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Electronics => Electronics => Topic started by: Alfa_Zulu on June 15, 2010, 12:11:27 AM

Title: Using NE555N For Servo Driver
Post by: Alfa_Zulu on June 15, 2010, 12:11:27 AM: hey,

I had the idea of using a 555 timer to output a pulse to control the position of a servo using a variable resistor to control the pulse. I didn't have any 8pin sockets laying around at the time so i soldered it straight in and the fastest pulse i could get was around 2Hz opposed to the 50Hz i believe I need to make it go to 0 degrees so i think maybe i overheated it (it also made a strange sound while soldering) so today I bought a couple of sockets and I'm going to attempt it again today.

could someone please advise me if I'm on the right track, Thanks

-Alfa
Title: Re: Using NE555N For Servo Driver
Post by: Alfa_Zulu on June 15, 2010, 01:14:23 AM: ok this is the circuit I'm using, C1 is currently a 10uf cap which i think is apart of the problem, I found a 1uf cap and I'm about to put it in the circuit.

this is a modified circuit I used before and it looked like it was running at around 50Hz

Thanks in advance

-Alfa
Title: Re: Using NE555N For Servo Driver
Post by: jka on June 15, 2010, 03:01:18 AM: Take a look at http://www.horrorseek.com/home/halloween/wolfstone/Motors/svoint_RCServos.html. (http://www.horrorseek.com/home/halloween/wolfstone/Motors/svoint_RCServos.html.) It has some info on servos and a couple of schematics involving 555's and servos. I haven't tried any of them, though.
Title: Re: Using NE555N For Servo Driver
Post by: amando96 on June 15, 2010, 04:50:49 AM: the values seems a bit high for what you want to do.
Title: Re: Using NE555N For Servo Driver
Post by: Alfa_Zulu on June 15, 2010, 05:22:40 AM: what values would you suggest?
Title: Re: Using NE555N For Servo Driver
Post by: amando96 on June 15, 2010, 06:19:07 AM: (http://www.hvlabs.com/Images/555servo.jpg)
Title: Re: Using NE555N For Servo Driver
Post by: Soeren on June 15, 2010, 06:15:55 PM: Hi,

Quote from: amando96 on June 15, 2010, 06:19:07 AM
(http://www.hvlabs.com/Images/555servo.jpg)
This circuit, as it stands (practically unchanged from Tonys old circuit (http://www.sentex.ca/~mec1995/gadgets/servo3.htm) that they nicked, without even a mention)), covers a pulse time range of 0.73ms to 1.46ms, so it will only cover less than half of the 180° servo travel (it won't even zero correctly unless component tolerances stretch the time a bit). Well at least HVLabs have noticed that it won't go 180°, but apparently they didn't manage to corret it.

For 1.0ms to 2.0ms change both R1 and X1 (the pot) to 3k7.
To handle most of all (R/C) servos out there, use 0.6ms and 2.4ms as the extremes (R1=2k2 and X1=6k8) and just keep within the range of the servo being tested (to avoid banging the end stops).
Title: Re: Using NE555N For Servo Driver
Post by: Alfa_Zulu on June 16, 2010, 04:49:26 AM: thanks Soeren, helpful as usual.

i might look at the previous schematic shown by amando96 with the increased resistor values.
Title: Re: Using NE555N For Servo Driver
Post by: amando96 on June 16, 2010, 07:20:54 AM: Yeah that wasn't the schematic i had seen before, i think it was by david cook, "robot room" but couldn't remember what it was then.