PJ013: Fun Controlling of Continuous Servo Motor

Click "Extensions", search "Servo", add it.

Since it's confusing to say direction as "clockwise" or "anticlockwise", because you can observe the servo motor from the top-down or bottom-up, the perspective leads different answers. 

Let's say "direction+" or "direction-" instead from now on.

• "direction+" is when speed is 0~100%

• "direction-" is when speed is -100~0%

You need a variable to help storing and changing the current speed.

Good practices of variable:

• Readable and understandable name

• Initialize it before use it! Good with on-start

• Typically 2 types of using:

  • Reader/Viewer/Consumer
    Fetch and consume it as soon, since the value could be updated quickly by writer on the other hand

  • Writer/Changer/Producer
    To change/update the value of variable, good to handle this job as accountable complete within a clear logical block of codes, avoid doing the change at different places where mixing other jobs or logic.
    Be careful of conflict parallel handling of the same variable.

If you don't know how to start, a straightforward idea like this will work to prove the concept, try it out, test it with the servo motor, can you change the speed and even rotation direction now?

Be noticed that, we say this is "prototype", because it's not such simple as a good work yet.

From Task 2, it seems things can work, let's look into it closer and check if it really does correctly or not.

This is very useful block for debugging to send real time data back to PC when the Micro:bit board is executing the program.

On-event v.s. On-status

If you use the "on-tilt" block, which is on-event triggering, it only triggers one time of the same event, but not trigger the same event even if you keep the same gesture.

Try out the on-status blocks, test and feel the difference!

By using "on-status" blocks, it's possible to continuously triggering the speed changing actions, the logic doesn't seem wrong, however, what does it feel in real world?

It's almost not a useful feature if we see it quickly hits the max speed when we keep the tilting just for a second!

Luckily, a small "pause" improve the user experience a lot!

Create a new variable, we will use it as boolean type, remember to initialize variable before anything.

1. Always check the availability before using the resource, if it's busy, you can decide to give up, or wait. Here, we simply give up.

2. "Lock" the resource by setting the variable as True

Now your are safe to use the resource.

3. "Unlock" the resource by setting the variable as False

As an optional exercise, a more professional way is to create 2 functions to simplify the "check-lock-unlock" actions for every user.

An easier way to understand this technique is like this

• "Can I use it now"

• "I'm done, others can use it now"

Now, looks at this in a professional view:

• "Fetch lock"
  = "Can I use it now"

  • Successful = Check and is available + Lock

  • Failed = Check and is unavailable

• "Return lock"
  = "I'm done, others can use it now"

  • = "Unlock"

The speed/direction is represented as -100~100 number range. So just map this number range to a range of levels to display.

There is ready-made bar plot, but it's only possible to map number range to a bar level. 

Try it out, find out the limitations.

The speed/direction is represented as -100~100 number range.