Archive for the 'Stuff' Category

 

More About the #RobotTrapShop and Building Up a New Workspace

Apr 10, 2020 in Stuff

While writing my previous post about moving back South, I decided that there was enough content about putting together the garage workspace to warrant its own post. You see, this is really the first time I’ve ever really built up a workspace for myself only. I’ve built up and operated/managed quite a few facilities now, and even if it was “my shop” in the sense that I oversee and get to use it a lot, it still was always shared.

There was my time at MITERS, the MIT student makerspace – then upstairs in my research group the MIT International Design Center. Then another shared workspace at the old mill building we called “The Mochi Palace” prior to it being converted over for company use.  I suppose there was Big Chuck’s Auto Body over the spring and summer, but that was a very temporary and focused setup. My hope is this shop will be in place – or at least travel with me – for a few years yet.  But I’d be lying if I said that brief taste of having a workspace that was just mine and wasn’t critical to the operation of something else, or had to be kept up in appearances for somebody else’s tastes, didn’t influence my ultimate decision to seek less costly pastures.

First, before we get to the shop, though, we gotta talk about The Move:

I’d already containerized my life pretty well due to the somewhat frequent moving of shops in the past few years, so I just continued ordering more of the same sized 27″ totey-bins. The FIRST Robotics branded ones date back to the “Recycle Rush” game a few years ago and were picked up for real cheap. This meant that beyond loose large automotive tools such as the engine crane and errant van parts, the move was quite well coordinated. What I didn’t get into totes got put into some large cardboard boxes left over from company-received shipment (e.g. of toolboxes and big plastic tanks among other things).  The 16 foot Uhaul truck was filled to about 4 feet in front of the door, which was earmarked for furniture.  This whole thing was tied up in the “web of lies” formation shown above, as we nicknamed it.

While I’m not that big of a stickler for organization, it was a good time to take account of everything heavy that I owned, and I actually sold off a lot of stuff on eBay over the fall months that more or less funded the entire move! Hurray!

First order of business: Puke everything inside the garage and deal with it later!

 

Couple days in and I’m working on setting the shelves back up, at least, so I can start throwing totes and robot parts onto them.

I also decided to just spend a weekend in early January and build myself some workbenches. I spent a while scouting Craigslist, classified ads, and equipment dealers, but wasn’t really finding any ones that looked good in the quantity I was hoping for. There were some, but I’d basically be buying new anyway costwise (Then I’d just buy new). So instead of dropping like $1000 on workbenches when I can blow on Overhaul instead, I decided to spend $100 at Home Depot and knock these out. I made two 3 x 8 foot benches in the “usual” hobbyist style – for some reason, basically every workbench I’ve seen be handmade is made this way. Guess it’s a pretty solid design for the effort involved.

I also made a rolling table for Overhaul and eventually other projects, just the same method but with the legs cut short so I could put it on a set of total-locking casters, and have it be…

…equal in height to the benches for easy transfer of things on and off!

Overall I was quite satisfied with the “Majority of 1 Saturday” work and cost. My only regret? Using the OSB as a top. I might skin it in hardboard or MDF later on. The tops are double layered 1/2″ OSB – nice and sturdy, but don’t run your hand across it. I coated the edges with some left over spray-on urethane I brought down, which lowered the splinter factor somewhat.

 

By mid-January, it’s almost looking like a functional workspace! I noticed there was a light fixture with a broken bulb up above the lower set of rafters, so I decided to get a gigantic 100W (actual!) LED “corn cob” light to put up there. It really lights the place up, but casts strange shadows due to the rafters.

I ordered extra shelves to unpack Big Chuck’s Auto Body and also finally give my screw collection a home.

 

When the opportunity presented, I also went on tool runs based on findings from Craigslist, Facebook Marketplace, and the like. I managed to land this ‘vintage’ Craftsman bandsaw for only $100. I was out to get a vertical bandsaw to at least be able to cut most sheet materials to make stuff if need be, and wanted to avoid getting a chintzy small one. This Craftsman was the perfect size – I could wrestle it around, but also trusted it was solid enough to do actual work.

