TRX4 battery hog - Voltage drop?

[BashNSlash]

Strictly trail walking, a 5000mah NIMH packs tend to get my trucks (w/ stock gearing and motor) anywhere between 40 minutes to just over an hour. A 2s lipo gives me just over an hour on average. The TRX-4 sport gives me more runtime out of the same packs.

After switching to a Mamba X w/ 2850kv motor, I'm able to nearly double those numbers easily.

 

[OSRC]

At this point, it is either battery condition or your LVC isn't actually at 3.2v per cell.

I typically burn through 3000ish mah per hour though, with a brushed setup.

Strictly trail walking, a 5000mah NIMH packs tend to get my trucks (w/ stock gearing and motor) anywhere between 40 minutes to just over an hour. A

Thanks for the feedback gentleman. 3000 to 5000mah per hour? Holy cow! I must drive like a baby, it's not uncommon to go on a 3 hour trail run on a single 5000 pack.

Last weekend the RC4WD D110 that was with me weighs about the same as my TRX, and was still going strong on a 4200mah pack after I had burned through nearly 2 3800mah packs. He was running a 35t 540/Outcry ESC.

What is confusing me (aside from the capacity/voltage issue) is it has happened with 2 different ESC's and 3 different battery packs. The Traxxas ESC tripped "early" too, which is why I replaced it in the first place. The only common denominator seems to be the TRX4 itself. This is the only truck I drive with a 550 motor... hmm..

In any case, I'm going to have to go Mythbusters on this. My internal battery clock tells me something is off, and I want to know what it is. If I have to live with it, fine - I have plenty of batteries and nothing is wrong per-se - but I just want to know. If nothing else, in the name of science!

 

[Ditchrat]

Thanks for the feedback gentleman. 3000 to 5000mah per hour? Holy cow! I must drive like a baby, it's not uncommon to go on a 3 hour trail run on a single 5000 pack.

Everyone drives different so you can't say someone or something is wrong. However for me if I am not getting a 45 minutes on 2200mah brushed something is wrong, with the expectation being a hour of run time.


Like I said earlier, it is really something that you have to figure out for each of your trucks on your own.


Having a kid that runs with me has really shown me how driving style can effect run times. Even more so as I have watched his style evolve and his run times really increase.

 

[Hydrocarbon92]

This is the only truck I drive with a 550 motor... hmm..

Funny story about "common denominators": I bought a real car from someone who always lamented the poor gas mileage. My 1st tank netted me 20% better mileage, then the 2nd, 3rd, and so on. I thought it would finally sink in for that person that their driving habits were inefficient.

Instead, they just thought I was lying. 3yrs later, same deal. lol

It's quite possible it's the truck, specifically the motor. However, if brushless is forgiving to a particular drive style brushed is not...it could still be you. See if you can arrange to swap trucks halfway thru a drive with someone who normally gets good battery life.

 

[Voodoobrew]

Going mythbusters:
Well scientific any how.
I use the imax b6 mini from skyrc as my battery charger plugged into my pc via USB.
I can charge and discharge it with a graph running on the screen showing voltage, amperage and mAh.
This is great but not ideal as it cant increase the drain to over about 2 amps. But still handy for showing how much battery capacity you get from full charge to a set low voltage.

 

[OSRC]

Science, round one, is in the books.

Since my common denominator is the TRX-4, I decided to try and do some comparison running between my it and my BOM and see if I could tell if the TRX is really a battery hog or I am completely delusional and chasing rainbow unicorns.

The BOM runs a WP1080 also, but a standard can brushed 35t. They are pretty close in weight, the BOM is just slightly lighter (surprisingly) Not exactly apples to apples, but I ran with it anyway.

Set up a course in my yard. 2 stop and goes, a bit of a technical hilly section and 2 full throttle passes up and down the driveway. Tried to drive the trucks in a similar manner as much as possible (Left the TRX in 1st gear to match the BOM's gearing) and ran in exactly timed 12 minute sessions.

Charged up my trusty 2S 3800 to capacity, and it showed 8.37 volts (4.19/4.18.) Did the 12 minute loop in the TRX in 38d weather - in pajamas watching outside the patio door by the way - and brought it back in and checked the battery and temps.

ESC, motor, and batt were ice cold- didn't even bother to temp them, and end voltage was 8.07 (4.05, 4.02) and according to my charger used 678mah.

Boom.

Let everything rest in the house to warm back up, then recharged the battery which again showed 8.37v (4.18/4.19.) Strapped it into the BOM and went back out. Well, the truck did, I was again in the comfy confines of the kitchen and did another 12 minute loop.

Came back in, and the motor and ESC were a bit warm to the touch, battery was cool. Tested the battery and it showed 8.07v (4.05/4.03) and used 633 mah.

