Controlling a Servo Motor

[Nigel Goodwin]

You don't have an electrolytic across the supply to the servo - try a 100uF across the 555 supply pins. Also bear in mind you're feeding the motor from the output of the 5V regulator, this may cause it to current limit? - and assuming the 9V supply is a PP3 type, this probably doesn't have enough power to feed a motor anyway.

I would suggest fitting an electrolytic across the 555 supply (always essential), throw the regulator and 9v battery away, and power it from 4 AA alkalines in series (6v).

 

[shaneshane1]

electrolytic across the supply to the servo - try a 100uF across the 555 supply pins? from what pin to what pin?

and also i have a ac/dc adaptor its DC output it 4.8V-300mA, its a mobile phone charger, do you think that will have what it takes to do the job, i dont know what mA the servo should draw?

 

[Nigel Goodwin]

electrolytic across the supply to the servo - try a 100uF across the 555 supply pins? from what pin to what pin?

Pin 8 to pin 1 - according to your diagram above.

and also i have a ac/dc adaptor its DC output it 4.8V-300mA, its a mobile phone charger, do you think that will have what it takes to do the job, i dont know what mA the servo should draw?

300mA sounds a bit low, and it's probably a non-regulated supply?.

 

[shaneshane1]

im not sure whether its regulated or not, do you have any idea how much current the servo should draw as a minimum at 4.8V???

 

[Nigel Goodwin]

im not sure whether its regulated or not, do you have any idea how much current the servo should draw as a minimum at 4.8V???

No, it's entirely dependent on load.

 

[jpanhalt]

im not sure whether its regulated or not, do you have any idea how much current the servo should draw as a minimum at 4.8V???

I believe the concern is the maximum current, which can vary with the servo type. Even the smallest servos, however, can draw well over 100 mA when working against a resistance.

When you said earlier that the servo worked fine for about 10 minutes, what was it doing then? Was it moving someting or just sitting in a fixed position? When the problem started, had you tried to move somehting?

What specific servo do you have, as there are differences. Is it digital or analog, plastic or metal geared? What is maximum torque and manufacturer? The model number would help. John

 

[shaneshane1]

lets say test purposes, with no load, any ideas give or take?

 

[shaneshane1]

I believe the concern is the maximum current, which can vary with the servo type. Even the smallest servos, however, can draw well over 100 mA when working against a resistance.

When you said earlier that the servo worked fine for about 10 minutes, what was it doing then? Was it moving someting or just sitting in a fixed position? When the problem started, had you tried to move somehting?

What specific servo do you have, as there are differences. Is it digital or analog, plastic or metal geared? What is maximum torque and manufacturer? The model number would help. John

it was under no load at all (sitting in a fixed position) the servo is a GWServo, plastic geared, torque is 3.4kg-cm, not sure if its digital or analog?

and i didnt change anything, it just started playing up.

 

[Nigel Goodwin]

and i didnt change anything, it just started playing up.

Have you tried replacing the battery?, or at least checked it's voltage under load.

You didn't have a capacitor across that either did you?.

 

[shaneshane1]

Have you tried replacing the battery?, or at least checked it's voltage under load.

You didn't have a capacitor across that either did you?.

yes, used a new battery, also used a 12V car battery, still same thing, and haven't used servo under load yet.

 

[jpanhalt]

I looks like you may have the mini-standard servo (S03N) which has plastic gears and is analog. It is rated at 4.8 to 6.0 V. The GWS site also has some application notes thatyou may find interesting:

http://www.gwsus.com/english/product/servo/servo.htm

Do you have a way to check the frequency/frame rate that your circuit is producing? GWS gives a limit of 16 to 23 ms (62 to 43 Hz) for that rate. If you are too fast or too slow, it may jitter. John

 

[shaneshane1]

I looks like you may have the mini-standard servo (S03N) which has plastic gears and is analog. It is rated at 4.8 to 6.0 V. The GWS site also has some application notes thatyou may find interesting:

http://www.gwsus.com/english/product/servo/servo.htm

Do you have a way to check the frequency/frame rate that your circuit is producing? GWS gives a limit of 16 to 23 ms (62 to 43 Hz) for that rate. If you are too fast or too slow, it may jitter. John

No i dont have a way to check the frequency/frame rate, do you happen to know a site that has a schematic for this particlar servo because i cant find one at all?.

 

[jpanhalt]

No i dont have a way to check the frequency/frame rate, do you happen to know a site that has a schematic for this particlar servo because i cant find one at all?.

I doubt you will find a schematic for that particular servo or any commercial servo for that matter. The application notes on the GWS site do give a little information about the proper signal the servo requires.

GWS also sells a servo tester for about $50 USD; however, before I would spend that much for a servo tester, I would spend the money for used Velleman oscilloscope or other inexpensive oscilloscope. An oscilloscope will help you much more in trouble shooting your robot as you progress on it.

Assume the problem is either in the tester circuit or the servo. Do you have an actual RC receiver you can test the servo with? Is there a flying club anywhere near you -- or hobby shop where you bought it --where you could plug your servo into a working system?

As for the circuit, trouble shooting it without some sort of oscilloscope will be hard. in the unlikely event (it seems to me) the circuit is ruining the servos, you could go through a lot of $10 USD servos before finding the problem with the circuit. John

 

[shaneshane1]

I finally got this dam servo working properly, i used 2 regulators, one for the circuit,(555) and the other for the Servo, you would think i would have though of that in the beginning!!!

I had to use the car battery because i dont have any other power supply large inuf.

The servo must draw some serious current because i couldnt even get it working properly of two 9V batteries in series.

Also the regulator for the servo gets really really hot after about 20 seconds of continues use, is there another type of regulator i can use, im currently using a TO-220 package 7805 1A fixed 5V regulator (+).

 

[audioguru]

A little 9V battery supplies hardly any current. Two in series supply the same low amount of current but then the voltage varies too much.

RC models use Ni-Cad or Ni-MH batteries that supply high current when needed, and don't need voltage regulators.

 

[shaneshane1]

if i was going to use it on a 12V car battery, what sort of regulator should i use?

 

[audioguru]

With a car battery you are throwing away half the power as heat in the voltage regulator.

 

[shaneshane1]

if i bought an ac to dc power supply, 10W, input Voltage 90-264VAC, Output Voltage: 5VDC Regulated, Output current: 2A.

do you think that will be ok to use for it?

 

[audioguru]

Your servo is made to have a supply voltage from a minimum of 4.8V to a max of 7.5V. A 5V power supply might actually be 5% low at 4.75V which is too low but it might work.
If you don't stall the servo then 2A is fine.

 

[shaneshane1]

i found another power supply in a electronics engineering catalogue that is 6V output and its current is 1.66Amps, that probly sound alot better.

the main thing i want to know is how many milliamps or amps does the servo draw under no load, (so just moving it back and forth at full speed), because i have no idea at all, does someone know a round about figure, give or take 100mA or so.