Mechanical Testing: Motors and Shafts

Choosing our Motors:

Choosing motors was somewhat of a dilemma. On one side there are very expensive ROV thrusters which would be the best motors we could get, but as one can see they are very expensive. On the other side there are non waterproof R/C motors, but we have to design a waterproof housing for them. As one might imagine we were not happy with either of the choices and therefore looked into two unorthodox ways of powering a submersible. First we looked into a waterproof motor because a waterproof container would be unnecessary. The water proof motor we ended up buying was a Johnson bilge pump motor cartridge. We also thought that using motors from rechargeable drills showed a lot of potential. They have both high rpm and high torque. We thought that this would allow us to attach large props and have a large amount of thrust with a relatively small motor. The only drawback to this type of motor would be the need for a watertight container. We ended up having a total of 4 different motors:

Johnson (small motor cartridge) – bought
Rule (small motor cartridge) – donated
Jabsco bilge motor – donated
Dewalt drill motor – donated

Extending our Motor Shafts:

One problem with the motors we chose was that each of them had short shafts of different sizes that wouldn't allow us to attach propellors easily. In order to fix this we decided to buy/create a universal shaft. We ended up buying a 3/8" aluminum rod to fit inside the seal in our containers. We cut 5 sections of metal rod into 4" pieces. Tapping one end with a 10-32 tap and drilling a hole on the other end for its respective motor. The threaded end will allow us to easily switch out props sizes while testing. To attach the new shafts to the original motor shafts we used an 8-32 tap and set screws. Pictures below: