9398 crawler poor motor output

[cammellostanco]

Hi everybody!

It seems that I just cannot get enough power out of the 2 std motors anymore. I tried with both alkaline batt as well as TOP enelopp rechargable, but no way, the crawler is not capable of pulling itself on the same slopes it used to when I tested it in the winter :(

What can I try? Any ideas?

[MrNumbskull13]

Send the motors to lego for a replacement?

[Marcel1980]

Never heard something like that

[AlmightyArjen]

Has the motor still normal torque when you connect it directly to the battery box without the IR receiver?

[750ACE]

I had this issue. Bad battery box go figure.

[cammellostanco]

Ok, i still have the warranty. But before changing the 2 motors (looong wait) what can I try? I will try the motors connected directly to the battery box anyway. The 2 motors are hardy used (10 times or less)

[peter_m]

I had this issue. Bad battery box go figure.

Ok, i still have the warranty. But before changing the 2 motors (looong wait) what can I try? I will try the motors connected directly to the battery box anyway. The 2 motors are hardy used (10 times or less)

You can check your motors with standard 9V battery (to see if it is Battery Box issue). Here is the description how you have to connect the battery (GND 0V and 9V) to the motor: http://www.mocpages.com/moc.php/168223

Of course you do not have to build the adapter - just take 2 wires and attach them as described.

Edited August 16, 2013 by peter_m

[FuzzyBallz]

Was looking at LEGO PF rechargeable battery 8870 earlier. I heard it's a beast. Only problem is it costs $75 for the battery + charger. Ouch.

[aol000xw]

I was very tempted by the 8878 myself but price and voltage made me try another route.

I modded a battery box to use 3.3V AA rechargeable LiPo batteries (3s2p). That makes 10volts of high discharge power.

I'm waiting for the connectors to allow balanced charge directly to the battery pack without removing the batteries.

Edited August 16, 2013 by aol000xw

[750ACE]

Was looking at LEGO PF rechargeable battery 8870 earlier. I heard it's a beast. Only problem is it costs $75 for the battery + charger. Ouch.

What do you mean its a beast? It holds a charge and weighs less but has less voltage. Not more power.

[Alternator]

Just brainstorming other ideas here - is it possible that with the change in season tolerances have altered slightly and there is more friction along the drive chain?

As for motors failing though, I've had it happen to me with a lightly used Medium motor (from my 8043 excavator)... Lego didn't replace, I'm guessing since I had the model for 18 months (not sure what I think about that).

In my case the motor wouldn't start without a nudge, not sure about it losing torque or not?

[cammellostanco]

hi guys, back again. I admit I was lazy and did not work at the lego for quite some time. Decided to revive it and troubleshoot the problem. I got a new battery charger and a battery tester, the 6 batteries work fine, BUT the 4x4 is still slugghish with almost no torque.

More testing tomorrow

[Phoxtane]

Are you sure you didn't push anything too tightly against beams, such as gears or bushes? That could be sapping some power. A good way to avoid this is to test the axles by hand while assembling them, and see if they can spin relatively freely.

Edited April 8, 2014 by Phoxtane

[OzShan]

I was able to remove the small black 16t drive gear from each drive assembly without pulling many parts apart (the first gear after the motor in the train). If you did that you could see if the motors are putting out much torque, or if the rest of the train is bound up. It should at least roll freely with the gears removed.

Good luck.

[gregorijs3kivi]

Was looking at LEGO PF rechargeable battery 8870 earlier. I heard it's a beast. Only problem is it costs $75 for the battery + charger. Ouch.

i founded on brick link battery and charger for 60 dollars

[JM1971]

I found with one of my m motors there is a crack on the connector plastic and it can either not work or lose power, bring back the old connecters that were completely removable and repairable, these new motors are designed to not last very long so you have to buy new ones when the cable breaks and it will because there are 4 wires and a break in any one will make it useless.

PS. I think the cheap AAA or standard AA box has more power than the lipo, did you try another box in case there is a fault.

Edited April 8, 2014 by JM1971

[cammellostanco]

Hello again guys, I did some testing, it appears that the issue is still there, I will be now going to test the other options you mentioned. Will update asap

[cammellostanco]

After just a few years....I revived my passion for Lego Technic. And yes... the problem with the poor output is still there.

Let me recap:

 

1. I removed both motors, checked the axles, etc. There is no excess friction and the motor look fin externally
2. Both motors still have their original specs speed (400/420 rpm) measured with the yellow Lego speedometer tool

I could not recover anymore the instructions to connect a 9V battery to the motor directly, any ideas?

[Kostq]

See if the rims are slipping.

[cammellostanco]

17 hours ago, GTS said:

See if the rims are slipping.

Thanks, I checked, the rims are fine, they are not slipping on the tire. I am going to make a video so the issue is clearer.

[cammellostanco]

This is a video of the noise that engines make.

If I lift the truck the wheels spin again, as soon as I put it down, the whining starts again and the motors does not spin.

The truck has the original open diffs, the only thing I changes is the reduction gears in the hubs.

Here the pictures where I swapped the gears to get more torque, did I overdo it?

 

Edited January 17, 2021 by cammellostanco

[Zerobricks]

The whining is the current protection kicking in. Also your gearing is all over the place, you are gearing up from the motor and gearing down at the hubs. Just build as it in the instructions and it should work okay.

Edited January 17, 2021 by Zerobricks

[cammellostanco]

OK, I replaced the gears as  per the original manual.

I am using brand new energizer lithium.

I had to disconnect the front motor since I lost the original hub gears.

It helped towards a solution, but it's not there yet

The only change is that the truck now goes back and forth faster 4 or 5 times, before stopping as before.

Edited January 19, 2021 by cammellostanco

[MikeTwo9398]

Did you try to use another battery box?

When I was experimenting with LiFePO4 batteries I found out that it was not working with all of my battery boxes.
A few showed the same results as the video shows. I could not find out why, maybe older/newer type of battery boxes caused it.
 

[CF 28]

Try isolating each electronic part. Turn the truck upside-down, plug 1 motor only directly to the battery box. Turn it on and use your hands to put a load on the tires. Does it have any power? Plug the other motor in by itself and try that one.

If you have a bad motor it should stand out. If they are both weak like this that it has to be the battery box or the batteries themselves. I've heard of someone having a similar problem when using Kodak batteries, which I guess were low output.

If both motors have good power like this then plug them both to the battery box and test it that way. If you're getting good results like this then it would point to the receiver.