Pan Tilt suggestions.

[Loriath]

Hello Everyone, I am new to the robotics side of things but have been interested ever since we dabbled in it during one of my college classes.

I've read the following tuts generously provided by SoR:

(Servo tut)                   http://www.societyofrobots.com/actuators_servos.shtml
(DC motor tut)              http://www.societyofrobots.com/actuators_dcmotors.shtml
(Electronics 101 tut)      http://www.societyofrobots.com/electronics_basic_components_tutorial.shtml
(FAQ)                          http://www.societyofrobots.com/robot_faq.shtml
(servo control atmega8) http://mil.ufl.edu/~achamber/servoPWMfaq.html

I plan to use an atmega8 because i've used them before in college, or trying something new with atmega168.

what my long term goal is to create a Remote Sentry for nerf, or airsoft or something like that, that tracks movement and fires whatever projectile i decide when the time comes, at the center of the mass the camera pics up. If the target is moving calculate the velocity and lead the target by so much. I know this is way to advanced for me as i'm new to this, so i'm starting small, a simple pan tilt function that allows me to manually adjust the horizontal and vertical direction of a web cam through a laptops keyboard. A fair degree of precision is required so a Servo would probably be best, but after reading the above tuts i'm not 100% sure on how to go about rotating a servo say 2 degrees or whatever value i decide to move it. All of the tuts i've found say that depending on the length of the high (5v) signal entering the servo determins its position. for example if its an 180 degree servo, 1ms would be at 0 degrees or left, 1.5ms would be at 90 degree or middle, ad 2ms would be at 180 degree or left, but how would you get it at 182 or 176 for examples? Any help would be completely appreciated, like I said im new to this but would really like to get into this wonderful hobby.

[SmAsH]

well, you would have to tweak the servo pulse length...
like instead of 2ms, you might have 1.75ms etc... that is the easiest way to do it that i can see.

[Ro-Bot-X]

Servos rotate from 0 (far left) to 180 (far right) degrees. If you try more, you might damage the servo. As for calculating the pulse per degree, it's easy. You specify the pulse lenght in microseconds, so for a full sweep (180 degrees) the pulse goes from 1000us to 2000us (sometimes actually the timing is different, like from 500 to 2500, you need to experiment with your servos). You divide the difference by the number of degrees traveled and you get the pulse lenght per degree, in this example 1000/180=5.5555. That means you can increment the pulse lenght by 5.5us to step one degree.

[Loriath]

Thank you  muchly . I kind of figured it was that simple. Do you guys think servos would be the best bet for my pan tilt project? After my reading I believe they would be but it never hurts to get someone elses idea.

[SmAsH]

Do you guys think servos would be the best bet for my pan tilt project?

id say yes, the only other kind of actuator i could consider for this is a stepper motor... but they're annoying...
i think servos will do just fine for this, about how much are you moving?

[Loriath]

2.9 Lbs for the paintball gun (but thats still a ways away) and about .5 lbs worth of paint balls. so 3.5-4 lbs all together. a servo should be able to move that if im not mistaking

[SmAsH]

just to be safe you should look for a servo with double that...  and remember one of the servos will have to be stronger than the other as it has to take the other servos weight too.

[Loriath]

ok thanks a bunch! any suggestions for sites that sell servos that will support that weight?

[SmAsH]

heaps, ebay, servocity and almost all robotic parts sites... http://www.societyofrobots.com/robot_parts_list_motors_servos.shtml
but make sure you shop around! some places will rip you off badly, also make note of shipping prices, they get you on those too...

[Loriath]

So i have been doing alot of research on servo motors and what one i should be using for my project. Im looking for a servo that can support about 8 Lbs and have a really quick reaction time. Im looking for something that rotates fairly quickly. I want it to be able to change angles really quick, or change poition really quick like the turret in this video

http://www.youtube.com/watch?v=RxBa5bQfTGc

that is my end goal, obviously not doing all that at once, but just getting the pan tilt going with manual controls. Anyone give me some suggestions on how to find the right servo motor for my project?

[SmAsH]

Anyone give me some suggestions on how to find the right servo motor for my project?

yep, just look through the datasheets and specs and see if they're what you want.

[Loriath]

I know that but in the data sheets when it says torch it says for example 3.3kg/cm torch does that mean it supports 3.3 kg of weight on it while turning? i dont really understand that. Also when doing video processing using webcam would a logitech QuickCam® Pro for Notebooks or the QuickCam® Pro 9000 be a good choice? at work i get products at 10% above cost so I can get either of these cameras at around $100. I cant afford the blackfin camera which seems to be popular when it comes to video processing. Any more help from you guys would be appreciated.