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  1. #1
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    Question Hitec HS-645MG Throttle Servo too stiff for the Throttle Return Spring! Any Ideas?

    Well the title says it all. I have a Revo 3.3 (#5309). After burning 3 Traxxas throttle servos due to the stiff spring found on these revos, I finally decided to get an HS-645MG. Installed it yesterday and noticed something very unusual. We all know how strong the throttle return spring on this model is, but even that failed to pull the throttle back to neutral when I checked the setup.

    How I checked? Ok, so I switched on the tx and rx (obviously ), pulled the trigger to Wide open throttle and then switched off the receiver/rx. As per the design and even technically, the return spring is supposed to pull the servo back to neutral to prevent a runaway. But the servo is so hard to turn that even such a stiff spring couldn't bring it back.

    Does anyone else have a similar experience or can suggest something, please help. I don't want to take any chances, just in case!

    Thanks

  2. #2
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    Sounds like that new servo is plenty strong for steering, try swapping it with the steering servo.

  3. #3
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    I already have my steering set up alright. I bought it especially for the throttle/brake after reading everywhere that it was the best deal for a throttle servo. So, if you have any experience with it as a throttle servo, please help as that is the only thing I need a solution for at the moment.

  4. #4
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    I was having some throttle linkage problems and ended up trying a ball bearing pivot from integy (yeah i know there stuff is cheap) it made everything much smoother and took alot of strain off the servo.

  5. #5
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    Quote Originally Posted by Utilityknife View Post
    I was having some throttle linkage problems and ended up trying a ball bearing pivot from integy (yeah i know there stuff is cheap) it made everything much smoother and took alot of strain off the servo.
    But there's no problem with the pivot or the linkage at all. Everything's fine and mint as I have been using it already with traxxas servos. What I'm saying is, do you or anyone here have a 645mg servo for throttle/brake and have you or others experienced the same thing i.e. the servo being so hard to turn that the return spring can't pull it back to neutral in the event of a failure?

  6. #6
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    After looking at my truck again i see what your talking about and I eliminated it due to strain on the servo and went with an electronic failsafe.

  7. #7
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    Well failsafe will only function till the time your electronics and servo work. But if there's a servo failure with the servo stuck at WOT or in case there's some other electronic failure, it is the spring that is gonna bring it back, not the failsafe. So, I cannot take that risk, you see.

    Failsafe is something that I personally don't see of any use at all. It's just an added weight only good till the time your battery or electronics are functioning right and if they are, one really does not need a failsafe in the first place. But if they fail, it will fail too, thus not serving the purpose it was meant for actually . But that's just me.

  8. #8
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    A proper failsafe hits the brakes before voltage is to low for the servo to operate as far as some other failure that would need the spring to pull it back I don't know, I've been running nitro for 10+ years and never seen a situation that would need it unless your servo gears strip out which I have seen that spring do more then once. Anyway good luck.

  9. #9
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    Quote Originally Posted by Utilityknife View Post
    A proper failsafe hits the brakes before voltage is to low for the servo to operate as far as some other failure that would need the spring to pull it back I don't know, I've been running nitro for 10+ years and never seen a situation that would need it unless your servo gears strip out which I have seen that spring do more then once. Anyway good luck.
    Very true. But if the servo fails at WOT, then even the failsafe will not help, though failsafe is very useful for the low voltage situation, no doubt. So, I agree with you there and thanks

  10. #10
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    if you still have the traxxas heavy spring on your truck remove it and use this...

    http://www.amainhobbies.com/product_...eturn-Spring-2
    you know.. i never had a sig.. but i do now...

  11. #11
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    Quote Originally Posted by kgombe1 View Post
    if you still have the traxxas heavy spring on your truck remove it and use this...

    http://www.amainhobbies.com/product_...eturn-Spring-2
    I have that spring too. It's not about the spring. It's about the servo. Even the original stiff spring can't pull it back to neutral when I cut off the power in order to simulate a servo failure at WOT.

    That's my problem. I hope I could make it clear now.

  12. #12
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    oh now i see.. yeah those servos are very hard to turn.. i am not a fun of HiTec.. sorry i should of read your entire post... good luck.. trying to figure that out..
    you know.. i never had a sig.. but i do now...

  13. #13
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    So what servo set up do you use?

  14. #14
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    Futabas is my choice of servos..
    you know.. i never had a sig.. but i do now...

  15. #15
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    I too have issues with the HiTec 645mg. Way too stiff when no power is applied to servo. I have had other issues with the 645mg as well with poor customer service and have switched brands to Savox. Even the very high torque Savox servos are smooth and easily return to the idle gap with a standard throttle return spring.
    No slipper/tall gearing/power = broken parts.

  16. #16
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    Quote Originally Posted by kgombe1 View Post
    Futabas is my choice of servos..
    Same here. I use a futaba brushless servo to work the throttle and brakes. Its fast and has no problem with the return spring, and the return spring will move it back to neutral if the battery power is cut.
    Revo LRP 30x
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  17. #17
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    I also use Futaba. I got them because Traxxas recommended them as a direct replacement. And they have a brushless motor, steel gears and more power.

  18. #18
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    Quote Originally Posted by Snook Man View Post
    I too have issues with the HiTec 645mg. Way too stiff when no power is applied to servo. I have had other issues with the 645mg as well with poor customer service and have switched brands to Savox. Even the very high torque Savox servos are smooth and easily return to the idle gap with a standard throttle return spring.
    So does that mean even the HS-7940TH and HS-7950TH servos with Coreless motors are hard to turn or stiff when no power is applied?

