Shop OBEX P1 Docs P2 Docs Learn Events
mobile robot project — Parallax Forums

mobile robot project

ltmhallltmhall Posts: 102
edited 2006-10-09 18:50 in Learn with BlocklyProp
I’m Building an autonomous mobile robot using differential drive and have a few questions. I’m using two continous rotation modified Hitec 422 servo motors, a Basic Stamp II (education board), two Dubro 2.75 in. wheels, and a NARP 4cm omni direction wheel.

1) If I’m using two HS 422 servo motors and a Basic Stamp II do I need an H-bridge. I was planning on connecting my servo motors to an L293 chip then connecting the L293 to a Basic Stamp, but a classmate told me I didn’t need one, I could connect the servos straight to the Basic Stamp. Please Help!

2) If I need to connect my servos to an H-bridge do I actually open my modified servos and connect the two pins of the motor to the H-bridge.

3) I read a regular caster is a very great ideal for the third wheel, does anyone know a good way to mount an omni directional wheel to an aluminum chassis.

ANY HELP WOULD BE APPRECIATED
<!-- / message --><!-- edit note -->

Comments

  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-10-08 04:51
    ltmhall -

    No H-Bridge is necessary. The width of the PULSEOUT controls both the speed and direction of the servo when it's modified for continuous rotation.

    Regards,

    Bruce Bates

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    <!--StartFragment -->
  • ltmhallltmhall Posts: 102
    edited 2006-10-08 14:36
    And you just connect the Pulse Width Modulation pin to the Basi Stamp II.
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-10-08 20:34
    Yes. Though it's not "really" PWM, it's more like a 1 mSec to 2 mSec width pulse repeated every 20 mSec. I've heard some people CALL that "PWM", but "classic" pwm is more like a square wave with variable duty cycle, and the motor moves at a speed proportional to the duty cycle.
  • ltmhallltmhall Posts: 102
    edited 2006-10-09 01:27
    So I could use a 3 pin male/male header connect my power pin to a 7805 5 volt supply, connect my ground pin to the vss terminal and connect my last pin to a pin on the basic stamp.
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-10-09 16:18
    Yes. Make sure the 'ground' pin of the 7805 is ALSO connected to Vss.
  • manxstampmanxstamp Posts: 57
    edited 2006-10-09 17:11
    It sounds like you're building a home-brew BOE-Bot and the downloadable text 'Robotics with the BOE-Bot' will answer all your questions on servo control with 'PWM', and the all important 'centering' process if servos have been modified for continuous rotation.

    You state that you are using the 'education board', in which case you can plug the servos into the servo headers and, supplying the board with 6 volts (from 4 1.5 volt batteries) you can use Vin (just set the jumper) for the servo supply.

    John





    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔


    Manxstamp,
    Isle of Man, British Isles
  • ltmhallltmhall Posts: 102
    edited 2006-10-09 18:37
    So I could use a Battery Holder with Barrel Jack mounts (supplying 6 volts) to power the board, then connect the servos to the servo headers on the board. This wouldn't
    require no 7805 regulator or 9 volt battery. The sevos will move quicker with 6 volts than 5 volts. Would this work. An d if so is this the best way to power the servos and board.
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-10-09 18:50
    The BOE has an on-board 3840-5 Regulator already. Plus, the BOE board has a jumper that lets you route Vin (the 6 volt battery voltage) directly to the supply lines of the 3-pin Servo connectors on the BOE. So yes, this would be a good way of powering the board and the servo's.
Sign In or Register to comment.