Before sharing the design objectives for the build of the second prototype it is important to shortly describe what would be a typical data collection mission. Firstly, driving 200 km with an 4x4 to a ranch over a bumpy road with abundant potholes that often will make you brake suddenly (or fly in case you were not able to see them on time).
Once arrived on the location, riding on even worse internal roads towards a water reservoir. Getting the measurement platform out of the 4x4 and finding yourself without any easy access to the water surface in order to put it safely in the reservoir (due to irregular or inclined slopes). Most likely there will be a heavy wind, hence waves in the reservoir are expected. You have no time to wait for the best moment of the day (less wind) to make measurements.
Design objectives:
- Platform as robust as possible. External components (motors, electronics, etc.) should be detachable for transport (save in a separate, shock resistant box?) but the set-up and deployment in the field should still be straightforward.
- Platform should be compact and easy to transport (at least smaller than the current kayak) and to be handled by 1 person while setting into the water. It should however be still sufficiently big (heavy?) to maintain the maneuverability of the first prototype.
- One should be able to 1) follow-up in real time the position of the platform on a map (in order to navigate it correctly) and 2) check/see the measurements (to make sure the measurements are going well and avoid getting stuck in case of spots where water depth is limited). Real time visualization (on a smart phone?) is key. In case this would not add too much complexity/vulnerability to the project, a camera in front of the platform with live transmission could be interesting.
3 current questions
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Maintain set-up with 2 motors: I am thinking of a robust catamaran maintaining the initial set-up of 2 motors. I like the maneuverability of the first prototype with 2 motors (See video) and I guess this set-up may also be useful in case of measuring flow in channels with a strong current. I notice several community members opt for 1 motor and a servo for direction. Do you consider it “overkill” to have 2 motors for a “relatively” small, unmanned platform (energy consumption)? In case I would add an autopilot in the future, would there be a difference between the 2 previously mentioned set-ups?
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Building material for the entire platform=Stainless steel or aluminum: I want to avoid plastic and carbon fiber for building the hull and whatever moving components (like branches for the motor or sonar). I had a bad experience with plastic components with a fish feeder boat. Any advice on what to consider to assure the second prototype remains “floating”? For the first prototype, I did not make any holes in the kayak to avoid any problems with assuring impermeability (I have no experience with it).
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Protecting electronics navigation: Due to the rather small capacity of the lipo battery, I only tested the first prototype for a duration of +/- 10 minutes. In case of using a 15.000 mAh battery, I expect at least to be able to make the platform move during 1 hour. Should I worry about the electronics heating up? Reading the following comment in a recent post (Thrust required to propel an AUV?) " made me wonder whether 1 hour would already be considered very extended periods? I also read some members include a “heat sink” for their ESC.
It’s worth noting that T200s and the control electronics aren’t designed/intended to be run at maximum thrust for very extended periods, particularly if you’re running at the maximum voltage (they can end up overheating and become damaged)
At this stage, all opinions and advice are welcome (not only limited to the 3 questions)! I focused first on the navigation part of the second prototype, hence maybe later I will post some questions regarding the electronics for measurement. Thanks in advance and I will keep posting any progress from my side…