Monsterborg motor coasting

Submitted by robotter on Fri, 05/04/2018 - 20:01

Forums:

I realise that calling the MotorsOff function actually puts the motor on hard stop, is there any way to allow the motor to coast to a stop instead of hard stopping? I suppose this will be less harmful to the motors and less likely to tip over when carrying load.

piborg's picture

piborg

Fri, 05/04/2018 - 22:16

Unfortunately the ThunderBorg does not have the capability to allow the motors to coast.

What you can do instead is create a function which will gradually reduce the motor power to nothing. This is gentler on the motors than a hard stop and should cause your MonsterBorg to slow down in a much more controlled fashion.

Here is an example of how this can be done:

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# Needed imports
import ThunderBorg
import time
 
# Function to perform a gentle stopping of the motors
def GentleStopMotors(TB):
    # Settings for the slow down
    stepSize = 0.02     # Power reduction per step
    delay = 0.01        # Delay in seconds between each reduction
    # Start by getting the current motor power
    speedMotor1 = TB.GetMotor1()
    speedMotor2 = TB.GetMotor2()
    # Determine the direction to change motor power
    if speedMotor1 < 0:
        stepMotor1 = -stepSize
    else:
        stepMotor1 = stepSize
    if speedMotor2 < 0:
        stepMotor2 = -stepSize
    else:
        stepMotor2 = stepSize
    # Step the motors down until they both reach zero
    while (speedMotor1 != 0) and (speedMotor2 != 0):
        # Reduce the values towards zero
        if abs(speedMotor1) > stepSize:
            speedMotor1 -= stepMotor1
        else:
            speedMotor1 = 0
        if abs(speedMotor2) > stepSize:
            speedMotor2 -= stepMotor2
        else:
            speedMotor2 = 0
        # Set the new power levels and wait
        TB.SetMotor1(speedMotor1)
        TB.SetMotor2(speedMotor2)
        time.sleep(delay)
 
# Example usage
TB = ThunderBorg.ThunderBorg()
TB.Init()
 
TB.SetMotor1(0.7)
TB.SetMotor2(0.5)
time.sleep(1.0)
 
GentleStopMotors(TB)

The function takes the current motor powers and reduces them at a fixed rate until both motors are off. You can change the rate of the slowdown by adjusting the stepSize and delay values.

robotter

Sat, 05/05/2018 - 06:26

Thanks for the quick reply and sample code workaround.

Is there any plans to implement coasting in the future?

piborg's picture

piborg

Sat, 05/05/2018 - 12:46

Unfortunately this is a limitation of the drive chips used on ThunderBorg, they will only go into coasting mode when a fault has been detected with the motors or power supply.

Our more powerful controllers (such as Diablo) have this functionality, so it is possible we will have smaller boards which support this in the future. At the moment we do not have any planned with the feature.

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