dannyvandenheuvelBecause I wanted a good accurate robot arm I decided to work with some smart servos, calculating the inertia to handle at least 500 gram I needed to work with more servos.
For the base joint I use a 24kg/cm smart servo, elbow, arm and hand I use 2 servos on each side from 12kg/cm and for the wrist and tool head rotation I use 1 servo from 12kg/cm. The gripper will work with a normal servo 10kg/cm.
I had to redesign the whole robot arm, a lot stronger and a bit thicker.
For the people how wanted the old drawings I will put them online if you want to play with it.
The power supply has to be upgraded to 7.5v 8.5amp, but it has almost the same dimmension so the hardware controller can be used without any changes.
A quick preview from the robot arm so far.
Tomorrow I will receive the smart servos from HerkuleX, also the leds on the servos will give a special dimension I think!
Because the servos work with a serial bus there will be just one or mayby two wires for all of them.
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When you take the power away the torck will go to zero, the only thing that will happen agains a real robot, it will fall because there are no breaks on the motors.
There will be a lot of benefits with these smart servo motors, you can take away the torck and move the arm by hand, all position feedback can be used to record and play afterwards. You have a lot of parameters you can read and write, it's very fast because it are small messages and the transfer rate is very high, so everything is gone work a lot faster simmultaniuosly than commanding everything from a seperate controller. Every servo has a controller inside of it. It's gone behave itselfs allmost as a real robot, it can move 320° with position feedback, you can smoothly accelerate and decelerate, you have precision speed. That's what I'm looking for. I strugle a long time without any decent succes to emulate a real robot with standard motors, I think this will be the best shot. Lets hope so :-) . I searched the web and all good working robots uses smart servos.
Most of then aren't cheap, but after a good long search I found sometime intresting.
If I gonna make a bigger one I am gonna use stepper motors with encoders in closed loop with brakes. Igus has these type of motors but they costs about 500€ a piece. So making this type of robot will cost about 5000 euros, that's way to expensive for a hobby. I am trying as close as I can with a low cost concept but with good realistic results. In my bussiness I use a lot of professional servos,stepers. that's the reason I'm not easy satisfied. I will build a system where you really can do a lot of tests and learn from it, hard & software based.
I will stop when I reach this point. 8=) and than perhaps I will build a bigger Thor!
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These are moving parts, so cables can be cut by the motor itself when they get jammed. What would happen if the wire breaks during the movement?
I understand that this is a small robot arm so this is probably an none-issue, but it is interesting to see how it would work when you scale this up.
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I am wondering, if you have serial communication for all motors, how will that impact performance? And especially how will that impact stopping the motors when they are misaligned and triggers an end-switch?
With a stepper-motor I can immediately stop. I am not familiar with these servo's.
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