Why?
If we look at the spec sheet - http://www2.usfirst.org/2005comp/Specs/Globe_Motor.pdf, it shows a stall current of only 22A. If you look at the snap action circuit breaker spec sheet, it shows it needs 10 full seconds at the circuit breaker rating to blow. Therefore, I see no problem with running the Globe on a 20A breaker, and using a spike, if you don’t need speed control. This could save a team nearly $100, if they didn’t have to buy another speed controller.
I agree. Especially if you replace the fuse in the SPIKE with an auto-reset, which is legal. You’re probably not going to stall the motor for very long, and if you do, you’ll burn it before you hurt the spike, I would think. The only thing your team needs to decide is if they need the variable control of a victor. If not, make it easy in yourselves, right?
By <R61> this is specifically legal for the compressor; however, it is implicit that for any other device, this constitutes an illegal modification to the Spike (since it is specifically permitted as a modification, in one exceptional case only).
Also, if we interpret 5.3.9.1 in a consistent sense, to “protect” a circuit refers to the presence of an appropriate breaker in the panel, and not (necessarily) in the Spike itself, if present. (I say consistent, because the same phrasing is used to refer to Victors, which lack an integral fuse.)
So while that section may have been the source of the confusion, it appears that FIRST intends that the Spike fuses remain as installed, and an extra breaker be used to protect that circuit in a redundant fashion. From an electrical standpoint, I don’t really see why this is necessary, or even desirable—why mandate the use of two devices of the same current rating to protect a circuit, when one circuit breaker would be simpler, or two circuit breakers would be more useful (albeit exceptionally redundant)? Even a manually-resettable circuit breaker ought to be allowed (but isn’t) in place of the fuse. This rule seems to be one that keeps appearing in this form, and I’m not really sure why.
I believe this is only legal on the spike running the compressor -
<R61> The control system is provided to allow wireless control of the robots. The Operator Interface, Robot
Controller, Speed Controllers, Relay Modules, Radio Modems, Batteries, Battery Charger, AC Adapter, and
9-pin cables may not be tampered with, modified, or adjusted in any way, (tampering includes drilling,
cutting, machining, gluing, rewiring, etc.) with the following exceptions:
• The dip switches on the Operator Interface may be set as appropriate.
• The user programmable code in the Robot Controller may be customized.
© FIRST 2006 FIRST Robotics Competition Manual, Section 5 – The Robot, Rev C Page 18 of 30
• The Speed Controllers may be calibrated as described in owner’s manuals.
• The fuse on the Spike relay for the Air Compressor may be replaced with a 20 Amp Snap-Action circuit
breaker.
But if you have to worry about the globe blowing the fuse, then you have a mechanical design problem (stalling the motor).
Huh, I could’ve sworn that it was on any SPIKE. It doesn’t make any sense to use one on the compressor. It wouldn’t seem that the compressor would ever draw that much current.
Strange. I thought the same thing, but the 2006 AND 2005 rules clearly state this. Hmmm…
In the past teams had problems with the 20A fuse in the spike for the compressor blowing. When the compressor kicks on with an almost full tank it is near stall current, and repeated long enough a fuse will eventually fatigue and blow.
Allowing breakers in the spike for the compressor is a compromise, to keep teams from going through matches with no air pressure. Other motors that you use, driven by the spikes, should never be near stall current.
Guys,
You are missing the point on using circuit breakers on the robot electrical vs. the protection provided by a fuse in the Spike. The circuit breakers are chosen with minimum rating for protecting the wiring. (See R82, 83, 84) A 20 amp circuit breaker will keep a #18 from setting itself on fire in the event of a short. The 20 amp fuse in the Spike protects the contacts in the relay from destruction but does not protect the wiring since it is at the end of a wire run. Since the compressor draws more than 20 amps during start but has a run current much lower, IFI and First have determined that the fuse may be replaced by an auto reset circuit breaker for the compressor control only.
The globe motor can be used with a Spike with the understanding that you have no speed control. Only one motor per Spike, please.
