Low Tech Before High Tech

All too often I see new engineers want to jump straight into a 3D model or full blown FEA when a simple hand calculation will do. In this case, I am working on a design of an RC submarine where I am trying to make a lot of things fit in a relatively small space. It could be tempting to jump right into 3D modeling, but it is a lot easier to play with ideas in 2D space and translate it into 3D once you have completed your iterations in 2D space. Basic ideas can be first done on paper, whiteboard, or in this case paper to PowerPoint.

Each component was modeled to its appropriate size. Once the initial configuration was determined, before moving into 3D modeling, an installation study was performed. Here I present the steps of that installation study.

Step 1

This step starts with the initial installation of the motor/servo/shaft sub-assy. It is at a slight angle to get over the water inlet boss at the 6 o'clock position. The rounded off bits on the left of the screen are flexible wires. Because of their flexibility I am not concerned about interference with the hard components. The next area of concern are the mounting ears of the servos. The diagram shows that they just make it in. If I did not understand how this was actually set up in 3D space, this might be an area of concern, but the nice thing is that the entire sub-assy could be rotated 45° about the shaft axis while installing and the ears of the servos will have substantial clearance to the water intake fitting on the bottom.

Step 2

I can see that as I further insert the motor/servo/shaft sub-assy that I will need to ensure that the clearance hole in the interface between the blue and orange interface to the right will need to be as large as possible.

Step 3

Now that the servo ears have passed over the water inlet boss, the sub-assy can start to rotate level and continue installation to the right. Again, showing some interference with flexible wires, but those can be rotated out of the way, or flex out of the way.

Step 4

Continued installation of the sub-assy shows clearance, but to facilitate not saying grumpy words, adding additional clearance in the bore in the far right orange part would be helpful in order to maintain clearance to the far end of the motor shaft.

Step 5

The motor/servo/shaft sub-assy on the left hand side has cleared the water inlet boss and can now rotate completely level and continue the installation.

Step 6

The o-ring of the aft watertight bulkhead is beginning to engage, as well as the shaft is now passing through the flange bushing for the propeller guide. This step may want to have a fixture to help align or at a minimum hold things in place.

Step 7

The stern appendage gear meshes are confirmed and the sub-assy is seated into place. The sub-assy can now be bolted into place. Once the sub-assy is bolted into place, the wiring in the aft tail cone can be worked in preparation for attachment of the piston tank.

Step 8

With the previous steps completed, now we can attach piston tank to tail cone assembly. The shrouded propeller will now need to be tightened to the drive shaft with a set screw. This would now complete the tailcone assembly for the 3" diameter SUBOFF model.

Conclusion

The overall amount of work that has gone into this effort is less than about 4 total hours. In the process, 3 major configurations were explored prior to the one shown here. Each of the other configurations had their advantages, but ultimately were discarded in favor of this current configuration. Some of those ideas may come back as I transition this design to 3D in the next week.