Geared vs Direct


#1

Hi

I am starting to want to get all the things ready for a build and would like to know whats the main differences between Geared drive say 500kv with a 5:1 reduction drive and a Direct drive say APS 80110 80kv?

Other than complexity and cost between the systems are there any other hydrodynamic pro’s/con’s between the systems making one more stable to ride than the other.

With the direct drive it would seem that the main option is the 80kv with a 7inc prop would a 130kv beable to work with say a 130mm prop?

Thanks


#2

The 80100 outrunner has the obvious hydrodynamical disadvantage that it is 80mm in diameter, the SSS 56104 inrunner motor is only 56mm. @borntosurf222 thinks that the power necessary to overcome this additional drag is rather big, but successful builds like @Mat or @jakebarnhill1 with pretty high speeds proof that it isn’t a big deal. You could go for the 6384PG for reduced drag, but this motor is less powerful and I assume that it will ultimately result in lower top speed.
The other hydrodynamical point is the losses induced by the moving rotor of the outrunner (if open water cooling or oil cooling is used) but you can make this factor negligible by smoothing everything with epoxy.
Apart from that there are many positive aspects resulting from the unbeatable simplicity of the concept. Also this propulsion unit type is pretty cheap as it consists only of the motor itself, so you can easily decide to swap it out later.
@jakebarnhill1 had surprising success with the 130kv variant, but a direct comparison to the more popular 80kv is yet to come.


#3

Everything Benjo said is correct. I would like to add that your weight may make a large difference too when using direct drive. I’m not sure how much either Jake or Mat weigh, but they look on the lighter side. If you weigh in at 90kg or so like me, a direct drive will give you less speed. I will be testing the 6384PG motor shortly so lets hope I have success with it.
Otherwise a gearboxed design need not cost the earth. I got a gear and pinion for £162 (neugart 7:1 made for torqeedo) and my motor set me back £106 (750kv).


#4

Having built two reduction gear drive system, and now this direct drive I would go direct.

I feel the weight of the rider is more of an issue to get up on foil which is where the board size and foil are critical. I am just over 115kg (255lbs), I use a small 56mm direct jet drive and get up on foil no problem, I ride at about half throttle at 20-25kmh easily. I have not tested top speed for fear of crashing hard but I can tag 30kmh with a bump of the throttle.

I watch one of our team builders ride our system, he is 79kg (175lbs) and he has loads of power and speed available. Once you are up weight is not as critical as one may think in my opinion. It’s getting up on foil is what you need to build for. Obviously the larger you are the less ride time you will have as it does use more power but it is what it is.

See my little jet drive below, super safe, powerful and fast.
56mmdrive


#5

Hi, I’m start to work about engine system and jet direct drive look interesting, easier and less complex than geared solutions.
I’haven’t good skills with electronics and system problems, but I can be helped by my cousin for build. I wanted to ask at who want to reply, since all of you have already developed and tested the solution with direct jet which engine and esc are better buy considering that as a power supply I would have 44.4v, 12s, 10C, 20000mah.
Many thanks
Giacomo


#6

We have used all the motors out there SSS, FreeRCHobby, and TPPower. All worked, but as for the kv that will really depend on your entire setup of impeller diameter, impeller pitch, and nozzle size mainly. WE have got up riding on 300kv, 400kv, 500kv, and also 685kv. Once you know your cruising speed and the RPMS at that speed you can work with the manufacturer to be sure you get the optimal KV to fit the motor curve. This will give you the least amp draw at the RPM you plan to be riding most of the time.

There is not simple answer and a the wrong motor will draw 5-20% more if not properly selected. I hope this helps? Unfortunately its a lot of trial and error unless you buy a something already tested and built.


#7

Hi Chris,
thank yo very much for your reply, looking on how many pieces you have printed and tested i understand that found the right balancing of the component is very hard, so i start some test in the jet direct drive as recommended.
I saw that you plan to produce and sell the propulsion unit, what are the expected times for the availability?
Thanks for all
Giacomo


#8

We are just wrapping up some final tests and tuning over the next 4-6 weeks, then we will be going into production. Things are working extremely well and we could not be any more happy and excited with our product. Production takes time so delivery would be obviously after Xmas.

The nice thing we have all manufacturing/production sources nailed down and tested already which is why it has taken us so long to get here. We never used a part in our build if we could not have easy mass production and customization. Its almost a matter of flipping a switch and sending funding to manufactures at this pit and all parts will be ready and shipped within 120 days :slight_smile:


#9

That’s epic. True. You can push up your leading rear wing bolt with a thin washer if you want to go faster without having increased lift and I can see you might prefer the fell as its a bit more forgiving. Keep in mind .5 degrees wing tilt in any direction is huge. Plus considering the planning surface of the board in relation to the foil and the angles of attack, it could be very difficult for the rider to get lift do to improper alignment.