    I was planning on buying them as a future upgrade for throttle and steering. If all Hitec premium servos are like that, then I'll probably look elsewhere. But I have used the Hitec servos with Karbonite gears (HS-5495BH), they were way too smooth, hence bough this 645mg expecting the same smoothness as well, but in vain.

    I don't know the reason for so much difference between servos made by the same company. Can anyone please explain?

    Quote Originally Posted by rock-rod View Post
    Same here. I use a futaba brushless servo to work the throttle and brakes. Its fast and has no problem with the return spring, and the return spring will move it back to neutral if the battery power is cut.
    Ok so, is it because of the motor or the gears that a servo is smooth or hard to turn? Or is there another reason as well?

    I would really like to know because I think I'm gonna have to get another servo because this hitec is pretty hard to turn. And I'm looking at KO Propo RSx Response , Hitec HS-7940TH & JR Z9100HVS only because Futaba servos are a bit overpriced while KO offers much better specs for a lower price.

    So can anyone please tell me if these servos will be stiff or not? I don't want to spend a lot of money and then realise that it doesn't work for my truck. So your advice is appreciated. Thanks!
    Last edited by Double G; 05-18-2013 at 08:12 AM. Reason: merge

  19. #19
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    stay away from the JR.. really fast and powerful servo, but dont last at all..

    get the 9352 futaba.. its a HV servo and its great

    http://www.amainhobbies.com/product_...ium-Gear-Servo
    you know.. i never had a sig.. but i do now...

  20. #20
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    Quote Originally Posted by kgombe1 View Post
    stay away from the JR.. really fast and powerful servo, but dont last at all..

    get the 9352 futaba.. its a HV servo and its great

    http://www.amainhobbies.com/product_...ium-Gear-Servo
    Wow man. That's a nice servo. Thanks for sharing the link . Turns out it is better than all of the servos I had listed in my post at least going by the figures. So, are you using it in your Revo currently? Is it smooth and easy for the throttle return spring to pull back when power is cut off? Also, how long have you been using it, like does it seem to develop a slop after some time like JR servos do?

    I ask because I'm gonna race and need something that is the best on the market and highly durable. I'm ready to spend the money till the time I'm getting my money's worth. Most of the racers including Steve Slayden recommend Hitec, so I decided to go that way thus getting hs 645mg. But after seeing this, I'm having second thoughts.

    Please advise.

    EDIT: Sorry for so many questions ...
    Last edited by The Wise Master; 05-18-2013 at 05:25 AM.

  21. #21
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    not using it in my revo.. but this is the third season on one set of those servos in my truggy.

    very smooth no slop so far, some guys recommend what they get sponsored by rem. that.. Slayden is an awesome dude, check which Hitecs he recommends
    you know.. i never had a sig.. but i do now...

  22. #22
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    I am using a futaba bls 452 brushless servo for the throttle/brake on my revo and this same servo on my tmaxx for the steering. Futaba was always the choice back in the 80s and I guess I am just old school with radio systems. I go with what I know works. It may cost a little more, but the quality is second to none.
    Revo LRP 30x
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  23. #23
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    Quote Originally Posted by kgombe1 View Post
    not using it in my revo.. but this is the third season on one set of those servos in my truggy.

    very smooth no slop so far, some guys recommend what they get sponsored by rem. that.. Slayden is an awesome dude, check which Hitecs he recommends
    Great! Thanks for letting me know. I think that will be the servo I'll get for throttle. Seeing most of the guys at the race tracks around the world using Hitec made me think that other brands didn't even exist . Maybe, those premium hitecs aren't that stiff after all because I myself have been using Hitecs in my other trucks without any problems. This was the first time I got an HS645MG and I guess this particular line of servos is stiff as reported by another member above.

    Quote Originally Posted by rock-rod View Post
    I am using a futaba bls 452 brushless servo for the throttle/brake on my revo and this same servo on my tmaxx for the steering. Futaba was always the choice back in the 80s and I guess I am just old school with radio systems. I go with what I know works. It may cost a little more, but the quality is second to none.
    Well, I think this must be the direct rival for the HS645MG going by the specs. Thanks for providing the model number. Maybe I'll get this for the time being and later on get the 9352 and shift this to one my bashers .


    Now, I know what to get for my Revo. But can anyone please advise if there is something that can be done to make the HS645MG smooth for the throttle spring to pull back when power is cut off, so that I'm able to run it for a while before getting a Futaba? Your opinions would really be appreciated!

  24. #24
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    If you can turn it with your fingers, then ad another spring or a stronger one. If you can't turn it with your fingers, then there's not much you can do.

  25. #25
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    Quote Originally Posted by Mark Ball View Post
    If you can turn it with your fingers, then ad another spring or a stronger one. If you can't turn it with your fingers, then there's not much you can do.
    Yes I can turn it with my fingers i.e. with the horn attached, but it's pretty stiff compared to an average servo that turns so easily. I'm already using the strong spring that comes on the 5309 revo, but won't the added spring put excess pressure on the servo?

  26. #26
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    Sure it will, but a servo as strong as that one should be able to handle it.

  27. #27
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    I have the HS-645MG as my throttle servo and have had no such problems (3 or 4 years old, but honestly, not much run time). The servo must be faulty. I use a really, really light return spring from a LOSI XXX-NT, and it returns to it's center position, no problem.

    We run a Hitec HS-7965MG for throttle/brake in my sons buggy, and have had no problems with it either. I was going to buy one for the Revo, but is packed away waiting for the day someone is ready to race MT's again.
    Last edited by Oomp; 05-19-2013 at 08:00 PM.
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  28. #28
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    savox servos are pretty decent as well

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