Week 16 – Final touches and float testing!

As the week draws to a close, let’s recap on what we’ve done the past week.

We 3D printed 2 propellers and 4 spool connectors to be connected to the servo motors controlling the container.

 IMG-20160203-WA0012 IMG-20160203-WA0010 IMG-20160203-WA0007 IMG-20160203-WA0015 IMG_20160203_143234_HDR IMG_20160202_083524_HDR

We also 3D printed new motor brackets as we made some dimensioning errors previously with the old motor brackets.

After the silicon sealant hardened, we had to waterproof the DC motors as per the steps below:

  1. Spray NanoProtech liquid electrical insulation inside the motor as shown in the video below.
  2. Duct tape any gaps or holes on the motor’s frame.
  3. Mix the green and white epoxy then apply it over the motor connection points.
  4. Apply lots of white grease on the motor’s axle before mounting the propeller onto the axle.
  5. Apply even more white grease after mounting the propeller on the motor’s axle.

After we waterproofed the motor, we tested it out in a bucket of water.

What we observed was that on land, the motor spun very fast with the propeller attached onto its axle. However, in water, its speed dropped significantly. This was because there was more resistance (water resistance) and hence the motor had to generate more torque, which in turn lowered its speed. The torque of a motor and its speed are inversely proportional given a constant voltage and current supplied to it.

After we assembled all the pieces together, we were ready to bring the vessel to the swimming pool for testing.

But, before that, we took a very artistic shot of Imp Bot.

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We knew that our vessel would not float as there weren’t any flotation devices on it at the time, and its buoyancy was too low, as can be seen in the video below.

If we let go of the vessel, it would’ve sunk all the way down to the bottom of the pool. As such, we attached flotation devices on it. First, we attached life jacket foam around the front and back of the vessel. Its buoyancy was still insufficient and hence we cut out 2 large styrofoam pieces and attached them to the front and back of the vessel respectively.

IMG-20160202-WA0019

And it floated! The vessel’s overall buoyancy was boosted up a lot by the life jacket foam and the styrofoam such that the 5kg chunk of metal was able to float well!

We tested out the motors underwater and they worked albeit rotating very slowly. They spun fast enough to move the vessel. We were contented with its speed. However, after a while of testing, we observed smoke in the electronics box. We immediately recalled the vessel to find out what went wrong. The wires connecting the battery to the breadboard melted and caused a short circuit. Ajay promptly disconnected the wire, although burning his finger very slightly. This minimised the potential damage to the circuit and the battery.

IMG-20160205-WA0021

The reason for this is that we made a mistake by using single core jumper wires instead of multi-core wires. The jumper wires weren’t designed to handle 2A of current and hence melted. Multi-core wires are however designed to withstand the high current. None of the other wires were affected.

With that, we are just left with calibration next week and making the video.

Ryanfranco

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