Efficient solar powered (electric) kayak

Discussion in 'Boat Design' started by ElectricKayak, Mar 20, 2015.

  1. Joakim
    Joined: Apr 2004
    Posts: 892
    Likes: 52, Points: 28, Legacy Rep: 422
    Location: Finland

    Joakim Senior Member

    It shouldn't be impossible to have ~90% efficiency for the propeller and another ~90% for motor+controller for this kind of application, but then you need to carefully select the components you use.
     
  2. ElectricKayak
    Joined: Mar 2015
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    ElectricKayak Junior Member

    I've been looking at motors and this one looks ideal to me. It's a Turnigy 9014 105kv Brushless Multi-Rotor Motor (BLDC). The link is http://www.hobbyking.com/hobbyking/..._105kv_Brushless_Multi_Rotor_Motor_BLDC_.html

    At 2600Watts and 117 Amps the power should be good. And at 105Kv rating it is a low rpm/high torque motor suitable for direct drive. Saving the gearbox is a big plus for noise and efficiency. Unfortunately the specs don't provide the info necessary to calculate efficiency (I've emailed and asked for more detailed specs) but this class of motor seems to be in the 85%-90% range. Without a gearbox even 85% would probably be a winner.

    Thoughts? Agree? Disagree?

    And a really dumb question...what is the simplest and cheapest way to control these motors? I've read up on the ESC but they all seem designed to connect to a Transmitter receiver which I wouldn't be using. It's not clear to me they can even be used standalone, and if so, how. What is the speed control signal for these things? Probably I'm missing something here...
     
  3. johnhazel
    Joined: Jun 2008
    Posts: 250
    Likes: 5, Points: 18, Legacy Rep: 60
    Location: Michigan

    johnhazel Senior Member

    There are transmitter emulators that you can use. You just plug the ESC into it and turn the knob. Try searching for "servo tester" on the Hobby King site.
     
  4. kerosene
    Joined: Jul 2006
    Posts: 1,059
    Likes: 66, Points: 48, Legacy Rep: 358
    Location: finland

    kerosene Senior Member

    Jeremy Harris has done a lot of work on small electric boats. he has some informational posts here on this forum. He is goo don boats but also on electronics.
    He is also active (was) on endless spehere (http://endless-sphere.com/forums/) which is electric DIY vehicle forum. People rig Turningy motors to work with "proper" motor controllers. I think they might work pretty well even without tinkering but not sure if there was some "pole location" issues.
    You will probably find all you need from endless sphere but its a bit hard forum to follow when one's level of knowledge is limited as most members now way more than I do. But with careful digging you can find info for us dummies too.
     
  5. alan craig
    Joined: Jul 2012
    Posts: 258
    Likes: 43, Points: 38, Legacy Rep: 14
    Location: s.e. england

    alan craig Senior Member

    That thread referenced by Portacruise "efficient electric boat" is about the best you will find for your purposes.

    The multi-rotor brushless will work on any voltage below its rated. The little 3mm stub is not really a shaft, it's a guide for the flat hub propellers it is supposed to be used with, which mounts with 4 screws and a load spreading ring. You would have to engineer an adapter from the motor to your flexi shaft. I imagine that the motor would make the same irritating squeaky whine as most brushless motors - mine does - so these two points might rule out BLDC motors. I only mentioned the 1200W capability because you won't need anywhere near that power level, so that motor would probably not burn out. EDIT Easy to control with a servo tester.

    Not much I can say about mine because it is a conversion of a petrol outboard, but:
    Never had a problem with starting or low speed control
    Never had a problem with overheating probably due to over specified components (e.g.. 36v/100A controller used at 24v/25A)
    Had problems with aero props collecting weed, so went back to the original prop which came with the outboard.
    Oh, mine is more suited to a rowing boat than a kayak.
     
  6. portacruise
    Joined: Jun 2009
    Posts: 1,115
    Likes: 32, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    See insert notes in message below:

    PC: Maybe sorting electric boat page by the Jeremy posts will help with getting to info more quickly. Then you can get to sections that discuss a particular subject.

    Hope this helps.
     
  7. ElectricKayak
    Joined: Mar 2015
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    ElectricKayak Junior Member

    Thanks everyone, and I found the "servo testers", thanks! Didn't know such things existed but it's good they do! :)

    I agree there is a lot of great stuff in the thread PC referenced. Now that I've matured my thinking I'll have to re-read parts of it. And I'll check out the endless-sphere site also.

