Electric Surf Board

Yeah that looks really amazing.
In the endlich you have also passed a workout for your arms.
Looks really funny but heavy...
 
Hi everybody,

I have the same waterjet project; thank you for these thread (I have almost all read) it is very interesting with some incredible designs! :)
I have a question, maybe can you help me...
I'm designing 2 waterjets (one with a 58mm impeller and one with 80mm impeller), but I have not chosen the motor yet (I will first test the 58mm version).
How can we know the maximum speed (RPM) of the impeller according to its size? a 80mm diameter impeller can not turn as fast as a 58mm (to avoid cavitation).
Is there a "rule" to know the maximum speed of an impeller? (in order to be able to deduce the "KV" of the motor)

Thank you for your help :)
 
Hello ZR38,

there is no rule because it highly depends on impeller design.
I was reading many numbers between 8.000 and 15.000 rpm.

For my project I ordered a powerful motor (Lehner Torqstar 3) and will test my relatively small impeller (60mm) from 0 - 17.000 rpm.
Diagrams of thrust/rpm and rpm/power will show where this impeller has best efficiency. And if my motor is too bored at this rate, I have to increase impeller size.
 
Hello srn,

Thank you for your answer.
I will do as you :)

For diagrams, how will you proceed? you will note the flow of the waterjet during your tests to then calculate the thrust? That's right?
 
Hello ZR38,
Good question, at the moment I think to measure the thrust a kind of spring-scale should be the best.
 
Would be interesting to build a flumen. So you actually could measure the impeller effency, the torque, amps, rpm and also optimize the nozzle and stator geometry.

have a look at this:

http://efoil.builders/t/home-made-flume/794
 
Also, I saw that you are going for a gearbox build. That's actually the way I was going too before I noticed that at that rpm range, the gearbox is going to be really really hot. Did you already think how to cool the gears?

Cheers
 
Frizzo said:
Also, I saw that you are going for a gearbox build. That's actually the way I was going too before I noticed that at that rpm range, the gearbox is going to be really really hot. Did you already think how to cool the gears?

Cheers

Interesting point, have not thought about this yet. My "Gearbox" are just two gears to increase the height of the shaft. I will measure the temp on the gears.
 
Frizzo said:
Would be interesting to build a flumen. So you actually could measure the impeller effency, the torque, amps, rpm and also optimize the nozzle and stator geometry.

have a look at this:

http://efoil.builders/t/home-made-flume/794

Hello Frizzo,

Thanks for your link!
When I have chosen my engine, I will rethink to this project :)
 
quick update

my mgm controller failed. they will not repair or replace it, and suggested i buy a new one.

thats pretty bad customer service in my opinion.

looking at alternatives, incl self developing a controller.
 
I don't understand this. I thought controllers had current limiting. Therefore really they should never fail unless there is a manufacturing defect or reverse polarity or something.

Anyway, good luck.

Andy
 
that was my thoughts when i sent the esc back for diagnosis.

nevertheless they will not honour their warranty in this case.
 
what did you do ?

the controller should also shutdown in case of too high temp ?
My MGM controller will arrive end of next week.
 
chris_kline said:
my mgm controller failed. they will not repair or replace it, and suggested i buy a new one.
If you did nothing evidently wrong with the controller, like hammering a nail in it, I would open a case in consumer protection institution of your location. This controller is everything but cheap and they should back their claims by law (in civilized society).

MGM statement:
Why should I buy this product?

5 Years Warranty
Premium Customer Service Exclusive PRO
AwardWinning 32-BIT SYSTEM
Top Care and Engine Control
Unique System of Battery Care
Battery Long Life Mode
Precise Data Logging + Data Analysis
Real-time PC Monitoring
More Performance, Efficiency, Speed
Each Piece Tested - 100% Warranty
Unique Parameters and Options
Gold up to 8-Layer PCBs, 105um
MGM COMPRO Industrial Technology
Made Using Top Technologies
 
Hey Chris
Can you give me some details of your installation.
Especially the lenghts of cables, cross sections, connections, placement of the additional cappacitors.
I had the same failure twice. My first thoughts had been also the same:
Should shut down automatically
internal safety algorithms
Couldn't bei damage without mechanical impact
...
But last but not least, high internal currents habe killed my MGM twice. In the end it is now working very stable.
But it was a very expensive and hard way...

