The most accessible and cheapest gearbox

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21

Hi Vladimir:

Trying to answer your questions:

Smaller motor:

A foil drive system is in principle like a airplane.

At takeoff you need

Accelerate the plane

Climb

Growing air resistance

Thats why a plane has engines that are 4-5 times more powerful than in levelled flight at ( low density high flight levels)

I do not recommended very small motors as they will take looong time to get you out of the water

I needed one day to find a prop in direct drine to take me fast out of the water ( approx 145 kg total wheight with a 2500 cm2 fanatic wing)

I used the motor data in the diagramms and the 75165 produces approx 14 Nm of Torque.

This motor was only for testing the gearbox as it produced almost 14 kW

So approx 40 NM will be on the prop shaft

The remote gives you RPM and Voltage and Amps which is power.

Power devided by RPM will give you torque.

It will have much less than 10% failure in it

Or you hold the motor and try to measure the static torque to hold it ( with a lever and a scale) somehow

Zero failure

Will copy the internet prop generator if I find it here

Have Fun

Robert

22

It would be interesting to see how this runs on one of the 56115 inrunners.

23

Last year i made an electric surfboard. I used a 4092 motor, a 6c battery, gearbox for a bicycle, same as in my current project, a 2:1 belt drive from the motor to the gearbox, and a 7 1/4 * 5" propeller. Total ratio 9:1. I got such a big thrust that I first I couldnā€™t stay on the board, lying on it, it pulled forward from under me. This is about the question of how small a motor can be installed. My weight is 70 kg, the weight of the board then turned out to be about 15 or 20 kg. motor, belt and gearbox stood inside the board.

24

Hi Vladimir,

congratulations to the printed parts I looked at the fotos I always failed to make it waterproof.

This is the prop program on the internet

I am 105 kg so I need a different motor.

9:1 is like first gear in a car if you can reach foiling speed its fine

In the forums they talk about 2 kw max power to start to fly that could be right somehow

And the less drag the underwater foil parts have the much better

I tried a prop ring around a direct drive 65161 and I failed to foil, so drag is even more important than a little bit more power.

Eflite says the ring causes 40% more drag and it is pretty. nice design some might think

I also looked on internet for ready to use gearboxes but did not find except a 500 USD Version

25

This is the prop link ( it did not copy it in before)

26

It wonā€™t work that way. Either the motor or the esc may burn out, or the esc will not supply current to the motor. It is necessary to measure in dynamics when the shaft rotates. I have seen homemade stands on the Internet that use either mechanical or magnetic braking to measure torque.

27

Thank you, Robert.
I also used this service to print my propeller.

28

Thats what I mean Vladimir

You let the Motor turn ( in pool or whatever) and you measure the torque on the motor housing

I will send a pic for you

Dont measure static torque it will kill everything as you wrote

IMG_0835
IMG_0835935Ɨ453 105 KB

29

Sorry I misspelled by static torque I mean the static torque on the housing but when the motor is running in teal condition

30

Yes, Robert. I misunderstood you about measuring torque. Now everything is clear to both of us, I agree with the diagram you gave. Only I donā€™t have a pool, and now itā€™s winter. Iā€™m thinking about how to measure on the table. How to brake the shaft: with a mechanical brake or magnets. I will try.
Yes, it is very difficult to get waterproof printed parts. I spent a lot of time and plastic on samples.
The gearbox is really expensive.
But you managed to make a printed one. You write that if you make a gearbox with a large ratio, it will turn out to be very wide, if I understand you correctly. But the gear stages can be arranged one behind the other along the axis of rotation, as in a screwdriver. Or will plastic gears not withstand high rotation speeds?

31

Hi Vladimir,

let me make a winter ready solution for you:

You certainly have the Vesc Tool or maybe a remote giving you some data like my flipsky vx3:

When you run the motor it gives you RPM Amps Voltage and most important power (Which is Volt * Amps) .

