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Thread: locking dif ??

  1. #1
    RC Racer
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    locking dif ??

    Hey guys (girls), I'm an e-revo owner looking to mod out my ride. I was looking at the locking difs on the summit, and thought that would be a cool mod with my 2 speed conversion.
    Now, I'm running a 3 channel radio, and don't really plan on getting the traxxas 4 channel, hate the looks of the stock radios.
    So, with this, we have a challenge. How do I control both the servo for my tranny, and the servos for the difs? I came up with the idea to plug both into the 3rd channel; low gear, locked difs, high gear, difs open.
    Since you've been using the difs, my question is, can you unlock the difs while at speed, or do you have to be stopped? Also, anyone find any flaw in my logic, locked low gear, open for high? It seems like it would work quite well, but I'm still kind of a n00b, appreciate the advice of those who may know better than I.

  2. #2
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    a noob as well. but- traxxas says diff's should be opened/closed at a rest. if you were geared low enough in 1st gear sounds viable.

    but... i have opened/closed diff's at low speed a few times and nothing's exploded yet. but just like in a 1:1 scale, if there is any binding the momentum of the vehicle can damage things...

  3. #3
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    yeah, I was worried there might be something like that. need them to disengage and engage at fairly high speeds, so I guess it wont work.

    oh well, it was a nice idea while it lasted.

  4. #4
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    i don't understand why you can't disengage and shift at a stop?

  5. #5
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    the idea is to be able to shift gears on the fly. it's like 1:1 scale cars, lower gear to get the speed up, then using that momentum, you **** into a higher gear to get to top speed.
    figured that the locked dif would be good for the acceleration, and the use for locked difs would be a lower speeds; but at higher speeds you'd want the difs moving to allow for better handling.

  6. #6
    RC Enthusiast
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    Sounds like some heavy modification is required for such an idea. There will be a need for a manual or complex automated clutch system to ease the shifting process during high revolutions.

    It can be done, but it will not be easy.


    Perhaps having a stronger and much faster servo/T-Shift-linkage system would work well at unlocking the diffs in high revolutions.


    I personally think that your logic would only be useful for high-traction surfaces. You need differential effects for the ideal amount of traction for proper acceleration in various different kinds of surfaces conditions.
    Last edited by FusionTiger; 03-26-2009 at 10:27 AM.

  7. #7
    RC Racer
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    Well, since the transmission is straight out of a revo, you may be able to use the centrifugal shift mechanism of the nitro revo. Automatic shifting and then use the 3rd channel for the diffs.

    The big challenge is understanding how the revo auto is installed and how to get the two gear clutch bell onto the 775 motor. You also may run into a problem with the automatic not being able to engage b/c the DC motor doesn't run at as high an RPM as a nitro.

    Fun idea, but more work than I'm willing to do. (or invest in $$$)
    morgue

  8. #8
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    actually, did some investigating on the revo transmission and all the 2 speed stuff is internal. So you could conceivably do it w/ a 3 ch radio. However, look at the math for the gear ratio's and if you can, go as tall as possible so that spur gear is spinning like crazy to engage the second gear.
    morgue

  9. #9
    RC Racer
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    I was talking with another e-revo guy who's using the nitro tranny. says it works with the electric, but you need a nitro chassis to bolt it to since it's not designed for the electric chassis. didn't seem to think that it was possible with the e-revo tranny however, it needs the servo to push the gears.

    I did just hear in passing about a company that had a receiver adapter that let you use multiple servos form the same port.
    the system used specific combination to unlock different functions, kind of like video game combo moves i would guess. would be useless for shifting, but if you used the difs on the "4th channel", that would work well. lock or unlock them as you please, just like the summit, yet use my 3 channel radio.

    now i've got to find who makes such a unit.
    e-revo, Dewalt 12v motor, 2 speed conversion, dx3s

  10. #10
    RC Racer
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    just get the Futaba 4PK and be done w/ it. You get better control of the truck also.
    http://2.4gigahertz.com/systems/futk4900.html

    And since you're from the Lower Mainland:
    http://www.greathobbies.com/productinfo/?prod_id=FUT4PK
    morgue

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