Does motor temp affect performance?
 

We just completed the Michigan State Championship last weekend and during all of the qualification matches we were running top notch. Drive fast, turn efficiently, cross bump with ease etc. Once we got into the elimination rounds, our robot performance started to drop drastically. We kept trying to figure out what was wrong but we really could not find a cause. In the actual Finals rounds we started to feel our CIMS (4 of them 2per side for drive train) and they were extremely hot, literally almost too hot to touch. We were curious as to if the temperature of the motors could have something to do with performance of our robot? If anyone has any info on how CIMs will work/break down, how temperature affects them, etc that would be great! Thanks.

Re: Does motor temp affect performance?
 

Hot motors have less output primarily because the have higher resistance in the windings of the motors which means lower stall currents, which means lower stall torque, which means that for a given load you need to operate closer to the stall point, which means you are less efficient at turning electron energy into shaft energy which means you generate more heat which increases the resistance of your windings... ...rinse and repeat.

If you are SURE that nothing bad has happened to your drive train and that you are just overheating your motors, then I fully recommend buying a 24 can case of "Freez it" or similar product and icing the motors before and after every match*.

I recommend keeping ahead of the heat because by the time you feel that the outside can of a CIM is warm the inside is HOT HOT HOT. Freeze 'em early, Freeze 'em often. That'd be my motto. If it weren't illegal, I'd put a small hole in the can of the motor and drizzle the liquid from the can right into the motor body itself that way the evaporating liquid would directly cool the bits of the motor that need cooling the most. As it is, you'll have to cool the case and depend on thermal conductivity to do the rest.

I loved you in Ypsi. Good luck in Atlanta -- buy a 24 case really. You'll thank me (again, assuming you have 100% certainty that your drive system is as it should be and it is just repeated, frequent matches that are causing the problem)

Joe J.

*I know some who argue that the thermal shock is too much for a motor but in the years I have been doing FIRST, I have never seen a motor fail this way and I have used this method on many many robots.

Re: Does motor temp affect performance?
 

One effect of heat is that the resistance of the motor will increase, which will decrease the amount of current (torque).

Increasing the winding resistance by 100 C increases resistance by 40%, so a super liberal estimate is that you could lose 30% of your torque. However, this doesn't factor in A) any other resistances in the path or B) that a 100C rise is really really hot.

I'm betting that they got hot -> increased resistance -> decreased efficiency -> got hotter, but the real cause for your drop in power was your battery giving up. Running that hot is not good, but it probably isn't your only issue.

Re: Does motor temp affect performance?
 

I agree with what Eric has to say here...

How old were the batteries you ran for elims? What were your charging cycles like? Have you ever run these batteries down below 12 volts?

Re: Does motor temp affect performance?
 

Our oldest batteries are only a couple of years old and they have all been load tested and seem to be fine. All the cables have been reattached so we dont have any loose connections either. I noticed that some of our battery cables were hot when we took them out of the bot as well. Any idea if that may have something to do with it?

Re: Does motor temp affect performance?
 

Joe,

Is there a noticeable performance gain by cooling motors like this, or is it just a good preventive measure? I was always told that cooling the motors in such a way could damage the motor, but your post has sparked my interest. Maybe I'll pick up a can as an experiment.

I would guess that some of it was due to Battery levels as well. In 2008 our robot was a real battery drainer, and as we would go through the elims our batteries never got the full charge time (Close matches, and we only had 2 or 3 batteries) so we would go out to the field with weak batteries. This wreaked all kinds of havoc on our robots performance, especially in autonomous mode.

Re: Does motor temp affect performance?
 

This effect is real and measurable. In automotive applications, it is often the case that a motor at -40C breaks the actuator because it has more power/stall torque (and the plastic is generally more brittle).

As to FIRST, the cooling effect of Freez It is fleeting in that you do not have an infinite sink of -40C to draw from so your motors get hot eventually anyway but if you start warm, then get warmer, then start warmer get hot, then start hot and get hotter, then start hotter and get boiling, you are fighting a loosing battle.

If you can keep your motors starting a match at just warm or warmer then you can keep from overheating by the end of the match (potentially).