 

One cheeky change I made though, right after getting it, was re-gearing the saw through its belt drive. It was definitely a wood-cutting bandsaw by intent – there’s only like a 2:1 ratio between the motor and the blade wheels. I changed this to a roughly 4.25:1, halving the blade speed. Once I put a 14 tooth variable-pitch bimetal blade on it, this thing was basically unstoppable in aluminum. I tested cutting a 2″ wide bar through its width (i.e. a 2″ depth of cut) and it was handled admirably. Just can’t do steel on it, since the blade speed is still much too high- I’d have to put a back gear on it or something to be able to cut steels.

In early February now, and I’ve basically set the space up for Overhaul work. You can see another Craigslist acquisiton to the left – the 3-ton size arbor press. I haven’t given it a permanent home yet, but it just gets clamped to whatever bench I need to smash something on.

Rewinding a bit back to the week of move-in… one of the first things to go up is the 3D printing station and Equals Zero shipping area.

Later on, I found this table on the damn sidewalk while driving home one day through the back residential streets. How quaint! Good thing I only have vehicles that can convey large volumes of stuff. I gave the top a quick sanding and oil coat, and here we are – supplemental shipping/assembly bench or electronics area.

Check out the row of Equals Zero stock shelves in the background. I found a “local minima” price solution that was ordering a certain Home Depot shelf size online (picking up in person) and then ordering a certain set of casters on Amazon. There’s more of these now, actually.

Speaking of which, I also handed Jeff Bezos some money to dress out this corner as an EE station. Hopefully I’ll pick up more instrumentation too, relatively soon! Right now it’s enough to put together Ragebridges and whatnot, which is all I need it for.

Obviously these facilities will evolve as I need them. For now, they’ll carry me through most of the projects I think I’ll get up to, and allow some basic consulting work to happen too. There’s the unfinished basement which is currently very underutilized because it’s not climate controlled and tends to be a bit moist and drafty – not a good environment for 3D printers or electronics. I currently have it just as cold storage, but might move more things there such as the van parts shelf if I end up collecting more tools.  But here we are! Welcome to the #RobotTrapShop.

A New Beginning: The 17th Chapter; Back to the A-Town

Apr 02, 2020 in Stuff

Geez, how many times have I made this kind of post on this site? Seems like I change local environs quite often! Thus is the nature of fast-paced, action-packed entrepreneurship and #startupthuglyfe. In 2015, I left my position as an MIT instructor and set up at the Artisan’s Asylum. It’s hard to believe Sadbot is almost 5 years old, but indeed, I built its first version in the fall and winter of 2015, along with the first experiments in what would become Brushless Rage.

Just over a year later, my buddy Adam Bercu (of team Brutus) and I rented a somewhat very derelict old manufacturing building unit north of Boston, finally having a place we could call “The Shop”. From here, Equals Zero Designs went a lot bigger time, and we took on almost a dozen local consulting gigs and contract design/manufacturing jobs. And from there, as things tend to evolve, the “startup” I’ve been hinting at since 2018 or so was formed.

Now, for 2020, I’ve set up in yet another new location:

welcome to the #RobotTrapHouse

Don’t get too excited, I didn’t buy it….yet

The plot twist though? It’s in Atlanta, Georgia! So what’s the deal… did you bring the company with you? Quite the opposite, rather: After two and a half years of co-piloting the ship from its humble inception, I decided I was finally comfortable in leaving Boston for good. Equals Zero did travel with me (as the pile of Ragebridges in the dining room can attest to), and I still retain some equity in the company, so I’m extremely supportive of everyone there helping making it succeed.

charles on startups

Now is the time that I’ll finally reveal what it is I’ve been up to, what with over a dozen posts hinting at Product this and Company that. The company is Kiwi Technologies, the product is a giant-ass drone for agricultural payloads, and I was its founding and early stage CTO.

I have a lot to say about going through the whole motion of doing a venture-backed startup company, and it took some time and separation for me to really be able to put it in words and organized thoughts. The short story is, I wouldn’t hesitate to do it all over again, and I enjoyed greatly the “wild west” days of chasing the business case while also moving rapidly with a demoable, potentially saleable product from concept to testing. I could probably write a whole book, much less a blog post, on How to Your First Startup at this point. I do believe we did as many things “right” as possible, because both Adam and I had extensive experience working with, working for, or advising startups in Boston that ultimately crashed and burned.