    I did notice Jeremy mentioned the efficiency of brushed and brushless motors were basically the same. I've collected some data for my MK motor and see efficiencies range from about 72% to 77% (cruise speed of around 60 watts versus sprint speed around 300 watts).

    Unfortunately the motor I linked doesn't have sufficient data to estimate efficiency but the 9225-160kv Turnigy does and around 300 watts output and similar shaft rpm it is roughly 83% efficient. It's copper loss is low but mechanical and magnetic losses seem a bit high. So roughly a 5% gain which isn't material in my situation especially considering the extra complexity, noise and expense.

    The 9225-90kv Turnigy looks similar to the motor I referenced. It has a relative low no-load loss but surprisingly high copper losses (Rm=0.186ohms). Quick calculations indicate the efficiency reaches highs of mid-80s but under high current it plummets due to the copper losses to below 70%. Perhaps this is why it is a relatively low current rated motor (36Amps max).

    If the motor I referenced has similarly high copper losses then it would be a no-go. Since it is rated for 117amps max, I'm hopeful it is more reasonable but we'll see.

    All to say, one could easily end up with something that isn't materially more efficient than the MK. The key info isn't readily available to properly calculate motor efficiency for various operating scenarios.

    Also I'm not sure my MK setup is fully optimized yet. There remains the possibility of pulling the MK out of the water and using a small drive shaft for improvement in appendage drag. It would be interesting know the drag of the pod itself but unfortunately I don't know how to calculate drag for that shape. I haven't seen an fully optimized MK setup versus a Brushless setup comparison. I'm starting to think it would be interesting.
     
  8. portacruise
    Joined: Jun 2009
    Posts: 1,115
    Likes: 32, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    The brushless Torqeedo vs. Mcdenny optimized might be a comparison for consideration. Maybe not a fair comparison because of the Torqeedo gearing. However it may be a lesson in the importance of torque matching, even over appendage drag/disturbance.

    MK warns not to run the motor out of water. I don't think is because of heat issues, maybe something to do with seals?

    Some efficient battery boat motors:

    http://www.torqeedo.com/en/technology-and-environment/propulsion-technology.html

    http://www.electricpaddle.com/specs.html

    PC
     
  9. Jim Caldwell
    Joined: Aug 2013
    Posts: 266
    Likes: 8, Points: 18, Legacy Rep: 48
    Location: Cleveland, Ohio

    Jim Caldwell Senior Member

    The brushless motor will need an ESC (controller) to deliver the timing pulses, that can be controlled with a servo tester.
     
  10. ElectricKayak
    Joined: Mar 2015
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    ElectricKayak Junior Member

    I thought people might be interested in a real world comparison of the stock MK versus the fully modified one (prop, fairing, spinner).

    Running at 5.1km/h the stock MK killed my 35AH AGM battery in 2.5 hours of lake running. Basically we ran it until we lost power, rested 10 minutes, ran it again until losing power then limped home. Battery SOC showed less than 10% remaining. Today we cruised around the same lake doing the same thing (speed/distance/time) and finished with about 65% battery remaining. According to my wattmeter we consumed 11.5AH.

    Combined with the improved efficiency and the battery Peukert effect, our range has more than doubled!

    The prop and spinner together cost less than $5 and were trivial to add. The fairing was made from a scrap of wood and needed a modicum of fabricating skills.

    The main trade-off is poor weed performance.
     
  11. alan craig
    Joined: Jul 2012
    Posts: 258
    Likes: 43, Points: 38, Legacy Rep: 14
    Location: s.e. england

    alan craig Senior Member

    That's a brilliant result. And if you double the size of the battery you will have double the range again obviously, but with that Peukert effect you will drain less % from the battery and it will have a longer life, because it will be draining at half the rate.
    Or, as model 'plane lipos are so cheap now you could experiment with them, or electric bicycle batteries. It seems that you already have solved your propulsion problem to the point where you do not need to consider using a solar panel.
     
  12. ElectricKayak
    Joined: Mar 2015
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    ElectricKayak Junior Member

    I thought it worth posting about the little wattmeter gadget I'm using. Mine measures energy (Wh), charge (Ah), power, current and voltage. As well as peak amps, peak watts and minimum voltage (sag). This unit really simplifies testing.

