ASK Cub Reporter- Your Wacky Questions, My Reticent Responses- Version 03.23.2011
Hi ya guys,
What is an acceptable motor temp on a Mini-T?
I have an EZRun 25A speed controller with a 7800kv motor on a 2S lipo. Its geared stock spur mated to a 15 tooth RRP pinion. The highest motor temp I have seen so far has been 168 degrees. Is this hot enough to damage the magnet?
Thanks for any and all advice!!!!!Ronnie W.
Cubby– Hey ya Ronnie, “cool” question ya got there.
Most magnets used in our rc motors are said to be damaged when they hit around 200 degrees. When our magnets get too hot, they lose their strength, causing efficiency and power to suffer, while the kv actual increases.
So you shot the can of your motor and saw 168 degrees, is your motor ok? I think a lot of internet pundits would tell you “yes!”, but I’m going to tell you “no!”. You see the can of your motor is much cooler than your rotor (magnet), so while your can is shooting 168, the core temp of your motor is going to be closer to 220. IMO, ideally, you don’t want to see can temps of over 140 if you want optimum performance and longevity out of your motor.
One last thing that isn’t discussed enough… You only need to overheat your motor once to de-mag it. Once is all it takes to forever be chasing the power, runtime and efficiency it once had. After running it too hot, even just once, no matter what you try, whether it be gearing, different timing, etc, you’ll never get it to run like it did from the factory.
I still cannot break anything on my Traxxas Slash (other than a transmitter) and I’m thinking that some more power should do that. I feel the need to blow-up my Titan 12T motor before I upgrade to brushless, so I’m looking at investing in this new-fangled “LIPO” technology. I’ve scoured your LiPo shootouts and kept up with all the new product updates. Shootout #1 labeled the Thunder Power 5000 40C as the “best battery” to put into a slash. Does your opinion still hold true? I know you cannot directly compare the results of the two shoot-outs, but there seemed to be many strong contenders in #2. Is there anything newer (and hopefully cheaper) than the TP 5000 40C that can give me some axle bending, A-arm busting, gear stripping, bumper busting power?
Tommy K.
Cubby– I can’t resist posting another of Tommy’s letters.
Good hearing from you again Tommy. Btw, I really like the stock Titan motor on the Slash, it’s quick enough to have fun, but not so fast as to get you into too much trouble. Spray the motor out once in a while with motor cleaner, put a couple drops of oil on the bushings and the Titans typically last much longer than what most of the “message board guys” say they will.
The battery companies have new product every few months, so much of the info in our Lipo shootouts is already outdated. Btw, I hear our next Lipo shootout might be right down your ally- we are planning on shooting out sub $50 2S packs. But… that shootout is still a ways off, so here’s what I recommend for now.
1. Be sure and buy a hard case. You might not think you will taco a soft pack, but you inevitably will. A lot of your landings and crashes are harder than you think, a hard case Lipo will go a long ways towards helping your battery live as long as possible.
2. Buy a Lipo that fits ROAR dimensions. If the pack you buy fits ROAR dimensions, it will easily fit in your Slash and fit pretty much any other rc you might buy in the near future. You’d be amazed if you knew how many people bought batteries that would not fit in their car.
3. All these people sending money straight to China are slowly slitting their own throats, so try to buy an American branded pack from your local hobby shop. When people buy straight from China, not only does an American battery company lose money, so does the American distributor, and your local American hobby shop. Wouldn’t any good American pay a bit more to keep Americans fed than ship their dollars straight overseas ?? Enough of the “I saved 30 bucks!!!” b@llsh!t, lets keep as much money as we can at home. Just say’n…
Lastly, I am Cubby, so I’m not gonna leave ya hang’n on a “real” answer. We haven’t done the sub $50 shootout yet, but I am going to recommend Venom as the best low-buck Lipo on the market right now (till I’m proven wrong in the shootout). Venom’s old Ni-mh packs had a terrible reputation (that was well earned… LOL), but the cells in their new Lipos are sourced from a good place, and from first hand experience around the BigSquid compound, they’ve been solid performers. They are not uber high-end race packs, but they have proven to be great packs for their price. Lastly, pretty much every local hobby shop in the country either has these packs in stock, or can get them quite quickly for you.
One last thing that is not discussed enough… keep your Lipos away from heat when you are not using them. Storing them in an air conditioned room (safely of course) is much better than your garage that is a 100+ degrees in the summer. When using or charging them, try to keep them out of direct sunlight. Don’t leave them in your full size rig that hits 130+ on a hot summer day. Be smart and safe with them of course, but try to keep them cool when not in use.
That’s it for this week, shoot us your emails. Got a question? Send us an email. Want to tear us a new one? Get at the back of the line, but shoot us a mail. Just wanna make our front page? Get in line for that one too, but send us an email! Cubby at BigSquidRC dot com!
YOUR Cub Reporter
