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hydraulic pump - convertible top- replacement for linear actuator
#11
That looks like it is totally overkill for what you want to do.

first you should probably calculate the pressure and the flow needed for the system.

Flow:
(<Stroke> x (<cross sectional area of the cylinderID> - <cross sectional Area of rod>))/Time
stroke of the cylinder by measuring the cylinder rod at its two extremes and the minus one from the other.
diameter of the rod is easy measured
Internal diameter of the cylinder is harder to measure. check if you can find it written on the cylinder somewhere
then you need to think about how fast you want to go from stop to stop and that is your time

Pressure will be harder and you may need to find a way to put a pressure gauge in one of the lines - alternatively you could measure the force on the cylinder and then calculate the force.

once you have this you can start to specify a pump and directional valve or bi-directional pump. looking at the Raymarine pump, it looks like it is 50bar max - that sound right, i bet it operates much less than that most of the time.
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#12
133amps at 12 volts is really excessive. I'm not sure this particular system is a good fit, what force does it take to move the rudder, and how much force does this system excert?
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#13
(2022-02-10, 02:13 PM)PieterO Wrote: Hi,

I have sort of the same problem question. I want to add pypilot to my existing hydraulic steering. 12V hydraulic pumps are very pricy.

My situation
I have an catamaran with hydraulic steering.  The steering wheel is the hydraulic pump with built in reservoir. The rudders are connected via a tiller. A hydraulic ram is mounted to that tiller.

I want to make it like the Schema below (withouth part 3). 
[Image: groupe_electrovanne_simple_com.png]

I want to buy a trailer hydraulic pump like this which is reversible and made for trailers like the picture below. Those units are 300 euro's. My questions are:
Is that feasible and do i forget something?
Can pilot just control the buttons via a relay or directly? It will be on 100% always then. 
Do i need check valve's so that the fluid wont spin the when when the auto pilot is working?


The motorpower is 1.6kw Rated and 3.0 kW max. @12V that is 133/250  Amps. Wonder what the true power draw is for my small cylinder.
I don't like the large fluid container, I want to try to get rid of it since there is already a fluid tank in my wheel. 

[Image: VEVOR-Car-Jack-Hydraulic-Pump-12V-DC-Dou....jpg_.webp]


Now, another option is to use a more regular hydraulic pump like this one: https://www.cactusnav.com/universal-auto...22520.html
That does require a motor driver, but I have to find out the amperage of te system.


Thanks in Advance.

I have a used Simrad RPU80 that was a takeout when I installed a new autopilot in a friend's boat.  Works fine.

It would be a much better fit for your system and it is 45 watts. Pretty clean and I am looking for $200 USD for it. You could probably find one more local on eBay as well.
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#14
Hi Pieter, I have used one of the pumps from Cactus and it works very well on my yacht. I am using a 10Amp H bnridge PWM controller for it. I had to do a few mods to the Arduino code to drive this. The pump drives a double acting ram that is directly linked to my transom hung rudder. I have a bypass valve across the ram to allow normal tiller steering. This has a switch to detect when it is open that is connected to the Pi and disengages Pypiloy automatically. I also fitted a linear pot in parralel with the ram to give rudder position feedback to the Arduino.
Regards
David
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#15
Video 
(2022-02-14, 10:26 AM)drbarritt Wrote: Hi Pieter, I have used one of the pumps from Cactus and it works very well on my yacht. I am using a 10Amp H bnridge PWM controller for it.  I had to do a few mods to the Arduino code to drive this.  The pump drives a double acting ram that is directly linked to my transom hung rudder.  I have a bypass valve across the ram to allow normal tiller steering.  This has a switch to detect when it is open that is connected to the Pi and disengages Pypiloy automatically.  I also fitted a linear pot in parralel with the ram to give rudder position feedback to the Arduino.
Regards
David

Guys, thanks!!

Next time I will be at the boat I will measure my cylinder size. I guess I wont need a bypass valve in my situation as my current steering is already hydraulic. I do wonder If I need check valves to prevent my steering wheel from spinning instead of moving the cylinder. Will check my Steering wheel pump if it has check vales.

Picture of my steering is attached. It is connected to the crossbar, operating both rudders.

I didn't knew linear pot's exist, so thanks, make things easier. I have quite a lot of arduino experience So i guess I will figure out how to program it.
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#16
(2022-02-14, 10:26 AM)drbarritt Wrote: Hi Pieter, I have used one of the pumps from Cactus and it works very well on my yacht. I am using a 10Amp H bnridge PWM controller for it.  I had to do a few mods to the Arduino code to drive this.  The pump drives a double acting ram that is directly linked to my transom hung rudder.  I have a bypass valve across the ram to allow normal tiller steering.  This has a switch to detect when it is open that is connected to the Pi and disengages Pypiloy automatically.  I also fitted a linear pot in parralel with the ram to give rudder position feedback to the Arduino.
Regards
David

Hi,

I am now setting up everything. I have have all the components. What changes did you made to the motor.ino? I have the 0.8L pump from Cactus like you suggested.

MY motor controller is an BTS7960 H-bridge. It basically has 8 pins. 
VCC, GND

Current sense Left
Current Sense Right
Left roration enable
Right rotation enable
RPWM --> Speed right
LPWM --> Speed Left

Reading motor.ino, not all pins are supported of my H-bridge. Is that the part that you adjusted?
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#17
the 8 pins are VCC, GND, A1, A1?, D2, D3, D9, D9
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#18
Hi, my controller only has two pins: PWM and DIR. If DIR is HIGH it drives the pump one way and if it is LOW it drives it the other. The PWM input controls the speed. I greatly simplified the Arduino code, the main change being in the position() function:

// this function is called from update_command function (which is called every 20 mS by a timer) to set the motor speed and direction. The parameter (value) is sent from the PyPilot app. 1000 = do nothing. < 1000 = turn to Port (check). >1000 = turn to Starboard
// The amount the value differs from 1000 = how fast to run motor???
// Force stop motor if bypass valve open added 13/01/21
// This function sets a global Var (PWMout) which is used in main() to do an analog.write to the PWM pin.
void position(int value)
{
int cValue = 0;
cValue = abs(1000-value); // calculate amount of movement required from neutral
if (value > 1000) {DIRstate=1;} else {DIRstate=0;} // set direction of pump
PWMout=0; // default is to stop pump
if ((cValue > 20) && (BypSWS == true)) // check cValue > deadband AND bypass is NOT open (FALSE if it is)
{
PWMout = map(cValue,0,1000,125,255); // map from 0 - 1000 to suit PWM out 100 - 255 (125 to give min speed for pump to run)
}
// debug
// lcd.setCursor(0,0);
// lcd.print("v= ");
// lcd.print(value);

// set pump direction and speed
digitalWrite(pumpDIR, DIRstate);
analogWrite(pumpPWM, PWMout); // write PWM value to output

lastpos = value; // keep a copy of the last command value (used in rate of change calculation
} // end of position function

Regards
David
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#19
If you can use if() statements to make this work as pwm_mode == 4? Then user can set this once at the top of the file to use it, I would like to merge this mode, maybe some other people find it useful.

Does analog write really give the best frequency? What does it use? Is it audible? This is why I set the pwm with registers directly.
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