Not to spoil your day … I don’t think the units would have enough thrust. These units are wonderful for small ROV’s etc. but to pull a person through the water you are going to need a MUCH larger propeller to increase the amount of water you are pushing with the units and something to scale the torque up for the propeller … like a gear box or frankly a larger motor that runs high torque and low speed with a bigger prop.
It all depends on how fast you want to go. Four T200s will definitely move you through the water, but not very fast. If this is for SCUBA diving, then a lot of the drag will come from the tank, BCD, air lines, etc.
You’ll need a pretty large battery for 1 hour. Here’s an example calculation.
Assume 4 T200 Thrusters running at 75% thrust (210 Watts each, 840 Watts total). In an hour, you will use 840 Watts * 1 hour = 840 Watt-hours of energy. Let’s round that up to 1000 Watt-hours to account for some margin and so we don’t completely discharge the batteries.
If you’re running 4s lithium polymer packs the voltage will be 14.8V and the total number of amp-hours required will be 1000 Wh / 14.8V = 68 Ah. That’s a large battery. Here’s a 10Ah battery that could be connected with seven batteries in parallel to provide 70 Ah. (Radio Control Planes, Drones, Cars, FPV, Quadcopters and more - Hobbyking)
We also have a battery guide and calculator on our documentation: Battery Selection
For the reed switch, I would recommend using an Arduino microcontroller and measuring the reed switch. When it is connected, you can turn the thrusters on. I can describe that in more detail if you’d like.
Yes, I understand. Any DPV’s need big battery packs. This is what I thought it to be like. I guess you recommend me not to Look for cheaper pack at EBAY…
Please tell me more about the microcontroller setup.
The microcontroller would look for a signal on the reed switch (either high or low). You would write the code such that when the switch is closed, the microcontroller sends the appropriate PWM signal to the ESC. This way you can also adjust the motor speed by setting the PWM level in the code.
You could also write the program to have several output level and touch the magnet to the reed switch momentarily to switch to the next level. For instance, you could have off, 50% power, 100% power.
There are endless resources, tutorials, and help forums available for the Arduino platform. I recommend starting with an Arduino board like this one https://www.arduino.cc/en/Main/ArduinoBoardUno
You would set the speed using the servo library included with the Arduino IDE (integrated development environment).
Working on about the same subject (diver-assisted propulsion when filming underwater, in order to get more smooth movement in the film), I found out that using Lithium batteries, although by far the most interesting battery technology available regarding power efficiency, might pose a serious problem from a totally different kind: you are not allowed to transport high-capacity lithium batteries by air transport. Have a look at the IATA rules concerned. So one might have to use NiMh batteries instead.
It looks like this thread is dead, but I have a couple observations. I’m using four T200s to push a person sitting in the water at 4 mph with a 4S battery (13.2V). Although a soft start is better for the T200s (easily done with an Arduino) you can also easily create a PWM on/off using a 555 timer circuit for a couple of bucks. Servo exercisers from Hobby King start at $6.
