Eric and Jon,
Thanks for the educational replys. You are speaking from a background in FIRST I just don't have yet. I appreciate the discussion.
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Originally Posted by EricH
The second assumption is VITAL. If you're going to make a new technology legal, ALL TEAMS must be able to obtain it, preferably with minimal research. The easiest way to do that--and cheapest--is for FIRST to buy about 2000 sets of the item and distribute it via the KOP. Otherwise, you get the vouchers which may or may not be of any practical use. If it isn't in the KOP, it should be available from AndyMark/IFI/BaneBots/local retailers.
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I agree that it should be commercially available, but don't see how it's necessary that it be in the KOP or available from those particular vendors. There are plenty of things that are legal that don't fall into those categories. Colson wheels, for example, or any gearbox you can dig up or cannibalize from a commercial product. And why should our collective entry fees go for parts we don't want or need? FIRST has recognized this issue and said that next year, teams may elect not to even get a standard KOP, electing to accept a voucher instead.
Quote:
Originally Posted by EricH
As far as the first assumption, YES! You do have to have characterizations! (We'll assume fairly complete, but not completely complete.) Why, you ask? How else are you going to size motors properly for the applications? Not all teams have the equipment to test the motors, or the budget to replace ones that fry during testing. Not having even an incomplete characterization can result in teams frying motors left and right--and even with an incomplete one... See Tetrix motors on minibots in 2011.
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It seems to me that FIRST has already departed from this premise. See last year's [R48], part I: "up to 2 window lift, seat, windshield wiper or door motors obtained through either the FIRST-Automotive Recyclers Association partnership or from a prior years’ KOP." Since we were already allowed to use junkyard motors, with no info on their performance characteristics, why not brushless, too?
Quote:
Originally Posted by EricH
The motor system is the same way, except that it's limiting the maximum available power from motors instead of making the technical group's life easier. Same available motor pool = same available maximum power = no advantage unless you can put more motors from the pool on the robot and control them. It's been opening up a bit lately, but I think the main reason for brushless motors not being allowed is that the legal speed controllers can't handle them. But when you open up the pool of legal speed controllers, you have to make adjustments to the control system, somehow, or force the controllers to work with the system.
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I think Palardy was right when he said pointed out that as long as PWD is used for signaling, the control system doesn't care if the motor driver is brushed or brushless. He also pointed out that using more powerful motors gives no advantage when all teams are electrically limited by the fuses on the power distribution board to a maximum of 480 Watts per motor (40 amps x 12 volts).
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Originally Posted by Jon Stratis
- What if a team figures their mechanism only needs a couple of amps, so they use a cheap 5A speed controller? Who puts out the fire when something goes wrong and it draws 20A during a match?
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This is a very good point. I wasn't able to think of a likely safety problem, and this is one. But, it could be simply solved with a rule specifying that any motor controller be required to handle a minimum of 40 continuous amps. Any more is unnecessary, because the fuse protection mentioned above.
You both brought up the issue of suppliers being able to carry adequate stocks of parts to supply all teams who might want an item. I'm glad you did. This is an issue that bothers me a lot, and has caused our team to redesign mechanisms when vendors run out of stock on popular items. The rules are very specific about how a vendor must perform in order to be "a legitimate business source for COTS items".
Specifically, last year's [23]:
C. "The Vendor must be able to ship any general (i.e., non-FIRST unique) product within five business days of receiving a valid purchase request. It is recognized that certain unusual circumstances (such as 1,000 FIRST teams all ordering the same part at once from the same Vendor) may cause atypical delays in shipping due to backorders for even the largest Vendors. Such delays due to higher-than-normal order rates are excused."
D. "The Vendor should maintain sufficient stock or production capability to fill teams’ orders within a reasonable period during the build season (less than 1 week)."
Notice that a small shipping delay is acceptable, but running out of stock is not. From my reading of Chief Delphi and the experience of our team, neither BaneBots nor AndyMark would remain legitimate COTS sources if these criteria were strictly applied. Does FIRST maintain a list of qualified vendors? Has anyone ever been removed from this list for non-compliance? Since FIRST seems to allow vendors to slide by with a "well, they tried their best" attitude, why should this standard be strictly applied to any other vendor? Our team has learned from experience to buy critical parts during the off season, so that when the build season starts, and AM and BB run out of their stock, we don't end up on the short end of the stick.
The low cost of brushless controllers and motors, and the wide range of available options (these days they are practically a commodity) makes the at-risk investment in a couple of sizes of motors pretty low. Pre-buying a half dozen $20 ESCs beats the heck out of stocking up on $120 Jaguars, like we do now.
I think you are both right about the dangers of fragmenting the control system. That would just be a terrible idea all around. But, when the time comes to reevaluate the standard hardware, I hope a more open, less expensive system like a Raspberry Pi/Arduino controller gets a fair shake. The drawback to something like that is it might come with very little vendor support. Having the NI support staff available to work out problems is a big plus for a big name vendor.