hi,
i need to build a 2 dof robot arm (actually 3 with end effector). my main concern is the power of servos. Two links have same weight of 200gr, and length of 1m. As a calculated i roughly need 15kgm torque at 2nd joint and 50kgm at first (base).
I dont really want to deal with extra bearings so i want to end the need for power by servos. I saw a 70$ servo+gearbox(external) kit. Can this solve my problem.
(i also need to use 180 or at least 140 degrees or rotation)
my budget is limited to 170$ for motors (and their extras).
thx 4 ur help.
Could you provide a link to that “70$ servo+gearbox(external) kit”?
I checked the site, but I don’t see any servo gearboxes.
I don’t believe that those would do.
15kgm is more than 21,000 in.oz.
The best hobby servo available is only a bit more than 400 in.oz.
That means that you would have to have a servo gearbox with 50:1 gear reduction.
Even if you could find one with that kind of reduction, you would only be getting 3-4 degrees of rotation with that high of a reduction.
From the sound of it, you’ll need an industrial servo, the kind that they move the car-welding arms around with.
That, or you could take an industrial motor and convert it to a servo with very expensive electronics.
Either way, you’re not going to find those on any hobby robotics store.
Sorry.
Oooh…
They seem to be saying that you’d still be getting 180 degrees of rotation…
While I’m not sure exactly how that works, I’m afraid it still doesn’t work for your purpose.
Again, if you were to utilize the strongest hobby servo, you’d only be getting an output torque that’s only a tenth of what you need.
they say the replace the internal pot with a “military grade” one on the final gear which just means a real slow high torque servo
nick
Well, you have to keep it in perspective, though.
Since most servos turn 60 degrees in less than .2 seconds, this new one with 5:1 reduction will mean less than a second for 60 degrees of rotation.
In other words, that means ~2.5 seconds to turn the full 180 degrees, which it rarely does.
In my opinion, this doesn’t really hurt most applications of a robotic arm, as speed is usually gratefully sacrificed for more power.
In fact… I was just thinking how nice these things would be on… say… a sumo bot…
that would obviosluy make that sumo a little(!) powerful 
thx for your opinions =)