View Full Version : [Question(s)] I am using arduino uno and want to make 3 dof quad walker

War Wolf
01-22-2014, 08:06 PM
I was inquiring if anyone else has attempted this and what other components besides servos and frames would I need to obtain including any shields to accomplish this project physically coding aside?

War Wolf
01-22-2014, 08:13 PM
Please keep in mind I am on an extremely tight budget and am only attempting this for my son who has seemed to fall in love with the mech warfare competition

01-22-2014, 08:54 PM
Yeah, I had that too. I was all happy building a rover for Robo-Magellan, and then my youngest fell in love with Mech Warfare. And... well, that was two years ago, and soon I'll have a working robot :-)

If you're on a tight budget, you can actually make a 2DOF quad walker! In fact, I would recommend a 2 DOF quad walker with reasonable-quality servos (Dynamixel AX-12 or Dongbu DRS-0101) over a 3DOF with lesser-quality servos like your typical RC hobby servo clones.

If you're on a REALLY tight budget, then I would recommend looking into the "twitch MX" style robot, which needs only 4 or 5 servos. If you use AX-12 you can probably build that for under $200 (before guns and camera.)

So, which shields, and other equipment, you may need, would depend on which kinds of servos you go with. At a minimum, you need a battery for the servos -- a 1000 to 1500 mAh LiPo with 2S or 3S configuration (7.4V or 11.1V) most likely, depending on servos. You also need some kind of connector junction to inject power to the servos, and separately split it off to the Arduino. You cannot draw servo power from the Arduino power-out. Then you need some kind of connector to actually talk to the servos. For Dongbu servos, there is just electrical connection; for Robotis servos, you need a bi-directional buffer (which may exist on a shield?) For RC servos you need headers for each of the servos, wired to pins on the Arduino; there may be a "servo shield" of some sort that deals with this.

Then you need some remote control -- most likely a Xbee serial adapter, which means that the serial port on the Arduino would be double-booked if you're using Dongbus or Robotis, so perhaps use SoftwareSerial and a low data rate for that. It still wouldn't be great, though.

If I were to recommend something, I'd suggest the OpenCM9.04-B instead of the Arduino. it's about the same price (or cheaper, if you go with -A and buy headers and solder in separately,) and it already has the right connectors for the AX-12A servos. Add a 6-port Dynamixel hub for splitting to the quad, and inject power by cutting one connector wire in half. Drawback: there are no ready-made shields for the Xbee, so you'd have to wire that in yourself. The OpenCM can be programmed with a variant of the Arduino IDE that you download from Robotis.

Another option is to use the Arbotix-M controller, which already has space for an Xbee, AND has output for Dynamixel servos, AND has outputs for RC style servos if you want to use those instead, AND is Arduino compatible for the software side (but not for shields.) Going this way may be easier and cheaper than trying to make the Arduino itself do the job.

Anyway, it mostly depends on what level of electronics and mechanics skills you have, and what particular kind of servos and 'mech you'd like to go with.

01-22-2014, 09:05 PM
Compared to the cost of servos, the extra $10 to get an Arbitix over an Uno is negligible and well worth it.

War Wolf
01-22-2014, 10:42 PM
I really appreciate the responses I will try what I can with the arduino at first a friend of mine is a wiz at programming I have a bit of electronic knowledge a bit rusty I must admit a friend of mine gave me a motor shield from radio shack whose literature claimed to be able to run im unsure at the moment but it was 10 or 16 servo motors I have it in storage but has anyone encountered this particular shield and are its claims true or just fluff could said shield be possibly used for this project or would it be a waste of time to try?

War Wolf
01-22-2014, 10:49 PM
Should my arduino attempt fail I will certainly attempt the strain on my already tight budget (wife is on my neck already ) and go with your other suggestions jwatte and txb dan

01-23-2014, 09:34 AM
Note: I think you are probably best off with most projects like this with high quality servos like the AX-12. But yes you can make a good robot using RC servos, such as ones from Hitec. Personally I would not use any of the low quality knockoffs, but that is just me. An example 3dof Quad is: http://www.lynxmotion.com/p-881-symmetric-quadruped-kit-botboarduino.aspx
Personally I now prefer the PhantomX... But the other one does show you an example with RC servos...

Not sure which one you have, but a few years ago, I purchased a Servo shield (http://www.renbotics.com/servoshield.php), which supported 16 servos. I actually hacked one up to run 18 servos. These use a couple of decade counters to control the servos... There were some issues with the library at the time, which I fixed and then it worked fine in my quick testing of the board. Much easier and more support if you use a secondary board like the Lynxmotion SSC-32 board to control these servos.

As for control boards, I am all over the place. As for Arbotix over Uno? It depends. Yes for AX-12 type servos I would consider it, but may also consider the new Robotis board. I am also playing with Teensy 3.1 board for controlling AX-12 servos. For RC servos, maybe not as no support for your RC servo shield. Would also consider Lynxmotion Botboarduino as it is like the UNO, but has extra stuff, like power connections and the like.

But if you already have the UNO and the Servo shield and some servos, try them out and see as there have been a lot of cool projects done with this type of setup.

01-23-2014, 03:57 PM
Six AX-12 with a TwitchMX design is cheaper than 14 RC servos. (Price of AX-12: $40; Price of RC servo: $20)
Note that I assume you need 2 servos for aiming in addition to locomotion servos.

War Wolf
01-23-2014, 05:19 PM
Thank you guys for all the insight. I was planning on making the leg portion and turret portion separately. And I do plan on having at minimum a pan tilt ability for the turret. Again. Thank you jwatte and to you as well kurtEck