#10

Hi Chris,
thanks for the informations about your progress.I will do some tests, but knowing that there may be a motor unit already made and running is a great comfort, for who like me, that haven’t so much time and skills.


#11

Hi Benjo,
I am a theoretical physicist so my communication skills can be sadly lacking.
Things that are obvious to everyone else usually elude me and vice versa so please let me elaborate… or rather clarify

  1. Direct drive is the only way to go
  2. https://www.youtube.com/watch?v=PB_Hy0bBoVo

The Bote Rover needs a 4.5 hp to get up on full plane

Waterwolf is up around 8 hp equivalent

So what I meant was for proof of concept 80mm is the way to go

Accepting that 30 minutes of run time for something so incredibly fun is not long enough so EVENTUALLY the university’s design is superior and not IP

With waterwolf about 30-70% of the 8 hp is just to overcome the drag of the huge motor hub…

and remember I want to motorize an old surfboard not make a hydrofoil…YET!

I have actually already designed this about 80% complete and am just waiting for someone to ask me…


#12

Hi burntosurf, I working now on a motorized surfboard too. (Based on this very good forum) My goal is a motor which can be mount on a normal windsurfboard without any major modification. This was my firs test:


It contains this parts:
200A Toro ESC
2*4S 16Ah 10C battery
SSS 790kv motor
1:8 neugart gearbox
The board is an RRD evo 158L with powerbox insert

But it is too difficult and heavy, as you see, so I ordered a 80mm outrunner. (We will see how it will perform)
And I have to solve te “tailheavy” beaviour.


#13

Why didn’t you try and stand more towards the front? Seems like you have enough speed to at least plane.


#14

Its easy, becouse this was my first ride. :slight_smile:
It can plane, I tried it. but I had to stand nearly on the nose of the board, which was unconfortable for me as a windsurfer and was hard to turn too.


#15

Hi Jezypeti

Way to go! Honestly I am so jealous because I have been too busy and too cheap to prototype just yet as I seem to like designing and making as much or more than riding but I think you are on the right track for sure.

I am assuming you have windsurfed before but just in case you have not or have never waterskied, i think you need just a bit more power to get a full plane and maintain it.

I got the feeling the board was read to plane and you confirmed that saying it would plane but only if you were very far forward so i wanted to ask you if once it was planing did you try to move back and how far back did you get before she went tail heavy again?

I feel like you are so close to full on success

have you watched waterwolf because they get to planing speed while prone (lowest angle of attack and drag for laminar flow) then pop up only once they are planing…doing this alos confirms to the rider where the CofG is?

Sorry to waste your time but just curious

Best regards
Peter


#16

Hi Peter,
thanks for your hint! (waterwolf promo video)
Its very useful. Next time I try to control my movement on the board much better.


#17

Hi Jez
And it is more like thank you Jezypeti for taking the time to do what I have not been able to and telling us all about it. Much appreciated.
Please let us all know if it helps…

when I taught water skiing, starting from the water it was crucial to have no more than a 45 degree or 30 degree angle of attck or the skiers arms give out from the drag

the angle of attack is like a lever…with waterwolf and fyi I am annoyed its such a beautiful thing for so much money…his angle of attack lying down/prone is about 10-15 degrees and no more

anyway thanks for the reply I have to finish this stupid order for work…borrrrrrring


#18

i am reading “waterwolf” are we talking about this:

it has a gearbox , no?


#19

Yes I am sure it does

It uses a high efficiency prop with an rpm of 1200 compared to most boats of 3500-4000

It has a few design flaws though, waterwolf I mean


#20

i am sure it use the same parts as https://www.torqeedo.com/fr

and you can over spin the V10P350 propeller to 4000rpm to get more speed, after what is the best the smaller one at 4000rpm or the big one at 1200rpm?..
knowing that the small propeller has way enough thrust for a efoil and may be a board to 30KM/H

https://www.torqeedo.com/fr/search?q=helice

EDIT :it probably use the V8P350 so it is not running at 1200rpm…

EDIT: after looking at specification on battery pack and the shape of the propeller, it may not use a gearbox
my guess:
a pack of 18650 samsung 30Q 14S13P
propeller V8P350
a 100KV outrunner or inrunner (alien or TP100)

i don’t know if 11nm is enough (do not think so for a surf board) https://alienpowersystem.com/shop/brushless-motors/aps-100100-inrunner-brushless-motor-100kv-10000w/