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Thread: Runaway T-Maxx

  1. #1
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    Runaway T-Maxx

    Hello Everyone,

    I'm recently new to the hobby. I bought my Maxx about 2 months ago and have had a blast mainly doing casual bashing on the weekends. Well yesterday I had my first experience with a runaway. I try to keep fresh batteries in the Tx/Rx because everything I've read says to do so to prevent these occurrences from happening. But I guess my definition of low is different than the trucks. I did just order the Traxxas Rx hump pack so I can charge it before I go out each time.

    Question #1. Is there an alarm or another optional failsafe I can get for the 2.4 ghz Tx/Rx to warn me when my Rx batteries voltage gets too low?

    Question #2. Why does the truck go wot when the Rx battery gets low instead of braking.

    Any light that can be shed on either of these two questions will be very much appreciated, and I thank you ahead of time for taking the time to help out.

  2. #2
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    There is supposed to be a last known neutral throttle position that the rx tx leans, though I am not sure how it learns yet.

    You can get a battery watch and mount it on the back window ir get the one that beeps when its low.

  3. #3
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    Thanks for the reply rrho170,

    I have checked, and the failsafe is working when I lose signal from the Tx, and the throttle does return to neutral in this situation. But from what I understand the failsafe is not intended to monitor low battery voltage from the Rx, and will do nothing as far as returning the throttle to neutral when the Rx battery gets too low.

    I did a search on Bing for a battery watch and all that came up were batteries for watches. Is that the actual name of what I am looking for to monitor my Rx battery voltage?

  4. #4
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    Do you have a throttle return spring in place? If you don't, mount one up ASAP!
    Last edited by Maxximum Overdive; 12-31-2012 at 11:40 AM.

  5. #5
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    Yes, The 4907 comes with a TRS but that didn't seem to matter. I guess the Spring only helps when there is complete loss of power from the Rx.

    After my incident I was watching the servo react to different situations. When the Rx loses signal by turning the Tx off, the failsafe kicked in and returned the servo to neutral. When I turn the Rx battery switch to off with the Tx on, the TRS brings the throttle back to neutral. But when the Rx battery is low it seems to lose track of what it's doing and has enough power to hold the servo in the last position it remembered.

    One other note: I had no steering either.

    Thanks for the replies.
    Last edited by Maxxed out Throttle; 12-31-2012 at 12:08 PM.

  6. #6
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    I had this happen to me. It didn't run away but I lost steering and throttle. I have a rechargeable battery pack on my truck and it lost charge.

  7. #7
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    I installed the OFNA failsafe on my 4908 and it works great. Goes full brake when signal is lost. It just plugs in between the throttle servo and receiver. IIRC it was only 20 or 30 bucks.

  8. #8
    Marshal Double G's Avatar
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    The 4908 came with the older AM radio so a failsafe was necessary. The Traxxas 2.4 radios come with a built-in failsafe and external failsafes will not work on the system.
    The Super Derecho

  9. #9
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    @ sefh - I think the only reason mine went wot was because it happened to go below the necessary voltage right as I pulled full throttle to get some extra lift off a jump.

    Right as it left the ramp the throttle went wide open. The truck attempted a double backflip and came down vertically on the rear of the truck creasing the brand new body I had just put on. It then some how how ended up on its wheels and took off about 20 ft. and hit a tree, flipped and spun out and landed on it's wheels again and went another 7ft. into a fence. Luckily with all the obstacles in the way I was able to be right on top of it to shut it down. Only damage being the creased body, which I'll take over serious damage or injury to someone or someone else's property any day.

    When my hump pack gets here I'll just make sure to charge it before the first run of the day, and every 4 tanks of fuel after that.

    I guess I just feel like after so many years of these trucks being made and the amount of money they cost there would be some kind of safeguard pre installed to at least notify us of low battery.

    If anyone can point me in the direction of an add-on voltage indicator that will work with the 2.4ghz system I would be very grateful.

    Thanks for all the input everyone.

  10. #10
    RC Turnbuckle Jr. Wildman4910's Avatar
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    Look out for the tree/crunch!

