Standardizing our props for more efficient collaborative research


#1

Our collaborative effort on prop research is not very efficient. Everyone tries a different motor and prop.Lucky dogs will have some success, some other are burning their motor, ESC, batteries and pocket money.

What about agreeing on a prop size ( and duct) and build a 10 different prop kit from super-low pitch to super high pitch , all 3d printable ? That way we could all start from very gentle props and upgrade pitches until we have the most reasonable torque / power consumption for each of our systems.

Then we could obtain reliable statistics about which prop suits best a specific motor plus reducer, thus improving the chances of finding the best batteries. and so on…

Is that a totally stupid idea ?


#2

But isn’t the prop size dependent on the motor too? If you have a direct drive you will probably need a larger prop than with reducer. And for direct drives motors with a wide variety of KV values exist which probably also need different sized props? I didn’t yet dig deep into this topic though.


#3

Different power lvls, different total weight, different torque, different speed requirements, different powertrain, different rpm, different diameters, different wings… Ugh. Maybe for exactly the same motor/gearbox/wing/diameter there could be some excel sheet but for all… :thinking:


#4

First, no!

But I guess if you want a efficient propeller it has to suit to your overall setup. So that might work for the standard PM or Hiorth build but definitely not if you have another gearbox or motor (battery or maybe even ESC). Also I don’t think that printed props can be more efficient than a standard alu prop (it is way slimmer and still doesn’t bend as much under load).

An easy guideline might be to watch slip and motor vs phase current. Slip is the difference between GPS/real speed and the speed of the propeller (calculated by RPM and pitch); and the difference between motor vs phase current determines at which load point you are using your motor/ESC (high difference -> inefficient ESC has to “gear down” and amplify the torque, low difference -> efficient propeller, ESC, Motor and propeller are fitting). Pitch and diameter will have an effect on slip and the currents, but I would first try a low pitch prop and alternate the diameter (since it is much easier just cutting the propeller instead of getting a new one with different pitch) and going to a efficient setup. Afterwards if the top speed is too low you can still get higher pitch.

Both requires data logging and an advanced ESC with phase and battery currents.
So the standard PM or Hiorth builds with Seaking are even more on a try and error…


#5

Somebody mentioned that there is a problem with 3D printed props - they flex under load decreasing efficiency.

We should add to this quest to find a production method that’s both garage-tinker friendly and economically viable.

I am this weekend going to setup a testbed in my bathtub with a smaller motor both to test out efficiency and to test out my waterproofing ideas before the big motor (which is still bakcordered) arrives. My idea is to put the motor on a submerged arm on a hinge, and a load cell between the hinge wings so I can measure force. Then it’s just a matter of maximizing force for a given power setting. I think.


#6

Aluminum sand casting doesnt sound 2 expensive with 3d printed part used as a mold. Or a hole in the sand, idk how to say it.


#7

Yes that is to have a beginner standard, based on models from PM, Hiorth, etc… to allow everyone to experience flying without burning money, ESC, batteries etc…

Aren’t most of us already using the same small number of motors, reductors and ESCs and even a small number of foils ?

We are an army of good will buyers / R&D testers in this forum and we could be much more efficient if we would sort of organize ourselves, and obtain predictable results.

We may build some decision tree such as

Surfer weight + salt / sweet water
=> board volume
===> desired speed
======> foil
=========> prop
============> duct
==============> motor + reductor
=================> ESC
====================> batteries

As you see, prop and duct choice should come earlier than motor / esc / battery choice. I think.

Actually this decision tree may be a subject for a new thread…


#8

It makes sense to do this, in my opinion the way is to optimize the blade outline and the blade profile to get an efficient standard prop.
This one then can be scaled and the pitch can be adapted, depending on KV, weight, foil, speed etc.