Would like to help you

Bye Fabian

P.S. self developing should be the best in the end 😃
 
fabianpusch said:
Hey Chris
Can you give me some details of your installation.
Especially the lenghts of cables, cross sections, connections, placement of the additional cappacitors.
I had the same failure twice. My first thoughts had been also the same:
Should shut down automatically
internal safety algorithms
Couldn't bei damage without mechanical impact
...
But last but not least, high internal currents habe killed my MGM twice. In the end it is now working very stable.
But it was a very expensive and hard way...

Would like to help you

Bye Fabian

P.S. self developing should be the best in the end 😃

thanks for the info Fabian

although its not really applicable for my case.

looking forward to hearing what IC your running on your custom esc when you get a minute.
 
Hello @all

I am again in Corsica and testing the board.
This year everything is running stable - after this morning run I have some swelled capacitors on the ESC.
What do you think stop or go on?
Two years ago I have killed the ESC :roll:

Greetings from Corse
Fabian
 
Is it the MGM ESC ?
I would contact the supplier directly. Maybe now they would just change the capacitors while when you go on, you destroy more..
 
Hi
yes it is the MGM ESC. I am a little sad about the situation. We have still 7 days left and I am not sure if I can do an additional ride.
At home there are some capacitors - f***...
I have already contacted the supplier via Email.
But it is weekend - so no response ;)
But in the end I do agree with you...it will destroy more.

Have a nice evening and a good start into the new week.
 
Hello Fabian,
did you read the log of the ESC ? Was ist long time full load? Too hot? High peak load ?
 
Hi & good morning

Longtime full load is about 240 Amps for 5 seconds.
Not too much - I think the problem will be the cable lengths from the battery to the controller.
There are indication high internal peak currents (about 600Amps) and this is too much for the caps.
Maximum temperature was about 105°C of the ESC, I think the problem ist that I have used some speeds of 70% - and that is not too good fort the FETs.

At the moment I am waiting for an answer of MGM if I can go on or have to stop testing...

Bye Fabian
 
fabianpusch said:
Hi & good morning

Longtime full load is about 240 Amps for 5 seconds.
Not too much - I think the problem will be the cable lengths from the battery to the controller.
There are indication high internal peak currents (about 600Amps) and this is too much for the caps.
Install the controller as close as possible to the battery and twist the wires. This will reduce the inductance and lower the stress on the capacitors (less voltage and current ripple). Long motor wires are not a problem, more the opposite, but long battery wires are!
Maximum temperature was about 105°C of the ESC, I think the problem ist that I have used some speeds of 70% - and that is not too good fort the FETs.
At the moment I am waiting for an answer of MGM if I can go on or have to stop testing...
105°C is quite high for a controller and the caps don't like this as well.
Speeds of 70% should be no problem if it has the so called "active freewheeling".
Only the very first or cheapest BLDC controllers don't have this.

From the specs the MGM controllers are not impressive.
They have no FOC control or other new stuff which you would expect in view of the high price.

Kontronik Kosmik ESCs for instance have FOC control with current measurement on each phase and outstanding efficiency, but unfortunately the largest model can only do 14s max and 200A. Otherwise i would suggest to try out a kosmik.
 
madin88 said:
fabianpusch said:
Hi & good morning

Longtime full load is about 240 Amps for 5 seconds.
Not too much - I think the problem will be the cable lengths from the battery to the controller.
There are indication high internal peak currents (about 600Amps) and this is too much for the caps.
Install the controller as close as possible to the battery and twist the wires. This will reduce the inductance and lower the stress on the capacitors (less voltage and current ripple). Long motor wires are not a problem, more the opposite, but long battery wires are!

I dont understand the issue with cable length. I understand that long cables have high resistance, but how about the current peaks at long cables from battery to controller ? Can someone explain this ? And is it really better to have longer cable from controller to motor than from battery to ESC ?

Thank you for further explanation and best regards,

Soeren
 
Yes that is right...short cables from battery to controller.
It is very complicated to explain this in english for me. But look for induzierte Spannungsspitzen, lange Batteriekabel vs. lange Motorkabel...
Also very interesting is the SLS Sinus Leistungssteller.
And in the end, the Kosmik would be a nice one.
Yes temperature was high, but in the end the ESC and the caps should handle this.
Freewheeling is always on
 
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