Arduino Forum

Topics => Robotics => Topic started by: DustBandit on Sep 06, 2011, 06:45 pm

Title: 360 Degree servo or stepper motor
Post by: DustBandit on Sep 06, 2011, 06:45 pm
Hi Guys

I have been reading this forum for the last 2 days and while being more informed about stepper motors and drivers and 360 degree servos, I am also more confused on what to do.
I need to get a servo or stepper motor to turn a gearbox control shaft in a rc car 360 degrees in 60 degree intervals, both ways.
The setup will be controlled by a 3 position on/off/on momentary switch on the Tx - if I trigger the switch in on direction the servo/motor must move 60 degrees in one direction and stay there. Trigger the switch again in the same direction and the servo/motor moves on another 60 degrees. The same will be true for the other direction. So this means I will be using the Hi/low value from the rc channel to determine direction.
From what I have read here, a servo modded for 360 rotation will not work as it will not give you you precise stops - which means I will have to go with a stepper motor.
My question to you guys please:
are these the components I will need for this project?
http://www.pololu.com/catalog/product/1202
http://www.pololu.com/catalog/product/1204
http://www.pololu.com/catalog/product/1615
http://www.pololu.com/catalog/product/1210
Also, the motor must stop when reaching 360 degrees and only be able to move back to 0 degrees in reverse steps, stopping at 0 degrees again.
Any help and ideas welcome and appreciated.
Title: Re: 360 Degree servo or stepper motor
Post by: keeper63 on Sep 06, 2011, 11:07 pm
Check out servocity.com - they may have something in a modified servo (but not -continous rotation-) that will allow for 360 degree rotation - for instance, the following (though for your application, the size may be an issue):

http://www.servocity.com/html/spg400a-4_3_360o_rotation.html
Title: Re: 360 Degree servo or stepper motor
Post by: DustBandit on Sep 07, 2011, 12:55 pm
Thanks cr0sh

I had a look, and yes, the size will not work.
Title: Re: 360 Degree servo or stepper motor
Post by: Nabe_RMC on Sep 07, 2011, 01:44 pm
How do you use SAIL WINCH servo for RC yacht ?
http://twitvideo.jp/04wLP (http://twitvideo.jp/04wLP)
http://www.gwsus.com/english/product/servo/s125.htm (http://www.gwsus.com/english/product/servo/s125.htm)
Title: Re: 360 Degree servo or stepper motor
Post by: DustBandit on Sep 07, 2011, 02:11 pm
The video seems interresting apart from the fact that I can't read what is wriiten there. It seems that the servo is moved by a pre-written program - I need the sevo to only move 60 Degrees when triggered - I have gathered that I need a controller to convert the signals from the rc tx to 3 digital signals 1 for the trigger and the 2 for the direction. I then need a servo/motor driver to turn the servo or motor the requiered amount of degrees in the correct direction from the inputs it receives from the controller.
i just need some one to please tell me what  controller and driver to buy for this application, and some one to help me write the code for it.
Title: Re: 360 Degree servo or stepper motor
Post by: Chagrin on Sep 07, 2011, 03:59 pm
A sail winch servo would give you the 360 degree rotation you need. It would be controllable by either an Arduino using the Servo library (http://arduino.cc/en/Reference/Servo) or by any RC transmitter/receiver. Here's an example (http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXAURN&P=0) that has 720 degree rotation; try Google to find other sizes/models.

The only difference between controlling a standard servo and a sail winch servo is that the sail winch will travel a greater number of degrees than a standard servo.
Title: Re: 360 Degree servo or stepper motor
Post by: Nabe_RMC on Sep 07, 2011, 05:19 pm
Quote
i just need some one to please tell me what  controller and driver to buy for this application, and some one to help me write the code for it.

If you use RC servo then you don't need driver.Because RC servo has built-in amplifier.
As controller,  you can use Arudino.
That video - "60sec timer"
http://twitpic.com/6he6pa (http://twitpic.com/6he6pa)
The code is only 20 lines.
That's Arduino!
But, do you want to roate same direction over 15 * 360deg?
and how to request angular accuracy?
GWS's servo - MAX 15*T ? ( TURN ) <- I think angular accurasy is poor.
http://www.gwsus.com/english/product/servo/s125.htm (http://www.gwsus.com/english/product/servo/s125.htm)
Title: Re: 360 Degree servo or stepper motor
Post by: DustBandit on Sep 07, 2011, 08:04 pm
Thanks Nabe_RMC

I seem to get some where now. It seems that i can use the arduino nano to read a pWM hi/low signal from the rc rx and the nano can also drive the servo directly.
My only concern now is if I can progran the nano to advance the servo 60 degrees at a time when triggered.
Title: Re: 360 Degree servo or stepper motor
Post by: Nabe_RMC on Sep 08, 2011, 06:52 pm
We can get the datasheets for RC servo control IC.
"M52461GP"  Classic
http://www.datasheet4u.net/share_search.php?sWord=M52461GP
"M64611fp" is called "DIGTAL" in Japan
http://www.datasheet4u.net/share_search.php?sWord=M64611fp
Perhaps we roate the RC serevo same direction continuously by giving unspecified long or short pulse.
We may realize it by lookking at the data sheet.
But the RC servo is limited to a continuous rotation in the same direction from the mechanical structure.
In the RC servo potentiometer that is used to detect the position.
http://cumic.exblog.jp/12953026/
http://www.exblog.jp/blog_logo.asp?slt=1&imgsrc=201007/15/65/e0164065_1645314.jpg

Without turning in the opposite direction, Do you want to turn over 360 degrees in increments of 60 degrees in the same direction?
To achieve it may be dfficult with RC servo.
I'm sorry for my remarks so as to be expected.
Title: Re: 360 Degree servo or stepper motor
Post by: DustBandit on Sep 09, 2011, 07:12 pm
Have a look at this video. This is what I am trying to get to, only 360 degree travel at 60 degree intervals and trigger from a pwm signal.
http://www.youtube.com/watch?v=Ly5aSqmeAeM
Title: Re: 360 Degree servo or stepper motor
Post by: AWOL on Sep 10, 2011, 02:46 pm
Trigger what with PWM, and using what criteria of the PWM signal?
Title: Re: 360 Degree servo or stepper motor
Post by: Nabe_RMC on Sep 10, 2011, 05:39 pm
Quote
This is what I am trying to get to, only 360 degree travel at 60 degree intervals and trigger from a pwm signal.

like this? I tried.
http://www.youtube.com/watch?v=IyzzIU2Xc2c

Here is the structure of the turntable.
Please watch this video 2:15 later
http://www.youtube.com/watch?v=DS9-59UHg-o
And It's easy to decode the PWM signal from a RC receiver.
"Decode RC Signal by one-chip micro controler"
sorry Japanese only
http://homepage3.nifty.com/tlgjpn/neo/tech/rc_receiver.htm
Title: Re: 360 Degree servo or stepper motor
Post by: terryking228 on Sep 20, 2011, 11:45 am
Hi,
There are a couple of approaches that may work:

- Mechanically couple a standard servo with, say, 120 degree rotation with a 3:1 ratio, using gears or two small spools/drums and thin strong string like braided fishing line. Then  each 20 degrees of servo movement gives 60 degrees on your shifter. calibrate values for each position and put in your arduino software.

- use a continuous rotation servo directly coupled to the shifter. Make a disk with holes 60 degrees apart and use an opto-interrupter or IR LED and Phototransistor to detect when in position. Count and keep track of position. Add microswitch to disconnect servo power if a fault causes rotation to unallowed location.

Have fun, and please let us know what works out!