motors and things...
I'm experimenting in moving from Blogger to a static site generator. I have zero interest in web development, but we live in the future, and Claude Code can do all the web dev for me - including migrating 16(!) years of Blogger posts. Here it is: https://robot-daycare.com/ Let me know if you hate it, like it, or find problems! Feedback is greatly appreciated. I may eventually set up forwarding…
This isn't one of my usual project blog posts, but I owe my dear readers some context for the lack of project content. The last year did not go like I expected. Part 1: I ride my bike a lot In mid May last year my friend Sam and I decided to ride the Great Divide Mountain Bike Route , a mostly off-road route from Banff, AB to the Mexico border in Antelope Wells, NM. We'd been talking about it for…
As I've mentioned in previous posts , robot land has an annual car-and-other-vehicle show. Last year I brought the trike, but the year before that I brought the electric kart I worked on with Bayley . Picture from Bayley Before the event, the kart hadn't been touched since the pre-Covid days. Bringing it back to life and ripping around the parking lot was a great reminder of two things: This thing…
Robot land has an annual car-and-other-vehicles show. Last year I brought the hybrid car powertrain go kart , but this year the kart's geting some upgrades (stay tuned), so I brought the electric tricycle instead. The trike has been hanging from a miters wall unused since 2019. The last time it was ridden, someone crashed it into a curb and bent the head tube inwards, so it needed some work to get…
I installed a DRO on the Clausing . I got Aikron scales and console - the LCD console, a 1 micron slim magnetic scale for the cross slide, and 5 micron standard width scale for the carriage. So far I'm very happy with it - the user interface is better than some US-made, much more expensive DRO's I've used, and being able to store a library of tool offsets is a real game changer - all the lathes…
Not long after my masters thesis went online, clones of the mini cheetah actuators started showing up on AliExpress/Alibaba. Within another six months, there were clones of the whole robot. A dream outcome for the project - early on in the project I joked that it would be great if I could buy the stuff I designed from China cheaper than I could make it for (hence the original name, HobbyKing…
Here's the detailed post to go with the pictures and videos I've been dribbling out over the last few months. Last episode the mechanism was mostly finished, and was just missing the guide rollers that constrain the screw to linear motion and react the motor torque on the screw. Looking at the CAD cross section, there are 3 sets of 3 rollers ride in shallow axial grooves on the screw. The roller…
I've been keeping my eye out on craiglist and machinery auctions for a small (but not that small) lathe for a while now, but small lathes (other than import mini-lathes) are pretty uncommon. Someone Austin knows just bought a house just a few miles away from me with this Clausing 4900-series lathe in the basement, so we visited to take a look: The scale of this lathe really didn't come across in…
Lots of progress on the jumping robot based on this mechanism . To start off, here's a cross section of the core mechanism. At the center of the mechanism is the varying pitch screw (or barrel cam ). The screw passes through a "nut" with two cam followers, which drives the screw axially as it turns. The nut directly supports the rotor of an electric motor (specifically a T-motor RI50 ). The screw…
I've made a lot of progress on the software and control side of the espresso machine , and learned some good lessons about designing the real version of the machine. This is the first post in a series about the firmware/software, more to come soon. To "spill the beans", as people at work say, here's a demo of the current state of the machine: Here's what's going on while making the espresso in the…
Over a year ago I started porting my motor control firmware away from mbed. I've been working on it in spurts every few months and and ended up re-doing a lot of things from scratch, so it took much longer than I originally planned. Find it here: https://github.com/bgkatz/motorcontrol The core motor control math hasn't changed ( foc.c is nearly identical to the old version). Lots of features have…
Even before getting a lever espresso machine, I've been thinking about how I might design one if I were to do it from scratch. This is the layout I've converged to: The basic summary is: - Electric motor driven pump pumps water through a heater. - If the water at the output of the heater isn't up to temperature, the 3-way valve after the heater will cycle the water back through the tank. - Once…
