Model Boat Mayhem

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Author Topic: Speedline Shannon Lifeboat - obtaining maximum potential from the Jet drives.  (Read 22316 times)

McGherkin

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Both the listed motors are 1250kv, the max RPM is the same for a given voltage.

Motor wattage doesn't tell you anything about RPM, and a 600w motor isn't necessarily going to draw 600w in normal usage. If it's only lightly loaded it'll draw much less in the way of watts, but if the impeller is fouled, obviously a big wattage motor is going to cause more havoc than a low wattage one.


I'm not sure the GPS is going to have a tight enough resolution - to get an accuracy of <5cm on a ££££££ sidescan sonar setup we were trialling in work a while back, we were using 2 fairly large GPS heads with a metre seperation, as seen here;
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TomHugill

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Playing devils advocate here We know the motors that have been supplied are the correct ones for hte jet drives BUT what is the MAX rpm of the jet drive unit as suerly if you go over the max reccomended rpm of this all you will encounter is pure cavitation inside the unit.....just  athought....Reason for asking is that I have a Graupener jet drive and it is reccomended that no motor above 700watts is used


Dave


I've got 28mm graupner jets and had the 40mm ones in my challenger. They both had 1600kv 2400w 3674 brushless motors. cavitaion is a matter of rpm not motor power, so matching motor kv is the thing here. On mine I was aiming for 20-25k rpm, on 4s that's 1680kv ISH
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kinmel

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If anything on 4s Lipo, I am seeing back pressure rather than cavitation.  I am using 30amp fuses and they have never blown, so Mr Ohm reckons that the motor is running at less than 440watts.
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C-3PO

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I'm not sure the GPS is going to have a tight enough resolution - to get an accuracy of <5cm on a ££££££ sidescan sonar setup we were trialling in work a while back, we were using 2 fairly large GPS heads with a metre seperation, as seen here;

Hi McGherkin,

Bit confused by this one and would like to understand as you may have spotted something I have over looked! - can you enlighten me or was your comment in relation to Furball's post?

C-3PO
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McGherkin

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Sorry, I'm going mad. Don't mind me!

I thought you were going to try and set up some sort of dynamic positioning system to keep the boat on one spot, which wouldn't work very well since the boat could be a metre in any direction before it knew it was out of position.

But for speed logging it should be fine.  :-))
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C-3PO

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Shannon Data Logger update

Data file recorded on micro SD card updated approximately once per second - it actually looks like it's working!! ( Now I've posted it I can see there is a mistake!)



Also been carrying out some range tests on the transmitter - signal still received by shore based telemetry unit even through 3 -4 feet of stone wall

Format is:
PacketID
Date
Time
Knots
Compass heading
Roll
Pitch
Temp 1,2,3,4
Radio Control RX Channel 1,2,3,4,5,6,7,8

C-3PO
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T33cno

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Aah yes its all very clear to me  :-)) {-)  Carry on  :}
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C-3PO

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Shannon Data Logger Update

This is the information that will be available on shore via telemetry. The third screen down on the left will allow the speed (and max speed for session), position of the transmitter controls for throttle and trim tabs, temperature of both ESC and motors to be viewed at the same time. A button on the shore based unit allows you to scroll through the available data screens.

The data is written to a micro SD card onboard the boat



C-3PO
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Flundle (Speedline Models)

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Brilliant stuff this. I am really looking forward to helping out here.
I bought two heli gyros (fast ones) to put in the line between the tranny and the trim-tab servos but I wonder if there would be any point really.
What do you think?
Adrian
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C-3PO

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Hi Adrian,

I think the jury is out as to whether this is going to yield results, I’m hopeful and it’s fun trying…

From a personal perspective I have learnt more about quite a few things to do with Arduino so even if its a total flop for me it’s been a worthwhile journey.

The interesting bit will be once this is installed on Kinmel’s Shannon and he can give it a spin.

With regards to Gyro’s I guess it may be a case of “suck it and see” – on a very similar concept using a sensor attached to an Arduino you can determine the way the boat reacts to the sensor data and by editing the program on the Arduino adjust those reactions so you can be in control of the adventure.

If you have any thoughts/observations or wisdom to share with regards to this topic then please let us know as you have been working with the subject for a long period of time and must have amassed a significant understanding of the beast.

It’s certainly an interesting topic and will be fascinating to see what the end point is in due course - let's hope it's not a black sack:)

C-3PO
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