I am trying to build a robotic arm(and legs). I have tried using servos, but have had a very difficult and frustrating time doing so. Ideally, here is what I need:
Actuator needs to be pretty strong. Servos are strong enough to lift small things, but are seriously lacking in lifting more than that. Whatever actuator I use needs to be able to lift a decent amount. For example, if I make a legged robot, it needs to be able to lift its own weight with a decent margin of error. If I decide to add a piece or some similar modification, I do not want to have to replace everything just because of a small weight change.
Actuator needs to be able to BE moved manually. A legged or armed robot in sometimes going to be moved by exterior force. For example, if it falls down a stair it should not strip gears or otherwise fail. The arm should be capable of having a human move it manually without being so frail that the interior gears break, which is a problem I have been having with servos.
Actuator needs to be relatively quiet. Not AS important, but noise actuators are really irritating.
Actuator needs to not be ridiculously expensive. People keep telling me to get bigger and better servos, and given that even a simple leg needs 3 servos each and an arm might need 5 or more, servos that cost 20 dollars each are just out of the question.
Do actuators that meet these criteria just not exist?
Powerful, quiet and robust actuators for robotics...
It may certainly exist...
Perhaps... Maybe...?
There are certainly robots that control like electronic suspensions that can withstand external forces.
But I'm not surprised if that the actuators used in such robots is cost over $2000 per units.
You may not be able to buy even one of the gears used in the actuator for $20...
By the way, high torque servos for radio-controlled models cost more than $100 if they are of reliable quality from well-known brands.
Even a radio-controlled model that looks like a toy when viewed from the who not familiar...
Fake and Counterfeit products sold "cheap" on sites like Aliexpress won't be very useful for heavy-duty applications like your project.
Alright then assuming that i simply have to work with what is readily available servos seem like the best option. does turning servos manually break them? to get acceptable quality ones it seems to be an absolute minimum of 20 dollars per servo. Is that pretty much what I should expect?
Do actuators that meet these criteria just not exist?
LOL ... I'd say, you just did not add enough $$$$ to get a quote. Cheep chinese copies of e.g. an actuator of cheeta type legs is ~ $250 up - and that's just for ~ 1Nm.
I'll pass along some good advice I recently got from the forum: figure out exactly what your motor requirements are (ie speed, torque, size, backdriveability, etc). Once you have that, it's easier to see what will and won't work, and also makles it easier for people to recomend solutions.
Sorry to be the bearer of bad news, but $20 is a cheap hobby servo. It sounds like you're looking for something that resembles an MIT Cheetah style actuator.
Based on the requirements you gave (less the cost), BLDC servos are the answer. Odrive is an open source solution that have been used by a number of people to build robot actuators. Definitely more than $20, but IMHO, it's the best, and is still cheaper than a DMM or clearpath setup of equivalent power. If you dont care about speed (motor RPM) you might be able to get away with running servos very slowly - we're talking less that 50 rpm. That would be cheaper, but with tradeoffs.
There are a bunch of great sources of information out there, especially when it comes to open source robotics. This guy has built multiple open source robots and has published the videos on YouTube: James Bruton - YouTube
