This Gearbox Knows Its Position At ALL Times

this is an rc servo they're used in all sorts of robotics and rc vehicles to move or turn things these things are awesome because you can just command them to turn to a specific angle and they just do it this makes it different from a normal motor which doesn't know its position and just turns when it's powered servers have the ability to turn to a specific location because they use what's called closed loop control unfortunately most of these cheap rc servers only turn 180 degrees and nice servo motors are pretty darn expensive so i'm going to take the 3d printed gearbox i designed in my last video modify it and then use closed loop control to make it act as a servo motor so first things first we need to print some new parts [Music] the main differences between the first and second version of this gearbox is the newest version uses a geared brush dc motor rather than a stepper motor and has the necessary electronics for closed loop control if you don't know what i mean by closed loop control don't worry about it just know that it's awesome and it's going to make this like the chat of gearboxes oh that was a bad analogy but anyways many of the parts are similar between the first and second generation of this gearbox but as a quick recap the gearbox has one sun gear which goes onto the motor three planet gears a carrier to hold the planet gears a housing that has the first ring gear a second ring gear attached to the output hub and this new version of the gearbox is a second output shaft that will allow the encoder to measure the position of the gearbox these parts are all assembled with a variety of bearings bolts and screws and a list of all these components can be found in the description below [Music] [Music] do [Music] do [Music] do [Music] as i mentioned earlier this gearbox has the ability to use closed loop control this means that the gearbox's ability to measure its position and then use a controller to move to a desired location a great example of a closed loop motor is a standard rc servo motor this type of system can be represented using a block diagram showing the controller and motor feedback of the position of the motor to the controller closes the control loop and allows the system to accurately control itself rc servers use a dc motor to move the output and a potentiometer to provide feedback to the simple built-in controller in my gearbox design the position of the output hub was provided by an as5600 magnetic encoder this encoder is a 12 bit resolution the output shift that the encoder reads to the gearbox has a one to two gear ratio with the output hub so i can effectively double the resolution of the encoder however this does mean that the magnet will be in the same location twice throughout a single rotation of the output hub which can be confusing for control purposes to solve this there's a limit switch on the side of the gearbox housing which rides in a groove on the output hub for half the rotation the switch is depressed and for the other half it is released this switch can also allow the motor to run a homing sequence if needed once the encoder and the limit switch are installed we now have everything we need to control the system except a motor controller to control the motor i'm using an arduino nano and it fits into this pcb i designed a while ago to actually power the motor i'm using an ibt2 motor controller this may be overkill but it's what i had laying around once everything was wired up i wrote some code to allow the gearbox to home itself this basically just turns the output until it triggers a limit switch and then records that encoder position the output hub position can then be indexed from that home position without the need to run a homing sequence every time now using a simple pid controller the output hub can turn to any angle there are definitely some improvements and tuning to be done in this controller to improve its accuracy but for now it works pretty well using a potentiometer to specify the desired motor angle is a great way to visualize the closed loop feedback of the system [Music] okay so you might be asking how much torque does it have well using a load cell we can find out by putting an arm on the gearbox of known length and recording the weight measured the max torque can be calculated for the first test the motor and the gearbox applied roughly three and a half newton meters of torque before it started like skipping teeth this result was sort of confusing because the first version of the gearbox was able to achieve roughly four newton meters taking apart the gearbox i could try to figure out what was actually causing the teeth to slip i figured changing print settings may have made the output hub more flexible and allowed to slip so i reprinted it with more parameters and higher infill this new version definitely felt a little more rigid than the last so i was hopeful that it might fix the issue re-running the same test yielded slightly better results this time at seven newton meters the gearbox started to slip this is more than enough torque for the application i need to use this for but to prevent this in the future i may need to adjust the pressure angle of the gear teeth the main reason i designed this gearbox is for a 3-axis turret i am building for one of my next projects this turret is almost a robotic arm but only has three axes which should allow it to point whatever it is carrying in any direction with more flexibility than a simple two axis turret to build this though we're going to need three sets of these gearboxes so it looks like we better get printing stay tuned for the rest of this project in a future video until then thanks for watching and be sure to subscribe for more i'll see you in the next one [Music] foreign

Channel: Michael Rechtin

Views: 254,853

Keywords: gearbox, 3dprinted, servo, rc, arduino

Id: RhnFUuMgao8

Length: 8min 5sec (485 seconds)

Published: Fri Feb 04 2022