Help in finding the appropriate motor [Student Team]

jskounakis

1 mW
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Jan 25, 2022
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17
Hello there,

tl;dr: Making an electric catamaran boat, can't decide on the motor, power/weight ratio, and controllability of RPM and Torque as a pair puzzles me.

This is my first post after lurking for a while in your forum, trying to troubleshoot and learn about EVs and general electronics.
[so if this is the wrong place for the post tell me and I'll post it where I should]

I am part of a student team from Greece taking part in the Monaco Energy Boat Challenge with an electrically powered Catamaran. This is basically how our vessel looks.

-Technical Details-
  • 10kWh Battery 100Ah 52V [2 x packs of 14S36P Panasonic NCR18650 Li-Ion]
  • approx 250 kg
  • approx 650N drag for 10m/s which results in 6.5kw needed thrust (propeller) and about 8.5kW on motor
  • Delivered power to propeller ~50Nm@1300RPM (known data for 7.2m/s)
  • 3 hour runtime needed for the endurance race [S1 duty, thus water-cooled motor (?)]

And here comes the challenge: I've researched an immense amount of motor manufacturers and can't seem to find the right one.
Here you can find a rough list of the most appropriate motors I've found. For the controller we've picked a VESC 75/300 in hopes that it will run whatever you'll throw at it.

Issue #1
How can this world have motors like Heinzman PMS120W as well as Torqstar 7050. LMT packs 10+kW in 2kg at a lower price and weight than Heinzmann. I'm guessing torque is a big part of why, which brings me to

Issue #2
Is it wise to grab an LMT motor with higher windings ending up with less kV = less RPM and higher Torque? Or would it be wiser to go for something in between like Motenergy ME1803?

Issue #3
Is it even worth it to look at something like Benevelli SMAC 200-052 [Datasheet] since it's 24KG and with similar specs to the ones mentioned above? Do you have any input on the manufacturer - I haven't had much luck on the internet/other forums.

Issue #4
Lastly, I've come across Plettenberg NOVA 15 which seems to run between 2K and 8K RPM and 30Nm Torque. Obviously, we'd be using a reducer (1:3 or 1:4) but our biggest issue is regarding just that: How controllable is an electric motor, with a reduction of 1:3, for example, would we be able to run at around 1500 RPM and 50Nm? How controllable are speed and torque as a pair?

Thanks in advance for any replies, we are eager to document our progress, trying to help others who are interested in similar projects.
 
There is a sailbot hub motor install there somewhere, I believe he might have changed the winding configuration wye/star.
https://ebikes.ca/blog/post/so-much-solar.html
 
jskounakis said:
Hello there,

tl;dr: Making an electric catamaran boat, can't decide on the motor, power/weight ratio, and controllability of RPM and Torque as a pair puzzles me.

(Edit to add: also look in this section https://endless-sphere.com/forums/viewforum.php?f=39
and maybe ask these questions there also?)

If I were to build such a catamaran I would choose a fixed motor under the rear of each float/beam. With a separate controller with reverse function for each motor. Then you don't need any steering system as you can put one motor in forward speed and stop or reverse the other motor to make turns. And mounting them under the beams makes them water cooled as they will be under water.

Something like two of these: https://flipsky.net/collections/wat...foil-ejet-boards-ebike?variant=42111183814897

I suspect you can optimize the thrust and efficiency by changing props.

Ask the Flipsky company if they want to sponsor your team with the motors and controllers.

Here some videos with the motor:


[youtube]-6onP9f0Jjc[/youtube]

Maybe contact this guy for more info as well:


[youtube]TWHClLt30Bw[/youtube]

[youtube]0jk6hQkB31I[/youtube]
 
Ask too much power from a tiny motor, and no matter the efficiency, it will burn down. Not enough thermal mass, not enough surface area.

Once you gear reduce a tiny motor enough to match a big one, chances are you've traded off all the size and weight advantage anyway. Model airplane motors look like a much better bargain than they are, except when you're trying to drive an air screw at a zillion RPM and negligible torque.
 
You're in a boat so efficiency trumps weight i imagine.

Look at the qs120 and qs138 motors. Lots of miles on the clock from lots of people. Water cooled versions available iirc. Can be run up to 8kW easily.
 
Thanks for your input everyone, I'll look into flipsky as a last-minute option if everything else goes wrong, since we are theoretically making an outboard with the motor inside the vessel.

Videos were of great help too!
 
jskounakis said:
since we are theoretically making an outboard with the motor inside the vessel.

If you make an outboard with the electric motor not in the water like a trolling motor but on top of a tail from a normal outboard motor you'll have less efficiency.

Taking a QS138 or even a QS180 motor and make a "trolling motor" from it would be awesome.
 
Water propeller drives are demanding. With a required true continuous output of 8.5kW at full torque (=full current) all the small motors are out, vesc 75300 controller too. These don’t have a continuous output at that power level - especially when driving a water propeller which is most efficient at high torque, low rpm. RC motors intended for air propeller drive use the propwash for cooling which means that in this application you can drive systems hard (and inefficient) without overheating.

It’ll require a larger size system with watercooling both for motor and controller since enough cooling airflow won’t be easy to get.

Something like this, downgeared 1:2 or so with a belt drive will fit your need. A higher voltage battery would be better though, combined with more gearing.
http://www.cnqsmotor.com/en/article_read/QSMOTOR%20138%204000W%20Liquid%20Cooled%20Mid%20Drive%20Motor%20With%20Belt%20Shaft/942.html

You’ll have a hard time getting better value for money than the QS mid drive motors :wink:
 
larsb said:
Water propeller drives are demanding. With a required true continuous output of 8.5kW at full torque (=full current) all the small motors are out, vesc 75300 controller too. These don’t have a continuous output at that power level - especially when driving a water propeller which is most efficient at high torque, low rpm. RC motors intended for air propeller drive use the propwash for cooling which means that in this application you can drive systems hard (and inefficient) without overheating.

It’ll require a larger size system with watercooling both for motor and controller since enough cooling airflow won’t be easy to get.

Something like this, downgeared 1:2 or so with a belt drive will fit your need. A higher voltage battery would be better though, combined with more gearing.
http://www.cnqsmotor.com/en/article_read/QSMOTOR%20138%204000W%20Liquid%20Cooled%20Mid%20Drive%20Motor%20With%20Belt%20Shaft/942.html

You’ll have a hard time getting better value for money than the QS mid drive motors :wink:

Seems like qs motors are very highly recommended, so we're thinking of getting one after all. I see that the rated power output isn't very clear though... It's labeled as 4000kW but also sold as 7.5kW and peaked at 13kW. Do you think the water-cooled QS138 4000W motor will be able to give out 7-8kW continuously?
 
Yes, i’m pretty sure the 90h motor can do this.

I’ve tried to overheat my 138 70h (at about 20kW) by maxing up a 1km hill with brakes applied repeated times. I didn’t succeed which says a lot.. It takes a longer time and harder push than i’ve ever managed so the qs motor 3kw rating of the 70h motor really is incorrect.
 
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