Futaba S3305 Failures

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Futaba S3305 Failures

Postby Frandito » Thu Dec 05, 2013 4:52 pm

I have had two failures of the Futaba S3305 servo in the rudder position, in the past six months.

Has anyone had similar?

What is a good substitute? The trusty 3004?

Thanks
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Re: Futaba S3305 Failures

Postby Merv49 » Fri Dec 06, 2013 4:34 pm

I use Hitec digital servos on all my RC applications. Been using them for many years with no issues and the prices have come down considerably. This one is very powerful and not expensive at all.

http://servocity.com/html/hs-5645mg_digital_torque.html
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Re: Futaba S3305 Failures

Postby Chuck Luscomb » Sat Dec 07, 2013 9:54 am

Hi Fran,

I use Hitec as well and have had few if any problems. In the rudder position, I use a 645MG High Torque which is not digital. They are the strongest non digital in a standard size from Hitec you can get. Costs about $30 each or so depending on where you shop. The Hitec HS645MG has a slightly better tourqe rating than the Futaba 3305 and they cost about the same.

That said, I have also used a Hitec 3003 which is their basic stock servo with about 40oz of torque and it also worked as well. I am sure the Futaba equivalent will also work for you.
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Re: Futaba S3305 Failures

Postby Tim » Sat Dec 07, 2013 10:31 am

I use the Hitec HS7955TG, 333oz in @ 6v. I used to use the 645 but they too burned out especially in B Rig conditions. The 7956 is digital and a little expensive. In heavy conditions I have found it much better choice. Thanks to David Ramos for that suggestion.
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Re: Futaba S3305 Failures

Postby s vernon » Sat Dec 07, 2013 2:35 pm

It ought to go without saying, but be sure to use only Futaba servo horns and Futaba compatible horns with Futaba servos and same advice for Hitec. They might look the same, but one has one more tooth on the servo than the other. TS (Tower Hobbies) such as TS-70 servo and Hitec servos are the same number of teeth I believe.

It can be too tempting to switch out a servo (changing brands) at a regatta ("Here use this." "Thanks.") and not change out the servo horn. Might work okay in light air and will slip in heavy air.

You can buy packages of servo horn screws at Tower Hobbies. I have misplaced one or two (dozen). For example If you search on the site for a servo like S3305 it will show you a list of compatible parts.
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Re: Futaba S3305 Failures

Postby Chuck Luscomb » Sun Dec 08, 2013 2:22 am

If your having issues with rudder servos burnging out, maybe you need to look at how your steering system is set up. If your servo arm is the same length from center of rotation out to the connection of your push rod as the rudder arm, then your will need a heavier servo like a digital to over come the excess loads you will encounter.

Having this set up puts more load on the rudder servo and can lead to early retirement.
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Re: Futaba S3305 Failures

Postby s vernon » Sun Dec 08, 2013 1:50 pm

Chuck,
Let me guess what you are talking about with servo arm and rudder arm lengths and servo working harder.

I guess I can edit this and tone it down a bit after Chuck has written the next post.

If the servo arm is shorter than the rudder arm then when the servo turns 45*, the rudder will turn say 40* and so the servo is not working as hard as when the two arms are the same length and the servo is turning 4o* to make the rudder turn 40*. My point would be that a less than strong servo will have a better chance of staying alive if the servo arm is shorter than the rudder arm.

I am a fan of very strong rudder servos.
Last edited by s vernon on Tue Dec 10, 2013 6:05 pm, edited 1 time in total.
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Re: Futaba S3305 Failures

Postby Chuck Luscomb » Tue Dec 10, 2013 10:38 am

Hi Scott,

I was not trying to be elusive in my post, but simply pointing out that if your boat is set up this way, then you will burn out some of the smaller torque servos like the 645MG. The solution is of course to install something with the power to handle the loads with 1:1 levers. Simple.

I use a slightly different set up in my boat where the servo arm does in fact travel more than the rudder arm. The gear ratio around amidships in this set up is of course 1:1 but as the rudder angle increases, the gear radio improves and helps the servo work easier. Out at full lock, the gear ratio grows to about 1.2:1. Here is a link to an illustration of what a full size boats steering system is set up like using this system. Not sure if this is the reason I still have the same 645MG in my boat that it was built with but it may be.

Hope this helps...


http://www.google.com/imgres?imgurl=htt ... CD4Q9QEwAA
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