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Let's talk 1/4 Scale Servos

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  • Let's talk 1/4 Scale Servos

    After watching 2 more 1/10th scale servos go up in smoke at ECC, and watching another TXT have flawless steering I have pulled the trigger on using 1/4 scale servos on the TXT.

    Now, you have to watch here and be careful as the biggest servos in terms of torque are analog only. The Hobbico CS80 and the Hitec 805BB, both are about 343 oz-in @ 6V. My biggest concern here is that yes the gears are big, but they are nylon gears. Given my ablitiy to break nylon gears, and stripping out metal geared servos, as much as I want the biggest of the big I have my concerns. The anolog servos are very cheap, in the $30-40 range. Now, I have the Hitec 5745MG digital servo. This puts out 260 oz-in @ 6V, and is a full metal gear servo. Being digital it is more expensive at about $80 a servo.

    The advantage to the 1/4 scales isn't massive torque above and beyond what the 1/10th scales are any more. Early on 1/4 was the only way to get very high torque servos. Now more airplane guys are using 2 1/10ths in place of 1 1/4, or just in need of 1 smaller servo so the 1/10ths are making the torque of the 1/4 scale servos.

    The advantage here is in heat dissipation. The FETs on the servo board get hot during use. Think of FETs as an ESC for your servo's motor. There is not much real estate in a 1/10th scale servo for heat sinks to be added, nor is there much airspace for convection cooling. In a 1/4 scale servo you have a much bigger board, case, and airspace surrounding the FETs, thus keeping them much cooler.

    In talking with Hitec keeping the FETs cool is key here. I was informed by Hitec that I should try a 1/4 scale servo or run 2 1/10th servos for steering. Given the cost options for being ready to run this weekend I went with the 1/4 scale servos. I am also a pinch gun shy that I could smoke 1 servo in the 2 servo steering and given the recomendation of not linking the servos together that worries me.

    Anyways, if you have a super that you have the room for this big of a servo in give them a look. They are not for everyone, but they are still very useful.

  • #2
    Re: Let's talk 1/4 Scale Servos

    great info! thanks for the nice right up! sadly, the electrical aspect of R/C's sometimes fly right over my head.

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    • #3
      Re: Let's talk 1/4 Scale Servos

      Originally posted by STEEL_CITY_CRAWLER
      great info! thanks for the nice right up! sadly, the electrical aspect of R/C's sometimes fly right over my head.

      Hey don't feel bad, it has taken a while for me to start understanding this stuff and asking a ton of questions.

      The only dumb question is the one left unasked. Just ask away if there is something you don't understand.

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      • #4
        Re: Let's talk 1/4 Scale Servos

        yeah a lot of people were running them at ecc. no failure that i saw. I hope it works for you man, if anyone can fry one...its you!

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        • #5
          Re: Let's talk 1/4 Scale Servos

          Originally posted by rockbound
          yeah a lot of people were running them at ecc. no failure that i saw. I hope it works for you man, if anyone can fry one...its you!

          Me too man. I think that with the wheel and tire combo that I have, the servo mounting location, and lack of airflow around the back of the servo all lend themselves to frying them.

          I think a standard Moab on a 40 series or an XL streched onto an XTM would be easier on a servo but an XL on a 40 rim has a huge sidewall and therefore a huge self-aligning torque to over come.

          With where the servo mounts there is minimal airflow to the back where the FETs are located and that doesn't help with cooling. The mount also has the servo running the longest recommend arm which reduces the torque the servo can put to the tires.

          Just wish the digital servos would put out 343 oz-in and not 260 oz-in. I may have to get an anolog servo for the front if this digital doesn't have the power.

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          • #6
            Re: Let's talk 1/4 Scale Servos

            Originally posted by Bustedcrawler
            Originally posted by rockbound
            yeah a lot of people were running them at ecc. no failure that i saw. I hope it works for you man, if anyone can fry one...its you!

            Me too man. I think that with the wheel and tire combo that I have, the servo mounting location, and lack of airflow around the back of the servo all lend themselves to frying them.

            I think a standard Moab on a 40 series or an XL streched onto an XTM would be easier on a servo but an XL on a 40 rim has a huge sidewall and therefore a huge self-aligning torque to over come.

            With where the servo mounts there is minimal airflow to the back where the FETs are located and that doesn't help with cooling. The mount also has the servo running the longest recommend arm which reduces the torque the servo can put to the tires.

            Just wish the digital servos would put out 343 oz-in and not 260 oz-in. I may have to get an anolog servo for the front if this digital doesn't have the power.

            hmmm, thanks for giving me ideas to consider, as i am SLOOOOOWLY in the process of gathering my stuff to build a super. i saw some losi zombies (i think) and i would considr using those. but they look and feel like they weigh a ton! jeesh so now i am having to consider wheel, and tire size...

            (actually, by the time i am ready for tires for a super, there will be more available....)

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