continuous servos

I haven't tried out the whole modified servo thing, but I don't think you can use it to be able to turn a specific number of turns.

The trick with the modified servo thing is that normally a servo has a potentiometer attached to the output shaft and this makes it able to measure the current angle it is at by simply measuring the resistance of the potentiometer. When you modify it you remove the potentiometer and replace it by two equal valued resistors in a voltage divider setup where you connect the measuring circuitry to the joint between the two resistors. This makes the servo think that it is always centered. There is no way to get back any information on how many turns the servo has done. You should think of the modified servo as a geared motor with a simple control interface where you can set it in forward, reverse or stop. I'm not sure of this - so anyone with better intel please correct me if I'm wrong - but I think that a servo turns faster with greater angles, so if you set the servo to turn to an angle close to center, the servo will not turn as fast as if you set the servo to turn to an angle far from center.

You can add wheel encoders to your project to be able to measure how many turns each wheel has done. You can see a small project for the Tamiya twin motors here.

From my exp with the Parallax boebot which uses 2 CR servos for it's motor drive, they were pretty consitent. The documentation(free to download btw) tells you how to fine tune them if they are out of sync. One thing to note, these are great for flat surface use and some light terrain, but I'm not too sure about their long term use as a major motive force.

So I have to buy a new standard servo because I have a continuous servo? There is no way to make a continuous servo into a standard servo?

How would I do that? What the programing code to go with that.

 First of all, the "wait" command need to go bye-bye. Use "pause" instead. You can get down to milliseconds with pause i.e. pause 1000 is just one second and you now you can break up that second into 1000 tiny, tiny parts -much more accurate. However, all I can imagine is one missed or screwed up code and the next thing you know you have wrapped the sonar leads around the sensor about 3 times before it breaks the board in half. You know, a servo is only 10 bucks and can be stopped at very precise stops. Using a "timed" stop, is going to get funny as your batts get low and the servo moves slower. If nothing else, use some solid stops and/or a couple little buttons to tell the pic that the servo has gotten to where you told it to go. -Just a thought.

 

www.rocketbrandcustom.com baby!!

I bought a handful of rotary encoders from Farnell. They're not exaclty what I thought they were, but they are great for direction and speed sensing.

Symbol dangerlevel = 70' how far away should thing be, before we react?

symbol turn = 300' this sets how much should be turned

symbol servo_turn = 20' This sets for how long time we should wait for the servo to turn (depending on it´s speed) before we measure distance

main: ' the main loop

readadc 1, b1 ' read how much distance ahead

if b1 < dangerlevel then

gosub nodanger ' if nothing ahead, drive forward

else

gosub whichway ' if obstacle ahead then decide which way is better

end if

goto main ' this ends the loop, the rest are only sub-routines

 

nodanger:' this should be your combination to make the robot drive forward, these you most likely need to adjust to fit the way you have wired your robots motors

high 5 : high 7 : low 4 : low 6

return

 

whichway:

gosub totalhalt ' first stop!

'Look one way:

gosub lturn ' look to one side

pause servo_turn ' wait for the servo to be finished turning

gosub totalhalt

servo 1, b1

'Look the other way:

gosub rturn ' look to another side

pause servo_turn ' wait for the servo to be finished turning

gosub totalhalt

servo 1, b2

' Decide which is the better way:

if b1<b2 then

gosub body_lturn

else

gosub body_rturn

end if

return

 

 

body_lturn:

high 7 : low 5 : low 6 : high 4 ' this should be your combination that turns the robot one way

pause turn : gosub totalhalt

return

body_rturn:

high 4 : low 7 : low 4 : high 6 ' this should be your combination that turns the robot the other way

pause turn : gosub totalhalt

rturn:

servo 0,95' look to one side

wait 1

return

lturn:

servo 0, 160 ' look to the other side

wait 5

 

totalhalt:

low 4 : low 5 : low 7 : low 6' low on all 4 halts the robot!

Servo 1,75' face forward

wait 1 ' freeze all for one second

return

I bought a standard servo and its all working. My robot is alive!:) next the YDM.