You'll now notice that I added a Feed tab to the top of the page. When I started the blog, I would wait until I completely finished a project, then do one gigantic writeup at the end. This habit was left over from when I used Instructables to document things. As my projects got more complicated, that blogging style stopped working. So I started the In-Progress section for shorter technical…
I've had a La Pavoni Professional lever espresso machine for a couple years now, which I got on ebay and fixed up. Getting it working turned out to be completely uneventful, so I never wrote up anything about it. I recently restored a Europiccola for my sister, and this time around the restoration was much more involved. It was in pretty rough shape when I got it - all the seals were shot, the…
Getting back to this mechanism . In the post about the dynamics with varying transmission ratio , I came up with the design for the transmission profile by a combination of hand-calculations, intuition, and guesswork. But we can do better. This problem fits nicely into a trajectory optimization. For an intro to trajectory optimization, I'd highly recommend this MIT Underactuated Robotics chapter .…
Until Google axe-murdered it recently, I used Google Play Music to store my music collection and stream it to my various devices. I didn't pay for a subscription, just uploaded all my music files to Play, and treated it as free storage, organization, and streaming. Rather than switch over to YouTube Music (I tried, it was utter garbage) or some other streaming service, I took this opportunity to…
I did another batch of Furuta pendulums and took a timelapse of the assembly: These were done in a bit of a hurry, and nothing was changed from last time . At some point I'll probably do a refresh of the design, though. After building 16 of these, I have a bunch of ideas about things I'd like to do differently, and I've gotten a few feature requests from the recipient as well. And now, back to the…
This was inevitable, but the pandemic has accelerated my home-shop setup. What with leaving the lab almost a year ago (I miss you Lab Haas ) and no MITERS for the foreseeable future, I haven't had access to any machine tools other than the tiny lathe for a while. Time to fix that. I've been following Pocket NC since 2012, after seeing them at the NY Maker Faire - they make a tiny but surprisingly…
I put together a mostly-3D-printed prototype of the variable-pitch screw idea . Although it looked like it would work in CAD, I wanted to get a feel for the mechanism in real-life before designing anything around it: The mechanism combines a cylindrical cam with linear motion constraint all on the same cylinder. The main pieces besides the screw are shown below. On the left is the linear…
I just noticed that as of this month, I've had build-its.blogspot.com for 10 years. It's hard to believe how long it's been and how short it's felt. Hopefully Blogger is still around in another 10. For nostalgia's sake, here's the oldest project-thing I've documented- strapping model rocket engines to a pinewood derby car : This video predates the blog - I think it was filmed in 2007. 2nd place…
An idea I've had in the back of my head for a while now is using varying transmission ratios to transfer kinetic energy between bodies. That sounds really abstract, but I'll explain. Here's a simple example that frames the problem. There's a mass, \(m\), which can translate in \(x\). Driving the mass is an actuator with inertia \(j\) and angle \(\theta\). There's a transmission between the…
A month or two back I tried out anodizing a titanium bicycle fork. Eventually I want to anodize, mask, and bead blast a frame along the same lines as Firefly , so the fork was a test-run to get a feel for the anodizing and masking process. I did the anodizing by soaking a foam brush in a water and baking soda mixture, clipping one power supply lead to the brush, and one to the part, and brushing…
I've been working on a large robot -size motor drive, with a design target of 75V, >70A (peak phase) continuous with heatsinking, and >150A peak. In order to make the drive as compact as possible, it's split into three separate boards stacked on top of each other. The bottom layer is the power layer with MOSFETs, ceramic DC link capacitors, and current shunts. To minimize the thermal resistance…
I built 6 furuta pendulums for a university controls class: Since the original furuta pendulum was all built out of scrap I had lying around, I had to redesign pretty much everything from scratch. Instead of using a hand-skewed motor like the original, I used a custom-wind of a T-motor gimbal motor. These have low enough cogging torque to work pretty well: Each motor gets a Microfit connector…
Here's a photo-dump of some pictures from assembling the herd of Mini Cheetahs. 150 Stators: 150 Front actuator housings with output bearing installed: 50 upper legs. The upper link was consolidated from 3 parts to 2 for the new robots: For assembly I got these fancy Wera adjustable torque screwdrivers, so I (and people helping assemble) could repeatably torque all the screws: A handful of the 450…