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Mount the transistors
The deployment transistors can either be mounted on the top of the board or the bottom. If you
mount them on the top of the board, the board will lay flatter on your sled, but the overall
height will be taller than if you mount them on the bottom. In general, we like top-mounting
for AV bays 3" or larger, and bottom-mounting for AV bays under 3". If you are building a
minimum-diameter rocket (the Eggtimer will fit into a BT-55 body tube), then bottom-
mounting is a must.
Top Mounting:
Insert the transistors into the board, so that the metal tab is facing the front of the board (the
side with the header). There is an outline of the transistors silk-screened onto the top of the
board, the close parallel lines should line up with the tab. Hold them in place with some paper
masking tape, turn the board over and solder them to the pads. Trim the excess leads flush.
Bottom Mounting:
Hold one of the TIP120 transistors horizontally with the metal tab facing down. The plastic
side of the transistor with the writing should be facing up. With a pair of needle nose pliers,
bend the leads upwards 90°, at the point where the leads get skinnier. See the picture below.
Repeat for the other transistor.
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