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### Topic: help needed for humanoid (Read 3918 times)previous topic - next topic

#### mohitgupta322

##### Oct 10, 2011, 10:15 am
Hello there!
I am making a humanoid robot with arduino uno and Android........ I want to ask several question....ie

1how I choose the servo motor I mean how to calculate the torque needed
2) can and how I connect 10 servo to arduino uno and bread board with seperate powersupply
3)any good tutorial on humanoid structure (not biped plzz..ie not only legs)just for reference

#### PaulS

#1
##### Oct 10, 2011, 04:13 pm
Quote
how I choose the servo motor I mean how to calculate the torque needed

Torque equals force times distance. How much does that you want to move weigh? That is the force. Where is the center of gravity of that object with respect to the point it rotates about. That is the distance. Multiply those two values to get the needed torque, then double that to account for friction, etc.

Quote
can and how I connect 10 servo to arduino uno and bread board with seperate powersupply

You can connect 10 servo control wires, and the common ground wire to the Arduino. Connect the power supplies + side to all 10 servos, and the - side to all 10 servos and the Arduino's ground pin.

Quote
any good tutorial on humanoid structure

Well, you see them all over the place, don't you. Shouldn't be too hard to make one.

#### mohitgupta322

#2
##### Oct 10, 2011, 06:02 pm
How do I find center of gravity

#### Grumpy_Mike

#3
##### Oct 11, 2011, 12:18 am
Find the balance point in two orthogonal directions, the intersection of these is the centre of gravity.

#### cr0sh

#4
##### Oct 11, 2011, 01:50 am
1) how I choose the servo motor I mean how to calculate the torque needed

Well - you've already got the answer to this - but I will advise you on something else:

Buy servos with dual-ball bearings on the output shafts with metal gears. Sure, it's a lot more expensive up-front to do this; but with a biped and the load (lots of side load) on the shafts, if you don't, your decision to go "cheap" may end up costing you more in the long run than if you had spent the money on the more expensive option in the first place.

IOW - don't be "penny wise and pound foolish"...

2) can and how I connect 10 servo to arduino uno and bread board with seperate powersupply

You could connect all the servos up to an Arduino, certainly, but I would personally go for a seperate servo controller. Such controller incorporate a dedicated microcontroller to actuate the servos based on a serial command stream sent to the controller via a TTL serial line. The command is sent, the controller responds, and holds the position. Since the controller is doing nothing but controlling servos, there's no extra overhead to your program. Just "point-n-shoot". Most of these controllers are fairly tiny, and allow for external power inputs for the servos. Most come in standard "sizes" for various number of servos (8-16 servos, usually); some can be expanded via daisy-chaining (thus, you only need one set of serial lines from your "master" microcontroller - in this case, the Arduino). Don't like the idea of purchasing something else for the project? You could build your own servo controller using a standalone ATMega328, and the Servo library. Communicate via TTL using the TX/RX (0 & 1) pins.

3)any good tutorial on humanoid structure (not biped plzz..ie not only legs)just for reference

As has been noted, there are tons of example out there of others who have built their own, but I would take a look at the commercial versions from LynxMotion, CrustCrawler, and others as well. Something to keep in mind is that both CrustCrawler and LynxMotion sell what are called "servo brackets" for allowing you to mount servos in various configurations to make the joints and such of the robot. You might want to look and see how they are designed, then develop your own versions, which can be made fairly cheaply from thin-gauge aluminum and a sheet metal bender (and/or a small vice).

Design your own in a CAD program or such, print them out full-size, then paste the printouts as "templates" to the sheet metal to cut and bend as needed. It won't be super-accurate, but good enough for your needs, and much cheaper than purchasing them (although, time is money and all that - so think about it)...

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

#### mohitgupta322

#5
##### Oct 11, 2011, 06:50 am

Quote
Buy servos with dual-ball bearings on the output shafts with metal gears. Sure, it's a lot more expensive up-front to do this; but with a biped and the load (lots of side load) on the shafts, if you don't, your decision to go "cheap" may end up costing you more in the long run than if you had spent the money on the more expensive option in the first place.

IOW - don't be "penny wise and pound foolish".

Thnx for the advise ..... No doubt you are right but unfortunately  my budget will not allow...I live in India where such servo is not easily available moreover if a servo is \$10 here they sell for \$ 18 and Indian rupees have less value than dollar . And if I buy from other online site like robotshop.com and other the import duties are double of the cost.

I think I should not be needing so much high quality as my robot will weigh 1-2 kg and small in size.