Re: fans on victors
 

Victor fans are not required by FIRST, but I'd definitely recommend them. The FETs work by switching the power to the motors on and off very quickly, which creates the heat. In reality, as I understand it, a FET will get hotter as the motor gets slower with the same amount of force needed to rotate it because it switches the motor on and off so fast (try touching a wire on and off of a battery that is connected to a CIM motor... the wire will get hot). The fans keep the FETs cool of course, and FETs are more efficient the cooler they are, and WILL release the magic smoke and stop working if you do not put fans on. I do realize that you said that you will have fans around your case, but I do not think that is enough. I would cut holes specifically for the fans and have some fans pull the hot air out of the case or move the victors to a different location.

Either two or three years ago at LSR on team didn't connect their fans, and their robot would only run for 30 seconds before stopping.

It's your choice, but, personally, I would recommend using fans.

Re: fans on victors
 

From my experience in designing a motor drive from scratch (Tech-Ed Independent study), power MOSFETS become warm and sometimes hot under normal operation. I was using 40A mosfets connected to a small RC car motor (24 turns) and they would heat up under normal operation. I therefore assume that the Victors use MOSFETS for their bridge (since thats what you use unless you use relays and that there are 12 mysterious TO-220 cases on there) and that therefore they would require some sort of cooling. I would consider it an error in judgement to run a victor without a fan since I have never seen a motor controller that did not have some form of heat dissipator, not to mention that the Victor does not have a heatsink unlike most industrial and commercial motor drivers.

Re: fans on victors
 

Boy,
I get busy for one day with FLL and the forum runs amuck.
Here is the whole scoop. Fans on victors are not required by FIRST but IFI wants to see them and that's why they are provided. From the 884 user's manual...
1. The fan must be wired so it is always ON when the Victor is ON.

and

The innovative FET switching architecture and an integral cooling fan ensures cool FET junction temperatures.


The FETs are rated at 64 amps each, for three in parallel that is 192 amps. But this rating is at 25 degrees C. As the temperature rises, the current must be derated such that at 100 degrees, each FET can only handle 45 amps for a total of 135 amps. Now seeing as the Chalupa motors (small CIM) have a stall current of 133 amps and with the derating factor of 135 amps at 100 C (remember that max allowable current goes down as the temp rises) if you want to live dangerously, then leave the fans off. Please don't be our alliance partner on Einstein.

As for weight, the Victor is only 4 oz total. The fan cannot be so heavy that it would mean the difference in meeting weight or not. A similar fan is speced out by the manufacturer at 1.25 oz or about 22 3/4" holes in aluminum box tube.

Re: fans on victors
 

Emphasis mine, I disagree with you here. 1.25oz is nearly .08 pounds. Get four fans off the 'bot and your looking at over a quarter of a pound! If I can loose weight by removing a fan or by drilling 22 holes, I'm chucking the fan first. Being able to instantly loose a quarter of a pound would have gotten more then a few 'bots under in the past. Heck, I've had robots on the scale over by a tenth. Thats one fan and some change.

If the fan isn't doing anything, and on low current motors it isn't, why keep it if you have the option? It may not be a good idea on a CIM or FP motor, but a globe? I wouldn't hesitate to remove the fan, even if I wasn't in dire straights to make the weight budget. It's just more weight that can be used for something useful, like larger wire.

As always, your mileage will vary. It's obviously outside of IFI's and FIRSTs recommendations, and teams that choose to do it should know the risks. But it's legal and does save weight. Doing it for fitments issues makes less sense to me, but hey, I've done it before for the same reason on non FIRST related stuff. Haven't killed a Victor yet.

-Andy A.

Re: fans on victors
 

Wasn't that a different model though? I remember hearing something about switching to the 884 in 2005, but that was my rookie year so I'm not sure what was used before that.

Anyway, my opinion is that you should keep the fans on. If one overheats, it's about $115 for a new one. I'd rather find some other way to dump 8 hundredths of a pound than potentially placing $115, a won match, and the time it takes to replace the victor in jeopardy.
Perhaps we need a conversion chart. One fan = X many speed holes = Y many links of chain = Z many inches of wire, etc.

Re: fans on victors
 

Andy,
We cannot make blanket statements on removing fans without some additional discussion. Teams may not be able to make the needed calculations to determine heat rise in the devices, air flow through an enclosed space or temperature dissipation in a match. The reality is that each team utilization is different and varies from match to match. Although the FET "ON" resistance is very low (.012 ohm) it still dissipates some heat. Due to the design of the Victor, the case of the FETs are shielded somewhat from ambient airflow so every milliwatt dissipated by the device does not get transferred to the ambient air. Referring to the IRL3103 spec sheet, the junction to ambient thermal resistance is 62 degrees C/Watt. Let's fudge that to 100 C/W due to the fact that the case is partially enclosed, and let's further increase it for the heat rise in the other electronics and wiring inside the Victor and the fact that 6 devices at a time are dissipating the same heat, and I am guessing the thermal resistance has now climbed to at least 150 or even 200 C/W. So as you can see, even small power can raise the junction temperature over a two minute match to a point where the device can no longer suppport even low currents. With the device trying to get rid of just one watt, the junction temperature has exceeded the max temperature specified by the manufacturer. By just calculating the derating factor for temperature the 94 watt max is reduced to 0.2 watts.
I will agree with you that it is unlikely a globe motor would cause an issue in light duty but stall current is still over 20 amps. I feel more confidant recommending teams keep the fans as a blanket statement. It will be the least costly alternative in the long run.

Re: fans on victors
 

As Al has pointed out IFI solved the heat disapation issue with the fans instead of heat sinks. One thing to keep in mind about the heat disapation.
Robot matches are only 2 min. 15 sec. However, during build season and practicing robots can be put thru much longer and tougher work outs putting much higher thermal stress on the victors. Keep the fans on. They are there for good reason.

Re: fans on victors
 

I would be concerned that 'plenty of ventilation' isn't the proper cooling that you need, especially if it's too tight for a fan. And 'ventilation' is much much different from forced air.

Re: fans on victors
 

I know the victor 885 can handle 120amps continuous, so the fan on that one is a no-brainer if you actually use it for something like that on an off-season project. I don't know what you are doing with your victor 884's, and I know they are different than the 885, but the fan is already there, and even if it isn't against the rules, it can only help you, not hinder. I can't right now think of any good reason to not have it on there. when playing with the team's old 2004 robot, it is very easy to blow breakers and heat up the victors to the point that they will cause minor burns if touched, and that is with the fans. its from a combination of the old power drill motors that were in the KOP and driving backwards and forwards quickly (doing wheelies) with a battery with a low voltage. (voltage down = current up, just enough to blow the breakers.)

also, been there done that with the extremely dense electronics box with ducted 120mm fans at both ends. is it possible? yes, is it convenient: no. there is actually not as much ventilation on the speed controller as you think. if you are in an alliance and you blow something, there had better be a runner up team because you wont repair or replace it in a timely manner.