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Joint Controllers
The joint controllers consist of leg controllers and hip controllers. One leg controller is located on each leg. It controls the thigh and knee joints and senses the thigh, knee, and compliant linkage position. There are two hip controllers, one for each side of the robot. Each hip controller controls three hip joints.
The leg controller collects sensor data and controls the solenoid valves for the leg hydraulics. It receives body position data and commanded position from the main computer and runs a control loop to determine the solenoid PWM outputs. It reads the hydraulic piston position and compliant linkage deflection and passes the data back to the main computer to be sent out to all joint controllers as part of the whole body position data.
###Functions Functions:
- Drive solenoid PWM (4x PWM, two per solenoid valve)
- Monitor string pots (Thigh and Knee)
- Monitor compliant link sensor
- Monitor 12V actual voltage
- Send position data to main computer via Ethernet
- Receive robot position data from main computer
- Compute control loop and update PWM
The string pots are powered at 1.8V. The compliant linkage sensor operates at 5V, so it requires a voltage divider down to 1.8V for the ADC input.
Dithering
In some hydraulic PWM systems, dithering is used to prevent stiction in the valves. We are currently not planning on implementing dithering. Instead, the PWM rate we chose should provide some of the same effects. If we do need to implement dithering it can be done in software without hardware changes.
###Enclosure
The leg controller will be housed in a WP-27F sealed polycarbonate enclosure. All connections will be through sealed cable ports.
###6x Leg Computer
4x PWM for valves
1x analog in for compliant link sensor (w/ 5v to 1.8v divider)
2x analog in for string pots
1x analog in for hip string pot (v2) - ???
TBD: 3 or 1 voltage sensor to eliminate need for 12v supply (v2)
The hip controller is identical to the leg controller with a few minor modifications. It has an additional solenoid output. Instead of reading two string potentiometers and a ride height sensor, it reads three string potentiometers. The string pots and ride height sensor have different voltage ranges and need different voltage divider resistor values to adjust their outputs for the 1.8V ADC's on the Beaglebone Black.
Add solenoid port
Add two more PWM drivers to control an additional solenoid
Change the voltage divider used for the compliant linkage sensor to be another string pot voltage divider