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Direct or indirect drive servos?

Old 05-20-2017, 11:18 AM
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sandal
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Question Direct or indirect drive servos?

Hi,

Does Hitec list whether their servos have direct or indirect drive potentiometers? I have tried to search but couldn't find it. I'd like to know if any of these are indirect drive:
HS-325HB
HS-422
HS-425BB
HS-430BH
HS-485HB
HS-5485HB

Thanks,
sandal
Old 05-22-2017, 08:08 AM
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Xpress
 
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All of our servos have the potentiometer directly driven by the output gear.
Old 05-27-2017, 04:23 AM
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sandal
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Hello Xpress,
thank you for your answer.

I am not sure I understand completely, and there may be different terminology describing servo potentiometers. My reason for asking is that indirect drive potentiometers are said to be longer lasting and more resistant to vibration. For that reason I would prefer to buy indirect drive servos.

I am referring to direct/indirect drive as described on https://www.servocity.com/what-servo-should-i-use:
"Indirect Drive - This refers to the potentiometer inside the servo. The final output shaft (the part that the horn/arm attaches) has to be supported not only near the end but also deep inside the servo case. Indirect drive is when the final output shaft is not dependent on the potentiometer for support inside the gear case. Normally a bushing or bearing supports the load. Direct Drive is when the potentiometer plays a supporting role in holding the output shaft in place."

Does this mean that it is safe to assume that all dual bearing (plain or ball) servos have indirect drive potentiometers?

I have found a few specification sheets from Hitec RCD Korea Inc., by Jun Hee, Lee. In some cases these list different specifications than hitecrcd.com. The HS-475HB is listed as 6-slider Indirect Drive, whereas the HS-5485 is listed as 2-slider Direct Drive. Hitec marketed the HS-(5)485HB as an upgrade from the HS-(5)475HB, and I find it difficult to understand that they would choose an inferior type of potentiometer.

Sorry for the long post. If you could explain this (or some of it) to me, I will be very grateful.

Thank you!
Old 05-30-2017, 09:25 AM
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Working with your explanation of direct or indirect drive, the servos that are listed as having ball bearings would not rely on the potentiometer whatsoever for support. Some newer versions of servos have refinements in their electronics selection, but I would be unable to tell you why they chose what they did. Keep in mind the less expensive servos are less expensive for a reason, they are generally not built as robust as some of our higher end servos and may not last as long depending on what application you utilize them in. For example, an HS-485HB servo would work perfectly in a .40 glow trainer as that is the target area for that servo, but the same servo would be ill-suited in a 35cc gas/petrol aircraft.

From the sounds of things, it sounds like you are more after Magnetic Encoder style servos (HS-M7990TH for example), but we only have a few of those. There are no physical contacts inside of a ME which gives them a much longer lifespan.

Last edited by Xpress; 05-30-2017 at 09:28 AM.
Old 05-30-2017, 09:42 AM
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Thanks for the explanation

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