Micro-T Overheating?

Smoke&Mirrors · Post by **Smoke&Mirrors** » Wed Jul 09, 2008 11:10 pm

I've got a stock Micro-DT with a Losi LiPo in it. It seems that now I can only run the truck for about 2 minutes before it just cuts out. The transmitter is fine and the truck is still on. I'll go grab it where ever it died this time and flick it off and then on and it runs again for a about 30 seconds. I'm assuming there is some sort of fail-safe for the motor. Does anyone know about this? Is my motor overheating from the LiPo and shutting off to protect it?

I'm planning on getting ceramic bearings from Atomic as well as the aluminum heat sink to increase runtime and help displace the heat. Do you think the heat sink will help and if not, what will? Thanks a million pimps. 33.333 points for any single question answered and 99.99999 points for answering all three (sorry guys, can't quite get that extra .00001 point).

SHAUN · Post by **SHAUN** » Wed Jul 09, 2008 11:31 pm

I honestly wouldn't waist the money on ceramic bearings, the BRP bearings will give you the same performance at 1/3 the cost.

Also, I would recommend going with a motor mount with a real heat sink on it, like the Hot Racing heat sink/motor mount.

Also, check your gear mesh, it might be to tight, hurting your performance and creating more than usual work load for the ESC/Motor, witch could be the source of your problem.

Smoke&Mirrors · Post by **Smoke&Mirrors** » Thu Jul 10, 2008 12:17 am

Great advice SHAUN, I'll definitely go with the BRP bearings. Could possibly post the links to the two items mentioned? I award you 66.66 points for helping me with the bearings/heat sink and gear mesh. That puts you up to the second tier prize level. You get a reliable PC!

SHAUN · Post by **SHAUN** » Thu Jul 10, 2008 12:57 am

Thank you, its no problem. I enjoy helping when I can

Here is a link to the motor mount, I have one and love it.
http://www.thetoyz.com/cart/thetoyz_det ... &cat_name=

I have a buddy that is running the Losi bearings, they are just as good as BRP.

Here are the Losi bearings on sale at Killer Hobbies.

And the BRP bearings on Ebay.

Also, if you are looking for "Hop Up" parts, check out HopMeUp on Ebay, they have auctions that start at one penny all the time. Also Killer Hobbies is having a good clearance sale right now.

Edited so the links will not stretch the page. -CD

tyhodge07 · Post by **tyhodge07** » Thu Jul 10, 2008 1:27 pm

most common problems are the mesh, hair wrapped around the axels, and not having bearings puts stress on the motor also. Also you might want to put some grease into the gearbox which will make it alot smoother and last longer. Also you will get a warm/hot motor while running a lipo, thats why the lipo voids your warrenty because the problems they can cause with the stock electronics.

crazydave · Post by **crazydave** » Thu Jul 10, 2008 5:46 pm

Try a new motor, and the smallest pinion. The DT is heavier and the taller tires giver it a higher rollout ratio, with the LiPo that puts a lot of stress on the tiny motor. I've had three motors give out on me so far, and it was mostly when I was running my 6 cell pack.

I have the Hot Racing heatsink motor plate, and it helps dissipate the heat faster, but my motors still get hot. Ceramic bearings are super smooth, I wouldn't say the BRP ones are as good, but I wouldn't say the difference is worth the extra cash either.

LBRC · Post by **LBRC** » Thu Jul 10, 2008 9:05 pm

#1 Micro-T problem gear mesh too tight, especially in a LiPo DT.

Causes four primary problems, with potentially permanent consequences.

1) The Brushed motor can easily draw over 2 amps but the 180mAh Losi LiPo is not a high current 12-20C LiPo so just to give it a benefit of the doubt lets call it 10C even so 10C x 180 mAh is 1.8 amps max current delivery. What happens is that you exceed the batteries max output current causing an apparent voltage drop which can trick the LVC into safety mode. To distinguish this from the next problem note that in this case you will loose steering.

