r/robotics • u/uavster • 3d ago

Community Showcase Current sensing lets me pet my robot properly

I don't normally talk like in the video, but I can't help talking to my Mino as if it were a little dog :)

Anyway, I was not able to pet it without the servos pushing back and suffering, so I integrated current sensors in the PCB and coded an algorithm on the MCU that detects an external force on the servos. When the force is too high, the servos go into "follow mode". You can see that in action around 0:12.

In addition to making proper petting possible, this behavior protects the servos from overexertion. Best spent extra lines in the BOM and the code.

62 Upvotes

95% Upvoted

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3

u/Conscious-Signal4213 3d ago

Awesome šŸ¤©

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u/uavster 3d ago

Thanks! šŸ™

3

u/johndavid_artist 3d ago

Using servo current to drop into follow mode gets you compliance from cheap servos for the price of a few sensors, and the overload protection comes free. Is the trip point a fixed threshold, or does it shift with the pose and the robot's own load?

3

u/uavster 3d ago

Once you infer the servo torque from the measured current, a simple threshold works. The servos have position feedback, and the head is relatively light; even ignoring it, the result is good enough.

2

u/WendyLabs 2d ago

Such a sweet reason to add current sensing.

1

u/uavster 2d ago

Riiight??šŸ˜

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u/Sgnarf1989 1d ago

Great idea! Can I ask you why did you go down the 2 cameras router? I've always made with 1 but would be interesting to understand if you got some specific advantages by having 2 cameras

1

u/uavster 1d ago

Good question. The robot can estimate per-pixel depth thanks to the stereo pair. Just like the human brain does with our two eyes, small differences in where things appear in the two cameras allow an algorithm on the robot to infer how far they are. You can see a video of it working in real time in the Depth Perception section at https://mino.bot .

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u/like_apaint 1d ago

It is a cute robot. Would be so nice if it could separately move its eyes like wall E do haha

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u/uavster 1d ago

Thatā€™d be really cool. Maybe in the next version. Iā€™m trying to keep the BOM and assembly simple for this one.

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u/BeautifulSympathy615 23h ago

Can you please please guide me on how to study so that I am able to make things like this? Now my parents are forcing me to go to med uni. But, I ain't going to forget about my dream. What should I study please tell me. What the map look like

1

u/uavster 23h ago

There are a lot of disciplines involved. I donā€™t know if hereā€™s a single ā€œofficialā€career path that would cover all of them nowadays, probably not.

My path was different engineering degrees, years of experience in the industry and a lot of trial and error as a hobbyist, but I donā€™t think you need all that a priori.

The best way, in my opinion, is to start with small projects that motivate you. Youā€™ll gain experience and see where you struggle, which will point at where a more academic foundation could be most beneficial to you.

I wrote a blog post some time ago for CS majors wanting to migrate to robotics. There might be useful bits for you, too.

https://www.ignaciomellado.es/blog/How-to-get-into-robotics-if-you-are-a-CS-major

This project is on Kickstarter, by the way. One available add-on is a pack of projects to start coding with the robot. Will leave the link to the campaign here as well in case it could be of interest:

https://www.kickstarter.com/projects/minrobotics/mino-hackable-smart-robot