New Speed Controllers :)

[Richard Wallace]

Originally Posted by Tom Bottiglieri

By the way, you would be much better off using thick stranded wire than one solid piece of wire. Current flows on the surface of a conductor, so the amount of current a single piece of wire can transmit is limited by its size.

Only the alternating component of electrical current tends to concentrate on the surface of a conductor. This is often called the skin effect. The effective depth to which current penetrates into the interior is inversely proportional to the square-root of the frequency at which the current alternates, so higher frequency current tends to concentrate on the surface, while dc is uniformly distributed over the cross-section of the conductor.

Since only a small component of the motor current in a FIRST robot is ac (due to the pulse-width modulation of the Victors), using stranded wire does not improve the current carrying capacity significantly over that of solid conductors with the same total cross section; i.e., the same AWG.

However, using stranded wire is still a good idea because it is less prone to damage from bending and flexing, and it forms better electrical connections when crimped to standard terminals.

[BrianBSL]

Are these actually new? I was pretty sure the 885's have been out for a while now. Maybe I'm just confusing myself though.

[Billfred]

Originally Posted by BrianBSL

Are these actually new? I was pretty sure the 885's have been out for a while now. Maybe I'm just confusing myself though.

I can't place a date or anything, but I know that the 885s have been available since at least last off-season.

[John Gutmann]

Originally Posted by Tom Bottiglieri

By the way, you would be much better off using thick stranded wire than one solid piece of wire. Current flows on the surface of a conductor, so the amount of current a single piece of wire can transmit is limited by its size.

By the way I know that, it was sarcasm because to run 120A through 1 wire you would need 0 gauge wire. which is about 1/2" in daiamter.

I can't even Imagine trying to run wires like that to a motor.

Besides you can really draw more current then the wire already on the motor will allow(if any), like the CIMs with out modifying it. Or if there is no wire you would have to go by cantact area, and the other motors dont have a big contact area.

[lukevanoort]

I really don't see these being used in FRC anytime soon, they're just too powerful. The price for a V885 is higher and the motors would be ungodly, an example of the type of motor these are for is the PERM PMG 132, it can pull 110A constant, it costs almost one thousand dollars! That is way to pricey for FIRST. Instead, I would also, like Gdeaver, like to see a little more computing in the 884. Maybe a just single, low-end PIC (although it might need shielding), some sort of sensing to keep you from frying it from wiring the inputs backwards, maybe a lower profile fan, and an improved PWM slot. (maybe like the old ones with just pins, then add a clip on the top to hold it in place) It could be the Victor 884-Xtreme (or 886), some cheap 20A speed controllers for the weaker motors would be nice too... (Maybe it's time for IFI to plunge into the Hobbyweight battle bot market with low current speed controllers, maybe name them the Rufus series)

[Andrew Blair]

Originally Posted by lukevanoort

some sort of sensing to keep you from frying it from wiring the inputs backwards

I can't believe it's not already there. That would be a great improvement.

Originally Posted by lukevanoort

and an improved PWM slot. (maybe like the old ones with just pins, then add a clip on the top to hold it in place)

Like these?

I like that too. http://www.robotmarketplace.com/mark...e_ifi_esc.html

[mtaman02]

Originally Posted by sparksandtabs

draining 120A continously will COMPLETELY drain your battery in 9 minutes flat. SO think about it if you have 2 motors (probally drive) running around 120. you battery will completey be drained in 4.5 minutes. Not to mention everything else your running. This means (estimate only) that by the end of the match your battery would be around 6-7 volts maybe. do you really wanna drain your batteries that fast? Besides doesn't that ruin them?

All this talk about draining batterys, don't you think maybe just maybe FIRST might hand out new batteries for next year b/c just like the field elements and some of the KOPs used they are old and we may just see some new stuff next year (Batteries, Control Systems, Motors and of course Field Elements) One could only hope =)

[Alex Golec]

Having little electrical background [besides knowing that the inputs must be wired correctly or the thing will melt], this is my perspective on the use of these-
As promising as these look, there is a setback to them: the $200 price tag, [only] $85 more than an 884. Unless the KOP includes enough victors to control every motor properly, there will be teams that will be at more of a disadvantage. Also, the 120A continuous draw seems potentially dangerous in situations where mechanical systems malfunction [robot damage] and cause the motors to run near stall. To me, it seems like you have your either-or choices of:
1)Victor Meltdown [and another $200 down to replace it]
2)Motor burnout and the stench of Eau de Fisher Price for the rest of day
3)Battery damage from high current draw.

My vote goes to the 884. Cheaper and Safer.

_Alex

[Tristan Lall]

Originally Posted by Alex469

Also, the 120A continuous draw seems potentially dangerous in situations where mechanical systems malfunction [robot damage] and cause the motors to run near stall.

The speed controller's current rating is the maximum that it can withstand. The fact that it can take 120 A actually means that it's safer—but that's not really important, because it's the circuit breakers that determine what current will actually pass through the circuit.