Servo Issues

B

BotB

Member
Hi, due to the nature of my animatronics project I require different servos for certain tasks, higher torque etc.

I am however having some trouble getting my some servos to respond.

I'm using this code to test my servos:
start:

servo 7, 0

pause 2000

servo 7, 225

pause 2000

goto start:

I'm using the PICAKE 28X1 board with the servo upgrade, I've used it before on a previous project with great results. I've had no trouble using the standard Futaba S3003 servo and the Protech B170 servos but when I'm using the Cirrus 601 BB and SuperTec Mega S04/2BB Servos I get little response, the servo will either move to one point and stay there or nothing at all...

The only thing I can imagine that may cause this is that I have no 330R DIL "chip" and am currently making do with several 330R Resistors in it's place.

Please feel free to ask any questions you may have.

Many thanks.
 
R

russbow

Senior Member
The 330 ohm resistors against a 330 ohm DIL will not make any difference.

However you need to consider SERVO and SERVOPOS. Have a look at manusl 2 pages 176 and 177.

Be careful of your values. Do they match the travel that you require?
 
B

BeanieBots

Moderator
As AC points out, not all servos can go as far as 225.
Try driving to the neutral position.
This is 150 for most servos but some are 130.
 
M

Marcwolf

Senior Member
Having used servo's for animatronics I can say that 225 is way.. off the scale for servos. Even ones that have been modified for extended range.

Running a servo to that position will either stop the servo working.. or emit a fouls smell of the servo electonics giving up the ghost.

Best try writing a little for next loop to gradually swing the servo from its center point in increasing swings until you get a good idea of the servo's capabilities. Not all servo are created equal. I have has some that will give 120degree range and other only 60degree

Hope this helps
Dave
 
W

westaust55

Moderator
Servos -link to basic servo tutorial

If you are new to Servos and their control, you might wish to have a read of this previously posted tutorial for analog type servo's
http://www.picaxeforum.co.uk/showthread.php?t=12120

Some servo's that I have just do not move at all if the specified position ( = pulse duration) is out of the Servo Motors operating range.
 
Last edited:
B

BotB

Member
Hey, thanks all for the replies and those Servo tutorials have been a great help. I've started to document the "limits" my servos operate in. I've had luck with the standard Futaba S3003 that ranges from 0,130,225 (right, center, left) but I've had no luck with the Super Tech S04 and Cirrus CS601BB, I get either erratic motion from them where they move to different positions from a consistent code or nothing at all. I can hear the servos "hum" indicating they must be "working" somewhat but I'm a little at a loss as what to do. I have several of each servo too to make sure it's not just one broken servo.
 
B

BeanieBots

Moderator
The CS601BB is stonking great big 6kg/cm servo.
Is your power supply up to the task of driving it?
What is your power supply? Is it shared with the PICAXE?
If yes, have you decoupled it (and the PICAXE)?
 
J

jppizhere

New Member
It is not the 225 that would lead me to have concern for the health of the servo, it is to 0 as that is way out of limits for any servo. 100-200 is usually a pretty safe bet on any servo you are going to find, you can push them farther to find their real range, just beware of servo death as a possible side effect.

From the manual

- Pulse is variable/constant (75-225) which specifies the servo position
 
B

BotB

Member
BeanieBots said:
The CS601BB is stonking great big 6kg/cm servo.
Is your power supply up to the task of driving it?
What is your power supply? Is it shared with the PICAXE?
If yes, have you decoupled it (and the PICAXE)?
Click to expand...
I'm using a 6V Cell (4 AA cells) for the servo power and the PICAXE has it's 4.5V power also, I believe it may be the 6V supply however, I can see that there may be a current draw issue. I shall try the power supplys at university to see if it is this.

On the subject of the 0 "position" for the Futaba, 75 does work but I appear to get a further position from lower values. I may well be wrong, I will re confirm the value tomorrow as I don't want to be killing my servos.
 
B

BeanieBots

Moderator
Servo 0 should switch off servo pulses and leave it 'limp'.
You may well get extra movement bellow 75 or above 225 but that will be dependant on individual servos. Driving them into their end stops can result in tears:(
 
B

BotB

Member
A quick, related question. What other power supplies should I try or use to power the servos, it seems that the standard 4 cell AA approach doesn't give me enough amps (or my batteries are draining fast) Should I try some Lithium Ion AA batteries or rely on a bench power supply? I have looked at RC battery packs but they tend to be only 4.5v or 7.4v, I know I don't want to burn out my servos with too much voltage and from the Servo tutorials posted here I can see that using a power converter can be problematic and inefficient.
 
W

Wrenow

Senior Member
Servos will run just dandy on 4.5-4.8v, which is why many hobby RC packs are 4.8v.
Many servos are not rated above 6v (some are, but not many). All you gain from the higher 6v voltage is a tad more torque and speed (and additional weal/stress on the drivetrain, of course).

As noted by several already, start form 100-200 as the range and go from there. Servo 7, 0 would not do you any good on any servo I have seen (aside from the fact that, at least in theory, you are sending no pulse whatsoever).

Cheers,

Wreno
 
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