operate the brake when it was called for. I'm not sure which way would be better.
I have already purchased the drive motor. It's a brushless 3 phase motor and is rated at 360 watts. It has a 9.55:1 speed reducing gearbox on the output. ( I don't have much knowledge of motors) It has It has a controller built into it. The controller accepts a 0-5 volt command signal. This is normally provided by a manually operated, twist grip driven potentiometer for a standard electric bicycle application. Here is a link to the motor: http://www.cyclone-usa.com/store.php?crn=200
As far as operator controls go I am thinking the operator would have an on/off switch. It should communicate wirelessly with Arduino no wires need to be run from the operator to the vehicle.
- Is this project within the capabilities of Arduino?
- If yes, what Arduino components would be required?
- Recommendations regarding Option 1 or Option 2 for control of motor and brake?
- What type of position sensor? This vehicle will be outside and exposed to the elements. Moisture and ice etc. and temperature extremes can be expected. I can design and enclosure if necessary.
- What type of actuator to operate the brake? ( I was thinking maybe a stepper motor operated screw actuator. I am thinking the maximum force needed to operate the brake would be around 45 N or 10 lb. The travel of the actuator would be 100 mm for Option 1 and 50 mm for Option 2.
Thanks much for your consideration and comments.