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Author Topic: Servo Selection  (Read 977 times)

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Offline aerowennTopic starter

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Servo Selection
« on: December 03, 2010, 12:08:38 AM »
So I'm in the market for the servos that will be used for my hexapod, the legs and body I've nearly decided on being 6061 aluminum, something I will discuss in the mechanical part of the forum. Anyhow, on to this topic.

I want something that is durable, strong enough, and a price cap of about $40

I've heard that plastic gears hold up better, metal gears are obviously stronger, what about mixed?

If anyone has a particular model they've had success with, please let me know, or perhaps suggest a particular type, I know there are tons of different servos out there, so I want to make the right decision the first time if possible. Also, something else I've really been wondering, are there standards on sizes and mounting holes? I'm using CNC on the legs, and it will use the through-mount setup, if I need to replace servos down the road and my originals are discontinued, this can pose a problem.

Thanks!

Offline Joker94

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Re: Servo Selection
« Reply #1 on: December 03, 2010, 05:56:36 AM »
Unfortunately choosing servos is not that simple as there are so many differences.

Do you have an idea about the size and a guesstimate on the eventual weight of the hexapod.

As for your original question I myself much prefer metal gear servos as generally they are more durable and from my experience do not strip gears as  easily.

But to get one thing straight do you mean $40 over all for the 6 servos or max $40 each. if you are talking 40 over all you might have to go for nylon great servos that are cheaper.

Have a look at hobby king as they have some really good prices on servos.

Offline garrettg84

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Re: Servo Selection
« Reply #2 on: December 03, 2010, 08:05:28 AM »
+1 for hobbyking.com

I'd agree metal gear servos are far superior. If you put your bot in situations where there are fast opposing movements to what the servo is pushing for your nylon/plastic gears will strip in short order. Depending on the torque you need there are tons of servos available.

I have quite a few of the hexTronik servos
10kg torque
13-15kg stall torque
~2 amps stall current
55g weight
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=2
best part: 8$ per servo


I can try to post a video (later tonight) of the servos in operation if you'd like to see em.

I live in the US it takes anywhere from 4days to 2.5weeks to receive a package from hobby king. They always come through in the long run though when you compare price.


What kind of power will you need for your bot? I have quite a few different brands of servos from hobby king and may be able to recoomend one or two. I only buy metal gear though. I had a few plastic/nylon gear servos and they were DONE after a crash or two with an RC plane. I have yet to strip out a metal gear servo and I've been lucky to not have any of them let out the magic black smoke.
-garrett

Offline aerowennTopic starter

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Re: Servo Selection
« Reply #3 on: December 03, 2010, 12:56:30 PM »
Great stuff, thank you both, I was thinking metal gears would be much better as well, but I was worried about durability in the long run. Then again, that wont matter if it get's into a tight spot and rips the plastic ones.


Quote
But to get one thing straight do you mean $40 over all for the 6 servos or max $40 each. if you are talking 40 over all you might have to go for nylon great servos that are cheaper.

To clarify, $40 each is my max

Quote
I can try to post a video (later tonight) of the servos in operation if you'd like to see em.

That would be awesome!

Offline Joker94

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Re: Servo Selection
« Reply #4 on: December 03, 2010, 10:23:16 PM »
I have heard some good things about hextronic servos from HK.

With a price of $40 each you will have no problem finding decent metal geared servos.

Another servo is the MG966 from hobby king, I use it on my 1.8m wing span RC plane that has a 28cc petrol engine andthey
are smooth, quick and precise at a price of $9.99.
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=6221

Another tip from Hobby king, if you want to buy something keep the page open a while while you are doing other stuff as sometimes(not always on all items) they offer a discounted price.(they did for me when i looked at the Hextronic servo and the 996s). the price may only be $0.10 to $1 cheaper but at the end of a big order  you mights be saving $5 to $10 especially when buying numerous units.

Offline Soeren

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Re: Servo Selection
« Reply #5 on: December 05, 2010, 09:37:00 PM »
Hi,

Another tip from Hobby king, if you want to buy something keep the page open a while while you are doing other stuff as sometimes(not always on all items) they offer a discounted price.(they did for me when i looked at the Hextronic servo and the 996s). the price may only be $0.10 to $1 cheaper but at the end of a big order  you mights be saving $5 to $10 especially when buying numerous units.
I regularly keep more than a hundred windows open and using Firefox or Opera, they get reopened when it crash or I restart. That way I have seen Hobbyking offer first one discount and then a better one (don't know how far it could be driven and frankly, I have seldom seen discounts worth hunting).

I'll agree that $40 should get some very good servos, hey, $20 should get nice ones as well.
Regards,
Søren

A rather fast and fairly heavy robot with quite large wheels needs what? A lot of power?
Please remember...
Engineering is based on numbers - not adjectives

Offline aerowennTopic starter

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Re: Servo Selection
« Reply #6 on: December 07, 2010, 01:12:52 PM »
Awesome! This all sounds great. I'm thinking I will build one leg first most likely, then purchase the remaining servos bulk so I might be able to pull a bit of a discount. I'm glad to see I don't have to sink $150 into a single servo to make this work properly, that kind of worried me :)

 


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