Controlling a Servo Motor

[Sceadwian]

Servo's are usually only run at +/- 45-60 degrees so that doesn't seem overly weird. Twitching/jerkiness could be a lot of things, I'd imagine it's most likley from sending the servo pulses too fast. Most servo's will start tweaking out if the control signal is sent more than about 80 times per second, they were designed with no more than 50 pulses in a second in mind. Have you checked your servo pulse train on a scope?

 

[shaneshane1]

i havent checked the pulse train, im running the 555 of 5V and it twitches a lot, if i run the 555 of 9V it doesnt twitch, the servo is still running of 5V, and the output of pin 3 of the 555 is about 0.40V at maximum, is that normal or should it be higher

 

[Sceadwian]

Something definitely sounds funny. Even if the servo is still only getting 5 volts Giving it a 9 volt servo signal is probably a really bad idea, it may be drawing power from the 555 when the servo signal is high, they weren't meant to be driven that way. How are you testing the voltage? You can't check a pulse trains voltage with a multi-meter.

 

[shaneshane1]

i was testing the output with a multi-meter, lol, im using a 9V battery with a one 5 volt regulator for the 555 and the servo, thats right, right???

 

[Sceadwian]

You can't test a pulse train (the 555's output) with a multimeter. Even a true RMS meter is going to have trouble with the square waves it produces. If you're feeding a 5 volt regulator with 5 volts it's not going to be able to regulate so that might explain things. You really need to provide a schematic of the circuit you have.

 

[jpanhalt]

I bought a new servo, and it works how it is suppose to, so my other servo was stuffed, i have followed the servo pulser diagram on page 1 by blueroomelectronics and it works, but its jerky and twitches a lot,

What type of servo (digital or analog) did you buy? Some digital servos (like JR) are known to twitch when using a simple 555-based driver. I have even seen that with some analog servos, but the twitching stops when connected to a real receiver. John

 

[shaneshane1]

im feeding the 5V regulator with 9V, the schematic is the same as blueroomelectronics servo pulser on page1, exept im using a 5V regulator, i dont know how to put the schematic on these pages anyway, can i just draw it up in ms paint and upload it???

 

[Sceadwian]

Yep, although for line art PNG is better.

 

[shaneshane1]

ill draw one up and show you

 

[shaneshane1]

here is the way i have mine set up, can you find anything wrong with it???

 

[Wingmax]

i cant work out how to put the schematic on the page,its saved to my desktop and its png format?

When you reply the post, on the tool bar on top you'll see the attach icon ( next to the smilie face, click on that, then you'll see another menu. Click browse, upload your file from your PC. I think that's all. But you'll be able to work out from there.

 

[audioguru]

Click on Post Reply then click on Manage Attachements. Click on Browse and double-click on your schematic. Click on Upload and wait for the file's name to appear. Then post it.

 

[shaneshane1]

thanks, here is the way i have mine set up, can you find anything wrong with it???

 

[audioguru]

The ordinary 5V regulator needs an input of 7.5V or more. The 9V battery voltage will quickly drop to 7.2V which is too low. Then the 555 and servo are starved of voltage.

Use a "low dropout" 5V regulator. It is made by all semiconductor manufacturers and still works hine when its input voltage is 5.4V.

The ordinary 555 produces supply current spikes of 400mA when its output switches. Then it drags down the voltage of the 9V battery so the servo is starved of voltage.

Connect a 100uF capacitor across the 9V and 0V terminals on the circuit board to supply momentary current when the 555 switches.
A Cmos 555 like an LMC555, TLC555 or ICL7555 produces a much lower supply current spike.

 

[shaneshane1]

could i run 2 9V batteries in series to the 5V regulator, or is that to much, or will it just operate the same?

 

[audioguru]

could i run 2 9V batteries in series to the 5V regulator, or is that to much, or will it just operate the same?

Simply look at the datasheet. The max input voltage for a 7805 regulator is 35V but a max of 25V is recommended.
Boy oh boy will it get hot with an 18V input and it might shut down when it drives the high current of a servo.
Heat in the regulator equals volts x amps.

 

[Sceadwian]

A 9 volts current producing ability isn't even close to enough for a servo without causing major voltage drops. Basic servo's can draw almost an amp stalled. Try a real power supply.

 

[shaneshane1]

thanks for all the help everyone, i got a brand new 9V battery and it seems to be working perfectly now and i soldered everything up and its working fine, what sort of real power supply do you mean Sceadwain?

 

[Sceadwian]

How about a generic 5 cell battery pack? The servo can get it's power directly from the battery and the 555 can get it's power from the regulator. You may need to use a low dropout regulator though. The tweaking was probably because caused when the servo draw enough current to drop the voltage down bellow the regulators dropout and the 555 started to oscilate with the servo pulses.

 

[shaneshane1]

hi im back, again, i got the servo up and running fine with my schematic, it was all working fine for all of about 10 minutes, now everytime i turn the pot the servo is really jerky, and i mean REALLY JERKY

so i tried changing the battery to a new battery, but still the same result! so then i tried it on the car battery, but still the same result, im not the smartest when it comes to this matter but the only thing i can think of that might be the problem is the 555 and/or the regulator

the 555 on the schematic is a LM555 and im using a NE555 (Dont know the difference) i cant get a LM555, and the regulator is just a fixed 5V , if i turn the pot really slowly the servo works fine, but any faster and it jerks all over the place, and just connecting power through the circuit makes it jerk as well, any ideas anyone???

iv also changed all the parts like 3 times to make sure that none of them were faulty.