Controlling 12 servos with my Propeller
fancychance
Posts: 4
Hi! I'm working on a quad walker robot that is going to have 3 servos per leg. My problem however is getting each servo hooked up to my board in an efficient manor. I'm using a Propeller board and I also have a 16 channel Adafruit servo controller, but the servo shield hasn't been working for me. How do you connect all your servos to one board for your robots? If you could help shed some light on interfacing all my servos that would be awesome. You'd definitely earn a spot on my thank you list when this project is done Thanks a bunch!!!!
Comments
http://forums.parallax.com/showthread.php/160137-Connecting-Servos-To-a-Propeller
Which Propeller board are you using?
http://obex.parallax.com/object/320
I don't see much of a use for the servo shield if you have enough free pins on the Propeller. Using a shield you have to send all the servo positions to the controller. IMO, it's a lot easier to let the Propeller handle the servos directly.
The Propeller Activity Board (PAB) has six servo connections. You can add another six connections to the breadboard. When using servos with a breadboard, I have the ground pins from two servos overlap so two servos take up five rows of the breadboard. There's room for three servo connections on each side of the breadboard.
You'll probably need some way to power the servos. I don't think the PAB's 5V regulator can provide enough current for 12 servos. There are lots of 5V switching regulators available. I think I mention a couple options in my hexapod thread (IIRC). If you read through the hexapod thread, you'll see some of the debate about using battery power directly with the servos. A lot will depend on which servos you use.
If you wanted to keep the PAB's breadboard free for other uses, you could add your own breadboard to connect the servos. There's also the option of having small servo expansion boards made through OSH Park. In the thread I started on the topic of connecting servos to the Propeller, there's a link to the Gerber files I submitted to OSH Park. These are the same servo expansion boards used on my large hexapod (my hexapod uses a total of 24 servos). As mentioned in the other thread, it's also easy to make servo expansion boards from perfboard and some male headers.
Not that there's anything wrong with Jon's driver, but there's already a driver in the Propeller Tool library which can handle 32-servos with a single cog.
01 Mechatronics has developed an electronic that replaces the control-circuit inside the servo
it's called the super-modified servo
http://www.01mechatronics.com/product/supermodified-v30-rc-servos
the motion-feedback is based on a rotational encoder that measures the rotational angle of a magnetic field.
(somebody here in the forum has done some work with this magnetic encoder but I don't remember his name)
It enables continous rotation with precise control of angle and speed
I guess for a pod-robot standard-servos will do. If you want more precision these servos might be an option
but has its price.
best regards
Stefan
Was it this guy?
He had some [url="
http://forums.parallax.com/showthread.php/140104-First-Magnetic-Encoder-PCB-Attempts"]PCBs made for the encoders[/url] which were the same size as the pots in the servos.
There are several other forum members who have posted information about magnetic encoders.
I think adding encoders to servos is a cool idea but it greatly increases the amount of work one has to put into a project using servos. It also makes any project using lots of servos much more expensive.
The 7805 regulators might work but you might need several of them. IMO, you're better off not using the regulators in parallel. I'm not sure about the 7805, but some regulators don't work well when used in parallel.