i am at the point on building the composite arf's kangaroo where i will install the speed brakes,

is it better to use servos to operate the speed brake???

or is it better to use air cylinders from bvm to operate the speed brake???

i already have 2 air systems for the roo, i can easily tap into the braking system to operate the brakes right??

or should i run a 3rd air system ? if i chose to use air cylinders

thanks

mark

I've built three, and used a servo every time. I find it quite simple. I don't suppose there is any reason you can't use an air cylinder. I suppose one advantage to servo is being able to slow the speed at which it deploys, or being able to partially deploy it???????

Sean is right...With a servo you can partially deploy the speed brake so that the model will rotate easier/sooner. (Partially deployed the speedbrake actually will provide some lift.) You can also control the speed of the speedbrake's deployment with your servo slow on your TX if equipped. On my Rookie (A cousin of the 'Roo) I have my servo controlled speedbrake slowed down so that there is no abrupt pitch change when the speedbrake is initially deployed.

By the time you add up the cost of the valve, cylinder, and servo to operate the speedbrake with air----You could have just bought a high torque servo and be done with it. (Not to mention adding another system that could potentially leak air.) Make sure the speedbrake will deploy to 90 degrees and that the servo arm and linkage are all in line with each other so there is no load on the servo at max deflection. The speedbrake is not very effective unless you get that 90 degrees of throw.

Kevin

I had two Roos and I used a servo both times. Worked great. I vote servo!

Second the vote... servo.
Tomcat

SERVO!!!

Servo: JR DS-8411

8411?? that is waaaaaaaayyyy over kill (although it would work no problem). I've used the Cirrus CS-80 there with never a problem. It's a 130 ounce servo analog metal gear and absulutely bullet proof for that application. Cost??? $19.99 at my LHS and I'll be glad to send anyone who wants one for $25.00 by paypal.com to try out. I used them on the flaps of my isobar and they were great in that application as well.

I used a Hitec 645 metal gear servo for my speed brake.


Kevin

i will stick to the servo set up for the spped brake, and for most of all the servos, i will use the hobbico cs-65
at 6.0 volts, 92.0 ounce at 0.13 sec speed, as for the elevons i am not sure yet what i will be using it will most likely be the jr 8611 servos, 260ounce at 6.0 volts and .14 speed

thanks for the advice

mark

Mark, 4 8611's on that plane on elevons is way overkill, you didn't stipulate if you were going to put two or four. Many roos have flown for years with 150 ounce torque per side. I'm flying two 4131's on each side at 180 ounce torque. I've pulled the most g-s that my thrust/drag setup will hold and never felt anything sluggish at all. Of course, you can do whatever you want, just hate to see you spend the extra bucks when it's not really necessary.

sean, i was thinking on putting 4 8611's on the tail of the roo, yes it is over kill,. since i will have sooooooooo much into this kangaroo,time and money, i did not want to take a chance on a wrong choice for the servo's.

so if i put the hobbico, cs - 65's servos 4 of them, on the elevons, 2 on each side , which have 92.0 ounces of tourque each, you are saying that will be ok???????????

mark

YES! Now what I don't know is the cs65 servo. In my opinion two JR or Futaba 75 ounce or better servo's on the elevons are all that's needed. I don't have faith in any other brand. Most others here are of the same opinion, but you know how opinions are. But if you have faith in the CS65 (meaning you've flown the piss out of them over and over and over again and have never suspected a crash due to the failure of one) then with 92 ounces times two, you have more torque than I have. I've flown the roo with 28 lbs of thrust with 180 each side and never once felt I was out of control.

Save the dough and make sure you've got Robart Retracts and struts and a good reliable turbine and you'll be fine. If you want, I can schedule a trip to Wilkes Barre (I have a project at the VA Hospital there) and help you do the final checkouts when you're ready.

sean that would be great, when ever you do make a trip here, the Va is only up the road from me,
as for the kangaroo,

robart 630 retracts, bvm wheels and brakes..
2 seperate air systems for brakes and retracts, with bvm gages, (kool gages)

jr radio, 8103 g410 gyro for nose wheel

power plant, jetcat p80

as for the cs 65? i use a few of them on my helis

as for flying, i do not have my waiver yet, going to wait to see what happenes in the next month or so.. but i will fly the kangaroo with one of my saito 180's on the back, and the reason is , i want to learn to fly the roo comfortable first, before i test fly the roo and a turbine both for a first time

sean thanks again

mark

I don't have any experiance with the saito 180 other than I've seen some stuff here on RCUniverse that says it goes great. Make sure you've got the CG where it needs to be. You're not gonna have any problems with this airplane. It's very forgiving. One thing that's undocumented and I highly recommend is get all the mechanical throw you can safely get (ATV's to 150%) on the up elevator. I had to enlargen the holes on my wings to get there. You will need it to get smooth landings on the ROO.

thanks