More motors please!

Lord_canti

I am completely 100% newbie. My school bought Boe-bots last year and i caught a glimpse of it. This year was my first attempt to build one, and it was very successful.

I'm thinking of using the boe-bot to build something a bit more complex, involving four to six independently moving motors. I found a motor control for 16 servos, but they all operate simultaneously.
http://www.parallax.com/html_pages/products/motorcontrol/motor_control.asp
Is their any way to do this without the motors running simultaneously?
Should·I buy something else?
If so, is it inexpensive?
would i have to buy another boe-bot?

A NEWBIE crying out·for help here!

Post Edited (Lord_canti) : 4/23/2006 9:05:26 PM GMT

PJAllen

MotorMind-B -- look for it at the Parallax store (·www.parallax.com )

Lord_canti

"MotorMind-B -- look for it at the Parallax store"

www.parallax.com/detail.asp?product_id=27961
I don't think it that's what i am looking for. It seems as if that controls DC motor speed and directional control. Thanks for your help though!

I need either a product, or a circuit design that i can use to individually control at least four servos. Does anyone have any circuit ideas?

This might sound absurd but... could i possibly suggest to the parallax owners if they could design a circuit to do this, if one doesn't already exist? I'm sure·I wouldn't be the only person who would buy one.

How would i go about contacting these people? I fear they would frown upon my lack of knowledge...

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-an inexperienced gearhead looking to be geared toward the head of·electronic bliss-

Post Edited (Lord_canti) : 4/23/2006 9:23:59 PM GMT

allanlane5

Ah, you SAID "motor", but you also said "servo". A "servo" (which sounds like what you're using) shouldn't be called a 'motor'.

Simultaneous movement is the difficult part. Getting them to move one at a time is very easy. Simply send commands to the Servo board one at a time. Note that a Servo needs to be 'refreshed' every 20 mSec to 50 mSec for it to 'hold' its position. This 'holding' is also a function of the Servo controller board.

Lord_canti

allanlane5 said...
Ah, you SAID "motor", but you also said "servo". A "servo" (which sounds like what you're using) shouldn't be called a 'motor'.

ummm... i knew there was a difference, but all i don't really know what it is. However, i do know what i need. Anything that can give me·atleast 90 degrees of rotation, and be fairly strong. speed isn't really a factor but 1 rps would be nice.

anyway, thanks! it seems like you really know what i need...
but i don't understand how i should connect the servos so i can get maybe 6 to work.

please help

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-an inexperienced gearhead looking to be geared toward the head of·electronic bliss-

allanlane5

Yup, Servo's provide settable positions. You want "non-modified" servo's for that. A Servo has inside it a pulse-width comparator IC, AND a motor driver, AND some reduction gearing, AND a variable resistor.

You give the servo a 1 mSec to 2 mSec wide pulse, repeated every 20 mSec to 50 mSec. The servo checks the pulse-width you've given it, and drives the motor (which turns the output shaft) to adjust the internal variable resistor to match the pulse-width you've given it. Result: a device with an output shaft that you can send to various positions.

A servo connection is three wires -- Power, Signal, and Ground. Ground MUST be connected to Vss for each servo. Power can be connected directly to 6 volts, or to 5 volts, but a servo pulls more current than a BS2 by itself. A BOE makes a good starting base, as I believe it has a couple of servo connectors on it already. You can connect additional 'signal' wires to the BOE bread-board area.

Let's see -- you send out a 2 mSec wide signal. 6 of those is 12 mSec. That gives you 8 to 38 mSec to do other programming -- very doable.

You send the pulse using the "PULSOUT" command. Since "PULSOUT" uses a 2 uSec 'tick', "PULSOUT ServoPin, 500" will generate a 1000 uSec (1 mSec) pulse, and swing the servo all the way one way. "PULSOUT ServoPin, 750" will center it, "PULSOUT ServoPin, 1000" will be all the way the other way.

To control six:

S1Pin CON 0
S2Pin CON 1
S3Pin CON 2
S4Pin CON 3
S5Pin CON 4
S6Pin CON 5

S1Val VAR BYTE
S2Val VAR BYTE
S3Val VAR BYTE
S4Val VAR BYTE
S5Val VAR BYTE
S6Val VAR BYTE

' Subroutines
MoveServo
PULSOUT S1Pin, 500 + S1Val
PULSOUT S2Pin, 500 + S2Val
PULSOUT S3Pin, 500 + S3Val
PULSOUT S4Pin, 500 + S4Val
PULSOUT S5Pin, 500 + S5Val
PULSOUT S6Pin, 500 + S6Val
PAUSE 15
RETURN

Since the minimum position is '500', the '500 + Val' reduces the number of bits needed for the 'Val'.

theye

may be you should try adding six servos to your by this way emmm i will try to make a shematic for this project i made

Post Edited (theye) : 4/26/2006 2:45:52 AM GMT