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Actuation & Control Schemes for Robotics

In this chat, we'll be learning about control schemes for robotics

Friday, April 27, 2018 12:00 pm PDT Local time zone:
Hack Chat
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Ryan Walker will be hosting this Hack Chat. 

This Hack Chat is at noon Pacific time on Friday, April 27th. 

Time Zones got you down? Here's a handy count down timer!

We wanted to kick the Hackaday Prize Robotics Module Challenge off with a robotics Hack Chat!

Interested in how people will use new and affordable electromechanical components to build the future of open source hardware? Expensive servo/stepper motors are no longer exclusively for high budget industrial use, but have become ubiquitous and affordable for the average hacker. 

Ryan Walker holds a diploma in Mechatronics and Robotics from BCIT. Previously he’s worked in prosthetics and industrial automation. He enjoys designing & building control algorithms & drive electronics that enable cheap hardware to excel!

TL;DR

In this chat, we'll be talking about robotics:

  • Control schemes
  • Ways you can actuate your projects
  • Wheels and things to make your project move
  • Automating

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Discussions

Elecia White wrote 04/27/2018 at 19:30 point

What books or resources do you recommend for people wanting to do more robotics, to learn about the algorithms like localization, noisy sensors, control, kinematics, and so on. Do you have any that take more of an applied perspective instead of a graduate-level, derive-everything book? (I'm currently reading Probabilistic Robotics and it is ok but getting from "derive Kalman Filter" to "use it in my robot" is a big chasm.)

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Stephen Tranovich wrote 04/27/2018 at 19:14 point

What is good to keep in mind when designing modular components with the intention to have them used in larger applications with unknown control systems?

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Roger wrote 04/27/2018 at 19:13 point

Standard RC servo will move to and hold a commanded position. Is there an alternative (and ideally inexpensive) actuator that can hold a commanded level of force? Usage scenario: Hexapod robots using cheap servos are common, and they walk well on level ground. What if we want to walk on uneven ground - each [not servo] needs to exert enough force to hold a percentage of the robot's weight before it takes the next step. But the distance required to reach that amount of force varies when walking on uneven ground.

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Krzysztof wrote 04/27/2018 at 19:18 point

That would be my electromagnetic linear servo project, I'm working on exactly this but didn't have time lately. Will continue in about a month with resistive linear slider (position feedback like in normal servos). This will be able to control force very simply, just add more current. https://hackaday.io/project/19547-electromagnetic-linear-servo

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Gene Hacker wrote 04/27/2018 at 19:40 point

Yes and controlling force applied is turning out to be critical for today's robots. Force/torque and impedance control(force as a function of position) are what make Boston Dynamic's walking robots possible. This is what enables robots like Baxter to work with humans safely. Now the cheapest option out there is to make what is called a force servo, a RC servo with a load cell for measuring torque. One modifies the servo so that it uses output from the load cell rather than the potentiometer. There used to be a kit for doing this: https://www.actobotics.com/html/force_servo_arm__ffsa-25_.html

But this has some downsides. For one, for impedance control one really needs to know the current rotation angle of the output. The load cell deforms a tiny bit so one needs a rotation sensor on the output somehow. While this deformation can be tiny, in a serial robot arm, the error can add up. Oh and it's really not the best to rely on whatever controller the servo has. It would be better to have a custom controller.

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bejecreimer wrote 04/27/2018 at 19:10 point

Whats the best and cheapest way to get torque feedback for various electric actuators (servos, linear actuators, dc motors, steppers, etc)?

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TegwynTwmffat☠ wrote 04/26/2018 at 08:14 point

What's the best camera, video, object recognition system for under 500 bucks?

It needs to be able to host a large number of library images away from clouds or banks of fog, it needs to be able to output coordinates for creating grids of objects. I was looking at the PYNC system recently featured in HAD blog which looked reasonable.

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Adam Vadala-Roth wrote 04/27/2018 at 14:48 point

Nvidia Jetson boards are the best for embedded computer vision. FPGAs can totally do computer vision but the development effort is significantly more.

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TegwynTwmffat☠ wrote 04/27/2018 at 20:04 point

Thanks Adam - I've seen those - they seem to be popular!

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ðeshipu wrote 04/25/2018 at 17:50 point

How can you transform the data from the force/power sensors in the joints into useful events, such as touching the ground, hitting an obstacle or being pushed? I have tried various hard-coded and custom-filtered approaches, but I can't help but wonder if there is some way of pattern-matching this kind of data? Some kind of regular expressions for time series?

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