Boom 2.

So between the two runs, the TRX-4 used very slightly more capacity, though the volts were exactly the same. I was expecting some volt drop in the TRX but the runs were basically identical.

Hmmm. Nothing out of the ordinary discovered, possible unicorns on the horizon.

Think there's more info to be had here. Test 2 is going to use my little 2200 pack since it tripped LVC in a whopping 20 minutes last time (though ran for over 2+ hours previously in my CMX). I'm also going to run for 15 minutes this time and any future runs. I'm not sure that 12 minutes is quite long enough to see what's going on.

 

[OSRC]

Testing round 2.

This time I tried my 2200 pack, same course, same driving, but for a timed 15 minute run. 42 degrees, coffee at the ready.

The TRX started at 8.38v, and ran for 14 minutes and 38 sconds before LVC kicked in and put a stop to the fun of running in large circles. Quick tossed my battery on the charger and saw 7.76 volts (3.91/3.87v) and used 807mah.

Battery recharged and balanced.

The Bom started at 8.38v and ran for only 14 minutes 14 seconds before LVC kicked in. Battery showed 7.78v (3.94/3.91) and used 739mah.

So, my TRX is not a battery hog per-se as far as I can tell compared to my other rigs. But something's going on. It needs a battery change far more often than my other rigs.

I did figure out some things while testing both trucks back to back though and I think I got it figured out. The Bom felt like it easily had 2x the power. No joke, it had both more torque, and more top end. Never would have noticed it when out on the trail since we tend to creep along and the TRX goes ok by itself, but running it more wide open around the backyard with another rig really showed the power difference right away.... Huh.

Not sure if the Traxxas motor went soft, or if a 2S lipo on a 14.4v 550 is not enough (Might have to get the stock Bronco out and compare...) . Either way, In spots where I'm part throttle with the BOM, I'm at full throttle with the TRX trying to keep up. Basically I'm running the motor much harder, all the time which is why I'm eating up batteries faster than normal. I think.

Now that I think I got a handle on what's going on, going to swap in the same brand 35t motor that the BOM has and go test run. I'm thinking I should notice a power increase. We'll see.

Also, appears my ESC's are set to cut off at 3.9v. Think I'm going to leave that alone for now. Good to know, the WP1080's manual does not list the voltages.

 

[Voodoobrew]

You have a 1500kv motor in the BOM and a 2200 kv motor in the TRX4, if at full throttle they are about the same speed then the trx4 is geared lower then the BOM. I am not sure what the FDR on the BOM probably close to (36:1 with a 13t pinion and 52:1 with a 9t pinion) is but probably not the 79:1 that your trx4 is in 1st gear.
With both of these motors being sealed can motors the 21t titan should produce more torque and speed then the 35t 540 can motor. Coupled with the already lower gear ratio the 21t titan should blow the BOM out of the water in terms of torque and power, however the BOM should be 50% faster then the trx4 in first gear.
You feel the 35t BOM is producing more torque which makes me think something is wrong.

Could be a worn out motor, but a worn out motor would usually draw less power not more I think because its the com failure that can't pass on the current.
Considering that your 2200mAh pack only gave you 740 usable amps before sagging to 3.2v I would say its not good. On my new 5000mAh packs I have seen them take over 5000mAh on the charger from 3.2v cells, but your driving is apparently much more demanding then mine. So I still think new batteries would help since yours are sagging so bad.

I'm not 100% on all this, but it could give you some help.
I think theoretically if you drive equaly weighted cars in good condition 1 mile in 60minuts, they should each use the same amount of power or mAh, since work=force*distance and power=work/time but in real life stuff is not always what the paper says it should be.

I would buy some HH 550 trailmaster motors instead of another 35t 540 sealed can motor. The HH motors are more reliable then the titan motors. if you want to compare them with the same motor, just swap the motor for this testing. And a 35t motor will be much slower then the current motor because of the gear ratios.

 

[OSRC]

Thanks VoodooBrew..I did not compare ratios on the trucks - again, not apples to apples, but the BOM ran circles around the TRX. Subjectively, it felt like a Miata compared to the TRX lumber truck. I would not have noticed if I didn't run them back to back, so at least something good came out of this.

The batteries kicked off (i think) at 3.9v, not 3.2 so feeling better about their condition. Not great, certainly, but they are a few years old. Answers my question about why I am hitting LVC with so much capacity left. I had thought it was set around 3.2, but apparently not.

Been reading up on capacity, C rates, LVC etc. Never really paid much attention to it before, but good info to know. I did order a Tenergy battery checker so I can check them off the charger. Both WP1080's are set to the medium lipo cutoff. Not sure if I want to go to low or not...not sure what the voltage threshold is. Might set one for a run and find out.

