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Sep 22, 2021, 06:04 PM
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Piece's Avatar
Thread OP
Idea

Our hobby needs more linear servos


Or at least a rotary design that wastes less fuselage volume?

I'm thinking of narrow fuselages and applications where the advantages of a traditional servo aren't worth the mechanical complexity of a rotary arm and linkage. A servo whose output is colinear with the longest axis of the case would solve a lot of problems in fitment and linkage design.

A screw-drive linear servo, similar to the Horizon UM servo but enclosed and scaled up to ~6g, would be just about perfect for sub-250g performance models, but none seem to exist. I found some "micro" linear servos that are way too big, and of course there's the Horizon type on the small end, but nothing really fills the gap.

Maybe it exists and someone knows where to find it. If not, I'd even be willing to work with a manufacturer to develop a quality RC-spec micro linear servo. It's just something that would allow a lot more flexibility in the designs I've been working on lately and I'm sure other people could use one if somebody produced it.

Anyone with any thoughts is encouraged to share.
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Sep 22, 2021, 06:18 PM
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AntiArf's Avatar
I would and have used Gotek micro linear servos on models in the sub 250 gram range, and heavier. I've used 5320-5330 servos in a number of builds that can be seen in my profile in the past few years, which I don't believe are not a strong as a Gotek. Some models are over 250 grams, such as the TU104 airliner with 5330 servos for the ailerons. I recently built and flew a 24" Spitfire at 6-1/4 oz with 5320 servos that has survived aerobatic flight, coming out of dives from large loops and inverted flight, with no servo issues. I've never had a 5320/5330 servo failure or a Gotek failure, and again I would believe the Gotek linear has a stronger geartrain. I would just use the Gotek servos which are available. People over servo. I've been using smaller servos than most use for years, and am not having failures. A 6 gram servo IMO is for something like the 46.5" HP Victor, where I believe I used a GWS Pico on the elevator. All other servos are smaller and lighter. https://www.rcgroups.com/forums/show...ht-video/page8
Sep 22, 2021, 10:13 PM
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Piece's Avatar
Thread OP
I've seen the Gotecks and they don't look any better than the Horizon flavor. If they are, it can't be by much at only 1.5g. Regardless of the model size, I'm looking for output to match an existing 6g servo (DHV56MG) even if it ends up being slightly bigger or heavier than 6g. The form factor is more important than the size/weight.

For example, this plane is 24", weighs 214 grams AUW, and goes about 80-100mph depending on the prop. The aforementioned DHV56MG is perfect, but it occupies the entire inside height of the fuselage, and the arm and rod need space to move, so I can effectively only fit an elevator control in a place where two servos (elevator + rudder) could physically fit just fine with a better linkage orientation.



Another example is my bug bicopter project. Similar issue - there's no way to mount the servos in a compact fashion and run a clean parallel linkage to the bearing block. The existing setup is the best I could do within the design constraints, and it'll leave two awkward pushrods below the tail.

Sep 23, 2021, 11:18 AM
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AntiArf's Avatar
Quote:
Originally Posted by Piece
I've seen the Gotecks and they don't look any better than the Horizon flavor.]
They don't blow H-bridges if you look at them the wrong way. That was enough for me right there.
Sep 23, 2021, 07:03 PM
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Piece's Avatar
Thread OP
This is almost exactly what I'm looking for, but the specs say it's not compatible with 5V input. Hmmmm.

https://solarbotics.com/product/22090/
Sep 25, 2021, 08:35 AM
Flying in OZ.
iflylilplanes's Avatar
The first servos I ever owned/used were linear, 1973 Futaba's, linkage setup was so easy, servo reversing was just swap to the other side. Sometimes I wish there were liner servos today, disks are not always the best alternative for setting up some linkages, the Solarbotics is nice but a little small for some uses.
Sep 25, 2021, 01:07 PM
An itch?. Scratch build.
eflightray's Avatar
SLEC, (UK), used to make rack and pinion add-on parts for rotary outputs, (many years ago).

A Google search found something similar. Replace the rotary servo arm with a pinion and add a rack. Looks like it could be an easy thing to make with a 3D printer, could be made for any size rotary servo.

Hope the image shows properly ----


Ray
.
Sep 25, 2021, 03:19 PM
Registered User
Hi,
there are many ways to get a linear movment. Like in my pic a thin springsteel strip is going around a drum . Also possible to place a springsteel wire is wind around a small grove in the drum. Drum turn by servo. With a thin springsteel plate stripe there are many options to drive flaps and ruder. Alsway to have the biggest leverarm when run most outside of the drum/cylinderpart . Will make a short drawing to show how.

Happy Amps Christian
Sep 25, 2021, 10:54 PM
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AntiArf's Avatar
Quote:
Originally Posted by Piece
This is almost exactly what I'm looking for, but the specs say it's not compatible with 5V input. Hmmmm.

https://solarbotics.com/product/22090/
Use the regulator they sell, or 2series ran D1N4001 diodes should work on a 5V BEC. I've been using D1N4001 diodes for ages with micro linear and 5320/5330 servos on 5V BECs. They weigh next to nothing. Haven't had an issue yet with four 5320 servos on a single D1N4001 BEC diode drop.
https://solarbotics.com/product/17145/
Oct 03, 2021, 09:11 AM
www.buzzardmodels.com
buzzle049's Avatar
I have successfully been running 5330s at 5 volts for years, although they are not rated for it as per the manufacturer, I can attest to the fact that they work. I have not tried the 5320 servos at 5V.
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Oct 07, 2021, 04:49 PM
Registered User
tkallev's Avatar
Oh, for my KPS-9 servos from days of yore ...


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