Similar to the Mars Rover Competition, the Naval Orange Race took place at the end of my freshman spring semester in my Intro to Engineering II class. This project was designed to be more challenging than the Mars rover competition since everyone in the class now had experience completing a group project. The process of creating the boat was filled with lots of pivot points and setbacks, but in the end, our group overcame the challenges and accomplished our goals!
In groups of 4 or 5, design a boat that can transport an orange from one side of the UCF Reflection Pond to the other.
The video on the top of this post and the graphic below will give you an idea of what the course looked like on competition day.
We started in the staging area and had to go around the pond to the finish area. The orange dotted line represented a barrier that floated in the water and wrapped around the fountain in the center of the pond.
If you have not seen it, this is what the UCF Reflection Pond looks like in person:
As you can see from the video at the top of this post, the fountain was on during the race, which was the hardest obstacle to overcome in the course.
Competition Specifications and Rules:
- You can use electronic devices, within a certain voltage
- You can not use flammable, combustible, pressurized, or other dangerous materials
- The budget must not exceed $80 (including tax)
- The vessel must not exceed 1m x 1m x 1m
- You have 5 minutes to make it to the finish line
- All vessels must be self-guided and self-propelled
- Absolutely no remote controls and no string or line-based guidance systems are allowed.
- The vessel must transport an orange, while keeping it dry, from one side of the pond to the other
- The orange must be grabbed by a member of the team who is standing in the finish zone without touching the water or the team is disqualified
For this project, my group built our design around what we could get our hands on for the best price. Our goal was to make the boat go as fast as possible, so that way we would have a good chance at placing in the final round of the competition. We knew that we would need to have a boat propeller in the water to do this, so we went to a hobby shop to purchase a drive shaft, a propeller, and a motor. While we were there, the guy in the shop was nice enough give us a free front end of an RC airplane. Which means we got an extra motor and plane propeller for free!
Now that we had our propulsion mechanisms, we had to figure out how to power those systems simultaneously and keep them from getting wet. This was the biggest challenge for us in the entire project. When I was younger I enjoyed playing around with electric circuits, so I took up the challenge of figuring out how to wire the boat. We went out and bought some soldering gear and wired the two motors into a parallel circuit, with a 9V battery power source. Trying to use a 9V battery was our first mistake.
Our thought process at the time was that we didn’t need the battery to last very long, but we needed a higher voltage in order to go fast. When we attached the battery, we were super excited because both motors started spinning incredibly fast! We immediately ran down to the reflection pond to test our boat. We put it in the water, expecting to speed off away from us! And….
It didn’t even move…
Our battery was so small that as soon as the boat propeller encountered the water there was not enough current which could be drawn from the battery to produce enough torque to power the boat propeller through the resistance of the water.
You see, in simple terms motors get their torque from the amperage draw of the battery and their speed (or rpm) from the voltage applied to them. So, what we had was a boat capable of going lightning fast, but a battery that could not give us enough power to push the boat through the water.
Back to the drawing board.
When I was younger I experimented a lot with remote control planes, boats, and cars. So, I immediately thought that we could use a LiPo RC battery that had the right voltage and were specifically designed for the motors we had. There was just one problem. PRICE! LiPo batteries were way out of our price range if we were going to stay under budget. If we could have used one of these batteries, we would have easily won the competition.
Back to the drawing board, again.
So, we went out and bought a Duracell 6V Lantern battery (seen below). I hooked it up and the motors spun at about 10% of the speed they were capable of. However, when we placed the boat in the water there was no loss of speed as compared to out of the water, unlike the 9V battery. We were on to something.
Long story short, we ended up having to buy 4 very large and bulky 6V lantern batteries. They were massively oversized for what we needed and almost sunk the boat, but at $7.50 each, they were the only batteries we could afford and still get the job done.
I ended up re-wiring the entire boat to have the two motors hooked up independently. Each battery was wired in series with one other battery to give us 12 volts per motor and enough current to push the boat through a hurricane haha. This gave us the fastest configuration possible while also staying under budget. I think our only other option would have been to use 16 9V batteries, but wiring those together in a way that did not blow the motors would have been a nightmare and we just simply did not have the time.
After all of this, we still had to figure out how to make the boat go around the pond successfully! We ended up using a bent closet hanger (seen in the video) to help our boat hit the wall on the edge of the pond and then begin to ride the wall to the finish line. We also adjusted the angle that the airplane propeller faced on the front of the boat to help with this.
After all of our hard work and late nights, we were finally ready for race day. When the day came we were given slot number 2. This was known by everyone as the worst slot that you could start in. We started directly in front of where the fountain water came crashing down on top of boats. It didn’t matter to us though! While 85% of the teams didn’t make it further than 10 feet, our boat successfully navigated around the pond! Our boat was also able to make it around the pond very quickly. This put us in the final round of the competition where we ended up placing in the top ten out of 215 teams!