2) In this case it’s the H-Bridge motor driver portion of the circuit board (FETs and related circuitry) that is being affected by the over tight pinion to slipper spur gear mesh. Easy to tell the difference because you still have steering but no throttle. The reason the difference is important is because in this case if you keep it up or switch to a higher current LiPo you will eventually damage the FETs and/or fry the CB.

3) The smaller the car the smaller the excess pressure needed to cause proportionally large damage. The motor shaft is riding on brass bushings and the slipper spur shaft is also riding on brass (or something softer) bushings any pressure between the gears is levering the shafts against those soft bushings, that’s bad. Especially for the extremely soft slipper shaft bushings inside transmission. The longer it goes on the more damage is being caused, after awhile even if you’ve fixed the excess pressure problem it’s to late because the damaged bushing hole is no longer perfectly round so it will continue to wear out at an accelerated rate, even with all the grease in the world, and will continue to deteriorate until it disintegrates altogether, meanwhile the excess friction caused by the damage is overheating the circuit board which is already operating at it’s max capacity with the 2S LiPo. If you open the trany and see gold colored dust you know that you’ve damaged the bushings, the more you see the more the damage.

4) Did you know that without a load at 4.8 volts a Micro-DT’s motor can turn over 45,000 RPM at 1 amp.

If you leave it running for any length of time at that speed it will fry the brushes and melt the commutator, at 7.4 volts even a few seconds without a load gets real stinky real fast. That’s without a load now what about with one you might ask? Guess what, it slows down but the current doubles, if, that is, everything is running nice and smooth, if not it can be much more. Again the motor shaft is turning inside those brass bushings, over 30,000 RPM at full speed with a LiPo, excess pressure leveraging the shaft against those bushings can cause it to easily draw over 5 amps, the stock circuit board is not meant to handle that type of current, and neither is the LiPo.

Easy fix, make sure your gear teeth mesh but under no circumstances allow the gears to press against each other even a little. Use a piece of paper between them when tightening the motor mount, when you remove it if you looked with a magnifying glass the teeth should only over lap a little over two thirds of their length and if perfectly centered would not actually even be touching.

The first mandatory Micro-T/DT upgrade is obviously ball bearings.

The second IMO, especially before a 2S LiPo, is a 3Racing transmission with ball bearings on the slipper gear shaft instead of bushings. The two ball bearings on the slipper shaft lessen the necessity of perfect pinion-to-spur gear mesh significantly.

Smoke&Mirrors · Post by **Smoke&Mirrors** » Fri Jul 11, 2008 2:54 am

Wow guys, thanks for the quick and knowledgeable responses. I think I'm going to have to award the full 100 points (so I rounded up, sue me) to LBRC. Now I'm sorry I got a little lost, but with my issue I loose motor function but NOT steering, which I believe is the latter of the two problems described.

In addition, it would make sense that the gears are meshing too tightly because I just wore down my middle pinion and went up to the largest size. So I will be sure to change to the smaller of the three pinions and readjust the mesh. Also, I'll probably order a set of the losi bearings that are on sale as mentioned by SHAUN. LBRC, could point me toward a source for the 3Racing Transmission? Thank you all and if anyone still advice, it's always welcome.

LBRC, congrats mate. You've won a fabulous arrangement of pixels that resembles a shiny car!!1!!11!! (with what looks like a flat front tire)

"Oooh, Ahhhh"

sidewinder · Post by **sidewinder** » Fri Jul 11, 2008 3:43 am

Thank you all and if anyone still advice, it's always welcome.

Wow, after that post by LBRC I wouldn't even try... damn that was impressive.

CD, you were running 6 cell in a Micro?

I'll bet that just flat out flys

crazydave · Post by **crazydave** » Fri Jul 11, 2008 8:54 am

Also, I'll probably order a set of the losi bearings that are on sale as mentioned by SHAUN.

