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Kayak Setup questions / battery options


(Johnny B) #1

Kayak questions have been asked before, apologies for this, but I need some help to determine if it’s possible to power an inflatable kayak using T200 thrusters. The tandem kayak is 4 meters long and 90 cm wide. The model can be seen here.

I don’t mind going from standstill to cruising speed via paddling, turning on the thrusters only once moving. I also don’t need to do any steering via electronic controls, since the paddles can be used for this as well. I have no requirements for slowing down, or a reverse mechanism, a simple on / off switch would suffice. Multiple speed settings could be useful, mostly to regulate the speed, preventing the battery from draining too fast. My idea is to mount the thrusters on the tracking fin at the back of the kayak, perhaps with the mounting brackets.

I suppose the BlueESC option would be the easiest to start with, and perhaps a micro-controller with basic controls to achieve the on / off functionality. If you believe that for this application, there would be enough thrust provided, then I would be grateful if you could help answer the following:

  1. Assuming mounting will be done with the brackets in front/back orientation then distance between the two thrusters will be only a few centimeters. Is there a minimum distance requirement for proper usage?
  2. I assume two thrusters working at a lower RPM would provide better battery consumption rates & thrust performance, compared to one running at a higher speed. Using the chart on your website, one T200 can generate 3 lbf of thrust, using 47 Watts. Coupling two units would yield 6 lbf & 90 Watts. The charts seem to suggest that a 16V battery would yield higher thrust at lower current (16V – 2.96 vs 12V – 3.87), and lower PWM. Are 16V batteries in large capacities available on the market, and are there any downsides to 16V installation?
  3. Supposing that I find a 8000 – 10000 mah battery pack, is it advisable to use them individually until they are drained, or is connecting them in parallel a better option?
  4. Are there any suggestions for a basic micro controller that could be connected to the BlueESC by someone without any prior experience?

(Richard) #2

Johnny,

Let me try to help here:

  1. If you are talking putting the thrusters in line, don't. Mount them side by side. You would need at least a foot between in line thrusters to minimize the effect of propeller wash from one into the other.
  2. 4S LiPo's are readily available in 8000-10000 capacities, but they are expensive. Be careful with your thinking here about thrust. The only way to get more thrust at lower RPM is to increase propeller size, which you can't do with the T200. You are bound to the published performance curves.
  3. I would keep the battery packs separate for reliability.
  4. Arduino UNO. Inexpensive and easy to use.
Having said the above, it is my opinion your idea will work in a minimal wind situation, but not with significant wind. The inflatable kayak has a lot of surface area for the wind to act on.</div> Hope this helps. Cheers, Richard

(Richard) #3

Johnny,

I don’t want to steer you away from Blue Robotics (a great company!), but a better choice at not much more the cost may be this: http://www.minnkotamotors.com/Trolling-Motors/Engine-Mount/Engine-Mount/

Richard


(Johnny B) #4

Hi Richard, and thanks for your quick replies.

Perhaps I was not very clear in my explanation. My idea is to install two T200’s side by side, one on each side of the tracking fin. I questioned the possibility to install them so close together not because they would be inline, but because the tracking fin is 0.5 cm thick, so the two thrusters would end up quite close to each other. Having said that, the propellers would be at the same level, so I don’t foresee any wash affecting them.

With regards to the thrust, I’m using the data from the published charts. This data suggests that the 16V power supply can achieve the required thrust levels (3 lbf) at lower PWM, and my thinking is that this would yield longer run times for the same capacity battery.

Point noted about the wind. Do you know if there is a plan to create slightly larger / more powerful thrusters in the future? As weight is not a big issue in my application, I don’t mind having several batteries with me, and overall run time we’re looking to achieve is about 1 hour per battery pack, at an average of 2.5 to 3 knots. Via HobbyKing, I see a 4S solution, but also a 6S solution. Given that the batteries are the same capacity, would the run times be longer if I use a 6S?

As for the trolling motor, I know there are a variety of options here, but none are applicable in my case as there is no frame / mounting bracket, as it’s an inflatable boat.

Regards,

JB


(Richard) #5

Johnny,

No question in my mind; the higher the voltage and the lower the current, to get the same power out from the battery, will yield longer run times. It’s all about battery internal resistance and heating losses.

I don’t think BR is currently working on a more powerful thruster.

Have you run a simple pull test with a spring scale to check actual thrust required to pull your loaded kayak at 3 kts? You may be right on with your estimate of thrust requirements, but it would be smart to do an empirical test.

I am not a fan of running LiPo’s in parallel, but many people do it. I certainly would not charge them in parallel.

Richard

 


(Johnny B) #6

Would love to be able to try that as an empirical test. Of course I’m lacking all the essential tools, like a spring scale, and a speed sensor, and a way to actually pull the loaded kayak at 3 kn in realistic conditions.

Any idea what kind of run times I would be able to get with this 6S battery?


(Richard) #7

I don’t think you should run the T200 with a 6s battery.

The T200 needs roughly 50 watts to generate 3 lbs of thrust at 16 volts. A 10000 ma-hr 4s LiPo ideally contains 160 watts of energy. This would give you 3 hours run time. Realistically, taking into account battery efficiency and voltage drop as the battery discharges, I would plan for no more than 2 hours.


(Rick Nelson) #8

Well, this is sort of on topic. I am using the thrusters for another application, but wanted to do a proof of concept before moving further. So I setup a control box with an arduino and a 4S 10000maH battery pack. I mounted the thrusters on a PVC frame that crossed the kayak, putting a thruster on each side. This happened to lie in a natural cross slot on my kayak under the stretch hold downs, so I didn’t attach it otherwise. I added two arms on the pvc crossover which allowed the thrusters to rotate up and onto the kayak when not in use and rotate down and into the water beside me. I ran the thrusters at various speeds and found that they could really make the kayak move when at about 1700 on the PWM setting, my selected top due to current draw above that. I ran back and forth across a bay and was seriously cruising. It ran for quite a long time and performed very well. Running the thruster at lower settings worked well, just not as quickly.

As was stated previously, I don’t think it would be much help in a wind situation as the torque isn’t there unless you had more thrusters.

For the batteries, I plan to run 2 packs in parallel for more run time. Charging with multiple packs will certainly be a challenge…

Recently I saw the packs that I had purchased were on sale for half the price, putting them at $29 each, so I picked up a couple more packs for my project.

 

My kayak was a composite 14’ manitou, weighing 44 pounds, with me at about 160 pounds.

One thing I did find was that I could have made the down legs longer on the frame. When I used side weight shift to make turns, the upside thruster was barely in the water.

 

Programming the arduino was pretty easy using existing library functions.

 

Hope this helps!