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  1. #1
    RC poster
    Join Date
    Aug 2018
    Posts
    7

    Need advice on Motor replacement

    Picked up a pre-runner for my daughter. Got it home and tested it. Then went back and bought another for me. That was last Christmas. I play with the truck off and on so it hasn't seen a lot of use. Yesterday I was doing figure-8 drifts on a slick surface and the truck suddenly came to a stop and wouldn't go at all. It wouldn't even roll. Pulled the motor out and it was siezed. Played with it for a while and it finally started spinning again. Ohm'ed it out and measured ok. Put it back in and nothing. Steering works fine. Took the whole thing up to the local hobby shop. They interconnected the wiring with a similar model and determined ESC bad/motor good.

    Had the option to buy a brushless motor kit that needed a Dremel mod to fit. Shy'ed away since the speed is fine for what I do. $60 bucks for the ESC and truck is up and running. After reading a few posts, sounds like the orig motor is over-due to die anyway. Now the brushless kit is looking a little better.

    Hobby shop has this:

    https://www.hobbytown.com/hobbywing-...030010/p279160

    For $45, it sounds great.

    This Pre-runner already has the steel diffs and driveshaft so I think I'm good there.
    Planning to replace plastic spur with metal.

    General thoughts on parts selection.
    Recommendations for metal spur gear that will play well with the motor gear. Gearing is fine as is.

    Thx.

  2. #2
    RC poster
    Join Date
    Aug 2018
    Posts
    7
    Picked up the brushless combo pack.
    First issue I see is the screw holes in the motor don't line up perfectly with the motor mount. Looks like I can waller-out the holes in the motor mount and make it work.
    Second issue is the kit does not include screws to mount the motor to the motor mount. The screws from the old motor are too big (diameter). Looking inside the brushless motor screw holes, I can see the windings are pretty close to the where the screws go in so screw length is going to be critical. Sent Traxxis an email asking for correct size. Looks like I'll have to order them from somewhere. Local hobby shop doesn't have them in stock.

  3. #3
    RC poster
    Join Date
    Aug 2018
    Posts
    7
    Found the screw holes were tapped to be 2.5mm. Picked up some 6mm long one and some 8mm long socket head (allen) screws. 8mm is too long. Was able to use the 6mm screws. One of the motor mount screws fits down inside a recess on the motor mount. This allows the screw to be too long and if used like this would contact the motor windings. Put a large flat washer under the head and 6mm screw works ok now. This also allows the motor mount to move a little which helps with setting gear mesh.

    New motor shaft doesn't have a flat for the set screw of the gear so had to make a flat.

    Got it all together and the car is definitely a little faster. The controller (ESC) setup was pretty easy since the kit contains a program card. Noticed there's no option for NIMH battery which I run when lipo is charging. Low batt cutoff is set as high as I can set it but the NIMH battery still dies before the ESC shuts down. Not a big deal, I'll pick-up another Venom 2000 batt. They seem to work well and fit batt compartment. Noticed motor still gets pretty hot after abt 10 mins of drifting. I believe the gearing is too tall since the ESC barely gets warm. Trying to decide if I want to install a wrap around heat sink/fan on the motor or mess with the gearing. Still looking around to see how hot it too hot for a brushless motor. Guy at hobby shop says stay below 235 degs F. Seems a little high, but maybe that's OK.
    Still running the plastic spur gear and need to find a decent metal replacement. Hobby shop recommends hot racing or Intengy brand. On the prowl for the spur gear now.

  4. #4
    RC poster
    Join Date
    Apr 2019
    Location
    South Carolina
    Posts
    1
    Thanks for updating this thread. I was looking at the same upgrade and was wondering if there were any issues to look out for.

  5. #5
    RC poster
    Join Date
    Aug 2018
    Posts
    7
    No prob. Just trying to post the info I would want to know.
    Well, went with Hot Racing spur gear. It's a nice looking piece. It comes with a small spacer which I wasn't sure I needed. Turns out you definitely need the spacer since the new Hot Racing steel spur gear doesn't have a nipple on the side that faces the front of car. If you leave it out the the spacer, the spur gear can slide forward and disengage itself from the driveshaft.

    The other side of the spur gear (facing rear of car) has a nipple with a cutout for a pin that goes thru the driveshaft and engages the drive gear's cutout. Once pin is in, you slide the bearing over nipple of the spur gear and that holds the pin in. Problem was the nipple was slightly too large to fit the bearing over it. Wouldn't be surprised to hear the nipple size was just right, then they gave it the black oxide coating. I was able to force the bearing on but when I tried to remove it again, I destroyed the bearing (kind of a cheesy little bearing). Discovered you can't just order the bearing. You have to order a kit that has all the bearings. Only $17 at local hobby shop and I have some spares now, so not so bad.

    Got the new bearing kit and once again, spur gear nipple is still to large for the bearing to slide on. Put driveshaft in drill with spur gear installed, held a small file against the nipple and was able to grind it down so the bearing would fit. Got it all together last night and went for a quick test drive. It make a little more noise now and when I let off the throttle, the tires stop turning and car slides (on slick floor). Didn't do that before with plastic spur gear. Think I need to re-adj the mesh between the motor gear and the new spur gear.

    Was reading somewhere that you should place 2 sheets of newspaper between the gears, push them together and tighten motor mount screws. The 2 sheets of paper is supposed to be just the right thickness. Sounds like a good place to start anyway.

  6. #6
    RC poster
    Join Date
    Aug 2018
    Posts
    7
    Oh yeah, while I was at it, I replaced the gears in the steering servo with metal gears. One of the old plastic gears had a tooth missing and steering would act funny ever once in a while. That mod was pretty straight forward except for binding when screws that hold servo together got their final tightening. If I loosen the screws, it seems fine. If I tighten the screws it starts growling after turning steering wheel indicating a bind. Took it back apart and was able to get output gear onto it's shaft a little further, still binds. Tried removing the small 0-ring which appears to seal the output shaft from water/dirt/etc. No more binding. Ok for now, but will most likely re-visit this issue later since I would like to have the o-ring in there.

  7. #7
    RC poster
    Join Date
    Aug 2018
    Posts
    7
    Got the motor gear to spur gear mesh adjusted by using 1 layer of writing paper between the gears. Drivetrain is working perfectly now.

    Car has had a torque steer issue when stock and it's gotten a little worse with the added punch of the brushless motor and LIPO batt. Seems to have some slop in the steering linkage. That's the next issue to address.

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