Pages: [1]   Go Down
Author Topic: Looking for High Torque Servos.  (Read 374 times)
0 Members and 1 Guest are viewing this topic.
Offline Offline
Newbie
*
Karma: 0
Posts: 2
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Hi!
Im working in a 6DOF Robot Arm and I need a High Torque servo for de DOF in the base.
The higher one I have found is a 40kg/cm or 555 oz/in one, do you know any higher servo.

Thanks.
Logged

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 549
Posts: 27425
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Where are you located, and where have you looked so far?
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Johannesburg. UTC+2
Offline Offline
Faraday Member
**
Karma: 114
Posts: 4961
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

kg/cm ....  oz/in

What are those units?

 smiley-yell
Logged

The Elders of the Internet know who I am
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

0
Offline Offline
Tesla Member
***
Karma: 148
Posts: 9752
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Powerful servos are available for some $$$.

http://www.robotshop.com/en/hs-1000sgt-heavy-duty-giant-scale-digital-servo.html

http://www.robotshop.com/en/invenscience-torxis-i00600-12v-high-torque-servo-motor.html

http://www.robotshop.com/en/dynamixel-mx-106r-serial-servo-rs-485.html

« Last Edit: August 30, 2014, 11:58:38 pm by zoomkat » Logged

Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

0
Offline Offline
Shannon Member
****
Karma: 222
Posts: 12725
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

kg/cm ....  oz/in

What are those units?

 smiley-yell

Quite!  For the uninitiated torque is in units of length _times_ force. The tangential
force times the distance from the axis to be specific.  SI units N-m (newton-metres,
ie newtons x metres).  kg are not a unit of force, although you can say "kgf" for
kilogramme-force, or in imperial units ozf for ounce-force.

Using newton-metres for torque has the great advantage that you can directly use

power = torque x angular-velocity,
note).

Torque can also be (to my mind much more logically) quoted in units of joules/radian,
just as force can be described in joules/metre (which is the definition of the newton).

Perhaps the world would be simpler if there was a named unit of torque  smiley

equation without conversion constant (although angular velocity is in radians/second
Logged

[ I won't respond to messages, use the forum please ]

Johannesburg. UTC+2
Offline Offline
Faraday Member
**
Karma: 114
Posts: 4961
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Perhaps the world would be simpler if there was a named unit of torque  smiley

Well, a toque [sic] is a kind of hat, popular with chefs, so I'd go with chefhats as the unit. Of course, we would then have to decide if that was a Metric (specifically, SI) or Imperial (read as: American) unit.

I can live with kg.cm since kgf is an accepted Metric (but not SI) unit of force, but it really grinds my gears to see a torque described as force / distance not force x distance.

Logged

The Elders of the Internet know who I am
I'm on LinkedIn: http://www.linkedin.com/in/jimbrownza

Global Moderator
Boston area, metrowest
Offline Offline
Brattain Member
*****
Karma: 549
Posts: 27425
Author of "Arduino for Teens". Available for Design & Build services. Now with Unlimited Eagle board sizes!
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Imperial is not American - that's more of a UK thing
http://en.wikipedia.org/wiki/Imperial_units

We're still going our own way in many things.
http://en.wikipedia.org/wiki/United_States_customary_units
Logged

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

Offline Offline
Faraday Member
**
Karma: 62
Posts: 3080
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The base of a robot arm should have a lower torque requirement that the elbow of the robot arm.

The elbow ( and the shoulder ) have to hold up the entire weight of the arm and provide torque to prevent the end of the robot arm falling down.

On the other hand,  at the base of the arm,   the weight of the arm should be carried by some kind of bearing,   and the servo only has to turn it,   not hold it up.
Logged

Phoenix, Arizona USA
Offline Offline
Faraday Member
**
Karma: 42
Posts: 5612
Where's the beer?
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

On the other hand,  at the base of the arm,   the weight of the arm should be carried by some kind of bearing,   and the servo only has to turn it,   not hold it up.

He's probably talking about the tilt of the arm, not the slew...
Logged

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

Phoenix, Arizona USA
Offline Offline
Faraday Member
**
Karma: 42
Posts: 5612
Where's the beer?
View Profile
WWW
 Bigger Bigger  Smaller Smaller  Reset Reset

Quite!  For the uninitiated torque is in units of length _times_ force.

While you may be technically right, it is easier for the layman to think about torque in "how much weight or mass will this shaft lift, given a lever extending from the center of the shaft" - which is why we see torque expressed as kg-cm and lb-ft (though for the latter, it is almost always said, and sometimes written, as "foot pounds" or "ounce inches" or similar). Sometimes a dash is used, sometimes a slash, rarely an "x" for some reason, though.

But I am sure you already knew this.

The thing is - most sites (not all) selling motors or other actuators don't list the information in the manner you prefer and indicate. Many of those sites aren't selling to scientists or even engineers, but rather mechanics, hobbyists, and other "laypeople" - that is, those generally without the formal training in such matters.

What I would personally like to see, is a web page or something similar that could relate and explain your method in a clear and concise manner, along with graphical examples - while comparing and contrasting that methodology to the more common "layperson" method of understanding torque. You yourself have explained several times how you view torque and how it works (and I commend you for that!). I haven't seen, though (maybe I missed it?) any explanation from you how that method compares (and translates to) the colloquial layperson method.

Furthermore, a site or page (or something) that could take all of that information, and show how to calculate the needed torque given a wheel on a robot platform - both for flat ground and for an angle (climbing a slope), and perhaps even for a joint on a robot arm (and maybe for something being slewed in a circle on a flat plane) - well, that would just be icing on the cake. Ideally it would show you how and why it all works, then have a section which you could plug numbers in and get a result back (via javascript or similar).
Logged

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

0
Offline Offline
Shannon Member
****
Karma: 222
Posts: 12725
Arduino rocks
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

The base of a robot arm should have a lower torque requirement that the elbow of the robot arm.

The elbow ( and the shoulder ) have to hold up the entire weight of the arm and provide torque to prevent the end of the robot arm falling down.

On the other hand,  at the base of the arm,   the weight of the arm should be carried by some kind of bearing,   and the servo only has to turn it,   not hold it up.


All the joints have bearings, of course, so that argument seems odd.

The base will have the largest torques as it handles more mass and more reach.  However
a rotation-only base is protected from gravity forces by a thrust bearing, perhaps
that is your point?  Not all arms are like that though. 

Remember dynamic torques have to be handled too so a fast moving
arm will have the largest torques at the base, whatever DoF it has, as
dynamic torques can be far larger than static in such a machine.

Static torque loads are straightforward to calculate, just do the sums once you've
got a good estimate of weights and sizes.  Dynamic torques depend on speed/acceleration
profiles.
Logged

[ I won't respond to messages, use the forum please ]

Dubuque, Iowa, USA
Offline Offline
Faraday Member
**
Karma: 49
Posts: 2553
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

You need something like a "crane" and not an "arm". One servo to raise/lower the boom and a second servo to pan the boom between tanks (where the tanks are arranged in a semicircle). Personally I'd just hang the board off a wire hook instead of trying to use a gripper, and if you want agitation you could put a continuous rotation servo on the end of the arm so that it raises/lowers the board as it spins.

You don't need much torque for the pan, and because you can counterbalance the boom you don't need much torque there either. Any standard size servo would handle it, but always a good idea to shop around and try to find ball bearing / metal gear servos. Hobbyking.com has plenty of generic servos that would meet those specs for not much dough (<$10).
Logged

Pages: [1]   Go Up
Jump to: