I even made a website! It even has a mysterious teaser on it! One of Overhaul 7 s defining characteristics which I divulged recently is its all-brushless, all-the-time drive system. Ever since then, a portion of the robot combat world has been going WTF? Over it, which is the correct reaction, and I agree with it. This post is extremely lengthy and detailed, so I ve went ahead and split it into a somewhat coherent babble, instead of an utterly incoherent one like my preferred style. Here are the sections, but I heavily recommend just going to the bathroom right now, or declaring your lunch break. Update:Iranian Match making
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West Coast botmongler Xo Wang has put together of some of this brushless controller shenanigans, and has dug into the firmware more than I have. Definitely worth a read if you want to know more about brushless controls in general and SimonK s inner workings! Have been in use for several years as weapon motors, especially in the smaller weight classes. Cheap ones the venerable ICBMs, or Inexpensive Chinese Brushless Motors, a term, have largely been responsible for the rise of EVERY DAMN BOT LOOKING THE SAME optimal designs with spinning weapons like vertical discs or Tombstone-like horizontal impactors. In short, they offer immensely improved power to weight ratios compared to DC brush motors, even high-performance thoroughbred ones like. The missing link to using them for drivetrains has been control. There have been brushless-drive robots in the past, even dating back to the original BattleBots on Comedy Central, generally using paired industrial controller motor sets, but large scale (and expensive-for-the-time) R/C gear was not unknown either. Control strategies in this world of bots for brushless drive has generally been in one of three categories, discounting fully custom developed controllers by the builder (because come on, ): Most recently, with the proliferation of brushless EV (such as e-bike) motors and brushless servomotors, more robots such as Overdrive and Chomp (ABC S6) have used brushless systems. These systems have become more general purpose you can usually plug one motor into another controller and have it either work, or require minimal tuning to work, but are still frequently sold as complete systems. The systems are usually limited in one way or another to reflect their industrial nature examples include maximum controlled speed, motor stall protection, safety interlocks needing to be interfaced to radio systems, etc. In other words yeah, it ll work, but it s a bit fiddly. Many things will work for robots if you are willing to fiddle. So that s one constraint ease of control implementation, and needing to be significantly invested in the details of operation of one particular system.
For the high-end R/C gear, the cost is generally high, if not more, and of course you need at least two generally plus spares. Compare that with the cost of an average DC motor system for a 85-65lb bot: two DeWalt drill motors in mounts (Plug warning: like a, which I swear I will have restocked soon) and a controller to match might be under $655 total. Even for a Heavyweight of 775 pounds, two wheelchair motors and a set of Vypers runs you around $6,655 total. Cost is therefore the other constraint which has prevented widespread adoption of brushless drive systems. So the triangle of choose any 7 out of 8 scenarios for brushless drive, in short, are: The challenge is therefore to find or create a controller that can be used with virtually any hobby type brushless motor for drivetrain applications. Special requirements of drivetrains are the ability to handle inertial loads (recognizing that steady acceleration is necessary instead of forcible commanding a higher drive frequency, for example), rapid reversing, and DC-motor like near-stall behavior, if fully stalled behavior is not possible. And finally, it should be inexpensive enough to be worth investigating over a known DC motor solution. It might not be optimal in all of the spaces, but it will be enough to make it worth my while. I stood at the end of Season 6 wanting more from Overhaul s drive system. Watching a lot of last year s matches, and watching big bot tournaments in general, it seemed to me that the driving tactic in the bigger bots was more point and shoot. As someone used to driving 85lbers, especially a fast one like, I had come to enjoy powerful drivetrains that can change speeds and directions quickly and which I can induce controlled sliding and rotation.