The problem with a brushed DC motor like the CIM is that it is totally enclosed. All of the heat is generated in the windings of the armature. How does that heat get out? Well, a little is conducted away via the shafts and a little is convected away via the air inside the can but that air has to then re-convect (if that is a word) the heat back to the inside surface of the can of the motor for it to be conducted away to the outside of the can and then convected away by the air outside the robot.

All this takes time. If you have time, all is well, but if you don't (as in the elims) the heat builds up.

If you open the can of your motors, you are likely going to smell something that to this day makes me ill, burnt motor insulation.

By the way, your gear ratio is probably not high enough but that cake is already baked. From what I saw of you at the MSC, you guys are doing just fine with the too tall of gearing you have. You just need to make sure your motors are cooled down between matches and you'll do fine -- next year, consider a bit more ratio ;-)

Joe J.

Re: Does motor temp affect performance?
 

Others have already mentioned increased resistance of the motor windings.

Heat also affects the magnets and magnetic circuits within the motor, decreasing the torque output for a given current.

Re: Does motor temp affect performance?
 

I have to add to Joe's statement about Freeze spray is that some products contain other chemicals that can wash lubricants out of bearings. Use with caution. Remember that the majority of the heat generation takes place in the windings that are mainly coupled to the outside of the motor through radiation/convection within the motor. There is very little air movement inside a closed motor. The only real connection to the body is through the bearings and brushes.
The effects of heat in addition to those above is the possible breakdown of the insulating varnish on the windings (eventually leads to failure), the change in efficiency of the magnetic structures in the armature and the expansion of metal parts inside and outside the motor.
If the motors were hot (could not pass the five second finger rule) and the battery wires were hot as well, this is a good sign that you are using a lot of current. You should consider a cooling scheme for the robot in between matches. High CFM fans come to mind.

Re: Does motor temp affect performance?
 

In 2008 we lost a severe amount of available torque for turning due to a misaligned gearbox. We took the AM supershifter box shroud off and replaced it with plastic spacers when we got to Atlanta. The plastic spacers allowed us to tighten the top of the gearbox more than the bottom of the gearbox, thus making the plates non-parallel. This led to our gearbox binding ever so slightly and it was enough to be extremely annoying on the field.

I would double check that all of your shafts, plates, gears and other critical parts are aligned properly. This year's highly interactive game may have knocked something loose.

Re: Does motor temp affect performance?
 

Our CIMs get burning hot every time. When running for more than a few minutes with them hot, you'll permanently damage them, resulting in a significant loss of power. Quite often they'll be black on the inside. We have a box of about a dozen CIMs this has happened to over time.

Re: Does motor temp affect performance?
 

Wouldn't the heat also cook the lubricant in the bearing/bushings? I have not had a CIM apart, but some destructive testing may be in order. ;)

Re: Does motor temp affect performance?
 

we've never had a problem with overheating motors, but i've heard of overheating fisher-price motors, but never CIMs (and we're running off ones from '07)

Re: Does motor temp affect performance?
 

Any motor provided in the KOP, in any year, can be overheated through misuse. The FP motors are particularly sensitive to operating in an RPM range (low RPM) that does not allow the internal fan to cool the motor.

Re: Does motor temp affect performance?
 

Well, the shock isn't much, considering the heat paths into the motor. But I have a problem with using so much freeze spray - it is mildly dangerous (as much as, say, WD-40) and isn't healthy to breathe. Instead, fans (such as those on Victors, or the larger ones in the KoP) can be mounted to blow air across the motors at all times, this will make a definite difference.

But, it is hard to argue with cold-in-a-can, I don't have anything that can compare.
This is not ideal; either the cables are damaged (if hot in spots only), undersized (if hot along their length), or have loose connections (if the connections are hot). This definitely affects the power the motors can see and use. Avoid bundling wires up too tightly; allow some space around them for cooling
The grease used is probably good to well over 200C, the bearings don't get that hot. No worries there.

last year we were able to mount our victors directly under the CIM motor, the airflow helped keep it cooler. Then again, Lunacy was not hard on the drivetrain.