There’s often a distinction in startup-world between a founding CTO and an operating or growth CTO. The first one is often a founder or co-founder and has to pull together many domains of knowledge in order to quickly advance product development. That, I felt, was where I shined the most. It was where I felt able to provide both the most value in terms of personal contributions, and (more importantly) to help organize and direct engineers’ efforts. But as the company’s needs grew from R&D and prototyping into becoming a more deployment and sales-centric organization, I definitely felt like my usefulness began to wane, as my interests were no longer aligned with the goals and needs of the company. That’s alright – this is why you hire good people, after all. We combed through our network hard, spearfishing for the people we thought would make for the best leaders in certain segments of the company, and eventually hired enough folks that could do my job(s) far better than I could – an actual electronics engineer, an actual software engineer with extensive firmware and controls experience, etc.

While I don’t like tooting my own horn (beep), I like to think that one of my personal traits that helped the company along is that I don’t really have an egotistical stake in anything. I don’t need to have my name be first anywhere, or be known as a revolutionary god-king or even feel the need to take credit for every accomplishment if we all contributed hard work to it. It meant, above all else, knowing when to stop, and that I think is something that a lot of engineers and inventor types have trouble with. In a way, this is also me admitting that I’ll never be an Elon Musk or Jeff Bezos kind of figure. But hey, you live and you learn more about yourself when challenged with things way outside of your usual modus operandi.

So we discussed my resignation and replacement in the middle of July 2019, and my last actions at the company took place more or less right after my Dragon Con trip – 30haul was the last thing I made in our shop, then we agreed that I would recuse myself from visiting or being around the company daily so as to help keep the leadership transition clean. After November, I would only visit to pack up and move out!

so what the hell did you build, anyway?

Without divulging too many insider details, the early days of “the company” in 2017 was still more of an Equals Zero side project. There was a lot of experimentation in trying to create a low-cost, high-thrust/high efficiency propeller pod using commercial, off the shelf (COTS) and especially hobby-grade parts, without just spamming outrunners and small props. We were, back then, intent on taking on the many Silicon Valley based aerial taxi/personal VTOL companies, places I called (openly, to our potential investors, maybe to the chagrin of everyone else) “Daddy’s Money Companies” referring to Larry Page bankrolling a lot of them.

As we prowled the network, agricultural application (“crop dusting”) entered the realm of possibilities and quickly revealed itself to be an industry worthy of transformation. Conceptual work solidified in 2018 with a first flying prototype (still looking kind of like a personal rideable VTOL, since we already designed that), and in 2019 with the first customer-targeted prototype using much bigger gear. The object seen on the website today is another iteration based on customer’s needs and feedback.

Again, maybe in due time, one day, I’ll go back through my photos and make some “build reports”. But as one of the biggest lessons I learned while part of this grand experiment was some times you have to shut up about what you’re doing in order to preserve its value to others, I’ll simply present one photo of what I was most proud of:

That there is an eight hundred pound all-electric quadcopter with a 120kW powertrain. The tank on top is a 50 gallon agricultural spray tank. All I can say is, I have a lot of personal business in this realm that’s unfinished, and one day I hope to revisit it.

anyways, back to the #RobotTrapHouse

The observant will notice that I had a post gap in the middle of the Vantruck restoration this summer, between late July and late September. That was largely attributable to me hustling the project along while making sure the loose ends were getting tied off at the shop, while making transition documentation. Then there was a gap until late November – during this time, I made a van trip to Atlanta to scout out housing and interview in-person at a few job candidates.

I was real excited to find this place in particular because it’s very close to a massive shopping center/retail area in an inner suburb, not out in McMansionland like what is very easy to get in Atlanta otherwise. It’s an older 3 bedroom, 2 bathroom house with a half-basement in the “split level” style, with a detached (!) 25 foot square, 2-car sized garage building in the back yard. It stood out so much against other housing candidates that, after visiting, I decided to open loop move: that I will capture it first, job offers be damned, because I could always try and run a consulting gig from the workshop!

