Wooden Robot Hand Part 2

Here's how I went about making the wrist:

I traced out and cut the wrist from some 19mm thick pine (same width as the wrist servo).

In the wrist I cut out a spot for the servo to mount and a large notch in the centre for the wiring. I made the top section a bit narrower so that it will match the width of the palm.

I finished up with a stain and varnish!

I used similar hinges to secure the wrist to the palm. I then mounted the servo to the wrist and made a small arm to stop the hand falling and to enable the wrist to move forward and back.

I originally had trouble with the servo arm. I first tried to attach the arm to the side of the palm, but the servo turned out to be too weak to hold the weight of the hand. So I made a small bracket out of sheet metal to add more leverage to aid the servo.

Below shows the servo, hinge and servo arm.

I next wired up a prototyping circuit board with some switches, resistors and a few leds. The circuit for all of this is shown a bit further down.

A you can see in the photo to the right, I also made a removable base by screwing two pieces of 12mm dowel to the base and then drilling two 13mm holes into the bottom of the wrist. I makes for easy programming and testing. It also looks pretty cool.

Next came mounting the circuit board to the wrist. On top of it I mounted some clear perspex with holes for the switches and leds to poke through. I also mounted two toggle switches onto the perspex, one to isolate the 9V to the Arduino and another to isolate the 9V to the three regulators that supply the servos.

The purpose of the servo isolation switch is to allow me to make changes to the program without the servos moving about.

I finished up the wrist by mounting the Arduino, screwing on the voltage regulators and attaching a battery.

Before I mounted the Arduino, I dressed in the cables from the switches and servos so that they looked nice when they went into the Arduino. I also added a piece of perspex to protect the Arduino.

For the voltage regulators, I used the LM7805. The ones I chose only had a 1A capacity, so to be on the safe side I used three (two servos per regulator). In hindsight, I could have used 10A regulators, but they would have taken longer to obtain and I was impatient!

I mounted them all on a piece of aluminium that can act as a heat sink. The regulators are mounted on the side of the wrist, in between the Arduino and the battery.

The battery is just an ordinary 9V battery with a piece of aluminium holding it in place. I discovered later that a 9V battery doesn't last long when operating the servos constantly. So I would recommend either hard wiring a socket so you can plug in a power supply adapter or just getting a bigger battery.

Here's the circuit I drew up for all of this. At the bottom of the image is the circuit for each of the voltage regulators. I only used one 0.33uF capacitor on the input side since the regulators were paralleled up.

Switch S1 and the green led is for the Arduino supply. S2 and the orange led is for the voltage regulator and servo supply. The red is just an output from the Arduino. The red led lights up when the servos are moving, just to let you know not to press any other buttons.

I will post the Arduino program I used soon.