Disappointing move to Lipo

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valve90210

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After lots of reading up and people extolling the virtues of moving to Lipo batteries I decided to give it a try in my new MT with an Absima 15t motor, which I have only run a couple of times and not for full packs as I've not had time or it's been foul weather.

Having read loads saying with Lipo it'd be punchier off the line and quicker and much better run times I was excited to try it, so I took it out to day with the freshly charged Lipo and yes it was punchy and quicker, however I had to stop after a a few minutes to let everything cool down as the motor was getting really hot.

After it cooled down I gave it another run and again it was great but still getting really hot. I decided I needed to getr on with a few bits round the house and left the car for a good couple of hours.

I then decided to give the car another go and do a couple of runs to see if it was any faster than the 25 mph I clocked it at with the 15t and a nimh battery. To my surprise it only hit 19mph... the same as my son's MT with an 18t motor using a nimh battery. It still felt punchier off the line and was driving nicely...and then it stopped. The motor was quite hot but not finger burningly so but it just didn't drive. I still had steering.

A bit of swapping about and tinkering later with one of my other cars and it seems the motor has died on me. I've now swapped it out with an Absima 18t which I've been running in my old Tamiya Fighter Buggy since Xmas and have run long periods (two 3500mah Nimh packs each getting about 30-40mins) and it's barely even gotten warm to the touch.

About 5 minutes with the Lipo battery and it's getting really hot.

So now I'm not sure what to do, should I be dropping the pinion a tooth or two to bring the temperatures down? If so, does that not defeat the point of upgrading the motor to a faster one and indeed the battery to a Lipo?
 
Nothing to set up on the esc, it's the very basic stock esc/receiver, had a low voltage alarm hooked up so I wouldn't over discharge the battery. The run time was probably pretty good but more because i kept having to stop and let it cool down than anything else really...
 
If running a 2s it really isn't that much more that your nimh. There is no reason for it to get hot, imo, and run slower.
 
Previously your battery was the weakest link. It appears now the motor is. And if you replace that, you may well burn out the ESC...

That's how it goes, these are really $250 vehicles you buy in installments, but the $130 base price sure helps to convince your wife :)
 
Gave the truck a good run yesterday with the 18t in using both the Lipo and an nimh.

First run was in the morning with the lipo running over dirt, grass and lumps and bumps. truck ran really well but the motor did get hot very quickly, annoyingly I didn't think to check the esc temp (it was early morning after a late night! lol)

Second run was in the evening running up and down my road (tarmac and the occassional short burst over the grass verges), lots of full throttle, braking and full throttle again. First off with the nimh. With this the motor got quite hot (not scorching and certainly touchable), the esc was just gently warm as was the battery.

I let it all cool down and then gave it 15 minutes with the Lipo doing the same type of driving over the same terrain (tarmac and verges). Again the motor got hottish (touchable but noticeably hot), the esc was barely even warm, the battery was ambient temperature.

I'm going to get myself a temperature gun and keep an eye on things in particular the esc but I think I might be able to sort it all out with a bit of a gearing change.

From reading up yesterday:
http://www.ultimaterc.com/forums/showthread.php?t=152992&page=2

Start with bigger pinion (2 more teeth) and if it is still hot motor, cool esc, keep gearing up. Check temps every 5 mins to be safe (once temps gets closer to 160, check I
Temps in shorter time).

48 pitch, you can gear up by 2 teeth
32, mod 8, mod 1, and etc, gear up by 1 teeth

"You may find the following helpful, I cant remember who originally wrote it but I have found it useful in the past."

"Author Unknown"
Although not always true, a rule of thumb is:
Hot motor, cool controller, cool batteries = under geared
Cool motor, hot controller, hot batteries = over geared
hot motor, hot ESC, and hot batteries = way over geared
Warm motor, warm controller, warm batteries = happy components

Hot, warm, and cool vary as well, so here's another general rule:
Hot for a motor = generally over 160F (71C)
Hot for a controller = generally over 150F (66C)(or "thermal" range for the controller)
Hot for batteries = generally over 150F (66C) for nimh, 130F (54C) for lipo
Warm for a motor = generally 100F (38C) through 150F (66C)
Warm for a controller = generally 100F (38C) through 130F (54C)
Warm for batteries = generally 100F (38C) through 130F (54C) for nimh, ambient temp through 120F (49C) for lipo
Cool for all components = generally ambient temp and up to 10 degrees F (5.6C) more

The reasons the above are not always true are numerous, but may include:
Sticky drive train - will put un-necessary strain on electronics whether geared correctly or not.
Poor quality batteries - batteries will heat up regardless of gearing.
Wrong motor for the application - will put un-necessary strain on electronics whether geared correctly or not.
Wrong controller for the application - will put un-necessary strain on electronics whether geared correctly or not.
Click to expand...

Depending on the readings I get for the esc, I may be able to gear up a bit on tarmac to give me a bit more pace, then gear down a bit for when I'm running on dirt and grass etc.

I think i'll see how that goes before deciding on whether to try another 15t motor...
 
