Re: Does motor temp affect performance?
 

You'd think that, but Liquid CO2 is rare stuff below about 5 Atmospheres of pressure. So much so that Dry Ice (solid CO2) at sea level does not "melt", instead it "sublimes", going directly from solid to gaseous phase. Look at a phase diagram for CO2, you'll see that the liquid phase is very, very tiny.
Use care, though, since CO2 displaces the oxygen we need to breathe; let out enough of it (say, a 20 lb cylinder's worth) and you could pass out from a lack of oxygen. Very unlikely in a typical FRC pit setting, but just because it looks and smells like air doesn't mean you can breathe it for long
Two excellent points.

Long wires have more resistance than short wires (same diameter). How much does this matter? Say your CIM is drawing 40 Amps, and there is 1/10 (0.1) of an Ohm's worth of extra wire. Ohm's law says V=I*R, and if I=40A and R=0.1 Ohms, V=4 volts - that's how much voltage will be LOST in the wire. If BOTH wires are 0.1 Ohm long, that's 8 Volts (out of maybe 13) that is NOT getting to the motors. How well do CIMs run on 5 volts?

Heat sinks work best with convection, especially forced convection, BUT heat sinks are also dumping heat through radiation - which doesn't depend on air at all (such as in space). That's one reason to paint hot surfaces black, since that 'color' radiates heat best*

The heat sink 'grease' helps with conduction - that is, getting the heat from the motor into the heat sink.



*Actually, the best radiator is a very, very dark green, but black is within a percent or so and is easier to do.

Re: Does motor temp affect performance?
 

Paintball CO2 tanks are filled from industrial welding tanks (in general) that have siphons installed on the valves so that they fill the smaller tanks with liquid. A 20oz tank for example is filled until it is weighed and measured at its empty weight + 20oz, the extra mass being liquid CO2 in the tank. Below 5 atmospheres it may be rare, you are correct - but the pressure inside one of these tanks is generally 800-900PSI, ie 60 atmospheres. I know for a fact that the tanks contain liquid CO2, partially because it is a concern with many paintball markers when running on CO2 that you should avoid having liquid CO2 enter the marker's valve system (velocity spikes will occur if it does), but also because many older markers are specifically designed to be run with liquid CO2 rather than gaseous. In fact there are markers still available today that can be set up this way if you just play with the springs in the valve trains.

Re: Does motor temp affect performance?
 

I'm going off of the Andymark specs, as we used the c-channel included in the KoP, meaning it should be a 0.15" drop to both of the middle wheels.
There are only ever 4 wheels touching the ground.
Our robot weighs approximately 110lbs, +- about 3 lbs.
From one of our mentors via email:

Re: Does motor temp affect performance?
 

Use care with water too, a mere 10 pounds of it can kill you if you drink it too fast :-)


~

Re: Does motor temp affect performance?
 

Craig,
I am willing to bet that the playing field carpet compresses more that 0.15 inch. That still leaves all wheels in contact with the carpet and the CIM motors near stall during turns. If you have a chance, you might want to experiment with omni wheels or smooth tread on the front or back wheels and see if that cools the motors down. Does your robot seem to "hop" a little during turns, a little jerky perhaps? This is another sign of stalling. The motors are able to develop enough torque to overcome the friction occasionally, which causes the jerky motion. During extended periods of turning, the breakers for the CIMs might even trip momentarily giving the same result.

Re: Does motor temp affect performance?
 

All things in moderation? xD

Re: Does motor temp affect performance?
 

This book has a lot of information on wire sizes and allowable voltage drop. I'm sure there's other places to find all the info but it's sort of compiled right there. There is even a chart on allowable voltage drop if you look a few pages through it. The chart basically tells you how much voltage you will lose based on the amount of feet of wire. The best thing to do if you cant change the length of the wire is to change the cross-sectional area(aka gauge).

By the way, that's a FAA certified book. And all of the information in it are guidelines that outline minimum regulations regarding aircraft electrical systems, such as motors, generators, wires etc.

Also, as for the charts, the intermittent circuit chart would be best for our purposes in FRC. The only upset is that there is no column for 12 volts, however I'm sure you could use the 14 volt column as a pretty close guide. 12 volt batteries run around 13.5 volt when on a full charge anyway.son

Re: Does motor temp affect performance?
 