So I actually laid out quite a bit of cash here – as I wasn’t employed at the time, I negotiated with the owner to pay up front the first 3 months. I figure if I couldn’t find employment or start something by then, it was never meant to be.

The move itself was held in 2 stages starting December 15th. First, I (with the help of many) packed up all of my mountains of robot junk and life needs (one vastly outweighing and outsizing the other…. guess which) and re-enacted this very common scene:

Then after puking everything inside and pretending to live like a human being for a few days, I flew back to Boston to retrieve my white elephant, which held some other less critical life goodies. This ended about as well as you’d expect:

So how on earth did you make it all the way to Dragon Con and back? Whatever.

I got close enough (mid-Virginia on I-81) that a friend and I were able to chain AAA tow benefits to drop it off in my driveway (!!!) where it can hang out unmolested. I’ll deal with YOU later.

Anyways, I spent the first couple of weeks getting a handle on the new environment and new job & coworkers, working on finishing Overhaul 3′s design (you know what’s coming next!) and most importantly…

Building up the future home of Overhaul and friends. I constructed a few workbenches and a 4 x 8 foot rolling worktable and ordered more shelves, as well as some other toys:

This time, I pledged to not buy anything that weighed several thousand pounds which could not also move itself. While this opens the floor up to more vans, it meant I was going to keep my machinery small. I haven’t had a personal tinylathe since the MIT IDC days, and since then the market structure has changed significantly. There’s a ton more options now! What you see here is an “8×16″ model, basically the 7 inch lathe with a 1 inch spacer on everything. I was fine with this since it gave me the additional diameter I would need to turn even some Overhaul-sized parts. This machine is worth a Beyond Unboxing post as a tour – one of many back-posts I need to make now that life has finally collapsed its wavefunctions and I feel some sense of normalcy™.

Wait! Did I say “more vans”? Because this is how you get more vans:

 

Yup. This is how you know I’ve finally snapped: I bought a Real People Car.

Ladies and gentlemen, welcome the current-events-relevant-named #Coronavan to Big Chuck’s Auto Body.

After starting my new job in January, I now have a Real People Commute – it’s 20 miles one way, which isn’t bad by Atlantese standards, but is much more than the 4-5 miles daily of life back in the denser inner suburbs of Boston. After Mikuvan crested 250,000 miles one day coming home….

…and after Vantruck got rear-ended a second time coming back from the local monthly car show, this time a hit-and-run…

…I decided that once and for all that having my meme fleet serve daily duty, especially a rare and unusual thing like Mikuvan for which parts are not readily available, was just too much risk. That was a crash which would have likely totaled out Mikuvan. Granted, I barely felt it and thought I hit a pothole or speed bump I didn’t see.

(Seriously, how do people miss the wall of Miku slowing down in front of them? I watched the guy pull an illegal turn and drive away with his front bumper hanging off, so I hope I got at least his radiator or something!)

Anyhow, I’ve been “meaning to” get a Real People Car as a next step, but figured it would be after a few months of Trial Edition on my new life. That schedule got advanced, and I decided to keep it pain-free and go for the Amazon Prime car buying experience of using Carvana, after being recommended it by a few friends. I can definitely vouch for the painlessness of the process. Maybe I could have saved a thousand dollars or two by playing hardball with local dealers, but I was in no mood to (with Overhaul’s build going full-speed at the time), and figured if I can’t earn a few thousand dollars equivalent over a few years, again, maybe something wasn’t meant to be.

I decided that any Charles RPC I got had to replicate Mikuvan’s functions as much as possible. I was leaning towards a reasonably sized truck, like a Nissan Frontier or similar. But really after hashing out the things I regularly tote around, keeping it #vanlyfe made far more sense. I also have rented enough Grand Caravans to know that Stow-n-Go seating is a blessing from the automotive gods – in under 2 minutes I can convert #coronavan from 7-seater to a long-bed compact truck.  So here I am, having gone from rad to dad.

Anyhow, that’s the story of my life for the past 5 or so months – which is pretty insane to think about how much has changed since November. I even have trouble grasping it really today, and think it’ll take a lot longer to fully sink in.

where to go from here?

Honestly? I don’t really know!

