Flywheel Consistency + Slew Rate Help

thewood · October 8, 2015, 9:42pm

My team’s double flywheel has a gear ratio of 35:1. The 2 84 tooth gears are driven, currently, by 2 turbo gears. 35:1 on its own is fast according to what I’ve seen, so torque may be enough. The ratio(1:35 * 1:2.4 = 1:84) is too high to be useful if I’m thinking about this correctly. It works and its quite fast, of course, but it gets slow very fast. I’m sure the speed achieved in the first run each time I run the test code isn’t sustainable as a result of the turbo gears. I am correct in saying that our motors need to be geared down to torque or high speed, right?


84 84 12 
      60 12

One more thing, I have been trying to create slew rate control code based on code from the forums (https://vexforum.com/showpost.php?p=389379&postcount=4) and it has not been working. I’ve set the motors to different buttons and adjusted for reverse speed, but nothing. The motors turn on every time and an extremely slight ramp up of the motors can be heard, but the gears do not move. The stopping works and speed decrease works in the same slight manner as the ramp up. Any tips for this?

Last question, once I bring down the motors to torque or high speed (assuming the flywheel will be able to be active at high speeds for longer periods of time), is slew rate control necessary?

EvolvingJon · October 8, 2015, 11:51pm

I would say even with torque motors 35:1 is to high. I think for a double flywheel anywhere 15:1 to 25:1 (external gearing) should be plenty depending on your motor and gear setup. I think this may be why your motors are getting slow quite fast. I have seen flywheels geared to 25:1 overshoot the goal at 75 power.

In terms of slew rate control you linked my post :p. Anyway I think what you are referring to is probably just code that ramps up you flywheels motors. Which I would recommend completely by the way. Can we have a look at your program? that would help us to diagnose any problems in it.

thewood · October 9, 2015, 4:31am

Here is the code.

and regarding my flywheel, I’m definitely going down to torque motors



#pragma config(Motor,  port4,           RF,            tmotorVex393TurboSpeed_MC29, openLoop)
#pragma config(Motor,  port5,           LF,            tmotorVex393TurboSpeed_MC29, openLoop)
#pragma config(Motor,  port6,           LB,            tmotorVex393TurboSpeed_MC29, openLoop)
#pragma config(Motor,  port7,           RB,            tmotorVex393TurboSpeed_MC29, openLoop)
//*!!Code automatically generated by 'ROBOTC' configuration wizard           //
task main(){

	int count = 1;
	int count1 = 1;
	int count2 = 1;
	int count3 = 1;
	while(true){
		{	if(vexRT[Btn8U] == 1 && count < 80){			// Ramp Up only if 80 and below
				count++;
				motor[RF] = -count;

			}
			else if(vexRT[Btn8D] == 1 && count >= 0){	        // Ramp Down only if above 0
				count--;
				motor[RF] = -count;
			}
			else if(vexRT[Btn8R] == 1){	              // Stop Flywheel
				motor[RF] = 0;
				count = 0;		                // Reset Count
			}

			wait1Msec(5);

		}
/*
		{	if(vexRT[Btn8U] == 1 && count1 < 80){			// Ramp Up only if 80 and below
				count1++;
				motor[LF] = count1;

			}
			else if(vexRT[Btn8D] == 1 && count1 >= 0){	        // Ramp Down only if above 0
				count1--;
				motor[LF] = count1;
			}
			else if(vexRT[Btn8R] == 1){	              // Stop Flywheel
				motor[LF] = 0;
				count1 = 0;		                // Reset Count
			}

			wait1Msec(20);

		}
		*/

		{	if(vexRT[Btn8L] == 1 && count2 < 80){			// Ramp Up only if 80 and below
				count2++;
				motor[RB] = count2;

			}
			else if(vexRT[Btn8D] == 1 && count2 >= 0){	        // Ramp Down only if above 0
				count2--;
				motor[RB] = count2;
			}
			else if(vexRT[Btn8R] == 1){	              // Stop Flywheel
				motor[RB] = 0;
				count2 = 0;		                // Reset Count
			}

			wait1Msec(5);

