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Control of ESC


(Tore Knutsen) #1

I cant find any description on how to control the motor speed via the ESC.

Can a ± 5V signal, to the ESC be used?


(Rusty) #2

Hi Tore,

The ESC needs a pulse width (PWM) signal. If you’re not familiar with that, it’s basically a 5V pulse with a precisely controlled length measured in microseconds. The ESC responds to signals between 1100 and 1900 microseconds with a “stopped” signal at 1500 microseconds.

Here’s the documentation for the Basic ESC, which describes this:

http://docs.bluerobotics.com/besc/

Here’s a tutorial that explains the PWM signal better (it’s the same signal used for RC servos):

You need something to provide the signal. It could be an RC radio receiver, a servo tester, or a microcontroller. Please let us know if you need more information and we can help out.

Best,

Rusty


(Robert) #3

I am working with a group of junior high students that are building an ROV. They are using T 100. They have the ESC for each motor and they purchased a FS-T6 RC controller thinking they could use it to control the robot. They get the receiver to connect and the thrusters to move, but they need the robot to run two thrusters together to go up and down (one channel forward and reverse on the same joystick). They are also trying to get the other joy stick to run two channels and two thrusters running forward and reverse. They assumed and RC controller could be used and adapted to pilot the ROV. Will this controller do that? Any suggestion as where they can go to get help?


(Paul) #4

You will need to program the FS-T6 to send the controls that you want. You may also need to use something like a “V-Tail Mixer” ( http://www.hobbyking.com/hobbyking/store/__6321__TURNIGY_V_Tail_Mixer_Ultra_small.html ) to allow you to use one control to turn the ROV ( one thruster forward and the other in reverse).

You realize that once the ROV is below the surface of the water, it will no longer receive the 2.4 ghz radio signal, right? The work around (albeit not always 100% successful) is to attach one of your tether wires to the transmitter’s antenna and have it’s end in the same housing as your receiver. Do -not- connect the tether antenna wire and the receiver’s wire, that will overload the receiver and probably burn it out. Ask me how I know. :wink: .

Good luck!


(Robert) #5

Do you suggest another RC controller t o use? They took the suggestion off your site to use the RC controller, but they are having trouble programming it. I was thinking of using the OpenROV controls and wondering if those would be compatible with the T 100s?


(Rusty) #6

Robert,

Paul’s suggestion to look for “V-tail” programming is correct. I’m not familiar with that RC radio but a lot of them have v-tail mixing built in. Can you tell me a little more about your setup? You have two forward thrusters and two vertical thrusters? The forward thrusters should definitely be set up in v-tail mode. The vertical thrusters could be connected with a Y-connector so that they get the same signal. If you want the vertical thrusters to act independently then the set up will be more complicated.

Also, as Paul mentioned, the RC signals will not work through water but if you have your ESCs and RC receiver on the surface then it will work fine. Do you have ESCs on the surface or in your ROV?

The OpenROV control board would be compatible with the T100s but the setup is not quite as straightforward.

Another option is building your own controller with joysticks and an Arduino to provide a signal. We have a short example program that uses an Arduino with two Parallax joysticks to control three thrusters in a similar configuration. You can check that out here: https://github.com/bluerobotics/br-esc-examples/tree/master/arduino/AnalogJoystickControl.

It could be easily modified for four or more thrusters.

Best,

Rusty


(Robert) #7

It is a tradition set-up with two vertical thrusters and two horizontal thrusters for forward and reverse. They have the receiver at the surface and the ESCs on the ROV. They are running the signal lines down the umbilical. The are getting the signal down, but can not get the radio programed to run the thrusters correctly.

What is the best place to get the Arduino Card and can you use any analog joystick? They used PWM with with analog joy sticks last year, but wanted to use your thrusters. We need a back-up plan if they can not get this RC controller working.


(Rusty) #8

Robert,

You can use any analog joystick, but the settings might be slightly different for some. You can buy the Arduino from many different sources like Sparkfun.com or Adafruit.com. You can get the Parallax joystick here.

-Rusty


(Robert) #9

Rusty,

Kids got everything you suggested and are working on the RC and Arduino. They loaded up the code and wired the Arduino. We had one of the Marine Tech students from Alpena Community College help them load up the program, still no movement from the thrusters. They were wondering if you have a picture of the wire set-up to compare it to?


(Rusty) #10

Hi Robert,

Sorry for the delayed response. I’ll put together a wiring diagram that should help you out.

Can you confirm for me that you got the Parallax joysticks and an Arduino Uno?

-Rusty


(Rusty) #11

Robert,

Here’s a diagram of the wiring for the example code provided here.

Let me know if you have any questions! We’re happy to help.

-Rusty



(Robert) #12

Yes, we have both. Thank you for your help. Kids wanted me to ask about a link to a picture of the T100s they can use, with permission, for the MATE ROV competition board and report. They would like to do some advertising for you to support your company and to show how much support you have given them.


(Rusty) #13

Robert,

Great. Let me know if you have any trouble. If so, a picture of your setup would be helpful.

All pictures of the T100 on our website are free to use under the CC-NC-SA 4.0 license. That means you can reuse them for anything as long as it’s not for commercial use. There are a lot of pictures here.

-Rusty


(Harold Scadden) #14

Do you have any idea what the impedance value is on the PWM signal line? I am working on some simple PWM circuits that I don’t need an MCU to run and I was curious as to what the load is.

 


(Rusty) #15

Harold,

The input line is directly connected to the microcontroller pin. The microcontroller has around 100 megohm input impedance. Both the Basic ESC and BlueESC are configured this way.

Hope that helps!

-Rusty


(Robert) #16

Rusty,

Do you have any documentation on the T100s that shows they are safe to use in the MATE ROV Competition? I have had a few discussions with other mentors about concerns of getting through the safety inspection.


(Rusty) #17

Robert,

We don’t have anything like that right now. Do you know what the safety criteria are? We’d be happy to help out verifying any features that are required for safety. What in particular are you concerned about being a safety issue?

Best,

Rusty


(Robert) #18

The issue is with the thrusters not being waterproofed. Scott Frasier has said that they have not been tested and anyone that is using Blue Robotics thrusters needs documentation that the thrusters have been tested and that they are no leaking current into the water. Wondering if you have any such documentation. I have been working with Alpena Community College’s explorer team and they are in the same boat. They are worried that if we go to internationals that we will not pass the safety inspection.


(Rusty) #19

Robert,

Okay. Every thruster passes a high voltage insulation test before it is shipped. The insulation test ensures that the thruster is fully sealed and does not leak any current. Our standard test is performed at 250V but most thrusters will pass at much higher voltages.

This is mentioned at the bottom of our thruster manual here, which you can use as a reference for the judges.

I’d be happy to provide more details if necessary.

-Rusty


(Harold Scadden) #20

The insulation resistance test certification should be totally adequate. Frankly that is what I use as a QA point for the cable assemblies that I fabricate for the military. We consider that the only valid test to ensure that the assembly is pressure proof and that the raw cable has no leak paths to ground (through the water in this case).

I don’t know exactly how the thrusters are being tested … other than hipot in water … but we always energize with a negative voltage level and measure that to ground (our hydro tank) or a copper plate submerged in a container with the assembly in it.

When Blue Robotics test the thruster at 250 V … it is qualifying that the unit is waterproof. Just because the motor is free flood is not an issue. Seen plenty of outboard electrical motors that are free flood for cooling etc. with voltage / current levels MUCH higher than the T100/200’s.