It is truly a strange feeling now that it’s “happened” and I’m no longer in Boston and nearby MIT. I have plenty of friends and a reasonable network here in the area from high school and from friends that went to Georgia Tech. Atlanta isn’t a startup hub (yet) like the Northeast tech corridor or Silicon Valley, but it does have a healthy maker scene and several smaller startup and tech incubators, a few of which I’ve gotten to know during the course of my networking and introductions back in October.

I currently work at the Georgia Tech Research Institute, basically GT’s Lincoln Labs, in the UAV division working with several different projects. They are all well summed up by “Putting fancy hats on drones”.

Everything’s changed so much that I’ll probably take at least this couple of months to just level out and work on little things, maybe get back to my electronics side. I’d like to leverage having #Coronavan now to take Mikuvan offline for longer periods of time and address issues here and there that have gone neglected. Maybe even do its Vantruck-esque exterior restoration this coming summer or fall.

In the mean time, for all of you, brace for incoming Overhaul 3 content!

Brushless Rage: The Final Board Revision, For Real This Time

Jul 16, 2017 in Stuff

It’s getting closer! This will be a minipost addressing the last design conundrum in the signal board – how to get the optocoupler input to play nice with a programming linker.  Last time, I discovered that the USB linkers didn’t play nicely with my oddball bidirectional optocoupler setup, so I halved the bidirectional opto and pushed a new board revision. Clearly, I didn’t get to the bottom of what the mysterious 1-wire bidirectional serial-like bus of the popular SimonK/BLHeli bootloaders want, so here is my short investigation.

What happened was while I could use the R/C input side of the optocoupler, the programming header only worked without a pulldown resistor. This, of course, meant the optocoupler no longer worked, so I was still in the same state as before.

I already understood that my preference for pulldown resistors is the opposite of “normal” practice which is pullup resistors, but wanted to try to see if it would play anyway. I guess not :(

So I fully decoupled the opto to watch what the bus wants to do when it’s being programmed. Here’s the sequence of exchanges between the programmer and the board. The programmer talks in 3.3v but the microcontroller responds in 5V, then there is an idle waiting period which is pulled high.

With the programmer plugged in but not transmitting, the line is pulled high to 3.3v. This works with the bootloader detector in the firmware such that when it wakes up, it will not activate the main program if it detects logic high for a certain time period.

The programmer initiates communication first at 3.3v. I wonder if it’s 3.3V because it’s an easy voltage to regulate down to from the 5V of the USB connector, and keeps the programmer compatible with controllers that might use 3.3V (as not all micros have higher voltage tolerant pins).

 

And the chip responds using 5V (or if this were a 3.3v board, it would also be 3.3v). I can’t be arsed to actually decypher or research the bus, I just want my electrical interface to work.  Open-collector (pull-up) logic buses have a benefit of being able to tolerate different voltage levels on different devices like this, so I guess that’s why it’s more standard practice!

As I feared, my pull-down style optocoupler forced the bus idle state too low for either process to begin. It seems like the default state is high impedance or at least a VERY high resistance pullup, because this was taken using a 10K pulldown resistor (which caused the opto to be extremely noisy, so it was going to be unusable)

Okay, okay, fine. I’ll change the opto circuit to be a pullup like a competent EE and use the Inverted input setting in SimonK.

Some little blue wire edits to the board to change the configuration permanently, and we have a working board which can both program with a USB linker AND take opto-isolated R/C signal in! The irony is not lost on me that the original, unmodified I2C bidirectional optocoupler circuit would have worked just fine with the bus, but I’m not going to go back to it at this time. :’(

Oh, by the way, the LEDs? They’re also pulled up by default and the chip pin is driven low or turned off to light them. Like the opposite of how I want it.

Alright, time to commit the Little Blue Wires to the board. I swear, this is the last revision! Right now with the edited board, all I need to do is flash the initial firmware payload on using a chip socket. From there, I can then use the AfroESC USB dongle to talk using the PROG header. A commercialized Brushless Rage will come with the bootloader-enabled firmware and Reasonable Settings already written.

