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Fabiano77
04-29-2015, 03:23 AM
Hallo

i'm new to the robot scene. I have buy this 17 dof kit
http://de.aliexpress.com/item/17DOF-Biped-Robotic-Educational-Robot-Humanoid-Robot-Kit-Servo-Bracket-Ball-Bearing-Black/32243442240.html

I use the Mg996r servos and a arduino mega.
i power it with 2x 6v 2850mah akku.
it works good but i have problems with the vibration.
When the robot stand i have no vibration, but when he walk or only one servo change position it vibration.
I have testet with one servo and 2x 6v and i have the same problem .
need i a controller? Or are the servos are bad?
What can i do?

thanks for helping me
Fabiano77

jwatte
04-29-2015, 08:49 PM
With "vibration," do you mean servo "buzz"?

If so, that's a common problem, especially with cheaper hobby servos. They aren't that good at keeping a position under certain forms of load, and there is no way to read data back from them or configure them.

Getting a higher-quality servo might help. The "real" solution is to step up to servos that allow you to control the internal parameters (typically, PID parameters,) using a computer connection.

Fabiano77
04-29-2015, 11:18 PM
Yes i mean the buzz. Ok so i must buy another. What servo can i buy for this height and weight?? I will buy direktly servo where can more than this for bigger projects in future. I found the dynamixle ax 12a, ax 12w , ax 18a, mx-24. what is the best solution for this hobby robot and cheap.
Will the ax12a work good ? And have the ax-serie metall gear?

jwatte
04-30-2015, 11:48 AM
The AX12A uses plastic gears, but is an excellent servo for the price.

That the difference between metal and plastic gears is not as big as certain hobby vendors want you to believe, depending on the specific use case and load. Many successful humanoid robots have been built on the AX12A. "metal" gears that are cheaply cast will generally perform worse than precision high-quality plastic gears. Precision hobbed metal gears (the kind you really want) won't be found in a $40 servo. But are found in the $200-and-up MX series. (At least I think they're properly hobbed -- or very very well cast -- tician will probably correct me if I'm wrong :-)

The AX12A probably doesn't fit the frame set that you have, though -- you'd need a new frameset. One way of getting servos and frames all together is to buy the Bioloid Premium kit.

Other options include:
- Bioloid Premium -- $1200 -- a great entry level platform (AX-12A servos)
- Darwin Mini -- $500 -- smaller size (XL-320 servos)
- Bioloid GP -- $2800 -- same size as Premium, but with significantly faster servos (AX-18A)
- Darwin OP -- $12000 -- bigger robot, more advanced servos (including metal gears, absolute encoders, etc) (MX-28T)
- HR-OS1 -- $1600 -- "smarter" humanoid based on AX-12A servos.
- Hovis Lite -- $730 -- based on the Dongbu smart servos (DRS-0101)
- Hovis Eco Plus -- $1000 -- like a Hovis Lite with a shell

The Dongbu servos seem competetive with the Robotis servos at the low end ($20-$150), but the Robotis servos are superior in the middle end ($150-$500) because the absolute encoder resolution used in the Robotis MX servos is better than the relative encoder plus potentiometer used by the Dongbu.

I very recently put together a Darwin Mini, and it's a really fun little dude. Or dudette -- haven't made up my mind yet. It comes with the OpenCM-9.04 controller, which can either run pre-programmed software to move, dance, and box, or you can make poses/motino using the RoboPlus software, or you can program it yourself with an Arduino-like IDE on your computer. (I'm typically attracted by that last option; your needs may vary.)