Note my little test was a lot of full throttle running - far more than I ever do on the trail. If i was chewing through 2200 packs in 14 minutes on the trail, I'd be pulling my hair out.

As far as the motor, the 35t BOM motor is rated at 7.4, and getting 7.4. The 550 in the TRX is rated for 14.4 and only getting 7.4. I'm nowhere near smart enough to get the efficiency/power implications of this, but I'd bet the 550 is much happier on higher voltage. Could be why it feels so soft compared to the 35t. OR it could be shot. Lots of trail runs on it...

I'm throwing in the 35t just cause I have one on the bench and it's the same motor the BOM has. Closer to apples to apples. Longer term, I've got a couple of brushless options sitting here. I could just throw one in and be done, but I'm having fun...

 

[OSRC]

Ok, I got this.

35t installed, and much more punchy. Doesn't have the top speed I was seeing in the BOM due to the gearing, but feels stronger all the way around. I'm definitely getting more torque though the higher RPM.

I have a stock Bronco here, so I ran them back to back a bit. The Traxxas 550 is super controllable and smooth at low speeds, but just doesn't have the RPM that the 35t does on 2S. At walking speed, I'm running the 550 much harder on the trail, which is why I'm chewing through batteries. I swapped to a 9t pinon a while ago, and that just made it worse. (I did switch back to an 11t for the last trail run)

So now that I get what's going on, now what to do about it.

I could mess with gearing a bit and try and get a little more wheelspeed out of the 550. I do like the feel of it, and think it's got the torque to handle it. It's ice cold after running so gearing up a bit should be fine. I do like how tractable it is at low speeds. Never really ran 550's, it's an interesting contrast to my normal 35t 540's.

OR I could bite the bullet and go to 3S like the rest of the modern world to get some more RPM on the motor. I run 2S exclusively for various reasons but I'm tempted to pick up 2 3S packs just for my TRX's.

OR keep the 35t (since it's soldered up and installed) and just play with the gearing and live with it for the winter. There's such a wide spread between first and second, it's tricky to find the sweet spot. With the 11t pinion, first is a bit too low, and second is just a touch too high. The Revo had adjustable ratios inside the 2 speed trans - close ratio, stock, and wide. Would be a nice option for the TRX too.

Eventually though, I'll go brushless. I've got 2 systems here, but neither is waterproof per-se, and I see lots of snow/mud coming over the next few months. Prefer to stay brushed until then.

 

[BashNSlash]

OR I could bite the bullet and go to 3S like the rest of the modern world to get some more RPM on the motor. I run 2S exclusively for various reasons but I'm tempted to pick up 2 3S packs just for my TRX's.

FWIW, even with nimh (8.4v) on my 2850kv Mamba X, my truck is "too fast". Don't go 3s if you don't need or want to.

Sent from my SM-N950W using Tapatalk

 

[JohnRobHolmes]

Your motor was worn out, and your LVC is way too high. Change LVC to 3.5v and you will get 90% of the capacity without hurting the cells.

 

[Voodoobrew]

He said he changed the LVC to 3.2v in post 3or 4 but the hw just has low, med, high for battery voltages.

My lvc is set to medium on the esc and after 100min of continues running (2s 4600mah lipo with Rc4wd Beast II) it went in failsafe mode. My lipo was then 3.25V/cell. Which seems low to me.

So if it is set to medium, you should end at a lower voltage then 3.9 per cell

If there both hw1080s then write down the settings and copy them so they are the same. Esc settings can change the torque feel a lot.
The 550 traxxas 21t motor is a faster motor then the 35t 540 motor. So putting the 35t motor in the bronco should make it slower. There should not be more rpm unless the titans you compared them to were severely worn.

 

[indybama]

Ive got a HH trailmaster 550 27t n i love it. But my truck is a scx10 ii with the OG scx10 3 gear tranny. Runnin 11/54. Smc 2s 7400mah 90c batts. Seems to run forever lol

Sent from my SM-J327VPP using Tapatalk

 

[OSRC]

Your motor was worn out, and your LVC is way too high. Change LVC to 3.5v and you will get 90% of the capacity without hurting the cells.

He said he changed the LVC to 3.2v in post 3or 4 but the hw just has low, med, high for battery voltages....So if it is set to medium, you should end at a lower voltage then 3.9 per cell

Both ESC's in the trucks are set to "medium" LVC...the manual does not specify specific voltages that correlate to the settings. I had thought it was 3.2v for some reason, but apparently not. 3.9 seems ridiculously high to me... was reading a few things in the 1080 thread and that doesn't sound quite right. BUT that's the voltage shown on the packs after I pulled them out of the truck and immediately connected them to the charger. Same battery, 2 ESC's, same settings. Not sure what to make of it. Maybe I'll set one to the low setting and see where it cuts off (I'd like to have my field checker in hand first though)

The 550 traxxas 21t motor is a faster motor then the 35t 540 motor. So putting the 35t motor in the bronco should make it slower.