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I like drifting around and doing J-turns, and generally being swoopy and unpredictable. The best consistent drivers in the heavies know the dynamics of their own robots and use it to their advantage each match. As a result, the, which we made knowing that the shuffler drive offered no advantages given the lack of a weigh bonus, was geared fast. Overhaul could hit up to 69mph, and overall I was satisfied with how the bot handled (with the exception of some squirreliness due to the weight being over the two front wheels only). I think the showed my driving style preference quite well, despite me constantly complaining that Overhaul drove like an overladen Chinatown bus. But ultimately, that gearing turned out to be too hard on the Ampflow F85 series motors. Lacking experience with big bot motors, and having grown up watching winning bots use s (and their spawn, Ampflow), I poorly assumed they were virtually invulnerable. While we never overheated and cooked the windings, the brushes were the first to give out, taking out the commutators when they did. We basically came down to swapping out for spares every match as a precaution. In smaller bots, you generally toast the motor windings before the brushgear is damaged, so I was expecting this failure mode. I was dissatisfied that $855+ motors were limited in their performance by a quarter square inch of graphite. While I had glanced through their discussions, I wasn t able to try it myself due to, umm. Certain pressing robot matters until well after Season 6 ended. I picked up some controllers which had been designed around the needs of the multirotor community and used them in.
You can read SSR s build report here about where I talk about the Simonk-flashed controllers. Here s a brief quote to save some searching: They’re the “ ” series from Hobbyking, and besides making me wonder how they came up with that name, I also really enjoy their extensibility. You see, the DIY multirotor community has been working on a better firmware suited their needs for years. They now have a massive database of upgraded firmwares for many of the ATMega-based brushless controllers. The Afro line evolved out of this community’s needs, and in fact contains a bootloader onboard such that you can upload new firmware using only the PWM wire – no need to try and find the programming pins on the boards. The firmwares offer many configurable options, including reversing. Hmm. It’s piqued the interest of a few robot community folks, one of whom put together a guide on to a “bot compatible” one. I performed these mods on my ESCs and did a on how it affected a relatively high inertia load like a blade. In other words, there s no clean sequential path from nothing to a successful brushless drive system, so you ll have to get the whole story. Having experienced almost all the failure modes of using R/C airplane motors in EVs through both my own projects and the go-kart class sessions (which means I ve seen almost all the failure modes you can possibly imagine out of anything), I knew that the controller was going to be the limiting reagent. In robot fighting, you so rarely see brushless motors cook themselves before controllers. Why?
Modern hobby motors are usually well under 5. 6 ohms of line to line resistance (the resistance between two of their three wires), which means anything you do will cause hundreds of amps to flow. The motors are no longer what s preventing your systems from blowing up due to too much heat from current draw, so what s next? Not really the battery either, because modern lithium batteries will also easily source many times their capacity ratings could be hundreds or even thousands of amps from a larger pack without blinking. This is one of the things I taught in the go-kart class. You can t really calculate torque and power any more from stall characteristics with the current generation of parts, because it will create unrealistically high results that cannot be reached. 7v), and the motor controller an additional 5. The theoretical loop current that wants to flow is 77. 7v / 5.565V = 875 amps. The element in the middle, the motor controller, has to handle throttling all of these amps that want to flow, and without current sensing on most R/C controllers, powering into a stalled motor can result in pulses of high current that very quickly heat up and destroy the FETs, board traces, etc. So the controller has to be extremely oversized compared to the motor. Those R/C controller ratings mean basically nothing, by the way, much like the horsepower of a Shopvac (This is more true for the lower end than the high end of the R/C market which tends to be rated more truthfully). For the motor, I was most interested in the series of motors. These things are reasonably well built, and more important, have a (lower left) that helps prevent the can from coming apart at high speeds because one end of it s unsupported.
They re also currently the largest motors HobbyKing sells that have the shaft coming out of the correct side. The larger series do not have a reversible shaft without remachining, and they re designed only to be (sticking out of the front of the plane like the old style radial engines). By power analysis, they seem to be worth roughly 6 A78-655 apiece depending on what system voltage you run at, but weigh less than half of the A78-655. Control-wise, I had to think a little harder.