Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: foxawax on April 15, 2010, 01:44:37 PM

Title: what servo to use?
Post by: foxawax on April 15, 2010, 01:44:37 PM: Hello hello,
I am deeply struggling guys, :-\
To illustrate, I want to move
the head of my robot from straight (position 0) to left (90 degrees) to
right (90 degrees);So a total of 180 degrees rotation with a starting point at 90
degrees.
Basically the same mvt as a human neck, horizontally.(later I will move up/down too)
I will controll the servo with a CIRRUS 3 CSX,40MHz FM 3 CHANNEL TRANSMITTER
Could you please tell me what kind of servo would be the best for my project? without special settings from the transmitter?
I've already tried to modificate servos by adding resistor but...I ve BURNT THEM ALL :'(
The best solution would be a ''servo stretcher'' but I cannot find any supplier in UK.
Oh, and I cannot afford a 50 quids servo either..
Please if you have a solution, you are welcome..
Thanks for your help,
>Regards
>Pierre
Title: Re: what servo to use?
Post by: chelmi on April 15, 2010, 02:57:57 PM: Maybe I'm missing something, but any "standard" hobby servo (HS311,...) could do that.
And you don't need to modify since your not looking for continuous rotation.
Title: Re: what servo to use?
Post by: foxawax on April 15, 2010, 03:23:33 PM: So I am too!
Manually, I can rotate the servo from 0 to 180 degrees but once it's plugged, when I push or pull the trigger of my controller, it only does 45 degrees in each direction..
Bizarre Bizzare ??? indeed..
That's probably what the stretcher is made for (extend the rotation) but can't find any in UK!
Thanks anyway ;)
Title: Re: what servo to use?
Post by: amando96 on April 15, 2010, 03:32:11 PM: your remote should have a potenciometer to control the range of motion, my cheap 2 CH kyosho perfex can give me 180 degrees of motion, or just 30 degrees of motion, and all in between, on both channels.

i'm not sure, maybe you can't see yours, it could be internal or something?
Title: Re: what servo to use?
Post by: foxawax on April 15, 2010, 04:20:48 PM: My Tx is the following:
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180486657753&ssPageName=STRK:MEWNX:IT (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=180486657753&ssPageName=STRK:MEWNX:IT)
and I am pretty sure that it doesn't do it, not all all of them does actually..
:-\
Title: Re: what servo to use?
Post by: Razor Concepts on April 15, 2010, 05:23:29 PM: I agree with foxawax, not all transmitters are capable of moving the servo from 0 to 180 (most actually cant, since for RC use only 90 degrees or so of motion is desired).

You could use linkages to make it turn more.
Title: Re: what servo to use?
Post by: Soeren on April 16, 2010, 05:13:46 PM: Hi,

Here's some data I found when Neils servo (an HS311) would only do 90° total movement with 1ms to 2ms:

For 180° total rotation:
Futaba will need 0.25 to 2.50 ms,
Graupner will need 0.6 to 2.4 ms ... with awful non-linearities by the extrema ...

HS-311
0.5 ms = 500 us : 0 degree
1.5 ms = 1500 us : 90 degree
2.5ms = 2500 us : 180 degree

I don't get the reason, but everybody seems to wanna break the standards.

...Forgot to mention:
Just change your code to whatever min. and max. times are needed - it sure cured the HS311 issue.
Title: Re: what servo to use?
Post by: chelmi on April 16, 2010, 05:32:40 PM: Quote from: Soeren on April 16, 2010, 05:13:46 PM
...Forgot to mention:
Just change your code to whatever min. and max. times are needed - it sure cured the HS311 issue.

He is using a transmitter
Title: Re: what servo to use?
Post by: Soeren on April 18, 2010, 12:15:05 PM: Hi,

My bad, then either finding a servo that keeps to standards, a pulse stretcher (whether bought or built - a PIC10F2xx would be quite enough for this), or changing the potentiometer in the servo to half the value of the existing one.