No, our robot turns cleanly and smoothly with no jerking motion, and I'm fairly sure only four wheels are touching the ground at any given time because of the way the front end basically just swings over when we turn (the bot is back heavy). Also, being that it's back heavy, the front wheels are almost always the ones that are elevated. With the robot then resting on the back and middle wheels, the distance between the front wheels and the ground is more than 0.15" - theoretically it would be 0.30" if the front and back wheels are equidistant from the middle pair.

I figure this is true because if the middle pair only were in contact with the ground and the other two pairs of wheels elevated the same amount, they would be as far off the ground as the center wheels are dropped - 0.15". If the two outer pairs are equidistant from the center, then as far as one moves down toward the ground, the other moves up. Therefore when the back pair moves down 0.15" to the ground, the front moves up the same amount, to a total of 0.30". And since the robot is quite back heavy, I wouldn't be surprised if the back pair of wheels compresses the carpet more than the center pair does, which leaves the front pair even higher off the carpet.

Re: Does motor temp affect performance?
 

13.5 is just surface charge. As soon as any appreciable load is applied, the voltage drops well below 13V. For example, running just one CIM at 36amps drops the battery to 12.3volts.

See attached GIF.

Re: Does motor temp affect performance?
 

Lead-Acid battery chemistry has a fully-charged voltage of about 2.1 volts per cell. This does not vary according to construction; it is a chemical property. "12 volt" batteries have six cells, so a fully-charged battery has theoretically 12.6 volts - reality is a bit more or less because of surface charge and inner resistance.

To remove surface charge, a load in Amperes of about the Ah rating (e.g., about 18 Amps for an 18 Ah battery) for 60 seconds, followed by a 10 minute open-circuit rest period, will generally be effective. Gel and AGM batteries may need a little bit more due to reduced electrolyte mobility.

Probably more than you wanted to know. :p

Re: Does motor temp affect performance?
 

Thanks, that's good information to know. Would the 14 volt column on the intermittent chart still apply then?

Re: Does motor temp affect performance?
 

Guys,
The AGM cells are just slightly lower than a standard lead acid cell. The chart shown by Ether is similar to the one in the MK battery literature which is nearly identical to the Yuasa charts. Kid, one needs to understand the application to understand the charts in the FAA book you show. Many of these charts are based as much on providing a specified voltage drop for max current on the wire. In the reference, they are looking at no more than one volt drop at the given 14 volt scale. (rounded up from 13.8 volts standard lead acid battery terminal voltage.) This insures that load devices like radios, instruments, and beacons maintain operation under varying current conditions. That is to say that a radio that draws max current of 7 amps @ 12 volts can be placed no further than 7 feet from the voltage source if #20 wire is used in order to maintain no more than a one volt drop at the radio. (from the chart) Additionally, wire that is carrying continuous current also adds heat to the wire through I^2 R losses. The effect of this heating on the failure of the insulation is directly related to the wire in open air or in a bundle or conduit. Wire size is then derated to compensate for this heating. Wire in the open can get rid of the heat easier than in a bundle. Therefore a #12 wire carrying 20 amps continuous should be derated to a max of only 11 feet long instead of the standard chart of 12 ft. I know this is a little confusing. Additionally, it appears that the two curves are interchanged, possible typo.
For our purposes, the NEC open air rating from which our wire/breaker table in Section 8 is derived, would allow a #12 wire to handle continuous current of 40 amps. The rating of the breaker for that branch circuit is specified for this current based on the size of the average robot and the length of time in which current flows in the wire. However, the voltage drop across the same length of #12 is almost twice as high as a #10 wire. At 100 amps that is 0.1 volts per foot for #10. I use this term, "wire foot", to describe this condition. So 4 feet of #10 is four wire feet, while 4 feet of #12 is 8 wire feet. At CIM currents of 100 amps, the #10 wire drops 0.4 volts while the #12 drops 0.8 volts. Remember to count both the red and black wire, please. Add to this number the "wire foot" equivalent for the speed controller, 4 WF for Jaquars and 6 WF for Victors, and 1 WF for every 2-4 connections and the losses start to add up. It is not uncommon for poor connections, long wire runs, and other losses to drop the available voltage to a motor by 1-2 volts. Remember that all robot current flows through the #6 wiring, which is 1/2 WF per foot. Add 4 CIM and few other motors to the total current draw and the wire supplied in the KOP for battery connections, will easily drop 1 volt before the power distribution panel.