So, a pneumatic grab had too many limitations - pipes would tangle and the grab would be big and bulky. The first few ideas I came up with are very similar. In my final design, the lift arms started off next to the 24-tooth gears but the gear box body protruded too far in to the grab, making it quite difficult to pick any thing up. The next idea was to move the lift arms to the end of the gear box body as shown in the pictures below but I started off by using a solid link. I later discovered a design by Eric Sophie over at MOCpages.com that used LEGO shocks they help maintain a good grip while lifting, and allow for some counter rotation when the grab is spinning though 360 degrees as the axle for the grab is fed through the first wrist causing, counter rotation when the wrist is moving. I can also cancel this out in my NXT program by spinning two motors at the same time to keep the grab is the same position.
 As you can see from the two pictures above and below the grab section is very simple, just made from around 50 pieces using LEGO's triangular lift arms as the gear box housing and a worm gear in the centre which can feed both sides of the grab at the same time. This prevents the grip being released.
 The grab could be easily changed to suit each different job because it just simply slots in to place connecting to the wrist with two LEGO 8m axles. The drive axle is slid into a clutch gear to protect the motor from being strained while grabbing a load. Once the load is gripped, the motor stops and the LEGO shocks continue to maintain the grip.  The above picture just simply shows where the grab connects to. The pictures below show the full workings of the grab and wrist, including the motors used to operate the grab and wrist. The grab and wrist is fairly self contained - it only requires a power supply to work as all the gearing, and motors are built in to the grab and wrist.   |
LEGO Facts
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Motorized Grab |