 

Detroit Maker Faire is coming up in 2 weeks, and I’m intending to take a batch of Brushless Ragebabies there to get them whipped into shape! And coming up soon, a writeup on modifying the FiTech Fuel Command Center to not melt down.

A Different Kind of Chinese Motor Controller?! Adding Dynamic Braking to your Inexpensive Chinese VFD

Apr 06, 2017 in Beyond Unboxing, Reference Posts, Stuff

Here at Big Chuck’s Robot Warehouse, we love our Chinese motor controllers. I some times think that at this point in life, I’ve become a kind of Chinese motor controller evolutionary biologist…. or at least like the Identifying Wood guy of underpowered gate drive amplifiers, I hope. Taking apart and examining motor controllers, which I’ve written up many times on this site in “Beyond Unboxing”,  is a large part of how I came to understand them, at least to the degree that Man can comprehend the transcendent nature of motor controllers.

Navigating the Pacific Rim of Chinese mass-market industrial products is not for the feint of heart – often times, products are sold over-rated and inaccurately advertised, and much of the knowledge base of using these products exists on hobbyist forums and message boards/email threads. This means anyone else outside of a circle of knowledge who tries to buy something and use it is often frustrated due to the lack of official documentation… and to find any good documentation often requires sifting through a forum thread or (heaven forbid) Github repository. That’s what I try to remedy whenever I cross paths with it, with some detailed writeup and explanation of what’s going on. Because at least that appears on a search engine result in a comprehensible fashion!

Today, we *gets out David Attenborough voice chipset* will be getting a closer look at a different species of Chinese motor controller. Rarely seen in the North American continent compared to its smaller, domesticated brethren, it is the majestic Giant Chinese VFD.

This one’s an adolescent male, with a 9/2016 date code. You can tell from his unadorned, angular ABS plastic case, compared to the more ornate and filleted females. He’s just begun to venture into the wild alone to expand his territory.

He stalks his prey, an aging Bridgeport J-head, from the safety of his preferred observation grounds, a nearby wall:

Okay, that’s enough, David. Also, lyrebirds are cool.

So why do I need a VFD? The shop has easily-obtainable 208V single-phase power which we had installed, as seen by the new junction box behind the mill. 208V is just missing the 3rd phase to become 3-phase, but that doesn’t exist in the vicinity and wasn’t going to be cheap to run. Hell, even if I had 3 phase, I’d still be getting a VFD anyway to have the additional running envelope and ability to change to arbitrary speeds. You mean keeping the Bridgeport in low gear and revving the motor to 13,000 RPM isn’t a good idea?

I did an initial sweep of the space of available Chinese VFDs back in January. Did you expect me to pay actual money for a real, working and supported product? Come on now, you know I’d rather jump into a pool of sharks. Chinese knockoff sharks!

As you can see, they all look kind of alike, and based on my brief research on DIY CNC forums and groups, they’re basically all the same genericized design. This is similar to other Chinese industrial products, including my favorite e-bike and R/C brushless controllers.

I have a rule called the “Law of Chinese Packaging Inertia” – if the Chinese product visually appears the same as a counterpart, it very likely is the same, or has trivial differences for marketing reasons. There’s been no better proof of this law than hoverboards seg-things, but it’s existed substantially in the past in the form of cordless drill motors for robots, the aforementioned e-bike controllers, and the like.

On eBay, there are numerous US-based resellers of the same products:

 

 

So I picked one which was severely overrated nominally for the motor it was to be running – a 3 HP (4kW) rated one, thereafter sorting by distance nearest and free shipping. You Only Line-start Once.

I figured I might as well err on the side of caution ratings-wise, since my other Chinese product rule is known as the “Harbor Freight Derating Factor”: derate by half if you intend to use it, and by 2/3rds if you’re standing under it. Vantruck weighs 3 tons. Have you seen how thin the metal is on a 3-ton Harbor Freight jackstand?! Don’t give me none of that shit…

The real reason, though, was because I picked the size originally for eventually powering the lathe, which has a pretty beefy spindle motor. I decided to outfit the mill first because it was a bit safer of a proposition to try something unknown on – there’s less rotating mass to bring to a halt.

Alright, my life is settling down a little after Motorama and the insurance & mechanics nonsense. Let’s wire up the mill!