You don't already have bearings? You have to have bearings before you upgrade to lipo. Then with the tallest gear, you're pulling way too much current, and triggering the battery shut down as LBRC said. That's pretty much what I was getting at before, but I learned a long time ago that if you get too tech-y on people they don't read or comprehend half of what you say, but it's great that there's people like LBRC out there that give you the full scoop. I've learned a lot from him.

EDIT:Oh yeah, and I still maintain that you should replace the motor. After the strain and heat I'm guessing you've subjected it to, the magnets will be weaker, the brushes and bushings will wear unevenly, and the brushes and commutator will be darkened with a form of oxidation that inhibits power flow. All of which will make the motor work harder and draw more amps.

Also I didn't mention gear mesh before because I already spoke to him about gear mesh last time he had a problem. So if he is still having problems, that would mean he did not adhere to my advice, and you guys gotta realize that I'm not going to try to help if people are unwilling to take my advice. I've been around the block with this crap too many times.

sidewinder wrote:
Thank you all and if anyone still advice, it's always welcome.
Wow, after that post by LBRC I wouldn't even try... damn that was impressive.

CD, you were running 6 cell in a Micro? I'll bet that just flat out flys

The 6-cell pack puts out slightly less voltage and weighs a lot more than the lipo, so it should be slower, but I swear the 6-cell pack has more snap. Probably delivering a stronger current. I like the 6-cell pack also because the extra weight makes the car feel much more planted and controllable, but my favorite part is you can make a pack for about $6.

EDIT: But ultimately I was burning out motors. If you wanted to run a 6-cell, I'd recommend picking one of these motors like the one ph2t sent me in this picture. It is slightly slower, but has plenty of torque to pull the tallest gear.

sidewinder · Post by **sidewinder** » Fri Jul 11, 2008 2:08 pm

That sounds good, do you know who the MFG on the motor was or is it unmarked? I haven't put together a battery pack since the days of the old saddle pack set-ups but I'll bet with a little pratice I can manage to solder some batteries

Now if I can just find some shrink wrap...

crazydave · Post by **crazydave** » Fri Jul 11, 2008 6:16 pm

sidewinder wrote:That sounds good, do you know who the MFG on the motor was or is it unmarked? I haven't put together a battery pack since the days of the old saddle pack set-ups but I'll bet with a little pratice I can manage to solder some batteries Now if I can just find some shrink wrap...

I'm sorry, I have no info on the motor. I believe it is an outrunner motor for a heli. If you want to take the time to search around, ph2t had posted about these somewhere, if not here, then at ripper7's or ausmicro.

Making the batteries isn't hard. I just picked up some 8-cell packs from bphobbies.com, they have 6-cell packs, but I was going to have to reconfigure them anyways, and the 8-cell packs were cheaper per cell. If you buy individual cells, they are usually available with tabs already soldered on. So since you are really only soldering each cell on one end, it's probably easier than what your used to.

Lowes sells larger gauge shrink tubing that might work, but you don't really need it. You can see I just use strapping tape to hold mine together.

LBRC · Post by **LBRC** » Fri Jul 11, 2008 6:23 pm

Smoke&Mirrors wrote:...LBRC, could point me toward a source for the 3Racing Transmission? ...

Different lable, but same thing
http://www.thetoyz.com/cart/thetoyz_det ... =MICRO%20T#

Smoke&Mirrors · Post by **Smoke&Mirrors** » Fri Jul 11, 2008 7:31 pm

Wow, that's a lot cheaper than I expected. So I just need to provide (or possibly replace) the gears. That's not bad at all then. My local shop has all the replacements should I need them. Can't thank you all enough.

sidewinder · Post by **sidewinder** » Sat Jul 12, 2008 1:44 am

Thanks Dave, things have changed...we used to have a big box of cells and we'd sit there and match them ourselves...well the guys at the hobby shop did, I never had the pactience. So the come already to assemble? Cool..I'll check it out. Now I have to go search for that thread..