We should check out rotary encoders and motors, while I’m in RSA. I’ve started looking at them now. There’s a wealth of info at a company that makes them, Dynapar.
Here’s the good stuff. Coupling: “Rotary encoders come in 3 major mounting styles: hollow-shaft (hollow-bore or through shaft), hub-shaft (hub-bore) or shafted. Hollow-shaft and hub-shaft rotary encoders mount directly to a motor shaft typically using a tether. Shafted rotary encoders mount using a flexible coupling.”
I asked a South African company about their Italian ‘Eltra‘ rotary encoders yesterday. Then Feetech from China asked this morning, if I needed servos. Well actually yes. I asked about their encoder motors, as they might be called, as a combination. They had 4.8V, 6V, and 7.4V such motors, whose encoders were of the magnetic measuring type, and give 12 bits of precision (2^12 = 4096, so 0 to 4095) as serial data.
The MG996Rs used for the basic table robot prototype were possibly adequate, but definitely on the hobby side. They felt more appropriate for a robot about half the size of the prototype. The prototype was successfully sat upon, by the chicken.
I started thinking about practicalities of powering a jetson nx (The devkit supports between 9-20V ) or jetson nano (5V) ot rpi (5V). and numerous motors. So probably uses a battery in the 9-20V range. Motor too. Probably 14.4V is what Lithium ion or similar batteries come as. Usually need to buy lithium ion batteries in the place where you’re going, rather than bring them on a plane. But you can always try. (Not a financial advisor (or otherwise)). They are probably still mostly imported for RC models (remote control, remember?).
But also wow, on the topic of rotary encoders and servos, this guy made a sub-millimeter accuracy by a 6 d.o.f. (degrees of freedom) robot arm
Used his own interesting and as yet mysterious encoder, which he put inside a motor. Says his robot arm cost EU 300. It’s super impressive.
The other option with power appears to be cool ‘just what you needed’ type products like DFRobot’s FIT0186, which has a built-in encoder! I ended up buying 4 x FIT0186s and 4 x FIT0185s (12V, 251RPM and 83RPM respectively).
I used an Arduino Nano, a DFRobot Dual motor driver, based on the TB6612 chip, plugging in the Nano for 5V, and 12V into the driver, to power the motors.
But after much wiring up, the motors work fine, but the encoders do not. I fixed up their example code to use volatile variables, and run the minimal amount of code in the interrupt service routines (ISRs), and even used two interrupts for a single motor, one for each hall sensor output, and put a 0.1mF capacitor between signal and ground. Tried CHANGE/RISING/FALLING triggers. Tried different motors.
I’ve looked at every forum post, and tried everything, and now I’ve posted on DFRobot’s forum, in case someone has got the encoder working. Not looking promising.
So back to the MG996Rs, I find that I ordered two batches from Mantech, supposedly the same genuine product from Tower Pro, and yet the one batch does not work properly with the PCA9685, uses a lower minimum pulse, and moves in the opposite direction to the other ones when using the same code. The duds keep creeping around, after you turn off the throttle.
Ok so I’m going to try with the one batch of MG996Rs that do seem to work, but we’ll need to make a new plan. Possibly, rigging an actual rotary encoder up, on the motor shaft. But for now, back to MG996Rs and the drawing board. We left the old robotable in Switzerland last year. So I made a new one with the remaining MG996Rs.
So I was able to get them fairly well calibrated by setting the min and max pulse, as that seems to be how servos work. They have a center PWM pulse, around 1500, where they are still, and then as you decrease the pulses per second, it goes one way, and as you increase the pulses per second, it goes the other way.
Unfortunately after much fuss, these continuous rotation servos turned out to be duds. At least for the way I was trying to use them.
Set the throttle to 1, sleep for a second. Set the throttle to zero, sleep for a second. Set the throttle to -1, sleep for a second. …And you have a new position. Unfortunately the positional control is unusable. I guess these are for wheels or an application where position is not so important.