A build with a feminine touch?

Here is the fusion 360 archive file. It’s still a work in progress.
The propeller is (supposedly) optimized for:

  • MTI65162
  • 3600 rpm
  • speed 7.5 m/s (17 mph, 27 km/h)
    Let me know if you try it. I’m not ready to test yet.

Think the 65161 (Flipsky)and other similar tested on this forum has more power than a 6 hp outboard right(at least on paper)? Those are used in 100-120 Kv versions, so yes a bit higher, pending on voltage, but not that much higher than the roundabout 3000 rpm a small outboard propeller is doing on a light boat. What puzzles me is why it looks like the diameter need to be smaller to work well on this application than on similar power on ordinary boats. Lack of torque? Pitch range is often close to the same though.

Lift and buoyance are different things. For propeller tuners, its a well known phenomena that on speed boats that does not have enough “bow lift”, by shortening/cutting the propeller tube, the stern will settle deeper increasing the bow lift. This happens obviously only at speed.
I do not say the tube is better than tapered, is just say that looks like practical examples in real world
is so far not supporting the theory that much. Maybe this one is easy to cure, You just have to design a tapered end propeller that works better then the FR one :slight_smile:

Good idea with driving in reverse, need to study can the gearbox take that force, might be that it can not.

Yes, fully agree, static test has pretty little to do with reality in higher speed, for tug boat yes, otherwise not that much.

ok got it! the Javaprop Web Version is limited… The software has to be installed then it works;-)

Are you running it on your computer or on the web? I think I read somewhere that from the web you couldn’t save.

Oh, just saw you found out.

By changing the required rpm from 3600 to 3000 on JavaProp, I got this one that vaguely ressembles the FR:

The conclusion is that I will design and print several propellers and test them. Hopefully one of them will work propellerly (laugh)…

3 Likes

Nice ride brcye. How long is the board? and the hatch. Can you share a photo of the hatch open.
thanks.

Here is my build log. Some open hatch photos on there.

About 4ft 5 inch long.

1 Like

The FlipSky 65161 100kv at half voltage turns at 8000 rpm and 16000+ rpm at around 60v. The motor has good torque but needs to spin in the upper rpm range to get it. A large prop will not allow your motor to spin up to the upper range. Also it puts more thermal stress on your motor controller and motor. The smaller diameter prop easily spins up to the upper range so everything runs cooler and faster developing more precieved horsepower uses less battery.
I have a file for that tapered prop. I printed one to test against the one on the unit now. The tapered prop is very similar in pitch, cup, and diameter.
Check out some pictures of submarine props on google or other search engines, 90% have a cone on the prop hub. Our motor setup is very similar to a sub with a large prop.

Never heard of shortening hub. Bow height is adjusted with a rocker switch called Tilt. Want the bow flat lower the tilt until it lowers the bow.
Want to raise the bow up tilt the motor up. A hollow tube will provide no lift whatsoever, the hydrodynamics don’t support the position of whoever told you that it does…

Now if you’re talking about shortening the prop shaft and moving the prop foreward in relation to the boat hull, then yes what your talking about will work. Inboard props are fixed and can’t be tilted so a shorter shaft puts more of the boat behind the prop and bring the bow down. Move the prop back and it raises the bow ride height.

Your outboard has the same quality gears foreward and reverse. They have to be able to take full throttle foreward or reverse. Check with your local outboard shop to be sure…

@tommyD no it does not turn that fast… but I think you mean the values for erpm, so rpm multiplied with motorpolepairs, correct?

You are right. Metr / vesc shows erpm. Just divide by three.

1 Like

What are you dividing and why? This is not a geared motor!

My specs show 16,380 max. RPM

The pole pairs in the motor windings act like electrical gearing. A single pole pair motor would turn at the same RPM as there are eRPM. A six pole, and thus three pole pair motor will turn only at 1/3 RPM at a given eRPM.

2 Likes

Tommy do you know the meaning of the kv motor value ? There is no way this motor has 16k rpm at 60v

18 pole if we are talking about the same thing.
The number I gave you is the actual top rpm not erpm as per mfg. testing.
Voltage is the factor that determines rpm and their test was at 48v and 60v. I think the 48 volt test achieved maximum rpm and the 60v test provided no increase in rpm but they suggested the 60v option for longer ride time.

when you have an 100kV motor, it means when you are driving with 60V, you will have maximum 6000 RPM
When you multiplicate it with the 3 polepairs, you come to a maximum eRPM of 18.000.
seems to m that those value is very close to your result :wink:

Prop speed calc: Almost 150 km/h on a motor with 18k rpm with 6" Flipsky. He will be fast :slight_smile:

1 Like

That’s what we all want to break the speedlimit :crazy_face:

Can see that the RPM topic was already addressed so will leave that.

But for information sharing purposes, would like to correct the comment about the impact of the tube.
The black magic :slight_smile: of propellers is a very complex topic, one never heard of something does not mean it is not existing… Kindly take a careful reading on this:

Reading carefully, the impact of barrel length is not only concerning very high speed, but also to hold plane at lower speeds, this covers actually well the speed range of foiling.

Hard to tell how to implement this information in real world foiling, just think it’s worth considering as one of the components impacting in the very complex topic of propeller design. Probably also the length of the motor tube has some impact.

The optimal diameter topic is also extremely interesting, much tougher to get specific information on than the pitch matter but maybe we leave that for another thread.

1 Like

Back to the build…

I will ASAP be testing the behavior or the MTI65162 motor, with or without prop, with load. So we will have real data (voltage, RPM, current, efficiency) rather than the cryptic, contradictory, cr*ppy and confusing stuff from the manufacturer.

(As a parting shot, I can see on the oscilloscope that the 65162 unloaded RPM is exactly equal to Kv * Voltage, as it should be, so 3000 RPM at 30 V)

Propeller: One consideration about a lower cruising rpm is to get a propeller design that can be printed at home and used, at least for testing. And although length, shape and diameter of the propeller hub must be considered, I suspect that there are more critical factors for now, such as…

… Propeller duct: for me this is not an option, even though it only offers partial protection to my toes, it’s better than nothing.

By now, everybody knows that ducts reduce performance at higher speeds because of increased drag.

However I found this article that is a lot more optimistic than most.

However however, I also found this paper saying that for ducted propellers, the simulation results don’t match experimental results very well.

So, for what it’s worth, I’m designing a duct based on a profile tested in the Polish article.

  • Duct Propeller clearance = 1% of Propeller diameter
  • Duct length = 50% of Duct diameter
  • Duct profile = DU10

For now, the spokes are straight. I saw that some designs have twisted spokes. This is not hard to implement, but I’m wondering: does it help? how much to twist them?

Screen Shot 2021-02-08 at 10.17.18 AM

1 Like