Re: Does motor temp affect performance?
 

Going back to the problem at hand.

If you have the ability to do it, gear down your motors a wee bit. All of these high temp scenarios can lead to some ugly consequences in the heat of competition (pun intended). You really are playing with fire (also intended).

Re: Does motor temp affect performance?
 

I can defiantly agree with that. We burned out a couple CIMs and ended up blowing out a victor. And I don't mean that beautiful magic smoke. They had to get the fire extinguisher because the fire was spreading down out electronics board. Defiantly an important lessoned learned.

http://www.youtube.com/watch?v=hJMuKH9WkZo

Granted we really did push the CIM way way too far with that design.

Re: Does motor temp affect performance?
 

And the irony is, more often than not you will get better performance AND less heating with a properly-geared system.

~

Re: Does motor temp affect performance?
 

If the wires are heating to the point where they need cooling, something else is wrong. Circuit breaker not tripping, too small of gauge, etc.

Re: Does motor temp affect performance?
 

Actually, I have to agree with Don here.

Take a look at http://www.powerstream.com/Wire_Size.htm - The rated currents for Chassis (unbundled) and Power Transmission (bundled) differ by about a factor of two.

Tight wire bundles can have an effect. I usually tell students to put it on the "nice to have but don't panic about it" priority level. I just don't recommend that teams put their entire power flow through those wire guides.

Re: Does motor temp affect performance?
 

For those of you that are interested, the tables that Erik has linked to are also derived from the National Electrical Code and in some locations, the NEC is the rule rather than local codes.
The transmission numbers derive from voltage drop in the wire for different currents. The desire is to have less than a specified voltage drop for a given wire length. This insures that your wall outlet maintains the 110 or 120 volt output when you plug in a toaster, space heater or hair dryer.
If Art Dutra happens to lurk by, he could be more specific than I on this subject.

Re: Does motor temp affect performance?
 

Hm. After frying a CIM at Waterloo, me and a teammate were discussing something like this, and as paintballers we discussed the possibility of spraying liquid CO2 onto the CIMs after every match or so. Would this work? Or is there something special about the freez-it spray?

Re: Does motor temp affect performance?
 

Craig,
Freez spray or CO2 work by evaporating from the hot surface and taking some of the heat with it. Unfortunately, the heat is inside the motor, stored in the steel armature and windings and to a lesser extent in the case and magnets. If teams use this approach they must also be aware that making cold surfaces in Atlanta humidity will bring about condensation. Water may not be a desired effect if it drips into controllers or Crio.

Re: Does motor temp affect performance?
 

Cool is cool.

The thing I like about the Freez-it stuff is that it comes out as a liquid if you hold the can just so and spray with the right velocity. This is important (or rather, nice) because it lets you direct the coolness right to the bits you are interest in.

For example, if you want Thing A cool, you drizzle some liquid out of the Freez-it (or equiv) and onto Thing A. Thing A causes the liquid to boil, which sucks heat out of Thing A like mad (it is a phase transition thing -- gobs of energy are required to go from liquid to gas).

I have no experience with CO2, but I don't THINK it comes out as a liquid but again, cool is cool. Expanding CO2 takes energy (though I don't know how it compares to the liquid->gas transition of Freez-it) and that energy comes from the surrounding environment. If you can control the CO2 such that you can get the heat out of a particular part or group of parts, it should work fine.

Joe J.

Re: Does motor temp affect performance?
 

Very good point. I recall that the motors can get a bit frosted if you cool them too much in the humid air of Atlanta. The good thing about the CIMs being a closed can I guess is that the water won't get inside the motor but you need to be sure not have any dew drops drip onto Victors, Jags, and/or crios.

Joe J

Re: Does motor temp affect performance?
 

Shouldn't be too bad I suppose, we only have our pneumatics tanks around the CIMS...

What I meant was that the freez it seems to be "antistatic" or something, and I read on their site that it's non-frosting, so i was wondering how important these features were.

I figured if you attach a Co2 tank to the reciever valve and turn it upside down, you should get liquid as most tanks aren't anti-siphon.

