controlling the engine

[Roy Toren]

Hi,
As part of a project I need to make the engine work until it gets to a specific position and then again
(A rubiks cube robot)
one arm needs to flip the cube and return to its start position.
the basket where the cube sits needs to turn 90 degrees again and again.
Is there anyway to make this happen without the SetPower or SetSpeed functions as they are unreliable because the power of the battery changes constantly.

Thank you,

[Tcm0]

You can either go with the “GetTachoCount” function (http://www.monobrick.dk/MonoBrickFirmwareDocumentation/class_mono_brick_firmware_1_1_movement_1_1_motor.html) or with the PID class (http://www.monobrick.dk/MonoBrickFirmwareDocumentation/class_mono_brick_firmware_1_1_movement_1_1_position_p_i_d.html). You can find more about PID at wikipedia: http://en.wikipedia.org/wiki/PID_controller.

[Anders Søborg]

Hi

From the documentation that Max already pointed to there is a function called speedProfile which lets you move to a position. An example of this is shown here. Please let us all know how work with your cube solver…

/Anders

[Roy Toren]

I have tried using “GetTachoCount” but it didn’t do the job.
I have searched through the documentation and found a few things that I think can work.
the first one is the PID although it seems a little tricky.
the second one is the vehicle in:http://www.monobrick.dk/MonoBrickFirmwareDocumentation/class_mono_brick_firmware_1_1_movement_1_1_vehicle.html

I saw that there was a function that uses degrees and percentages as input, I think it would be best because then there wont be any error range, like when you try to control the engine speed or power(does not rely on battery power)
I want to hear your opinion about the second one since I got an answer for the first option.
Thanks.
Ps.
I added a picture of the robot so you guys could see.
The design was adopted from this site:
http://mindcuber.com/mindcub3r/mindcub3r.html

• This reply was modified 10 years, 2 months ago by Roy Toren.

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[Roy Toren]

I forgot to mention and I can’t edit now.
I have also tried the speed profile, it works for a while but after the 10th turn with the hand robot there is starting to be an error range, that gets bigger with time.
I have to be as accurate as possibly can, the speed profile and power profile are not reliable since they rely on the engines power at that specific moment.
I have also tried leaving the battery charging while running the program and the error range keeps on coming.

[Tcm0]

As I said, PID is probably your best guess or at least the most acurate.
It seems that you use the NXT color sensor and not the EV3 one. In that case the first link from the other topic to the RGB mode would be right (:P to Anders).

[Roy Toren]

I have read a little bit more about the PID.

I Have some questions about it:

the first one is what values should I enter in this function :
Position PID (Motor motor, Int32 position, bool brake, sbyte max Power, float P, float I, float A, int seattle Times)
(What is the position?, settle time?, P,I,D ?)

The second question is how do i use it in my code, assuming my motor is connected to output A.

And as for the color sensor, which one of them is the NXT and which one of them is the EV3? I have posted two pictures of different ones.
can you please answer me in the topic?
Thanks

• This reply was modified 10 years, 2 months ago by Roy Toren.

[Tcm0]

Sorry, but I havn’t used PID so far :/ http://www.inpharmix.com/jps/PID_Controller_For_Lego_Mindstorms_Robots.html gives a good introduction. There are also calculators avaible to calculate the PID. But maybe you’d better google before asking me as I don’t know so much about PID.

[Anders Søborg]

Hi

Have a look at this example. You might need to tune the P, I and D values to get the desired response…

/Anders

[Anders Søborg]

Hi

I am actually a little puzzled by this. I think the reason that you are getting an error over time with the speed Profile is that you are suffering from gear backlash and not that a speed profile is not precise (since it moves to the desired position each time). If in fact that you have an error over timer due to the fact that the motor moves to the wrong position (tacho count) then a simple reset of the tacho should be enough. Could you please provide some more details on why the speed profile is not good enough?

/Anders

[Roy Toren]

The PID works alot better with the testing I have done.
I have configured it like this:
PositionPID PID = new PositionPID(motor, 360, true, 50, P, I, D, 50);

I left the P I and D the same as in the PID example since I don’t really know what they do, i guess 360 is a complete circle of the engine since it keeps coming back.
I also need the engine to go in reverse(with the engine) in PID, is there anyway I can do that?

As for the speed profile, I used it and it is probably the backlash, due to the fact that the engine is turning a cube so there is alot of friction and power involved.
The speed profile does work, but the second it starts to make an error it does not fix it unlike what i have seen until now with the PID

[Anders Søborg]

Hi

I also need the engine to go in reverse(with the engine) in PID, is there anyway I can do that?

Try with minus in front of the target position

/Anders

[Roy Toren]

I have tried using it like this:
PositionPID PID = new PositionPID(motor, 360, true, 50, P, I, D, 50);
PositionPID revPID = new PositionPID(motor, -180, true, 50, P, I, D, 50);

but it didn’t seem to do the trick, the engine only does the 360 command.
I am aiming for the arm that flips the cube to start on the cube and then do the flip(that’s the 360)
but then I want the arm to leave the cube and go up a bit without flipping it again(that’s why I need to reverse the engine)

[Anders Søborg]

Hi

I think that you are doing something wrong. The code below works fine…

using System;
using MonoBrickFirmware;
using MonoBrickFirmware.Display.Dialogs;
using MonoBrickFirmware.Display;
using MonoBrickFirmware.Movement;
using System.Threading;

namespace MonoBrickHelloWorld
{
	class MainClass
	{
		private const float P = 0.8f;
		private const float I = 1800.1f;
		private const float D = 0.5f;

		public static void Main (string[] args)
		{
			Motor a = new Motor(MotorPort.OutA);
			PositionPID PID = new PositionPID(a,1000, true, 50, P,I,D, 500);
			PID.Run().WaitOne();
			LcdConsole.WriteLine(a.GetTachoCount().ToString());
			PID = new PositionPID(a,-1000, true, 50, P,I,D, 500);
			PID.Run().WaitOne();
			LcdConsole.WriteLine(a.GetTachoCount().ToString());

		}
	}
}

/Anders

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