Where in the world is RageBridge? Well, right now, it’s in the hands of the Shenzhenistani, as I have committed 100 boards to be fabbed and assembled as of Wednesday night.
That’s right. I’m all in. Come late January and going into February, I and my cohorts and enlisted minions hope to be able to begin filling orders. A new website is being set up and populated, and soon it will even have meaningful content to link to! Right now, it’s kind of a hollow shell and embarrassing to look at.
Here’s what went down after the publication of the Market Survey, which you should STILL take if you haven’t!.
(By the way, if you haven’t gorged yourself on How to Build your Everything Really Really Fast… well, it’s right there.)
While the survey was filling out, I was in fact busy designing yet another board revision. I promised no more, but in fact I wanted to add a few last finishing details. The adventures of the previous update with the boost converter told me that I had to better isolate the processor and current sensors (consumers of 5V logic power) from the current-laundering schemes of the 15V boost converter. One suboptimality was the placement of the 5V bus capacitor:
The red circle is the ceramic 5V logic regulator output capacitor, basically the big 10-gallon bucket of electrons that smooths out the wavy voltages coming from the inductor (L1). The issue is that it is on the other side of the inductor as the rest of the 5V circuit, indicated by the green highlight. Imagining that every trace was a resistor (which it is of course), the voltage-smoothing effects of the capacitor are very limited on the side which needs smooth power the most!
Oops. Chalk it up to Energetic Board Design. While this resulted in no problems in testing, I still wanted to change it. The ICs all have their local bypass capacitors, but they are very small (0.1uF). So, any disturbances injected onto the 5V rail will cause worse voltage fluctuations than if there were a large capacitor sitting on it. Think dropping a rock into a bowl of water vs. the proverbial 10 gallon bucket.
The fix was to … add another capacitor on the other side. Pretty simple.
It involved a little component-moving, but now there is another ceramic capacitor of equal size on the other side of the inductor. I also necked down the trace width severely going from said inductor to the 5V logic side compared to the path to the gate drive boost converter to function as a sort of resistive bottleneck – the power consumption of +5V logic is going to be pretty steady, but the boost converter will pull power in pulses. It’s another attempt to shield the more sensitive logic from the rough and tumble of the power side.
But that’s the little change.
The big change is the clearing of space for, and subsequent installation of, a small potentiometer to ADJUST YOUR CURRENT LIMIT!
Directly inspired by the market survey, I realized that a staggering amount of people wanted control of what the limit was. A larger percentage simply wanted adjustability, but a significant number also wanted the ability to completely disable it.
Well, I obliged, and agree that it’s a good idea. After all, 1 current limit does not fit all motors, and I fully believe in the freedom to explode your electronics if you choose to do so; because it’s another sale for me, right?
A 4mm miniature trimpot connected to my LAST ANALOG INPUT will function as an adjustable current limit input. Then, in the latest code, the pot is read a few dozen times (to make sure it’s not crazy) once at power-on to establish the limit. So, it’s not something you adjust live, but can be changed on power-cycle. After a certain threshold, the current limit is removed entirely and hence physically limited only by the motor and system resistance, plus or minus grenading the transistors.
I tested the proof of concept on the black board by … gluing a potentiometer onto it.
Pretty much. After getting this to work, I committed it to the board design with some more component moving and rerouting of traces to clear a path to the last ADC pin.
Here’s a picture of the version 5 boards, also the release candidate.
Because at this point it was basically the 2nd week of December, I elected to pass over MyroPCB, my usual board house, in the interest of just getting a board or two from Advanced Circuits (my other preferred place). It would take much less time, which was of the essence – I wanted to make sure it wasn’t delayed by the Christmas holidays. So, sadly, these board versions are green. Rest assured, however, that the boards being produced are completely murdered out. Black board, black chips, and black FETs. I ought to have the thing black conformal coated for that effect. Too bad, though, that the capacitors are brown with white striping. Hey Panasonic, throw me some black-on-black caps!
Under the left board is a production sample heatsink plate. I sourced these using my e-tentacles on mfg.com, and they come with a silicone insulator pad bonded to it. So, assembly of the boards will be just plopping the thing onto the heat sink. I’m going to build another version of my Nifty Bullet-Connector-Based Test Jig to power and function test the boards when they arrive. Inevitably there will be some duds, so I’d rather spend a few hours with comrades and pizza sniffing them out.
I’m sufficiently amused by the whole process of setting up a board for production through Myro that I kind of want to write all up, step by step, as a case study. It’s definitely not trivial and there was much legwork to me done on my end, like setting up the bill of materials (BOM) with specific details that I would otherwise have hand-waved or ignored. Myro’s quoting and purchasing process is also a little… mysterious. Getting boards done through them before was invaluable experience for stepping up to assembly.
With all that said, here’s the current battle plan:
The boards will be ready to ship, if all goes right, by the 1st week of February. I intend on bringing a pile to Motorama Robot Conflict 2013 – if you’re going, feel free to swipe one off me there.
Orders will be taken through my brand new website e0designs.com. Quit laughing – I know there’s nothing worth reading there yet. January will be spent making a better manual, collecting test data for current and temperature, and refining the firmware.
The trim levels and pricing are the following:
- $180 gets you the board, with heat sink plate, but without wire pigtails. A header pin group will be provided but not installed for people who want to, for instance, solder signal cable pigtails.
- $200 gets you the board with headers and 6″ long power and motor wire pigtails soldered, ready to connect using servo cables to your signal source. No connectors are included.
The tech support policy is send your questions to a future form service that will be on the e0designs.com website.
And finally, the return policy is flat fee, no questions asked for exchanges stemming from failures and burnouts, except for dead-on-arrival which will be the buyer’s responsibility to ship back for exchange or refund within n days, where n is a number to be determined. The fee is not yet settled. Think Castle Creations’ policy regarding these kinds of things.
Finally, in a commitment to make the controller world a better or at least more varied and colorful place (…says the creator of the black board), the source code and design files will be made available on e0designs.com when shipments begin. Who wants to try and race me to the first quadruple-FET-per-leg Ragebridge?
Keep in mind these terms are not final and are still being discussed and vetted!
But that’s not all.
Whatever happened to the DeWuts?
Remember the cheesy 3D printed DeWalt motor holder? I handed the design off to my preferred Sketchy Chinese CNC Co. Ltd. in mid-December to be duplicated in steel and aluminum. I’m actually more excited about this than the RageBridges for some reason, probably because I still like mechanical things and Überclocker 3 is counting on these hardcore.
Anyways, these ought to be coming home to roost in mid January (soon! Oh, how soon…). I intend on pushing these out to the new web shop too, for shipment also at the beginning of Feb.
The anticipated price for these is $100 for the full kit, bring-your-own motor. The full kit constitutes the three 6061 aluminum billet components of the mount, the 1566 steel integrated output shaft with retaining ring, the Delrin gearshift locking lever with securing hardware, and motor mounting screws. With the average cost of aftermarket DeWalt drill motors and gearboxes being about $70-80, figure on having a DeWalt 12-18v drive setup ready to roll for a bit under $200. I’m not planning on full-assembled kits yet, but after more thinking and discussion this could change, too.
Overall, this has been a very exciting start to the 2013 year, and a great if somewhat belated start to the Third Five-Year Plan (A post on the progress made under the Second Five-Year Plan will be forthcoming).