I have my SES arm, as standard, using RIOS, which is working great, but i want to make it more stable and accurate - so i have some questions:
Will swapping the servo’s with stronger, higher model varients improve things?
If i bought digital servos and swapped them with the current analog ones and still connecting them to the unmodded SSC32 board? would this work and improve things without any mods or will i need firmware changes?
What about the OpenServo project - can i use these with the SSC-32 board or will i need major changes?
Has anyone got any other ideas on improving things?
Basically, the robot does what i want (picking up microchips and holding them in a programmer for firmware programming) but i just want to make the whole system a little stabler and give it more accurate positioning
Im really interested in any ideas at all (or experiences) no matter how major or minor they are
and finally, hats off to Lynxmotion - this is a great robot, i love it
What servos are you using? That might be the biggest problem you have, the software (RIOS) works suberbly. The SSC-32 is an excelent servo controller and does a very good job for controlling the servos. I believe it comes with the 645’s? Are you still using them?
Open Servos are not compatible with the SSC-32 unless you have them set to accept PWM (standard R/C) servo control. You can control an Open Servo using PWM and read back status information using I2C.
The SSC-32 has 2000 discrete positions, 500uS - 2500uS, this is really more than the average servo can accurately respond to. So in a way the SSC-32 is waiting for servos to catch up to have more resolution.
The standard digital servos (5645) have more accuracy, but actually resolve with less resolution. 1200 discrete positions, 900uS to 2100uS, but this is only after programming with the HFP-10.
The Robot digital servos, (5990) have even less, 800 discrete positions, 1100uS - 1900uS, but no programming is required.
The RIOS program has an IK engine that converts the desired X,Y,Z position of the end effector, into the arms servo positions required to get the end effector into position. I am not sure what the real end result resolution is, but I guess it’s a grid of points spaced around 0.125" to 0.250" apart. I know Laurent mentioned the latest RIOS update had some improvements to the IK engine resolution.
So you know what the arm is capable of now. Going to a digital servo will increase the repeatability, and may increase the resolution.
Hello,
RIOS resolution is 2uS, so 1000 positions from 500 to 2500uS.
this is 3 or 4 times more precise than Analog servos dead Band / resolution.
if you add to this the geartrain play you can’t be more precise with servos.
to increase re-positioning accuracy, you can add a kind of stop (if the arm must stop always at the same point), then the arm could gently lean on, reaching its target.
if you need it to move a bit more while pressed against its stop you can add a teflon part to be able to slide on it easily.
So, lets take an example here, if i replaced every servo on the arm to HSR-5990TG servos - thinking more powerful = more stable, and digital = more accurate - am i going to see an accuracy improvement? i know the cost is high, but if i can get this to work reliably it will pay for itself in less then a week!
i am floating of by about 4 to 5 mm everytime, if i can get this down to about 2 then im home dry
Everything tells me more power = more accuracy. However I do not have the time to accurately test this. When it comes right down to it, if I don’t know, I must just say I don’t know.
High resolution industrial equipment tends to use stepper motors. I’m afraid that’s not really very helpful to know because stepper drivers are hard and cumbersome to build and work with, plus they’re nowhere near bolt-in replacements for servomotors. There’s a reason why hobbyists like servos, and there’s a reason why industry likes steppers.
Servos have come a long way and they’re great for hobbyists but once you start getting into sub-mm accuracies and high torque at low speeds there’s no way they can compete with stepper motors.
