More usage examples for continuous motor control?

[LiamDobbelaere]

Hi, I was trying powered-up the other day and I noticed a pretty big delay when trying to control motors using a controller. I assume this is because I keep sending StartPowerAsync and awaiting it, which seems to be expensive performance wise?

All of this happens inside of a while-loop, so the code is running as fast as it can, though waits for the Bluetooth commands to go through.

If StartPowerAsync isn't the way to control motor speed continuously, what is? I'd love some more examples on how this can be accomplished.

if (currentAccelerationValue != lastAccelerationValue)
{
    await aMotor.StartPowerAsync(currentAccelerationValue);
    lastAccelerationValue = currentAccelerationValue;
}

if (currentTurnValue != lastTurnValue)
{
    await bMotor.GotoPositionAsync((sbyte)(currentReading.LeftThumbstickX * 90), 100, 100, SpecialSpeed.Brake);
    lastTurnValue = currentTurnValue;
} 

[tthiery]

Yes, there is a Bluetooth Ping Pong. Problem with the protocol is that hubs have a buffer ... so if you send them commands too fast, they might drop them.

So let me see how I can help you. From your code snippet, I assume you have somewhere input for currentAccelerationValue and currentTurnValue which you synchronize into the motor using that loop.

Depending on your use case I would recommend on of the following:

• directly dispatch from your UI or handler or whatever the command and await the feedback. Bluetooth should be much faster than your UI input.
• considering that a loop with Bluetooth may take some ms .... maybe implement a threshold when you start sending commands to it
• you do not need to await the response of the StartPowerAsync / GotoPositionAsync, you can just let them hang or you can resolve the tasks later. There is a risk that you having commands being dropped by the motor in this case. There is a risk that the dispatching of the commands to the bluetooth stack is out of order because you would also skip the await for the SendMessage and not only for the receiving.
• if all of the above is not matching your use case, you can consider
  • directly using the ILegoWirelessProtocol as demonstrated in the README. The related motor messages you can see in the implementation of the motor.
  • I am also open for a pull request if you want to implement a "fast-mode" in the StartPowerAsync method.

[LiamDobbelaere]

The detailed feedback is much appreciated, thanks! I'll give it a shot later and see if I can get it to work faster. It's good to know about the command drops and out-of-order delivery if you send too fast. Maybe a threshold will work just fine.

[LiamDobbelaere]

For whoever comes across this, I ended up solving it using a command pool. Basically, waiting for every command to complete is too slow, but sending them all at once overloads the device's buffer.

public partial class MainWindow : Window {
    List<Task> commandPool = new List<Task>();
    const int maxCommands = 2; // can be tweaked
// ...

private void TimerTick(Object stateInfo) {
// ...
    // trying to send commands every tick
    if (commandPool.Count < maxCommands) {
        commandPool.Add(aMotor.StartPowerAsync((sbyte) -currentAccelerationValue));
    }

    // remove completed commands every tick
    commandPool.RemoveAll(t => t.IsCompleted);
// ...

[tthiery]

Cool. If you have other questions, just create an issue