 

Actually, speaking of “have you ever”…. have you ever seen inside a 1HP Bridgeport J-head “pancake motor”? I have actually never looked inside one until now, somehow, and it really is an axial-flux motor! For some reason I always mentally wrote it off as a very stubby conventional motor, but this makes so much more sense. Have a look at these photos! I didn’t take apart the motor since I “get it”, but that was a good trivia day.

 

I had to remove the drum switch (for manually powering in forward or reverse) and then drill an access hole in the 1/4″ thick cast iron junction box for a cable grip. This was when I discovered the previous operators used a 3-conductor service cord on a 3 phase motor with no ground. The ground was an extra piece of hookup wire mashed into the cable grip, electrical taped around the machine, and eventually into the 4-prong twist-lock plug. Well, at least it was grounded.

Wiring was pretty easy after that, and the instruction booklet which came with it was very Technical Chinglish but easily decypherable (and comparable to other more English manuals for VFDs).

Has anyone seen THE USE OF MANUAL???

These things will allow you to change a lot of parameters about the motor, and you can set the V/F line to have 2 slopes for more torque in certain operating regimes, etc. They call this “arbitrary” V/F curves, but no, it’s not really that. It came with a bunch of parameters set assume 50hz mains, which I changed to 60hz. Other parameters control what inputs the drive unit listens to – I hooked up an external potentiometer and told it to use the potentiometer to control the speed, as the unit DESPITE BEING ADVERTISED WITH ONE IN THE PHOTO didn’t come with a knob on the control board! See the very first photo above.

I cut the faceplate open to try and see if there was one hiding in there or something. Nope, missing. This will become a trend.

Most of the parameters I ended up leaving stock until I had a better feel for the system, since I’d not set up a VFD before. These inexpensive units are generally open-loop VFDs – they don’t have a tachometer input, though there seems to be an option in the settings… I’ll have to look a little more in detail.  They just bang out a frequency, and you can set how fast it increases that frequency for acceleration; if you set it too fast, you fall off the optimal slip region for maximum torque and your motor actually takes much longer to spin up (Induction motors require the supplied field frequency to be just a little faster than its rotational speed for torque production).

 

I call this the DOUBLE DANGLE

 

Slowing down was the hard part. Nominally, this thing had “braking”, and included terminals for a dynamic braking resistor, subway train style. I added one found in the bowels of MITERS – a 120 ohm, 50 watt unit. A little undersized, but it’s not like I’m stopping this motor every 10 seconds for a tool change.

Despite having the options selected, I couldn’t get it to actually perform any braking. I could either 1. set the ramp-down time to nearly as long as the machine would take to coast down by itself, or 2. just use “coasting stop” mode which was exactly the same damn thing because it just lets go of the output.

Attempting to set the spindown time faster simply resulted in the unit shutting down outputs and displaying an overvoltage error. Yes, it would make sense – when the motor regenerates power into the controller, it needs to go somewhere. In EV controllers, it’s back into the battery. I’ve never heard of a ‘grid tie VFD” for controlling machines before, though conceivable it could track the mains voltage to try and dump current back into the building, but why would you do that…. Or, you burn it off in a braking resistor.

Without any of those sinks of power, the voltage on the DC power rails of the VFD will spike upwards uncontrollably. It looks like this one will shut off at 400V on the DC power bus. I investigated a little more with stopping from different speeds, and it’s definitely correlated to the energy contained in the rotor and how fast I try to slow it down. So, it thinks it’s doing braking, but nothing is happening.

Well, I could leave it in coast mode, but what fun is not going down without a fight with a poorly documented Chinese product to the death?!

 

Step 1: Crack it open. Here’s what the power stage looks like. All the familiar trappings of a motor controller are there! Immediately, I can see that one of the gate drive optocouplers is missing…. probably the one that tugs on the braking IGBT.For a rundown on the symptoms I described here, read that article. It’s nice.

With some more research (read: forum threads… literally, read forum threads, like this one and this one) I found hints that a lot of these Inexpensive Chinese VFDs ship without any of the braking components populated. Given that this thing came with no potentiometer either, I’m entirely unsurprised. What I don’t get is what market they expect to sell to; a lot of them are advertised for process pumps (e.g. water pumps, blowers, oil pumps and the like) which I presume is a thing that doesn’t really need braking and doesn’t need constantly variable speed control, but maybe just 2 or 3 speeds and an on/off.

