Digital Electronics

The Boe-Bot and Servo Motors

The Boe-Bot and Servo Motors

This presentation will

• Present an overview of the Boe-Bot Assemble.

• Detail how Servo Motors work, and how they are used to control the movement of the Boe-Bot.

2

The Completed Boe-Bot

3

Assemble : Chassis (1 of 5)

4

Assemble : Servo Motors (2 of 5)

5

Assemble : Battery Pack (3 of 5)

6

Assemble : Wheels (4 of 5)

7

Assemble : BOE (5 of 5)

8

Servo Motor Connections

Servo Motors are connected to…

• P13 – Left Servo• P12 – Right Servo

9

Vdd / Vin Jumper Setting

• The BOE provides a jumper that allows the Servo Motor to be powered by Vin or Vdd.

• If you are using a 9 v battery or a Wall-wart transformer, the jumper should be in the Vdd position.

• If you are using a 6 v battery pack, either setting will work.

• Since we will be using all three power sources, the jumper should be in the Vdd position. 10

Jumper

Servo Motor – Power Position

11

Power Switch Positions

0) OFF

1) STAMP

2) STAMP and Servo Motor Connectors X4 & X5.

PULSOUT Command PULSOUT Pin, Duration

• Pin : Specifies the I/O pin (0- 15) to use.• Duration : Specifies the duration (in 2 µs increments)

of the pulse.

Example:

PULSOUT 12, 400

Sends a pulse of 800 µs (400 x 2 µs) to pin 12.

12

Controlling The Servo Motors

13

DO PULSOUT 12, 750 PAUSE 20LOOP

750 750 x 2 µs = 1500 µs = 1.5 ms

20 ms

Controlling The Servo Motors

14

DO PULSOUT 12, 750 PAUSE 20LOOP

DO PULSOUT 12, 650 PAUSE 20LOOP

DO PULSOUT 12, 850 PAUSE 20LOOP

Motor Still

Full SpeedClockwise

Full SpeedCounter-Clockwise

Servo Motor Test

15

LeftMotor (13)

Right Motor (12)

Spin Right

Spin Left

Reverse

Forward

Calculating Motor Time

16

The code below will move the Boe-Bot in reverse. Assuming that the code overhead (i.e. the time it take for the microcontroller to execute the code) is 1.6 ms, verify that the code will cause the Boe-Bot to move in reverse for 3 seconds.

sec 3.0012 122 x ms 24.6 : Time Total

ms 24.6 : Loop (1) for Timems 20.0 : 20 PAUSE

ms 1.7 s 2μ x 850 : 850 12, PULSOUTms 1.3 s 2μ x 650 : 650 13, PULSOUTms 1.6 : Overhead Code

Motor Time Example

17

Calculate the For-Loop-Limit that is required to move the Boe-Bot forward for 4.5 seconds. Again, assume that the code overhead is 1.6 ms.

183 182.9 loop / ms 24.6

sec 4.5 Limit-Loop-For

ms 24.6 : Loop (1) for Timems 20.0 : 20 PAUSE

ms 1.3 s 2μ x 650 : 850 12, PULSOUTms 1.7 s 2μ x 850 : 650 13, PULSOUTms 1.6 : Overhead Code

ResourcesParallax Inc. (2004). What’s A Microcontroller.

– Retrieved July 15, 2009– fttp://www.parallax.com/tabid/440/Default.aspx