Servo Overkill

[dsl_raven]

I'm looking at Tower's webbie and they've got a servo comming out capable of 230-300+oz/inch of torque - depending on voltage.

It's enough that it draws 700mAH just sitting there idling. It can of course draw way more under load. I'd rather use a quarter-scale (this is) servo just from the point of torque vs. cost over smaller 'high performance' servos. The individual gears are also almost always tougher and larger, spreading load over a wider area. The boat's a 7.5 tunnel, so it can carry the weight no problem.

I have a current-limited variable DC power supply, so I was actually considering using a light NiMH pack for the receiver and a separate NiCad (mmm.. yummy cadmium... muahhhhh) at about 1000mAH for the servo. The servo includes a harness that's set up this way. Also, you can run it directly to the receiver. I know this would complicate the electronics, not to mention crowd the bay...

Is all this effort worth it or should I stick with a big NiCad and straight-up quarter-scale servo? I wouldn't mind having the extra beef on hand, but I dont' want to complicate things if I don't have to.

The boat's an outboard tunnel, natch.

 

[Bob Kensill]

Take a look at the Hitec 705mg servo. It is more than enough power for any outboard and sells for about $40.00.

 

[Ron Olson]

Yes, that's a lot of overkill for a 7.5 OB tunnel. A cheaper one that works fine would be something like a Hi-Tec 645MG servo. I think that something that big would be better suited for a large scale plane.

 

[Don Ferrette]

Stay with 1/4 scale size servos on the o/b tunnels (like the 705MG previously mentioned). Even though the standard size servos have high torque ratings, you give up the strength of the larger gearsets in the 1/4 size servos, something you really need swinging that heavy o/b unit hanging off the back of a boat.

 

[nitrotoys]

Or the 3302 futaba 1/4 scale servo,

its plenty for any boat.

Tom

 

[dsl_raven]

Cool beans. I just think it's funny that you can get 300oz-in out of such a small servo, quarter-scale or nay. Yeah, it'll either be a HiTec or Tower quarter-scale standard servo on a 1200mAH NiCad pack.

 

[nitrotoys]

I personally have had bad luck with the hitecs in boats.

I am running 3302s open for throttle and steering, Oringed the gear on top, there waterproof. And i have gotten the boat wet several times.

There still ok

Tom

 

[Don Ferrette]

I'll second the Futaba 3302 for top choice. I've had no problems with them at all. B)

 

[Bob Kensill]

The difference between the Futaba and Hitec servos is the gears. The Futaba servo has one metal gear and the rest are plastic. The Hitec servo has only one plastic gear and the rest are metal.

 

[izitbrokeyet?]

I went through a time when I thought Hitec servos SUCKED! Then I started keeping my receipts and turning them in for warranty work. If I have a suspect servo...it goes back and gets replaced/fixed no questions asked

lately I'm thinking Hitec is pretty good

Just keep those replacements flowing Hitec!

 

[TimD]

Guys,

whats the current servo of choice for 67 and 80 sized riggers? I was using 1/4 scales but they are very heavy!

Tim.

 

[Bob Kensill]

Try the Hitec 5645 or 5945. They are both more than enough for a 60 hydro.

 

[Ian Inverarity]

Tim,

I use JR DS8411's for my 67 and 90 riggers, and also on the 90 mono. Metal gears, fast, high torque with the centre holding of a digital, on a standard size servo! I have a DS8511 which is supposed to be even stronger, but it is a little larger and I havent tried it yet. Neither are particularly, er, cheap! B)

Ian.

 

[TimD]

Ian,

I just got the Big JR servo for the mono. They aint cheap - thats for sure!!!

Tim.

 

[Ian Inverarity]

Tim,

Is that a digital? I used to use those in big monos a few years ago, they weren't digital. I stripped the gears twice in flips before I changed the rudder linkage, but the gears are cheap! Good servo.

The digitals are my preference tho. You know my rudder rates, that cant be done with poor servos! B)

Ian.

 

[TimD]

Tim,
Is that a digital? I used to use those in big monos a few years ago, they weren't digital. I stripped the gears twice in flips before I changed the rudder linkage, but the gears are cheap! Good servo.

Ian,

No - not digital. The servo has been updated from the older version recently. Unbelievable power.

Can you explain the linkage story a bit more for me? Better to know in advance!

Tim.

 

[Ian Inverarity]

Tim,

At the rudder end I use the small Dubro clip on ball links. They need to be drilled a bit to go on the 4-40 rods. In the event of a bad flip the ball link pops off rather than breaking servo gears. Most of the time you can simply pop the ball link back on for the next run. If you break servo gears you are probably out for a days racing! Even the 90 Sprint has this setup... B)

The problem with monos is if they flip and then hit the water backwards the load on the servo is huge, and something has to give!

Ian.

 

[TimD]

I guess I should invest in a gear set "just in case"

Thanks again,

Tim.

 

[dsl_raven]

Monos, nothing. A tunnel has it's whole friggin engine on the 'rudder', so a backflip would definately be baaaad.

I'm going to use a pull-pull setup most likely.