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3D Printed AR2+α
In Robot Builds
3D Printed AR2+α
In Robot Builds
Zach Allen
Mar 20, 2019
Hi, Everyone! I haven't posted in a while, but if anyone is following this and is wondering about how to get the software to work on their Raspberry Pi, @Chris Annin pulled my code/documentation into his repository: https://github.com/Chris-Annin/AR2/tree/master/RaspberryPi Updates: I'm still working through my somewhat-modified 3D printed AR2 robot, but have recently shifted focus to the stepper drivers. In @Max Favre's build log, we discussed using Trinamic's motion control drivers for the stepper motors. There's a product on the market called SlushEngine, which is an open-source project by Roboteurs - you can check out their website and GitHub repo here: https://roboteurs.com/, https://github.com/Roboteurs/slushengine. This product seems like a great option, but at a pretty steep price, especially compared to the drivers @Chris Annin picked from StepperOnline. I'm working on making a driver system similar to the SlushEngine, but with TMC5160 drivers by Trinamic. They offer a lot of impressive functionality, but I won't go into all of that in this post. They offer a small form-factor, as well as high amp-per phase current. Additionally, they offer 256 microsteps per step, which gives them very smooth and precise operation. One of the best selling points for this application, which the SlushEngine also offers, is direct positioning. As in, the motion controller is built into the chip, and you only have to give it a position command and it does all the hard work internally. That means no step-direction, no Arduino required, and no real-time OS (e.g. RPi Raspbian OS). I've modified the SlushEngine project for the TMC5160s, but it's very much a work in progress. It works entirely (and exclusively) on the Raspberry Pi, which aligns with my goal for the project - drive the AR2 with only a Raspberry Pi, preferably the $5 RPi Zero W. My milestone tonight was getting the library at a point where a very short Python script would make the motor run 5 rotations (arbitrarily picked) back and forth. While I want to tap into the functionality of the drivers more, I'm going to start a parallel path of adapting my already published RPi code with this new driver. Overall I think the AR2 software, written in Python, will work great with these drivers. The drivers have inputs for limit switches, so the home position can be recorded by the driver. This should greatly simplify the homing scheme. One of the trickiest parts I believe I will deal with is syncing all the motors. Meaning getting all the motors to run the same amount of time, regardless of how many steps they have to take. There's no problem getting them all to start at the same time but for precise and complex motions, having some sort of CNC-esque logic will make this a lot better. Overall, I'm quite impressed by these drivers, and hopefully I can get this library matured and integrate it into the AR2 software quickly. Another important piece of the pie is obviously the driver circuit board. Now that I have a working prototype with Trinamic's pre-built breakout board, I will begin to tackle designing the PCB, sourcing the parts, and assembling it all. I'm not sure the price-point will get below the StepperOnline drivers, but it will hopefully be cheaper than the SlushEngine. Since I'm building off the SlushEngine project, instead with Trinamic's famed silent stepper drivers, I'm calling the project "ShushEngine". I'm bad at coming up with names, so let me know if anyone has any better ideas. You can find my GitHub repo where I'll be constantly updating the code at: https://github.com/ZJAllen/ShushEngine Here's a quick video showing the motor spinning with the code written behind it.
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3D Printed AR2+α
In Robot Builds

Zach Allen

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