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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 12-02-2012, 02:17 AM   #1
wgt500
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Default When do you trash can a working srevo??

I've been using Tower pro MG90S metal gear servos lately in all my planes. I started using these when I had several nylon gear servos strip causing 2 really bad crashes which nearly destroyed 2 planes.
Today I had a very bad crash at about 50mph straight into the ground. All servos survived without visual damage; however, I get concerned about the safety of using an electronic device which has sustained this kind of impact. I buy 5 of these servos from Grayson Hobby for $35 shipped to my front door. That's only $7.00 each. Am I being stupid for saying that is the price of a bad crash and they should all 3 be trash canned in case they were damaged internally, which could result in a crash in the future? What do you guys think?
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Old 12-02-2012, 02:33 AM   #2
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Originally Posted by wgt500 View Post
I've been using Tower pro MG90S metal gear servos lately in all my planes. I started using these when I had several nylon gear servos strip causing 2 really bad crashes which nearly destroyed 2 planes.
Today I had a very bad crash at about 50mph straight into the ground. All servos survived without visual damage; however, I get concerned about the safety of using an electronic device which has sustained this kind of impact. I buy 5 of these servos from Grayson Hobby for $35 shipped to my front door. That's only $7.00 each. Am I being stupid for saying that is the price of a bad crash and they should all 3 be trash canned in case they were damaged internally, which could result in a crash in the future? What do you guys think?
I've kind of had the 1/3 rule on my model airplanes. Somewhere around 1/3 for the model airplane, 1/3 for the power system, (not including the battery pack) and 1/3 for the radio system.

With that, a straight in crash at 50 MPH may have caused hidden internal damage to your radio and its servos. With servos at $7.00 each, they might be using those phenolic circuit boards inside, rather than the green colored fiberglass circuit boards. This phenolic stuff is rather brittle, and when subjected to stress, tends to crack. Those hairline cracks are pretty difficult to spot. I've got a ten power binocular microscope that helps a little bit.

But at $7.00 each, methinks they should just be junked, and replaced.

They are far more expensive, but my models have been using the Hitec 645MG servos. They are robust, and those metal gears are quite nice. (Most of my models are running one kilowatt or so. Two are running near 3KW. All use those 645MG servos. The giant scale models use one servo per aileron, and one servo per elevator half.

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Old 12-02-2012, 03:00 AM   #3
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Just took one apart and they are using the green fiberglass board and they don't look damaged on the inside, but that's only a visual inspection. Never know about the electronics. Appreciate your thoughts.
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Old 12-02-2012, 03:07 AM   #4
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Originally Posted by wgt500 View Post
Just took one apart and they are using the green fiberglass board and they don't look damaged on the inside, but that's only a visual inspection. Never know about the electronics. Appreciate your thoughts.
That's interesting, fiberglass boards in a $7 servo?. I've got some Futaba S3003 servos that use that cheap phenolic stuff.

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Old 12-02-2012, 01:05 PM   #5
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thats a great question as i also have a bunch of hitec standard 485's that have been in wrecks and i wondered if they'er ok.

what i do right away after salvaging parts from wrecks is to set them aside to a speacial parts drawer in the work shop. label the parts for the wreck they were in since some motors and escs are ok but i had new standbys ready for use.

but as far as servos go...i plug them into my servo tester and test them first for any skipping or excess sounds in the gears /motor. then its the pressure test. with a very little presure by hand on the servo arm i feel for any skipping or gliches...then i give them a stronger hold to really see if they are ok. if all's well i'll use them. if the servos are cheap hextronic 900's and i want to build a nicer arf or foamy it's new all the way! i'm sure others will say otherwise on crashed servos but this is what i do. note; do not hold the sevos to hard,check for there strength via manufacturer and dont test them to their limit....hold them just enough so your convinced they are working under load.i also always reduce the end point settings to 90% on servo throws.i use the control horn holes to get max throws on planes so not to bind my servos in flight.


hope this is helpful. stu edit; welcome to wattflyer wgt! i see you just joined..great bunch of folks to answer questions and we'er always looking to learn from each other.

narrow is the place to land...wide is the space to crash....choose the narrow way!
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Old 12-02-2012, 02:04 PM   #6
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I am using the MG90S on my mini-bicopter and never really given it any thought. At 7 bucks each, sounds like a good maintain procedure to change periodically. Thanks for raising this issue.
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Old 12-05-2012, 02:02 AM   #7
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All three servos from Saturday's crash were trash canned. Just not worth taking a chance on damaging another plane or losing control and hurting someone or their property. Planes seem to travel great distances very quickly when out of control! I'm new to the hobby and have a lot to learn. I value your opinions.
Thanks!
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Old 12-05-2012, 03:03 PM   #8
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In general, the electronics in a servo have almost unlimited lifetime if not abused by reverse voltage or over voltage. Gear trains are another matter. Nylon gears will outlast the metal gears by a large margin although they are more easily damaged by excess shock loads or sever strain. Metal gears wear quite quickly and will eventually start to show excessive slop but are much more resistant to shock loads. There is no reason that a servo can not be used for years as long as you can replace the gear trains if they wear or become broken.
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Old 12-05-2012, 03:56 PM   #9
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When I first started in the hobby, I used a lot of GWS Pico servos. After a couple years (and more than a couple crashes...) The pots began to go bad...They would jitter, not return to center, and just generally act strange.

I agree with stuart above-after a crash I put most of the equipment aside until I can give it a good test session. You could go as far as getting an inline wattmeter to make sure there everything is fine. I actually end up with more ESC failures after crashes than servos, so long as it doesn't go in right on a control surface.

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Old 12-05-2012, 10:44 PM   #10
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I totally agree about the ESC failures following a crash. I've experienced timing malfunction and BEC voltage problems after several crashes. The ESC from Saturday's crash is also in the trash can. It still worked, but sustained some physical damage.
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