- The objective is to construct an autonomous solar boat that completes a water track in the least possible time
- Length of the track is 1400 mm
- Source of light is three halogen bulbs of 500 W
- There's a tunnel on the track, so there will be relatively less light under it
- Size constraint for the robot is 250 mm x 200 mm x 200 mm
- Area constraint for the solar panel is 150 cm^2
- Needs to have a mechanism to discharge any stored energy before the race
I personally would go with the paddle wheels. I am implementing them into my own project. You could use a servo to power it and get some pretty decent speed out of it. The servo would obviously need to be modified for continuous rotation and you can pretty small and cheap servos with low power draw. There are many ways to waterproof a servo. Just google it and find what works best. I use a slightly varied method of this.
3 x 500W Halogen bulbs
3 x 500W Halogen bulbs should make for quite good lighting for the solar panels, since they’re pretty close. If possible you should get a similar bulb and see what the voltage and current output are for your solar panels under similar conditions. The solar panels you linked to seem like a good choice, ~11.4mW/cm² is pretty high for common encapsulated panels, and with 4 panels you’ll be close to but not over the 150cm² limit.
A solar engine will actually cost you some of your energy, so don’t worry about using one unless you really need to. Hacked servos are also nice, since the built-in motor drivers are usually quite efficient, although you will probably find that you’ll need over ~4.8V to drive them well.
Pager motors are cool because they’re small, but they usually aren’t very efficient compared to other small motors. I’d look into hacked servos and high-efficiency lightweight gearmotors like the ones Solarbotics.com stocks.
The tunnel is short and quite far down the track, so you can probably just coast underneath it using momentum, provided your ‘boat’ is fairly streamlined. The tunnel is also very low, so you won’t get much light inside at all. If you angle your panels to catch light inside the tunnel they still won’t generate much power, but on the other hand they’ll generate less power during the open parts of the course - most likely a bad tradeoff.
If you want to store a little energy just to keep the boat going inside the tunnel, grab a few big capacitors. They’ll charge and discharge quickly enough to be worthwhile, unlike rechargeable batteries which are too slow. Capacitors are also lightweight and efficient, so they won’t slow you down.
Thank you both for your
Thank you both for your replies.
I don’t know much about servos, but from what I’ve seen I suspect they need a microcontroller to run? We planned not to use one since it introduces extra complexity. This is our first bot, so we want to keep it simple.
Big capacitors look like a good idea. But how exactly do I use them? How should I set it up to ‘fire’ at the right moment? Will I have to use something like a current detector (or light detector?) that will close the capacitor circuit when the current / light goes below a threshold value? Looks sort of similar to a solar engine.
You don’t need
You don’t need microcontroller for servo. You have to modify servo anyway so you can take away controlling electronics and use just the motor and gearbox.
Since you want to run the
Since you want to run the motors all the time, there’s no need to trigger the caps, they’ll work automatically.
When the solar panels are lit up, they’ll charge the capacitors, but when the solar panels get dark the caps will discharge back into the circuit. As long as the solar panels are powering the circuit, the caps will just sit there and hold their charge. The lower the solar panel output voltage is compared to the cap voltage, the faster they’ll discharge, conveniently ‘topping up’ whatever the solar panels can’t provide (until they run out anyway).
Make sure to put a high-current diode (1A or higher) on the solar panel leads going to your circuit. When the panels are lit they’re like a battery, but when they go dark they’ll actually consume power stored in your capacitors instead of charging them. The diode makes sure that current can flow out of the solar panels, but can’t flow back the other way.