		}
/*
		{	if(vexRT[Btn8U] == 1 && count3 < -80){			// Ramp Up only if 80 and below
				count3++;
				motor[LB] = count3;

			}
			else if(vexRT[Btn8D] == 1 && count3 >= 0){	        // Ramp Down only if above 0
				count3--;
				motor[LB] = count3;
			}
			else if(vexRT[Btn8R] == 1){	              // Stop Flywheel
				motor[LB] = 0;
				count3 = 0;		                // Reset Count
			}

			wait1Msec(20);

		}
		*/
	}


}

4149G · October 10, 2015, 8:14am

We are geared turbo with 7:1 external for a total of 16.8:1 and we overshoot with only 80 motor power. And that is with only one motor per flywheel. These crazy high gear ratios are definitely not needed.

Unit332 · October 10, 2015, 3:48pm

Somewhere in the range of 16:1 is appropriate for launching full field. Even with this ratio I have seen good systems burn themselves out. A 35:1 with turbos would likely be either unable to move or take half a minute to warm up and would die equally fast.

EvolvingJon · October 10, 2015, 4:51pm

Haha, yeah I know. Still its quite fun to see your balls launched at super high speed into things

@thewood
You code seems fine, but I dont understand why you dont just combine the motor speed control into one if statement?
Something like this that tackles all your motor control in one bunch.


#pragma config(Motor,  port4,           RF,            tmotorVex393TurboSpeed_MC29, openLoop, reversed)
#pragma config(Motor,  port5,           LF,            tmotorVex393TurboSpeed_MC29, openLoop, reversed)
#pragma config(Motor,  port6,           LB,            tmotorVex393TurboSpeed_MC29, openLoop, reversed)
#pragma config(Motor,  port7,           RB,            tmotorVex393TurboSpeed_MC29, openLoop, reversed)
//*!!Code automatically generated by 'ROBOTC' configuration wizard               !!*//

int targetFlywheelSpeed = 80;

task main()
{

      int count = 0;
      while(true)
      {
          if(vexRT[Btn8U] == 1 && count < targetFlywheelSpeed)
          {

            // Increase count
            count++;

            // Set Motor Speed
            motor[RF] = count;
            motor[LF] = count;
            motor[RB] = count;
            motor[LB] = count;
          }
          else if(vexRT[Btn8D] == 1)
          {
            // Decrease Count
            count--;

            // Set Motor Speed
            motor[RF] = count;
            motor[LF] = count;
            motor[RB] = count;
            motor[LB] = count;
          }
          else if(vexRT[Btn8R] == 1)
          {
            // Reset Count
            count = 0;

            // Set Motor Speed
            motor[RF] = 0;
            motor[LF] = 0;
            motor[RB] = 0;
            motor[LB] = 0;
          }

          wait1Msec(5);
    }
}

Apart from that you code looks fine, you should also increase the wait time as the motors can only update at around 50hz and you should just reverse the motors :). Remember that you do have to hold down the ramp up button for it to ramp up. You can let go when the motors are at your desired speed.

abatra83 · October 10, 2015, 9:53pm

Hi,
I agree with what others have been saying; you definitely don’t need an extremely high gear ratio to do what you are doing - a 15:1 with high speed motors should be just fine… However, make sure that when working with your launcher you are careful to avoid points of friction as this will definitely cause your motors to time out (as it did with my team). If you end up experiencing issues with motors timing out, make sure to space out your gears and to try to add washers at all points where gears/wheels contact metal.
Good luck!

thewood · October 11, 2015, 2:09pm

We had our first competition yesterday and I had the motors geared to torque(1:1) to get a 35:1 ratio. At 127, it was definitely way more power than needed. With lower motor power it worked very well, mainly when feeding in driver load balls by hand. I didn’t use the ramp up code and just had it move at a low speed then high speed. I’ll implement the rampup code again sometime this week, now that I have a much lower ratio. Still, for the sake of the motors, I think I may take advice from here and move to a lower external gear ratio.

@evolvingjon thanks for the refinements/advice!!