Thats enough to calculate the motor torque.

If the motor has 90 % efficiency ( which is a good start) take only 90 % auf the value you calculate.

You will be accurately and just a few % off.

So Power in Watt devided by RPM in Rev per Second ( I must doublecheck that unit as my physics exam is 40 years gone, the value is called omega) should give you torque in NM

P / RPM = Torque in NM

That works also in Winter.

Good luck, let me know if I can help

Robert

32

Gearbox:

There us a meaningful limit for the gear ratio I think more than 10:1 will give you too large props and you max speed us limited.

I calculated the 3:1 for me which is close to optimal for my props

Also your torque at 10:1 is almost same as a small car engine your 3D Print Gears may fail immediately

The gearbox hat 65 mm Outer diameter and if you put a second stage behind your torque triples

Rotation speed does not kill, its torque that kills. Speed just makes noise.

But water has to cool the gears thats why the gearbox is an open design

Try ratios od 3:1 around its a good compromise of efficiency, prop size, and the speeds you can max achieve above the efficiency speed you like to go

33

Of course, Robert, the laws of physics also work in winter.:wink:
Only the motor needs to be loaded with something, otherwise it will not produce power, it will simply gain maximum speed, and thatā€™s all. And will consume little current. I still have doubts about measuring current and power using vesc. Iā€™m not sure if the vesc draws constant current from the battery rather than pulsating current. I ordered a shunt and will look at the current waveform on an oscilloscope. And yet I want to measure the mechanical power.
I have already started a stator from an asynchronous motor with a permanent magnet rotor from vesc. The rotor rotates, but I can easily stop it with my hand. Now we have to rewind the stator winding. Iā€™m not at all sure that Iā€™ll get 90% efficiency. in the stator the plates have a thickness of 0.5mm. Theyā€™ll probably get warm. Iā€™m just interested in measuring the efficiency and taking the load characteristic.

34

No, Robert, I didnā€™t say that the propeller needs to be bigger. I was talking about using smaller motors. They often have a lot of power, but they have a lot kV, that is, they are able to reach high rpm, but they produce little torque. That is, you can calculate the gearbox in such a way that the torque on the propeller remains the same, but on the input shaft there will be high rpm with a small torque.

35

Hi Vladimir

understood you want small motor with high KV then you need exacte what you wrote, absolutely correct

Will be curious how it will be with your unit it is also interesting for this foil assist ideas

Robert

36

UI= Torque x Omega , only if Omega in radians per second, where one turn = 2*PI radians and 1min = 60 seconds
N rpm = N *2 PI /60 radians per second
So UI = Torque x (N x 2xPI / 60)
Torque in Nm = UI * 60 / (N * 2 * PI) where N in rpm

37

Yes!! I remember now from 35 years back :slight_smile:

Thank you!

38

This seems like a step back in time to me?

Gearboxes were the norm before the 6516x motor and wet outrunners and then hardened metal gear planetaries were used. These were noisy and seem to fail in use after some time so the 3d-printed versions donā€™t offer much more promise than as an fun engineering exercise.

If you still want to take this further iā€™d try to order some gears from iglidurĀ® Designer

They have a printing service with low friction engineering plastics that isnā€™t so expensive really (at least wasnā€™t before the ukraine war, now all print services seem to be 3x the price)

39

Not actually a step back in time. Gears have a place, but probably more in a DIY setup. Gears cut from acetal would be great. It would be interesting to see how small a motor you could get down to with a geared setup. I definitely wouldnā€™t bother gearing down a direct drive motor thoughā€¦

40

the SSS motor builds are well known? And how would the plastic gears be better than a real planetary gearset? I fail to see the logic.

The other thing with looking for smallest motor geared setups is that you will max out the rpm to be able to get the appropriate power and speed when geared down for the torque needed. It can be exhilarating for one session riding the screaming banshee, then tiring for the rest of the lifetime.