Types of Connections
Cortex: Robot Arm Controller primarily communicates using analog inputs, servo pulses, and PWM signals. Connections to the controller side are:
- 4 analog inputs for the 3 joints of the controller and the gripper positions
- 2 analog inputs for the gripper force sensors
- 1 8-amp PWM output for the force feedback motor
Connections to the robot are similar, with:
- 3 servo pulse outputs for the three joints of the robot
- 1 analog input for the gripper position
- 1 8-amp PWM output for the gripper motor
Connecting Controller Analog Inputs
The three analog inputs for the joints of the controller and one for the gripper are labeled “USER INTERFACE POTENTIOMETERS”. The pins are arranged as 3.3v-signal-gnd, so the attaching the potentiometers backwards will not damage the board or the pots, but will cause them to read backwards. This is occasionally desirable if you want your robot to mirror your movements instead of mimic them. If the gripper potentiometer is reversed (GRP) it may case the force feedback to behave incorrectly. If you find the controller gripper moving to max or minimum position try reversing the potentiometer. If using Robomotive Labs supplied potentiometers the 3.3v-signal-gnd (POS-SIG-GND on the board) connection corresponds to yellow-red-black wires. The inputs are labeled as channel 1 through 3 and GRP. The order is not important (except for GRP, which must be the gripper) as long as it matches the robot arm, but for simplicity we recommend the setup below.
The force sensors are also analog inputs, with 3.3v and GND pins. The force sensors are variable resistors, so it does not matter which pin is which, but we’ve used red a black wiring, so for simplicity red can be connected to 3.3v and black to ground. The inputs are labeled “FORCE SENSORS”, with “F IN” and “F OUT”. This relates to the direction of the grip. “F IN” is a closing grip (ie. the sensor on the inner side of the controller) while “F OUT” is an opening grip (ie. the sensor on the outer side of the controller).
Controller Gripper PWM
Cortex uses an 8-amp motor driver to supply force feedback to the controller gripper. Depending on the size of your motor leads you can solder directly to the circuit board or use the included screw terminals. If using a servo based gearmotor the screw terminals are probably the way to go. The connection is labeled as “-CON+”. The voltage reverses depending on motor controller output, but “+” and “-” are provided to assist assembly. If using the servo based gearmotor from Robomotive Labs or per our instructions your motor will move in the proper direction if the red wire is connected to “+” and the black wire to “-“.
Connecting the Battery
Cortex can take anywhere from 4.8v to 16v. Note that input voltage is not regulated at the servo outputs, so they will see full battery voltage. Check your servo specs to be sure you’re not exceeding their limits. Robomotive Labs typically uses HS-311 servos, which are rated to 6 volts (5 NiMH batteries). Hookup is straightforward with positive and negative connections. Cortex is reverse voltage protected, but it’s best not to test that.
Robot Servo Connections
The Cortex servo outputs are labeled “ROBOT SERVOS” and are set up just like standard RC receivers. Standard servo leads can plug directly into the Cortex: Robot Arm Controller. Pins are set up as Signal-Positive-Gnd (yellow-red-black), so connecting the servo backwards will not damage the servo but the servo will not function. Channels are labeled 1 through 3, and should be connected to match the order used on the controller side.
Robot Gripper Connections
The robot gripper position is labeled “ROBOT GRIPPER POTENTIOMETER” and is similar to the controller potentiometer connections, with a 3.3v-signal-gnd (yellow-red-black to POS-SIG-GND).The gripper motor is attached in the same way as the force feedback motor on the controller. The “+ROB-” connection is labeled as “+” and “-” to co correspond to the red and black wires on the servo based gearmotor, but the connection delivers voltage in both directions depending on force inputs. As with the force feedback connection, the motor can either be soldered to directly to the board or the included screw terminal can be used.
If your robot isn’t responding right away don’t fret. Follow these steps:
- Move each controller joint one by one, make sure the corresponding robot joint moves.
- Squeeze the controller gripper in, make sure the robot gripper moves in.
- Squeeze the controller gripper out, make sure the robot gripper moves out.
- Move the ROBOT gripper in and out. Make sure the CONTROLLER gripper moves in and out.
Robot Gripper Moves in Wrong Direction
Check that the “F IN” and “F OUT” connections go to the correct force sensor. If this is correct reverse the robot gripper motor wires, even if it means red will be on “-” and black on “+”.
Controller Gripper Only Goes to Full Open of Full Closed
Move the robot gripper to be sure the controller gripper doesn’t move to the opposite extent. If not reverse the motor connections, even if it means red will be on “-” and black on “+”.
Controller Gripper Jumps from Full Open to Full Closed
Check robot and controller gripper potentiometer connections. Reverse one of them.