I'm not sure about that - at least on 2S. Now that I have a TRX4 with a 35t and a stock TRX that's basically new with a non questionable 550 and identical gearing on the other shelf, sounds like a DRAG RACE is in order!! "thumbsup""thumbsup""thumbsup" For science of course, not just an excuse to go run trucks aimlessly in the backyard tomorrow.

 

[Voodoobrew]

the recovery from voltage sag is about a second, so you can't measure it from in your car unless you have one connected to the balance plug and hit the throttle while watching the meter, which needs to read fast, at which point the car will trigger LVC.
I will try to run a battery dead at the lake tomorrow and then check the voltage, I never manage to drain my batteries to the LVC, I usually switch cars and batteries before then. Takes a few hours to drain my 5000mAh batteries. but since my HW 1080's are all set to medium we can find out.

WE DRAG RACE IN THE NAME OF SCIENCE!

The chart on this Holmes Hobbies page (https://holmeshobbies.com/motor-recommendations) can show you a rough difference in speeds between motors, slight variations occur between motors and manufactures, but not all that much. in the chart your 35t 540 would be any 3 slot 450 35t variant, and the titian would be any 3 slot 550 21t variant

35t 540 would be about 1500kv or rc4wd's might be 1750kv
21t 550 titan would be closer to 2200kv so about 25% faster

 

[OSRC]

Sunday morning drag races!

Decided to pit the new stock 550 vs. the 35t... Perception can sometimes change reality, so I figured some hard numbers would set me straight. I did a 20ft strip, 5 runs in both directions, no body on either truck, same gearing, same 4.75 tires, standing start and topped off the battery between trucks. (8.37v each time BTW)

New 35t: Avg. 5.32 seconds
New 550: Avg. 4.57 seconds

So my perception is crap, the new 550 dusted the 35t.

SO I got curious and reinstalled the OLD 550 I took out of the Defender. Looked pretty clean, so just oiled the bushings and dropped it back in. That motor cracked off a ten run average of 4.78 seconds!

Science!

So after all this, seems like the TRX4 in question is not really using any more battery per-se than other trucks, and the motor itself seems fine. Assuming that my batteries are ok, what's left?

Going to leave the LVC set at medium for now. Just for consistency sake.

Wondering if the gearing is throwing me off. First gear is way, way low...something like 64:1 IIRC. So I'm going to experiment with gearing next.

I just ordered a single speed trans conversion. I like the 2 speed in concept (not to mention its been very reliable and slop free) but the ratio is so wide that to gear first where I want it, second would be basically useless. May as well make the swap and lose some weight.

Once it's re-geared up, hopefully I'll get a trail run in and see where I stand.

 

[JohnRobHolmes]

The only thing left is the LVC being far too high.

 

[lonleycreeper]

I am going to chime in here.

I suspect it is a bad battery. Now hear me out before you dismiss me.

I did a similar test with a standard scx10 on 4.75 tires. The tool I used was a 4000 mah 50c shorty pack and a lipo alarm, often used in airplanes.
On the rock with any thing more than 40% throttle the alarm was going off (set at 3.3v per cell )voltage. Meaning drawing enough voltage to sag a 200amp rated battery pack. As soon as I eased off the throttle the pack went right back to almost full full voltage. I no longer run those packs, but they were in good condition, with but maybe dozen charge cycles.

What I think is happening is you are sagging your pack in early voltage cutoff.
With my amp meter hooked up, my 2.2 F150 pulls 20 amps spinning the tires on concrete in low gear, against a wall. I use 3s 2200 mah 30c batteries and get about 1 hour of run time per pack. (Avg 2 miles). Those 4000mah 2s batteries I go nearly the same distance, but draw more amps.

 

[Voodoobrew]

I ran my two months old 40c 3s 1500mAh battery dead putting around in my front yard, in my trx4 with a trailmaster sport, HW 1080, and 9tpinion. When I got it to the charger it was at 9.63v and climbing, that's an average of 3.21v per cell. My guess is medium cutoff voltage on the HW 1080 is 3.2v per cell.
The fact that your batteries read so much higher when they come off the truck makes me think you got old batteries, and by your own admission not the best perception
If you want more run time I would consider a brush-less setup, 9t pinion and newer 3s batteries. let me know how fast you want to go and Ill give you an idea of what kv motor would be good. or base it off the kv's I gave you earlier and on 3s realize it will be 50% faster. I woulden't go over 2200kv but thats just me.