Файл: Advanced Robotics with the Toddler (Paralax, student guide, v1.3, 2004).pdf

doneTiltFlag = 1 Counter = 0

ENDIF ELSE

currentTilt = currentTilt - TiltStep

' from left tilt = decrement

PULSIN Yout,1,Incline

'DEBUG "Incline = ", DEC Incline, CR IF Incline > YAxisRtLimit THEN

Counter = Counter + 1

'DEBUG "Counter = ", DEC Counter, CR ENDIF

IF Counter > escVal THEN newTilt = currentTilt IF currentTilt <= newTilt THEN

IF (currentStride < newStride) THEN currentStride = currentStride + StrideStep

' from right stride = increment

IF (currentStride >= newStride) THEN currentStride = newStride

IF (doneTiltFlag = 1) THEN doneMoveFlag = 1

' uses doneMoveFlag to increment ' states

ENDIF ELSE

currentStride = currentStride - StrideStep

' from left stride = decrement IF (currentStride <= newStride) THEN' jump if still moving

currentStride = newStride

Chapter #9: Acceleration-Based Motion · Page 205

Page 206 · Advanced Robotics with the Toddler

oscilloscope trying to find a quicker way of executing your code. If your goal is to try out new and fun behaviors, or sensors, or whatever, on your Toddler, there is another way. Since the whole problem was the servos and their need for regular updates you can use a “Co-Processor” that is specially programmed to handle the servos. There are two major distinctions in “servo controller” Co-Processors. One type is given the new servo position and it sends the servo to that position at full speed. It then gives the same pulse widths every 20 ms to the servo until you send a new value. That type is better suited for wheeled robots with modified servo motors. They aren’t very helpful in a walking robot. The issue with a walker is that it is constantly changing the value of the servo output pulse in a ramped fashion. As you recall, that is what the StrideStep and TiltStep were used for in the Do_Movement subroutine. Happily, there is another type. A “ramping” servo controller remembers where each servo is and ramps (adds constant steps like Do_Movement did) to get to the new position. It essentially executes the Do_Movement subroutine for you. Many Co-Processors have more than just servo controllers in them. One we recommended is from Blue Bell Design Inc. (www.bluebelldesign.com). It has 8 ramping servo controllers, 5 analog to digital converter inputs (10-bit), and extra inputs and outputs. Best of all, it will be available on a compatibly sized PC board for easy installation on your Toddler! The Blue Bell Design Co-Processor is discussed in Appendix C.

CHALLENGES

√In Do_Movement, the PULSIN command reads the value of the Memsic 2125 accelerometer. Since we know the code is too slow to keep up with 20 ms refresh on the servos, and there is plenty of code space left, is there some way you can use the current state of the accelerometer signal to pick up an average of 1.5 ms in the worst case? What is the worst case state of Yout? Why is it the worst case? Hint: What do you know about how PULSIN works that makes a difference?

√Tune the timing of your Toddler for optimal speeds, tilt, and stride. How good can you get it to be?

√You know that Toddler really doesn’t need to use its vision and check the bumpers every 20 ms. Can you think of ways to make the state machines in vision and bumpers run on alternate cycles? What happens to the evenness of the servo steps if the duration between servo pulses changes cycle to cycle?.

Appendix A: Parts Listing and Sources · Page 207

Appendix A: Parts Listing and Sources

All parts used in the Toddler kit are available individually from the Parallax Component Shop at www.parallax.com. If you can’t readily find the component you are looking for in the Component Shop enter the name of it in the on-line search box using the stock code.

The Toddler Kit comes in two flavors:

•Gold Anodized Toddler Kit - 27310

•Blue Anodized Toddler Kit - 27311

Toddler Kit Bill of Materials

Parts and quantities subject to change without notice

Page 208 · Advanced Robotics with the Toddler