Interesting. Please do report back on your test results. The link you shared was interesting as the "rule of thumb" that had been shared with me (by people both online and off) was that if the motor was too hot, you needed to gear down.

When I started running a LiPo in my AMP MT, I only added in an LVM. Then I installed a Dynamite 15t 550 motor with stock gearing. After about 40-40 minutes of running on a dirt road at full throttle for 90% of the time the motor would hot (I could touch it for about 4-5 before feeling like I might burn myself).
 
Well that's what I've read a lot too but then I saw that link and now I'm thoroughly confused...lol

I've seen a lot of people mention 15t motors on Lipo and not having a problem, I'm wondering If I had a duff motor maybe? It was pretty warm just on the nimh battery (nothing I'd consider hot but certainly warmer than the 20t in my sons truck
 
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I get my stock 20T motors scorchingly hot (like, cannot keep your finger on it for more than one second...) just by running it in my backyard. High resistance surface is the culprit for me (bumpy, badly kept lawn).

It seems the LiPo's current capacity means that the little bursts of acceleration that occur constantly on this surface are much fiercer, and this heats up the motor a LOT even if the car is not actually going that much faster. A lot of heat is wasted on spinning up the wheels as they lose contact with the ground perhaps, I don't know.
 
I think I'm going to try changing the pinion gear down a tooth or two and see what happens with my temperatures. If I can find a halfway reasonable set of pinions to try, which at present is a struggle in the UK it seems.
 
A 2s lipo vs a fully charged nimh - the output is slightly better.
The difference is your performance will be stronger for longer as an nimh putters off after the battery gets to half life or so I have found.
Sounds like it could be a gearing issue if the motor is overheating, or running it on high resitance surface like long grass.
 
<<I've seen a lot of people mention 15t motors on LiPo and not having a problem, I'm wondering If I had a duff motor maybe? It was pretty warm just on the NiMH battery (nothing I'd consider hot but certainly warmer than the 20t in my sons truck[/QUOTE]

I'd check everything for resistance = make sure all wheels are spinning freely and gear mesh is not too tight--any of these can cause the problem. Also you are on the right track to go a tooth or two lower.
The reason your esc is not for Lipos is only cuz it doesn't have Low Voltage Cutoff. If you run the pack to the end you can actually ruin your Lipo!!
Also after a few cycles your Lipo might get stronger.

This is not just a toy--this is the real world = As you analyze and solve this problem you are learning about machines, physics, electronics & etc--your son may learn more from solving a real problem like this than in a week of school!!
 
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Music411 said:
A 2s LiPo vs a fully charged NiMH - the output is slightly better.
The difference is your performance will be stronger for longer as an NiMH putters off after the battery gets to half life or so I have found.
Sounds like it could be a gearing issue if the motor is overheating, or running it on high resitance surface like long grass.
Click to expand...

I was only running it on concrete when it was getting way too hot. I did wonder if my slipper wasn't set right, would that cause huge amounts of excess heat ion the motor?

nimbuzz said:
I'd check everything for resistance = make sure all wheels are spinning freely and gear mesh is not too tight--any of these can cause the problem. Also you are on the right track to go a tooth or two lower.
The reason your ESC is not for Lipos is only cuz it doesn't have Low Voltage Cutoff. If you run the pack to the end you can actually ruin your LiPo!!
Also after a few cycles your LiPo might get stronger.

This is not just a toy--this is the real world = As you analyze and solve this problem you are learning about machines, physics, electronics & etc--your son may learn more from solving a real problem like this than in a week of school!!
Click to expand...

My Lipo definitely seems to have gotten stronger over the last few runs with the 18t motor in it, been running it up and down my street and it's going really nicely, getting a little warm but nothing major.

I have tried it with a 16t pinion but to be honest it didn't make a great deal of difference on the temperature (going by my fingers - will check with a temperature gun when I get time) and from the line it was quick but I could tell it wasn't as fast as with the 18t and not as fun to drive on my street.
 
Yeah, I've read the thread and commented in it, however I can't seem to find that particular model on ebay UK so was asking if the model I'd linked to was any good?

Also, how about this one, any good?
http://www.ebay.co.uk/itm/142222348959

I notice it doesn't come otherwise a programming card so I'm guessing you can't change any settings or anything?
 
@valve90210 the 3100KV you posted is pretty much what I have (only mine is orange and waterproof). This is a mild upgrade. As soon as the street dries out I will compare stock to this motor. Probably I can ramp up the gearing some and make it faster, like @Bigpoppa99 .

The second one you posted is a more powerful motor. The can is longer and it's 3800KV. It should be faster and have more torque than the other motor. I'd expect this to be a serious performance upgrade, and your spur gear or transmission may not take kindly to it. If you want a programming card, you'll have to buy it separately and pray that it is compatible.

The weak point on these ESCs is the little fan. Mine is noisy and wobbly from the first time I turned it on. I don't expect it to last.
 
Hmmm, I'd rather a mild but reliable upgrade rather than a ridiculously powerful upgrade that eats my transmission and leaves me constantly pulling wheelies...
 

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