Re: Does motor temp affect performance?
 

FWIW:

http://www.vapco.com/prod_freezeitspray.html

Freez-It contains menthol, camphor, eucalyptus oil, and isopropyl alcohol.

Menthol, camphor, and eucalyptus oil are mostly harmless in small amounts, but have a strong odor. Same ingredients are in Vicks Vapo-Rub that Mom used to rub on your chest when you had a cold (oops, am I showing my age?).

Isopropyl alcohol, unlike ethyl alcohol (the drinking kind) is toxic if ingested or inhaled in sufficient amounts. If you get an unexplained headache that should be a warning sign.

Get enough folks using that indoors and it may get banned. Although I suppose the venue at Atlanta is large enough it might hardly be noticed?

CO2, by contrast, is relatively safe, except for the stored-energy concerns.

If you've got enough room around your CIM, try attaching an aluminum or copper heat sink with lots of surface area (fins).

Re: Does motor temp affect performance?
 

With or without the additional surface area, airflow is key. You want to get as much hot air away from the case as you can. The earlier suggestion of adding a fan is a good one.

Re: Does motor temp affect performance?
 

Heatsinks do have an effect, in 2008 we attached one to our compressor to help it stay cooler during long practice periods. It worked but only because it was mounted in such a way that at speed our robot's motion caused airflow over it. Heatsinks aren't helpful because they provide extra thermal mass they are helpful because they provide a lot of area to dissipate heat from.

Either way, you are addressing a symptom and not the issue. 1918, my suggestion would be double check your transmissions, make sure they aren't binding anywhere. Double check your wiring for any loose connections (loose, not out). If you can you might want to tweak your ratios a little bit. Obviously THAT may not be feasible. Perhaps replace your fuses too. They might not be tripping when they should. I know no one wants to pop a fuse but they are a safety precaution, burning a motor or starting a fire is much much worse. Plus if they pop you know you did something wrong. Perhaps try replacing the motors too.

Next step would be adding the fans/heatsinks/CO2 baths to alleviate the symptoms until you can figure out the root of the problem in the offseason.

Worst case, ask your driver to tone it down a bit.

Re: Does motor temp affect performance?
 

Yeah, a fan is probably the first thing to try.

But the converse is true too: with or without fan-forced airflow, surface area is key. So if more cooling is needed, adding a heatsink could make a big difference.

Re: Does motor temp affect performance?
 

This is more of a side note and won't fix the overheating issues, but may help you get better performance from your drivetrain.

I've heard that if your wires are longer than they need to be then the resistance of the wires can start to affect the voltage (at high amp conditions like pushing match) that the motor is receiving by a decent amount and cause you to not preform as well.



If you do add a heatsink and it doesn't work as well don't forget to try it with thermal paste.

Re: Does motor temp affect performance?
 

In this application, a fan is definitely the first thing to try (assuming you don't have a mechanical issue that is causing the heat problem to begin with).

If you don't have airflow, you're relying on radiative cooling, and in that case surface area is very important. But in order to get enough radiative cooling to make a significant difference, the motor has to be hot enough that it will likely already be permanently damaged.

Re: Does motor temp affect performance?
 

Heatsinks work best with forced airflow. But they also work without fan-forced airflow. The large surface area creates convection airflow. When the robot is moving, the resulting airflow also helps.

Has anyone here ever done a comparative evaluation of fan-only vs heatsink-only vs heatsink-plus-fan on a CIM motor? Would be nice to see the data.


~

Re: Does motor temp affect performance?
 

I can't think of a rule that would specifically prohibit a bit of dry ice being used to cool a motor. In fact, I've thought, from time to time, that it would be interesting to wrap the CIMs in custom dry ice cooling boxes and keep them super-chilled for the duration of the match.

But we have yet to be disappointed with CIM performance in normal, uncooled, use, so it's a pretty low priority. Not to mention the sort of thing that I'd want to clear on the Q&A first.

Alternatively, an ice filled aluminum mold that fits over the CIMs might work between matches, without the need for aerosols.