All Chalupas (large and small) and all FP motors must be connected to Victors per R87.
Bearing in mind that this is (of course) totally illegal for FIRST purposes, what would be the effect of placing a jumper (or, alternatively a 100 A fuse) on the Spike, and a 20 A breaker in the panel, as usual? For a reasonable length of wire, wouldn’t the 20 A also lend sufficient protection to the Spike, or is the Spike so sensitive to a current spike ( :ahh: ) that it requires protection very close to the source of the fault? (If that fuse doesn’t blow very quickly indeed, I don’t see how that could be the case, though.)
putting a 20A fuse in the fuse box would work the same as having it in the spike itself. If you wanted to do that I dont know why it would be against the rules
but why would you want to? When a fuse blows that circuit is dead for the rest of the match. Breakers are better: if something momentarilly stalls a motor, or even if something gets across the motor terminals both a fuse and a breaker will protect the components and wiring
but only a breaker will keep trying to reset (and restore power) during a match.
You are correct that electrically it would perform the correct protection. But there are still two very good reasons to follow the electrical rules for the robot. The first is inspectors will be happier and secondly, IFI will be more likely to repair damaged units under warrantee when they know they have been used in accordance with the rule book. Remember that the fuse on the spike is nearest the motor and any fault there will not be isolated by several feet of wire (resistance) or the proximity to other bodies that may slow the reaction time of the fuse.
The electrical rules in particular have been well though out and cover as many bases as possible in an attempt to keep your robot running without settting the field on fire.
We had used the globs on spikes in the past, and in my opinion they get better use off a spike than a victor. Most of the applications for globes only require directional movement, not variable speed.
We passed inspection with it at VCU in '04, but when we got to Nats we were told “we weren’t allowed to run the globes off a spike”. I couldn’t believe it, so we ended up taking that mechanism off the robot (goal hook)
I concur, globes should be used for simple applications, thus not meeting the 22A stall, and should be perfectly fine for a spike.
Shayne,
We used the Globe motors to steer our crab systems in the past. This required a Victor controlling the motor.
Yeah, I would agree if you’re using them for something like that, then definitially.
My team personally sticks to using them for low speed low torque applications, or not at all.
I’m just saying that I think it should be ok if someone only needed the functionality of a spike for them to use it, and I’m still confused as to why we were flagged for it at Nats in '04…
Oh well :o
Shayne,
In 2004, Globe motors were required to be run only from speed controllers. The rules have changed.
I figured as much.
Thx!
Last year at our regional we were forced to take the globe off a spike, we were fortunate to have an extra victor…
It is EXTREMELY late in the build, but I am still slightly confused on this issue. The 2006 Tips and Good Practices states:
WARNING!
Attempting to drive a Van Door motor, Globe motors or Fisher-Price motors directly with the Spike Relay Modules could damage the Spike Relay Modules and is, therefore, prohibited.
However, R87 states that only CIMS and Fisher Price motors need be run off of the Victors.
So which is it?
It doesn’t greatly affect us, but it will save time on Thursday in Cleveland if we don’t have to switch from Spikes to Victors.
Thanks!
Kev
This figure might be read to imply no (because a Globe is shown only a Victor but not on a Spike)
This part of the rules seem to imply yes (what is not forbidden is allowed)
<R87> CIM motors and Fisher-Price motors must be connected to Speed Controllers. They may not be
connected to Relay Modules.
The rules specifically state that the figure is for “convenience” (implying the text/figures in the rules trump the figure).
Bottom line: I think it it allowed.
I have not been following the Q&A or Updates, if someone has a ruling from one of those, please share.
Joe J.
The following Q&A links teams to the “Guidelines, Tips & Good Practices” document which states that hooking a Globe to a spike is illegal. It also points to the Power Distribution document, which shows the Globe motor hooked up to a Victor. I took this to mean we had to wire the Globe through a Victor. Although, it has been stated in the Q&A that the “Guidelines, Tips & Good Practices” is only a set of guidelines, and not a rulebook.