    LiPo? Naw NITRO!!

  11. #11
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    I run a venom failsafe on my 3.3 maxx. It plugs into the throttle channel and puts on the brakes when your rx pack drops below safe levels. I had a runaway and totalled a MAXX at WOT. When the vacuum force of the engine overpowers the servo's ability to hold the slide carb shut it opens to full throttle due to the motor sucking air through it.

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  12. #12
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    Thanks for the find Wildman.

    @bashhound - Do you happened to have the part number for the venom failsafe? And it does work with the 2.4 ghz Tx/Rx?

  13. #13
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    http://www.rchobbyexplosion.com/Veno...p/vnel-107.htm

    Should work fine with 2.4 plugs in on the output of the reciever so it really shouldn't matter if its am/fm or 2.4. Just make sure you set it up and test it to be sure.


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  14. #14
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    Thanks bashhound for looking that up for me. I e-mailed venom directly to inquire about the compatibility of that failsafe with the TQi 2.4ghz. So when I hear back I will report my findings.

  15. #15
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    Np. I know how it feels to watch my truck accelerate out of control, now I wont run my old nitros without one. Its like a $20 insurance policy for a $600 truck.!


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  16. #16
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    @ Bashhound.
    Thank you for posting this. It's a cheap insurance policy for sure. Off to go buy one.

  17. #17
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    I did find that for the TQi 2.4ghz system, when you add the docking base and the Traxxas link app for Ipod & Iphone you can monitor the Rx voltage in real time right through the app.

    Also the Nitro trucks that come the the TQi 2.4ghz system come telemetry ready for Rx voltage, so no added sensor for that particular option.

    Quotes from Traxxas website:

    "The Traxxas TQi transmitter can be accessorized to deliver live telemetry, enabling you to see motor/engine rpm, temperature, speed, and battery voltage as you drive"

    "To enable telemetry in your model, you will need a TQi transmitter and #6518 receiver (this is the receiver included with the TQi, and installed in any vehicle that includes the TQi). You will also need the #6510 Docking Base, an iPhone or iPod touch (2nd generation or later), and the Traxxas Link application (free from the Apple App store)".

    "The final items you will need are the correct sensors for your model. Receiver voltage can be read directly from the receiver, without a separate sensor".

  18. #18
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    The TQi will return your your servo to neutral when it loses radio contact so a seperate failsafe will think it is still in radio contact, however more often than not a dead rx pack causes a runaway and thats where a failsafe comes in handy to put the brakes on.....kinda like a lvc for lipos

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  19. #19
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    With the 2.4 ghz Tx/Rx having such a slim chance of losing signal, it seems like having a low voltage failsafe would be more beneficial than the loss of signal failsafe. That way the truck would stop when the voltage gets low.

    But without the loss of signal failsafe, would the TRS return the servo to neutral anyway when there is loss of signal? or, would the servo just hold in the last position remembered?

  20. #20
    RC Turnbuckle Jr. Wildman4910's Avatar
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    Most will hold the servo to the last position it had from the TX, the TRS will/should pull the throttle to natural if the RX looses all/most all power.
    That being said if it still has the juice left to hold the servo but not receive/use the TX signal the the TRS does you no good as it's fighting against the powered servo.

    A Low voltage alarm or visible meter is the best way to keep tabs on the RX battery charge.
    Look out for the tree/crunch!

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  21. #21
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    Quote Originally Posted by bashhound View Post
    http://www.rchobbyexplosion.com/Veno...p/vnel-107.htm

    Should work fine with 2.4 plugs in on the output of the reciever so it really shouldn't matter if its am/fm or 2.4. Just make sure you set it up and test it to be sure.


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    Update from Venom on this particular failsafe:

    "It's not designed to work with 2.4ghz, but I have heard that some people have had it work for them but I do think it hinges on the type of transmitter. Since it's discontinued I have no way of checking it for you".

    I guess I'll keep looking and in the mean time invest in a monitor of sorts for the Rx voltage levels.

    Once again thanks for all the help.

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