Gearing question (not what you'd expect)

[Cotharyus]

I'm about to start messing with gearing in a car of mine using two different motors and batteries. I figure the same gearing isn't going to work for both of them, and it's probly pretty useless to ask "What ratio should I run?" - so what I want to know is, when should I stop pushing. I know the motor will get hot. But how hot is too hot, and where do you back down to? Like you tune a nitro to maybe not run any hotter than 270F, what should be the "do not exceed" temp on an electric motor?

[End Overend]

I've searched around a lot on this topic and never really found a definitive answer.

Here is basically what I found:

If you can leave your finger on the can of the motor for longer than 2-5 seconds than you are in an OK temp range. There are several problems with this though. First people have different pain tolerances and what's hot for you might not be hot for me and vise versa. Second they never state if that's only for a 4 minute main or for an entire pack in practice. My motor is much cooler after 4 minutes then after 10.

The other mode of thought is to run laps at the track. Keep gearing up until lap times drop, when they do drop it one tooth and you should be good.

Basically neither method is very good.

I wrote an e-mail to the manufacturer of my motor and gave a description of my car, track, spur gear, battery, etc. and asked them for a recomendation. I then took tha recomendation and used that pinion, one bigger and one smaller and ran it around the track. The one that I was best with and that kept the motor within acceptable operating temps (to me) was the one that I went with.

I know it's not a lot of help but it's about as good as you may get.

[RonnieRayGun]

check your instruction manual, there should be a chart or something for you to refer to.

[JeepsDaddy]

140 is a pretty "normal" temp for a race motor (taken on the side of the can)..... 160 is pushing it... go much higher than that, and you will notice a reduction in power due to heat... go much over 200 and you'll de-solder your motor wires...

peace out... :)

btw... the 5 second thumb rule is a good one if you don't have a temp gun...

[Cotharyus]

Very interesting. I can honestly say I have one crap motor. Hopefully the 14x2 KR that should be getting here today can handle things a little better than the 21 turn I have that I bought as a cheap replacement for my stock motor. Even gear what you might call "painfully low" that motor gets up to 132 (measured on the heat sink about two minutes after the run) when running a full pack out in a parking lot. Thanks for the tips. BTW, for anyone lacking a temp gun, Sears is having a sale on thier temp gun this week, its 49 bucks.

[JeepsDaddy]

you can also gear too low.... ie- if you are topping out in 10 feet.. you'll be running wide open nearly all the time, and your motor will get hot from being wfo all the time.... and of course (you probably already know this) be sure and check for any source of drag or binding.... a little bit of drag in your hand equals a whole lot of drag at 40K rpm, and will cause a motor to run hot...

peace out.... :)

[Grizzbob]

There's also another little tidbit to chew on...some motor designs will naturally run hotter than others, but how much they'll suffer from it seems to vary a bit. A great example is Reedy's MVP, I've been able to get good power from them, & they don't seem to drop off in performance late in a run, but man do they run HOT!! I've seen mine run as hot as 240 degrees F right after the end of a run, but my lap times never dropped & the motor kept pulling hard all the way through the race. Plus, it'd be able to run like that all night, no performance drop(despite every instinct I have telling me it's gonna die, lol). Of course, at the end of a race night, the comm HAD to be trued & the brushes replaced, but I do that anyway, regardless of which motor I've used. It's about the STRANGEST motor I've ever had(though the newer Monster by Trinity has some odd quirks of its own, like changing its "mind" about what brushes it wants to run). But most other motors I've had would be pretty obvious if they ran too hot, you definitely could tell they weren't runing right(& the lap times would bear that out)....:cool:

[highroller]

For me, motor's can vary a bit even ones of the same brand. What I do is go by the size and layout of the track along with some of the dyno information I get, comparing it to other motor info. Then I'll gear on the conservative side for the first run (which I may have someone time). I may end up doing 3-4 practice runs (4min) for a new motor/battery setup until I figure it's in the ball park, checking the comm & brushes, motor winds for discoloration and heat. On very hot days I'll put the motors on ice or freeze it overnite.
Grizzbob, maybe you got an odd set of brushes or they got labeled with the wrong compound.

[Cotharyus]

highroller - when you say you put your motor on ice, do you mean dry ice, or do you just put it in a back before you drop it in the cooler? Not that need to duplicate what you're doing, but I thought it was funny and had to ask :) - I don't think my motor is under geared, and it certainly isn't binding anywhere, I think the orion 21 turn I have just runs hot. It always runs hot, no matter what. Before I put my 14x2 KR in, I'm going to wait until my pinions get here - I looked at my old one, and I was suprised it still worked. I think I threw my mesh off when I spun it the other day.

[jforkner]

Cotharyus,

I just installed a new Kr 12x2 in my Losi XXX-4. This is the first mod motor I’ve ever run and it replaces my stock MVP. I geared it with an 18t (48p) pinion on the car’s 92t spur. That’s two teeth less than Losi recommends for a 12-turn motor. I’m afraid to put on a 19t or 20t. The car is so quick and fast now, it borders on uncontrollable.

As was stated in a previous post, the MVP runs extremely hot. The new Kr runs noticeably cooler.


Jack

[highroller]

Regular ice cubes in a cooler. Allow the motor to cool first (if hot to cold can crack the magnets), put in a plastic bag then put on ice or get one that is already on ice. I usually take about 6-8 motors to the track to practice and race with. The race ones are usually close in the same power output, and I may not be as critical about the practice motors. With mod racing I may even carry 3-5 extra armatures to reduce rebuilding time.

If I can hold or touch the motor then it may be fine, looking at the brushes for discoloration or comm surface and finally wire may indicate if heat is affecting the motor.

[Cotharyus]

Jforkner - Thats cool, uncontrolable is my specialty, just thing, I've got a couple of 7-cell packs to push this thing once I get a handle on it. :) I've also got a parking lot thats a touch over 1/8th of a mile long to play in.

Highroller - thats mad, I love hearing about serious racers. One of these days I'm going to find the time to get to a local track (about 1 hour away no matter which one I go to) and watch the action. In 16 years of messing with these things, I've never raced one, but I sure would like to give it a try some day - probly after I retire :)

[highroller]

jforkner,
too many guys feel that by going to a lower turn will make them faster than using a higher turn motor - it doesn't. All less wire does is change the acceleration curve. Less wire allows the motor to accelerate quicker which can cause the tires to break loose if you are too heavy on the throttle in a less that adaquate traction area. Even for racing we try to use a motor that uses all battery energy for the length of the race without overpowering the track. On one oval track we could use a 6 double, while on another a 7 triple is as much power the track will take, I have been able to use a 7 double but have to be very smooth getting back on the throttle. Speeds and lap times with the 7 turn motors are still close to the 13 turn when we only used 2400 batteries.
Cotharyus,
RC racing is nice if you keep a goal in mind: 1. have fun 2. set personal goals 3. wining is nice but helping can be much more fun.
I don't win as much as I did years ago, the past 2 years have been dry. But still when I can lend someone my motor or battery or suggest a change and they go out win, break the track record or whatever and they are happy then all isn't lost. Sometimes making someone happy is just as good as winning myself. To me without good competition it didn,t push me to get better, with better racers it pushed me to go up a notch.