Building A 52 INCH Robot With Arm


Making The Hand


Anyone who has a "VEX" set will recognize these parts. You can use any gearbox motor if you can get the vex gear to stay on the motor's shaft. The motor I used here was left over from another project. A note you need to know about this motor is the brown cap gets screw down to the plate on the motor which the motor turns.

Drill a center hole thru the cap so that a #8-32 by 1 3/4" screw will fit. Take the screw's head and grind down the two sides a little so that the head is now a rectangle with two curves ends. This makes it harder for the screw to break loose when glued in. Put the screw thru the cap with head pointed towards the motor plate. Put the nut on and tighten.

Depending on the gearbox motor you use, the wood size my be deferent. Cut two 3/4" thick piece of wood 7" by 2 2/16". One of these pieces will become the rail's base, the other the back plate of the hand's motor box. Cut two 3/4" thick pieces of wood 1 10/16 by 2 2/16" these will be the sides of the hand's motor box.

If you look in the photos you will see two L shaped brackets. They are 1 7/16" by 1 7/16" with one end shaped to fit the rack gear. These were made from an old bed frame. What can you find that will work? These were cut by using an saw with a cut off disc used for cutting metal. No fancy tools were used in making this robot.

Drill two holes thru the bracket and thru the side of the rack gear. Mount the bracket to the rack gear by using two screws with nuts.

The VEX metal parts must be cut. It's best to use a hack saw blade since a cut off disc takes too much metal with it. For the people who know nothing about VEX. The metal parts come with a little starter cut to show where you can cut. We will be using the smaller part, so cut that off. We will be using two. Using the screws that come with the rack gear, screw it into the metal slot using two screws with two metal washers. Now here comes a problem; if you tighten the screws all the way in, the rack gear can not move. If you do not tighten the screws, they will come loose in no time. The solution is; using everyday aluminum foil made tiny little balls and push them down the screw's holes. Take the rack gear, screw it back into the metal slot. If the rack gear still binds, repeat. When you get the rack gear to slide right, take out the screws and put a little glue into the screw's holes. Put the screws back in and let dry.

Take the rack gear assembly and screw it down onto the rail's base. I did NOT use drywall screws here. You want to use a screw with a flat head so that the rail assembly can be adjusted by a small amount. Take the other rail assembly and space it the width of the gear by putting the gear between the two rack gears. Now screw down the 2nd rack gear assembly. Take out the gear and side the rack gears in opposite directions. Put back the gear in the center and mark where the gear is.

Drill a hole large enough for the #8-32 by 1 3/4" screw to pass thru without binding. Take the rail assembly off the rail's base. Cut the rail's base from the top to the hole wide enough for the screw to side thru the slit.

Put the gear onto the screw. This is a very tight fit. I used a channel lock plier to hold the gear as I turned the screw. Turn the gear on the screw until the gear comes even to where the rack gear is with the cap close to the rail's base but not binding on it. When everything looks ok cut off what is not need from the #8-32 screw. Put glue on the head of the screw that is inside the cap and let dry. Put glue on the nut and around the base of the gear. When it is all dried screw the cap back on the motor. Side the motor gear assembly thru the slit until it hits the hole. Using a hot glue gun seal the slit. Put back the rail assembly.

Cut a 3/4" thick piece of wood 1 9/16 by 1 9/16. This will be the motor's base. Place the motor on to this base. See if the motor is parallel to the rail's base. If it looks good then screw the motor's base to the rail base. Glue the motor to the motor base. Nail the sides on to the rail's base. You will notice that the motor's rear shaft is sticking up. Mark and then drill this spot on the back plate so that the rear shaft has a place to go. Screw the back plate on.

The two fingers of the hand are made from two 3/4" thick piece of wood 3 1/16" by 1 11/16". You can cut a notch into the wood where it will be screwed into the bracket. Doing it this way lets the hand open a full 3" and you can cover the bracket and screw heads with cardboard. Drill two holes into each bracket that will allow the screws you are using to pass thru the bracket's holes. Mark and drill pilot holes on the fingers. Now mount the two fingers and screw them in place.

Using two 1 1/2" # 6 drywall screws attach this hand assembly to the bottom of the roller assembly.

THE END OF PART 2










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