The Claw Bot
August 12, 2009
This is my third bot. I used a few ideas from my other two and added the lifting arm and grippers. I am hoping to be able to search for, lift and carry a beer can, full would be usable but I doubt if the power is there with the present motor.
Updated Photo: 1/13/2010, Added a Function Test Video 1/16/2010
Mechanically the bot is complete. I have enough code to test all the functions.
I used a CD drive motor and a custom made gearbox to propel my bot. Still had a few slotcar gears and other parts so they were used for the gearbox. See my previous bot for more info on the gears.
Arm Lift Gearbox:
The Arm-Lift unit started out as a old project. I added another CD drive motor to it, geared 4:1 with 48pitch gears. 12t pinion and a 48t spur. Inside the box is a worm gear drive that gives a 30:1 reduction ratio. Total reduction is 120:1. The worm gear allows the bot to carry an item without the arm falling down when the power is turned off.
Earlier version of my bot before the counter-balance arms were added.
The chassis is G10 phenolic 1.6 mm thick. This has to be my favorite material for strength and rigidity. A vendor that I deal with has a laser so his shop cut the chassis for me. A Futaba S3003 servo handles both the steering and sensor rotation.
Steering link is not finished yet, probably by the weekend. The steering turns 45 degrees in each direction. Same set-up as the previous bot. Sensor will be the Sharp IR #GP2D120.
I added the vertical arms as a counter-balance to lift heavier loads. I was surprised at the amount of torque that tiny motor has. I can add weights to the tie together rod (white plastic detail) to increase the amount that can be lifted.
I am using (3) circuit boards for controls. Main board is a RK Education #RKPT18 Proto board. It uses a PicAxe-18X microprocessor. Comes with a built-in On-Off switch, Reset switch and a power on LED.
Picked up another RK Education board. This one is the Relay Board. Nice PCB. Has a transistor to switch relay, ability to wire in separate battery pack and includes all the diode protection circuitry and screw terminals for all wiring connections. Power on LED is there also. Size is 37mm x 46mm. Since the 18X only has (1) PWM pin, I am using Oddbots design with a Relay board to shift output to control either Drive Motor or ArmLift Motor.
Motor control is FWD-Stop-REV using half of a L293D chip. This chip is mounted on a RK Education Motor Control PCB. I like this board as the size is 35mm square and has (3) mounting holes. Pretty easy to place almost anywhere. Screw terminals add to the ease of wiring and moving to other projects. Three AA rechargeable batteries power this bot. May have to add a 4xAAA pack if I need more power on the lift arm.
I have mounted the L293 Motor Control pcb on top of the arm lift gearbox and made a bracket for the Relay PCB behind the steering Servo. Got to build a plastic part to mount the Main PCB at the far rear of the chassis.
Here is a photo of the solid model that the bot was built from. Robot was modelled in SolidWorks. Right now I am waiting on some ordered servos for the gripper "squeeze". Bit more mechanical work left to do but I am getting closer.