    I also find it indispensable during operation. The instantaneous amp readout is handy for throttle control and the "Ah consumed" makes a perfect fuel gauge.

    It works well with solar panels too. Aligning them becomes trivial and the Wh readout shows how much total charge the battery received. Removes all the guesswork.

    I didn't know these things existed before this project, but they do and I can't imagine running an electric boat without one. The accurate fuel guage is worth the price of admission alone. I have the SKRC WM-010 but there are plenty others to choose from.
     
  13. portacruise
    Joined: Jun 2009
    Posts: 1,115
    Likes: 32, Points: 48, Legacy Rep: 218
    Location: USA

    portacruise Senior Member

    The temperature effect on voltage and capacity can be significant particularly in cold climate areas. Here's a way to estimate for flooded lead systems, don't know if applies exactly to SLA.
    http://www.trojanbattery.com/Tech-Support/FAQ/Temperature.aspx

    The best charging voltage rises while the discharge voltage declines with colder temperatures for flooded lead systems.

    I think Tesla cars have provisions to maintain optimum temperature on their lithium battery pack for that reason...

    Hotter temperatures generally decrease cycle life. Increase in DOD generally reduces cycle life and charging protocol also affects cycle life. My laptop has a charging protocol option promoting longer cycle life by not fully charging the battery.


    Don't know if solar cell ratings would be affected, since the sun would generally warm them above ambient.

    PC
     
  14. ElectricKayak
    Joined: Mar 2015
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    ElectricKayak Junior Member

    I had forgotten about the Torqeedo until PC mentioned it. Interesting they only claim a peak total system efficiency of 45% for their 403 Ultralight kayak package.

    I also noticed they had performance data (presumably extrapolated based on sea trials) for that package as tested on a touring sea kayak. So I installed the MK system on my sea kayak, did a few tests, and compared the results.

    The Torqeedo system:
    -------------------------
    Ultralight 403 with integrated battery (29.6 V / 11 Ah)
    Touring kayak (Prijon Prilite T470), 15.4 ft, 50.7 lbs

    Speed in kph Range (kms) Run time in hours
    Slow speed 4.2 42 10:00
    Half power 6.1 26 4:10
    Full power 9.8 7.7 0:48

    Modified MK system (17' touring sea kayak):
    ----------------------------------------
    Speed in kph Range (kms) Run time in hours
    4.2kph 46 11
    6.2kph 27 4:20
    9.8kph 8.4 0:51

    Top speed for me was 11kph. FWIW, I accidently tested at 6.2kph rather than 6.1 for the half power setting.

    Of course the modified MK system is 2.5 times the weight (about 40lbs verus 16lbs)! Although a lithium battery drops the weight closer to 25 lbs with a big chunk of that being the motor.

    As an aside, my inflatable kayak has similar performance at 4.2kph (about 40+kms range). It's pushing the wall at 6.1kph though and only lasts about 3+ hours. It can't get to 9.8kph even if falling off a cliff (top speed drawing 40 amps is 8.2kph)

    I've attached some pictures of the system installed on the sea kayak. Since I'm in this deep I'll probably install it on the 22' double for comparison. The double has a lot more wetted surface so I'm not expecting much especially at the slow speeds but it will be interesting to see how it compares.
     

  15. ElectricKayak
    Joined: Mar 2015
    Posts: 78
    Likes: 0, Points: 0, Legacy Rep: 10
    Location: Canada

    ElectricKayak Junior Member

    Pictures attached this time. I plan to shorten the motor tube once I decide on the length.
     

    Attached Files:

Loading...
Similar Threads
  1. highamperage
    Replies:
    18
    Views:
    5,010
  2. Annode
    Replies:
    106
    Views:
    3,000
  3. 07MAM
    Replies:
    18
    Views:
    2,731
  4. johnnythefish
    Replies:
    34
    Views:
    5,276
  5. xichyu
    Replies:
    22
    Views:
    2,614
  6. xichyu
    Replies:
    7
    Views:
    1,614
  7. Wavewacker
    Replies:
    58
    Views:
    7,664
  8. SailorDon
    Replies:
    17
    Views:
    6,666
  9. johnnythefish
    Replies:
    24
    Views:
    8,557
  10. JosephT
    Replies:
    37
    Views:
    4,519
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.