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traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Tue Sep 18, 2018 10:17 pm
by John
Hi,new here. I have a PW F150 monster traction truck I install upgraded ml toys gear boxes and installed 2 traxxas 3785 titan motors 12T and put on the correct pinion on them. after It goes 20 seconds it stops. after reading some posts here I lifted up rea end and found that drivers side goes forward in both high and low but passenger side goes in reverse while in forward. please help I'm going crazy.

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Wed Sep 19, 2018 7:59 am
by Hammer-fm
Does the passenger's side go forward when the gear selector is in reverse, or are you saying it always goes backward?

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Wed Sep 19, 2018 4:23 pm
by John
Hammer, when in reverse the pass side will go forward and drivers side will go in reverse.

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Wed Sep 19, 2018 6:09 pm
by John
Hammer. Would it possibly be timing on the one motor

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Wed Sep 19, 2018 7:53 pm
by RawLiquid
Cmon guys, this should be obvious...


1) lift the rear wheels off the ground, preferably prop it up or set it on its nose.
Try each of the following and take some notes on which wheel turns which way, my direction notes are in relation to the vehicle and what motion it would cause.
1) Reverse - one wheel should turn in reverse, the other should not be turning
2) Low - one wheel (same one as in reverse) should be turning forward, the other wheel should not be turning
3) High - both wheels should be turning forward.


If the second wheel turns the wrong way while in high, you reversed the polarity at the motor. Simply swap the wires at the motor and all should be good. Very easy mistake to make, and fortunately the hardest part of the fix is often getting at the wires to swap them.

:) RawLiquid

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Wed Sep 19, 2018 10:31 pm
by John
Thank you raw liquid. I will try this tomorrow. Hoping this is it. I can stop hearing my wife saying stop messing with everything and making it go faster. I can’t help myself lol I love this stuff.

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Thu Sep 20, 2018 1:00 am
by Hammer-fm
"found that drivers side goes forward in both high and low but passenger side goes in reverse while in forward."
"when in reverse the pass side will go forward and drivers side will go in reverse."

These symptoms are a clear sign that you just have the passenger side motor polarity reversed. Take that gearbox out and swap the connectors (not sure if you use bullet connectors or spliced ; if you spliced, cut at the splice, swap, and resplice).

One clarification relative to RawLiquid's post: In 1st and reverse with no load you should expect both wheels to go in the same direction -- not one moving and one not (unless you have something dragging severely on one side). They won't necessarily be the same speed although I'd expect them to be fairly close. The "one-wheel only" behavior is pretty typical when it's on the ground and you're running in 1st or reverse but shouldn't happen when neither wheel is loaded.

Either way, the simplest thing is to check 'high' and if they're going in opposite directions, fix the one that is wrong :lol: .

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Fri Sep 21, 2018 12:54 pm
by John
That was it. Both wheels spin in same direction in all gears. Runs for a few minutes and then stops again. Have to wait a few minutes or so then it will work again. I’m guessing there is a circuit breaker somewhere in the wiring

Re: traxxas 3785 titan motors 12t in F150 truck stop working after 20 seconds

Posted: Sat Sep 22, 2018 12:06 am
by Hammer-fm
The factory battery has a circuit breaker inside. The motor you are using is rated for 8.4V and although it's probably quite a bit faster than stock, it probably also pulls a lot more current during both acceleration and at top speed. You are likely just exceeding the breaker's capacity. You can buy an aftermarket battery and install a 40A+ fuse instead or buy a somewhat milder motor. Traxxas doesn't post specs on their motors, though the Traxxas forums does have one poster claiming it is 25000 RPM @ 8.4V -- this doesn't sound unreasonable for a 12T (the 21T Nichibo $2.49 special at Jameco is a 21T and spins 23000 RPM @ 12V).

If that's true, I would expect >35000 RPM at 12V and I would thinnk the motor will have very limited longevity and it will probably be pulling 3-4x the current of the stock motors at full speed.