That’s another thing about Chinesium I can appreciate, even if I find it frustrating. Everything is stripped down and rat rodded to the point of doing only 1 thing, but it will probably do that 1 thing very well.

Staring at the P+ and PR terminals for the braking resistor under a backlight shows that there’s nothing connected to PR. It looks like there should be a wire jump…

Probably to here. The missing IGBT is connected via a wire jump to something. It’s functioning (based on the pinout of most IGBTs of this package) as a common-emitter  switch, one leg tied to ground and the other leg pulling on something. That something is supposed to be the DC rail (P+) through the braking resistor (between P+ and PR). My board seems to be a newer revision than the ones found on those threads, as a lot of the parts which were 8pin through-hole parts are now SMT parts, and the layout is different. Either way, from my investigation, 2 parts are missing: Q23, the bremschopper, and PC11, the optocoupled driver which tells it what to do.

So, if I haven’t reiterated, I fucking hate digging through forum threads to find the answer to my question. All y’all need to learn to keep a website. Read on if you want to add dynamic braking to your Inexpensive Chinese VFD!

I figured the parts used for this extra drive circuit should just be the same as the rest, so I ordered a pack of the IGBTs used on the board – FGH60N60SMD. The optocoupler driver TLP701AF didn’t have an exact match in-stock at Digi-Key, so I went for a similar equipped part number, TLP701HF.  The -AF part seems to have tighter switching time tolerances. In a single switch configuration here, I figured it doesn’t matter.

By the way, fully optocoupled drive is something I really, really want for Brushless Rage… but it takes up a whole lot of space compared to some driver ICs :(

Mounting the IGBT onto the power stage required some creativity. I cut up a spare RageBridge silicone insulation tab for it, and mounted it on the heat sink plate where it should go. Then I bent the legs up to the point where they should fall right into the empty solder eyes on the board. I decided to do it this way since trying to solder the IGBT to the board first wouldn’t have guaranteed it being able to lie down flat on the heat sink.

On the board itself, I made the wire jump from Q23 to the PR terminal.

And finally, I reflowed PC11, the optocoupler, onto the board.

And you know what?! That was it!

Man, whoever made this just couldn’t be motivated to put the extra 3 parts on it, eh? Guys, we saved like 80 cents! Yay!

Granted, again, if 99% of your users just drive their hydroponic pot farms with it, they’ll never need the braking feature and you might as well leave those parts out. For everything else, there’s my fucking MasterCard. Ugh.

Here’s a test video showing the braking in action. I cycle through the viewable parameters when the motor is running so you can see the DC bus spike up before the resistor does its job.

“DCB” is an added braking option where after the frequency gets low enough, it will just short the leads of the motor together. This provides extra braking power for speeds that are too low to generate any voltage to push across the braking resistor.

So there you have it. That’s literally the only thing stopping these controllers from being more useful running machinery! Now that I have additional parts, I’m going to purchase another one and wire up the lathe too.

The Life of Charles: Untold Tales of February Through Now-ish; BattleBots, Markforg3d, 2.00Battleship, and Chibi-Mikuvan Upgrades

Jun 16, 2015 in Chibi-mikuvan, Electric Vehicle Design, Events, Stuff

Isn’t it sad that the last meaningful post on this site was in February? I think it’s a travesty. A combination of perfect storm factors has overwhelmed even my blogging habits. I’m kind of like the Waffle House test of blogging – if even I stopped blogging, you know some shit went down. And I do have some very interesting news to report. In no particular order of criticality or intensity, I present…

  1. The extent of what I can say about Battlebots on ABC before the season premier!
  2. I got a new shiny thing, a MarkForg3D Mark One continuous-filament 3d printer!
  3. Porting (heh) 2.00gokart to the water: The making of 2.00Battleship for this summer’s SUTD program.
  4. When it’s not robot season, it’s go-kart season. Time to make some changes to Chibi-Mikuvan!

(more…)