I think the best advice, however, is to see if the gearing or gearboxes can be adjusted to reduce current draw... perhaps a better off-season project than a Thursday morning in Atlanta project.

Jason

Re: Does motor temp affect performance?
 

It would be most interesting if teams experiencing hot CIM motors could provide some information about their robot design.

In the case of CIMs used for driving, that data might include ratio of gearbox, sprocket teeth count if using chains, how many CIMs (2 or 4 or ?), and wheel diameter and type of wheel.

Re: Does motor temp affect performance?
 

I don't think that's the stuff Joe was thinking of. (That Vapco product is not an appropriate substance to be using within a motor.)

The correct stuff is based on various fluoroethane compounds.

MG Chemical sells a product that works well for this purpose. In fact, I think I've seen 47 using exactly this product, many years ago. 188 has also used it to good effect (primarily in the days before 120 A circuit breakers and CIM motors).

In a pinch, an "air"-in-a-can duster, inverted so that the liquid is released, will work as well (they're generally composed of the same chemicals).

Re: Does motor temp affect performance?
 

Last year we had CIM heating issues. We were running one CIM for the entire drivetrain so we were asking a lot out of the motor. To combat the heating we used an inverted air duster. Any brand will work, but I recommend getting one that does not have a bittering agent.

Re: Does motor temp affect performance?
 

I would think that the dry ice would tend to freeze the lubricant in the sleeve bearings on the CIM prior to a match. You might just raise the current from the added mechanical resistance. Unknown what the expansion/contraction of the various parts under these severe conditions would be. However, bronze inside of cold aluminum around a steel shaft seems to send chills down my spine.

Re: Does motor temp affect performance?
 

- 6WD powered by 4CIMs through AM Toughboxes
- 6" Plaction wheels with roughtop tread
- roughly 18:1 gear ratio from CIM to wheel

however, we have a plywood tray holding our pneumatics, roughly at the base of the toughboxes, and a plywood electronics board practically sitting on top of it. No way to avoid it, as we're a tunnel bot.

Pictures here:
http://i298.photobucket.com/albums/m...e399f66d76.jpg
http://i298.photobucket.com/albums/m...5f2f2a56_o.jpg
http://i298.photobucket.com/albums/m...cfa3da23_o.jpg

Re: Does motor temp affect performance?
 

Hey Craig,
All six wheels on the ground? You have trouble turning quickly?

High friction wheels on carpet in turns causes high (and I mean very high) currents in CIM motors. Assume that the CIMs are going into stall every time you turn. I bet it would not be unusual for the CIMs to be running at 100 amps in turns, each. 100 amps means about 1200 watts per motor, all things being equal. Yes that is like four 1000 watt light bulbs in your robot making heat. The fix is changing the height of the center wheel, change some of the wheels to omnis or a combination of the two.

Re: Does motor temp affect performance?
 

No, we have a dropped-middle wheel design

Re: Does motor temp affect performance?
 

Craig,
You have to be more specific. How much is it dropped? How many wheels are actually touching the carpet, how many in turns? How heavy is your robot? What is the final ratio? etc.

Re: Does motor temp affect performance?
 

As a side note, I would check out the victor/spike/jag going to a hot motor. Last year we had a malfunctioning victor that was rapidly switching from full forward to full backward, causing our cim to be scorching hot.

Re: Does motor temp affect performance?
 

May I ask how this was diagnosed? Seems like a very odd failure mode.


~

Re: Does motor temp affect performance?
 

I've machined an aluminum heat sink for a CIM, and installed it with thermal paste. I think it had about 40 fins, about 3/16" wide, but only about 1/8" tall. It was the length of the motor. Didn't make any appreciable difference in temperature after running. I installed a high-flow fan pointed straight at the back of the motor (directed along the length of the fins). Didn't make any appreciable difference. I was running the motor under a constant load that made it draw about 25 amps continuous. Within 4 minutes, it was time to stop and cool for 10 minutes.

The heat comes from the windings within, with not a lot of ways out. Time, and dropping the temperature of the surroundings (endbell especially) is the only thing that will cool it sufficiently.

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.