Building A Wrist For The Hand


Page 2


Next we want to make an optical encoder wheel so that the robot knows how much he turned the wrist. What an optical encoder wheel does is to break a light beam as the motor turns there by giving four pulses for 1 turn of the wheel. Lets build one for the wrist motor.

The encoder wheel is made from cardboard from a cereal box. I used a compass to trace out a circle on the cardboard that is 1-1/2" in diameter. I used a paper hole punch tool to put four holes in the encoder wheel. Use the small hole that is made by the tip of the compass to find the center of the encoder wheel. Use a square file to make a square hole so that the encoder wheel will fit the motor's shaft.



Put a little glue on the hub of the small gear. Slip the encoder wheel down the motor's shaft until it on top of the small gear. Put some more glue on top of the encoder wheel and let dry.



Next we want to make a base for the hand that we made so that the hand can be attached to the wrist. From a 1" by 4", cut a piece of wood that is 3" by 2-6/16". Drill a .144 or 9/16 hole 1" down from the long side of the wood and 6/16" from the short side of the wood. Drill another .144 or 9/16 hole on the opposite side. Find the center of the wood and using a compass draw a circle two inch in diameter. From the long side go up 6/16" and over until you meet the circle put a mark there. From the other long side do the same. In other words you want the # 8-32 x 1-1/2 screws from the turntable to fit into the base without the # 8-32 x 1-1/2 screws hitting the walls of the hand. Drill a .144 or 9/16 hole where you put the marks. We need to trim the corners of the base so that the corners do not hit the motor shaft when the hand turns. Mark a line 1/4" from the tip of each corner; this is how much we want to trim from each corner.



Screw the wooden base to the hand so that the base is even with the walls of the hand (do not glue the base to the hand at this time because we will need to take it off again to wire up the hand's motor).



Put one more nut on each of the turntable # 8-32 x 1-1/2 screws. Attach the wrist to the hand by putting the turntable # 8-32 x 1-1/2 screws thru the holes in the hand's wooden base. Put one more nut on each of the turntable # 8-32 x 1-1/2 screws that is sticking thru the hand's base.Tighten all the nuts so that the hand is level.



That is all for this month.

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