Hobby Servomotors Could Be Much Better 

Thank you! Love your rockets! I am subscribed for quite a long time :) BTW I am planning to build a new TVC rocket with these servos. I think that I can use current position readings from TVC to build an improved flight simulation. It was hard to tune control algorithm without knowing the exact response characteristics of the TVC mount.

we caught you here!!!!

​@@Positive_Altitudecould you provide PCB design of servo controller?

considering this is essentially remaking dynamixels he should just look into the dynamixel protocol and utilise it. Half duplex serial. Ive implemented using their protocol for my own servos and other systems. its robust.

I have seen some I2C hubs for robots that allow increased signal drive and auto addressing.

I learned about this when I was half-way through the process already. But I think it will work at this scale. Calculations shows that I will fit into 400pf line capacitance limitation. Waveform looks scary (I was also dumb and placed SCL and SDA as adjacent wires in the cable, so there is also a quite bad crosstalk). But despite this I had 0 failures so far. I think I2C could be used like this if you take care about noise and line capacitance a little bit, and not going crazy with wires. I would say up to ~1m should be fine. Also STM32 has an improved current sink, so in theory if host controller is STM32 too, it is possible to use pull-ups with much lower values than I2C standard suggests. That will help with waveform and capacitance. But still no resistance to noise is an issue. I am thinking about CAN too, but there is no CAN in STM32G0 so it will bump up the cost but probably it is worth the money, because CAN is amazing (never used it so far). Thanks for the feedback!

I love can too, but i dont think any small Stm32s have it :(. Major gap. Iirc mmoat small PICs have it.

There is STM32F042 with CAN, very small and DIY solderable.

I am thinking about both sharing design files for free and selling these boards in future :)

Thank you! That boosts my motivation to go forward :) Hope you are having a great day

100%

Yeah, that's a good advice. I really started to appreciate dual-shaft and hollow shaft motors. They gives a lot of options to simplify the design. But one of the goals is to try to keep everything very cheap. These motors are like 1-3$ piece (from Aliexpress), but this limits my choices. Thank you!

Thank you :)

Go for it! Starting could be hard. I probably spent a year thinking about the rover, before I started actually doing something. I was scared of the amount of efforts required to finish it (and I still not very close :) ). But when I started I was making progress way faster than I though. And it is also fine to take breaks if you feel burned out. So I would say that if you have an idea and you are passionate about it, just go for it. The faster you start, the faster you will get to something you will be proud of. Good luck!

Yeah, that's right. I did not want to overcomplicate things and said that is just a PWM, which is almost true. But I got your point, thanks!

Thank you! Yeah, that could be awesome. I will focus on improving brushed DC motor for now, maybe will bring CAN to the next version as it is a good idea. I have researched BLDC motors before and I think the brushed motors should go away at some point if we can make a good and cheap controllers for BLDC. But this is another layer of complexity on top of what I already have, it was too much to bite at once. But I hope I will get to BLDC servos/ESCs at some point :)

True, I hope I will find a more or less cheap and suitable MCU with CAN support.

Thank you! I will make a next version with some fixes and will make it open-source. I have a passion for making things cheap too :) This is the way for everyone to have a good stuff. Good luck with your project!

That's cool I will be happy to take a look. I used very simple trajectory and never researched this topic before, but if you have a good answer already I will happily use it.

Thank you! I use Prusa i3 Mk3 from my local hobby space. It's a good printer but maybe a little bit outdated right now. I think there are better options on the market for the same money right now.

I will 100% open-source it since the next version. The current version has some issues. Not very critical but it could be better. And the firmware is quite sketchy right now.

@@Positive_Altitude awesome! I can't wait to see it

I learned it when it was too late. Hope it will be ok, otherwise I will switch to CAN, but it will take significant effort. For now I reduced the problem by using 3 I2C interfaces instead of 1 as I planned. So now it's 5 servos per bus. And two servos works fine. I hope 5 servos will work too. Thanks for the heads-up!

Thank you, it is Texas Instruments INA180A2. It amplifies the voltage across 10mΩ resistor x50 times and then I read the value with ADC.

Thank you! I am using KiCad. I think it has the right balance of features/complexity for hobby projects.

@@Positive_Altitude thanks for the reply. I dabbled with Eagle a long time ago, then played around with Kicad a little and now am looking at EasyEDA. I think if a project comes along where I need a PCB it will be either Kicad or EasyEDA.

Oh! Cool! Do you mind if I contact you some day? I would love to talk with you about servos :)

Yeah, I decided to not dive too deep into this. But in fact everything is very simple. Position control is just P regulator. Velocity control is PI (well, almost: I term is applied to velocity delta, P term to current velocity, not to the delta). Current control is just PI. So it is like 3 simplified PID regulators chained. And it is not my invention, google for "PIV regulator" that's exactly what I implemented. Maybe I will make a video about it, but not sure if it will be soon.

Oh , thanks

Yeah, going to add them in the next version

Thank you! Yes I am planning to sell the next version of these boards, but so far I don't have a website and don't sell them. The PCB itself is very cheap. I made panels of 4x4 boards (you can see some holes on the edge after I separated individual boards) and 5 panels cost about 8$ without shipping, so 0.1$ per PCB. Components are about 5$ per board total (encoders are 2.5$ piece unfortunately). The biggest question is assembly. I don't know yet how much the factory assembly will cost, it also depends on the batch size as the "setup" cost could be significant. I assembled them myself with a simple soldering iron :) Rover is still in progress, I am designing the "body" right now.

Yes, I am going to keep all designs/software from this channel open-source. But right now the board has some minor issues. I will make an updated version and make it available.

Yeah! That's sounds cool! How big is the robot? I am working on the next version of the servo. The version in the video has some issues. I will share design files when it will be ready.

If you are talking about the board, the next version will be available. The one in the video has issues. And I will make a video about it when it will be ready.

Much appreciated :)

Thank you! It works like a charm. It is even possible to setup debug in VSCode. There is a project stm32-rs and there is support for all series of STM32. I am very happy with that.

I am using Rust. It is a great alternative to C/C++, a low-level language too but with some degree of memory safety features provided at compile-time. I like it because I can use one language for embedded, desktop applications, backend and even for frontend (thanks to .wasm). So I can share my code all over the place.

Thank you! Not shared on GH yet, because there are issues and no documentation at all. Maybe I will do that during the next few weeks. But anyway I am working on a new, improved version, that will be shared from the very beginning. I hope I will get there in 1-2 months.

Thank you! Design files for the board will be available when I make the next version. The current one has some minor issues to fix. The rover is still in progress, the "body" is not designed yet. I will share the design files when I will finish.

Though about it. But I decided that it is too many wires. The sensor requires at least 5 wires that will be very annoying to route. So, instead I tried to make this board very small. It is only 20*20 mm