Anyone use the Dynamixel AX-12A with a Propeller? Tips?
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Has anyone used Dynamixel AX-12A Servos (Robotic Actuators) with a Propeller? I just bartered into a set of 5 AX-12A servos and a handful of Biolid pieces that should enable making a rather nice robotic arm. These things are really nice but are $45 a piece! However, from what I have gathered so far from the data page, it looks as though I need to be willing to learn quite a bit to make use of them as they aren't just a servo that works with a single PWM signal.
I am only after a simple yet sturdy arm for my underhouse robot project that I started a year ago. My camera will be on it's own pan/tilt setup so the arm will only hold a paint marking pen, a spring loaded probe (to check for dry rot), and the bug spray tube/nozzle. So, I am thinking I don't really need the Hulk version of an arm that these Dynamixels would create. So...........
Should I dive in to how to use these things or save time and hassle and just sell these off to go with a basic arm with standard servos?
Dynamixel AX-12A web page and AX-12A data page
I am only after a simple yet sturdy arm for my underhouse robot project that I started a year ago. My camera will be on it's own pan/tilt setup so the arm will only hold a paint marking pen, a spring loaded probe (to check for dry rot), and the bug spray tube/nozzle. So, I am thinking I don't really need the Hulk version of an arm that these Dynamixels would create. So...........
Should I dive in to how to use these things or save time and hassle and just sell these off to go with a basic arm with standard servos?
Dynamixel AX-12A web page and AX-12A data page
Comments
The links in that post are broken, so here's another thread: http://forums.parallax.com/discussion/122369/dynamixel-ax12
And another: http://forums.parallax.com/discussion/153927/anyone-using-the-dynamixel-ax12a-servo
There is this in the OBEX: http://obex.parallax.com/object/152
Anybody have any experience here?
Ken Gracey
The issue I had were with MX servos running on the AX code. The AX worked perfectly with JM's code in this thread - http://forums.parallax.com/discussion/153927/anyone-using-the-dynamixel-ax12a-servo
If you are using the MX, the notes toward the bottom of that thread are the only modifications you would need.
I have an AX-12A, MX-28, the USB programmer, and would be happy to help anyway possible.
To answer the original question, the AX-12A would be a vast improvement over regular servos. Whether or not the cost is worth it, probably depends on what the arm is doing. What did you have in mind?
The AX12x supports continuous mode. You can set a goal RPM and it will do its best to maintain it. I would go with AX-12W, they make better wheel motors vs. joint actuators - http://www.trossenrobotics.com/p/ax-12w-dynamixel-robot-servo.aspx
I can measure the precision of the RPM with an AX-12A if you're interested, I don't own any AX-12W, though.
Ah. I misremembered, then. I recall not being able to get either servo to work. But that was probably because you asked me for help. You'll know better next time!
It's worth mentioning, the connectors on the Dynamixels are not what you'd find on servos. This is the connector that plugs into the Dynamixel, http://www.mouser.com/ProductDetail/Molex/50-37-5033/?qs=AplfTeSvkkCfnVdKv8UuEg==
My rover5 with ax-12 and standard micro servos for the gripper. Went with standard as they are lighter and smaller and it was an old lynxmotion gripper I had on the shelf. Working software archive attached. Its for my controller which is XBee based. Build Link for the bot.
The project that I just started is an ax-12 prop based hex using a prop board i made. I recently got a 3d printer so I'm printing alot of it. My progress in spare time is the bottom plate and battery shroud. Started 2 weeks ago plan to move the legs this weekend and design a top plate. Im keeping the the bioloid brackets just printing my own tibias.
Take a look at the code it's an IK-Arm code for the configuration in the first pic. This work is 7 years old, updated for the pwm portion of the code. It works i'll get it working as I need to drop an xbee into and I'll post a video. Agave robotics started working prop ax-12 but they gone. I use Dan's code and have John's version but never tried it.
Put the Ax arm on your bot. Super strong and worth the effort. I have to dig thru some old back-ups to find the cad files on the plates for the arms.
Xanadu, thanks, that was the thread that I settled upon as having the most information. I noticed the code there is updated from the OBEX release.
As for what the arm is doing, it will be holding the spray nozzle for a tube feed of bug spray, paint marking pen, and a spring loaded probe for checking for dry rot. The idea is something that looks like the "Inspection Robot with 24” Arm" picture as shown half way down on this page at InspectorBots. I am thinking maybe a 16" arm would be fine for my needs. This post on the thread I mentioned before has pictures of the bots that are the inspiration for the total setup.
Ray/Gordon, thanks for the other links and info. I do believe I need to look into them more before I make a decision. There isn't a lot of info on the forums.
Paul, the arm on your Rover5 looks along the lines of what I am after. If you can find the files for the arm links, I would like to see them.
I had something similar. I remember getting around 0.5" of repeat accuracy with the cheapest servos available. I think 90% of the wear and tear on my standard servo arm came from powering it on. The AX don't flop around when you power them up, another bonus for an arm.
If you took an average servo at $30, added the current protection, feedback and a power up circuit to stop it from flopping around you're at the $45 price for an AX. If you go with $10 servos it would work fine, just not as well, and less reliably.
The 6 pack for $200 puts the AX-12A at $33.33 each. I don't see how that can be beat with standard servos.
If you're getting them less than that on a barter I say go for it, you're in for a real treat if you're used to working with standard servos.
One weird thing about the AX, and it could be PEBKAC, is that when I send it to a goal position it will stop near that goal but not on it. For instance;
The above will get stuck inside of the loop, even with an unloaded servo. However, I found this to work fine;
Those couple of ticks translate to a tiny little bit of travel, nowhere near the slop in a standard servo.
If you ever plan on putting the camera on the arm, the AX would be the way to go. I think the standard servos would vibrate the camera. The AX can hold their position well without using a lot of current which will add some run time.
If you decide to go Robotis, and need the programmer, let me know I'll ship it over. I only needed it until I was familiar with everything, and especially for the MX programming troubleshooting. Anyway, I don't think I would use it again.
Here's Mr Floppy arm -
Regarding the issue you mention with the goal position. This is due to the compliance margin setting in the servos. The default is 1 in either direction, so the servo will stop motion when it is within 1 of the goal.
The "Punch" setting may also impact the stopping position relative to the goal position, depending on load.
Thanks, makes sense now. I will check that out.
I don't know if they use different pots in models intended for use with wheels but I avoid using pots on joints getting a lot of movement.
BTW, I am using my phone to post this. My internet is down until probably Thursday. I am not likely to post to forum often (if at all) untill then. And yes it is driving me crazy!
I think there is an Omni bot video in my "Fun with Spin" playlist.
IIRC I had to tweak the speed settings to get the robot to "spin straight".
Since I have 5 servos, a thought is that I could use 3 for the arm and 2 for the pan/tilt for the camera. I may have to make some mounts or brackets to make it completely work, but I have access to two different laser cutters and a CNC. (I'll be dangerous once I get up to speed in Fusion360)
Thanks for offering the programmer. The code I looked at appeared to have commands for reprogramming the IDs of the servos but not much else, so a programmer would be a major plus. I'll keep you posted....
Duane: is the 3 wheeled omni bot you mention this one?
https://www.ebay.com/itm/123296775306