Servo

Status
Not open for further replies.
W

watzmann

New Member
Hi All;

i have a servo motor and going to control it using Microcontroller pic , but i liked to try it at first so i connect it's vcc to 5volts .but i didn't use it's signal at all

then i found that my motor is moving i think to it's initial position and then stoped there ..... and it seems it's trying to continue so it shakes


why that happened? and is it normal
 
Servo shouldn't move without a control signal...

Here's a link to a 555 based servo tester, simple, works...

**broken link removed**

**broken link removed** , is the main R/C page, maybe of use...
 
I don't know that much about servos. I started learning (not much progress) to fly a Blade CP Helicopter about 2 years ago. Got 4 servos out of an old crashed Aero-sport 60, hence my need for the servo tester, which worked great. You will get the grinding sound when you attempt to move the arm past the stops The servos I tested were weathered and dirty, but turned out to be fine. Haven't worked out an AVR assembler routine to run them yet, but have a couple of projects in mind.

Anyway, the tester I posted the link to works good, the parts don't have to be exact, the caps and pot I used were close, but within a few standard values...
 
You need to supply a servo a digital signal or it won't do much. Some cheap servos sit an stutter if no signal is present.
**broken link removed**
 
watzmann said:
but mine isn't cheap
Click to expand...

It probably is!

I doubt the cost makes any difference though, I imagine most use identical chips inside - the price difference is most likely due to better mechanics.
 
The ones that don't stutter are digital and much more expensive than the common analog ones.
Most digital servos start at $100, they look like standard servos on the outside.
**broken link removed**
 
Could be noise on an adjecent line. Ground the signal line and see if the same thing happens, if it doesn't then it's just noise. If the signal line is left floating internal noise from the servo circuit itself could cause it to move, let alone anything it may be near. Testing any device that relies on a signal with the signal line left floating is simple pointless unless there's some reason to believe it may occur during normal device operation.
 
Has anybody seen a website, or tried theirselves, to build a servo circuit for a large DC gear-motor. Like a wheel chair motor, power window, windscreen wiper... Always wondered if it's been done or do-able.
 
Yes, I've seen inside an R/C servo... Was more interested in the circuitry to take the PWM signal and drive the motor. Was looking to hook one up to an R/C reciever, like any other servo.
 
HarveyH42 said:
Has anybody seen a website, or tried theirselves, to build a servo circuit for a large DC gear-motor. Like a wheel chair motor, power window, windscreen wiper... Always wondered if it's been done or do-able.
Click to expand...

Oatley electronics make a Jumbo Servo Controller. Looks like a standard IC with heavier mosfets.

Mike
 
HarveyH42 said:
Has anybody seen a website, or tried theirselves, to build a servo circuit for a large DC gear-motor. Like a wheel chair motor, power window, windscreen wiper... Always wondered if it's been done or do-able.
Click to expand...

There's a project on the web using a windscreen wiper motor as a servo to steer a large robot powered by a petrol engine, Ackerman steering like a car.

They simply fixed a potentiometer to the output shaft of the motor, stripped an old servo (to get the IC, which is difficult to buy), and added a higher power H-Bridge. They essentially made a larger version of an existing RC servo.

You could easily make your own without the special IC, using a PIC to read the incoming pulse, the pot and controlling the H-Bridge. In fact if it's not fed from a normal RC receiver, you could dispense with the pulse reading, and use a simple serial data signal.
 
You could use a pulse stretcher.
**broken link removed**
This would be incredibly simple, but would only give you 50-100% duty cycle. Not sure how to go about less than 50% duty cycle with simple logic, but a PIC would be a good sollution as well. Servo signals are trival to work with a micro controller. The added advantage is typical servo signals are only 50hz, if you use a PIC you could read the 50hz incoming servo signal but output a much higher frequency signal to the h-bridge. This is one of those areas where AVR's are better than PIC's, the resolution is higher for I/O timeing. But pretty much any micro controller will give you 8bit PWM out at a decent frequency.
 
Last edited:
Sceadwian said:
This is one of those areas where AVR's are better than PIC's, the resolution is higher for I/O timeing.
Click to expand...

Perhaps you would care to elaborate on this silly suggestion?.
 
We're getting way off topic here. It was bad enough I hijacked the man's thread, but no way do I want to take the blame for starting another PIC WAR.

I was just playing with some small servos past few weeks, but have much bigger ideas then I could expect them to handle.
 
Using an interrupt based routine to detect pulse width modulated signals an AVR running at 1MHZ has a resolution of up to 1usec. A PIC's highest resolution at the same clock would be 4us. Unless they have an asynchronously triggered timer counter that can be started and stopped from a rising and falling edge signal that I don't know about.
 
Status
Not open for further replies.

Similar threads

N
  • Question
Servo Drive Transformer
Replies
7
Views
3K
Neilf
N
D
16 Servo Board
Replies
1
Views
1K
Dr_Doggy
C
Main controller for 16 * 16 array of servos.
Replies
10
Views
2K
gophert
P
Less noisy alternative to servo. Muscle / nitinol wire?
Replies
14
Views
3K
hyedenny
H
R
What servo motor to use...
Replies
1
Views
898
MaxHeadRoom78
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…