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Servo Choice for BVM e brake

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Old 08-12-2017, 02:18 PM
  #1
turnnburn
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Default Servo Choice for BVM e brake

I went to fly my 63" BVM F-86 Sabre today and found I had no brakes. Brake system on this bird is the BVM e-brake (not sure if it is version one or two (I dont know the diff between the two systems). I think mine is version 2 but Im not sure. I purchased the plane ready to fly and this was the braking system installed. This is my first time using this system. No problems with it until today. Started trouble shooting when I got home and found that the servo (JR 8411) was not moving or even trying to move, After I removed it from the plane I find that the servo is completely locked up in brakes off position and is totally dead. I dont see any gear train issues so I think the servo motor is frozen. My guess is that this was either caused by too much voltage ( I am running unregulated 6.6v life batteries) or from heat damage from engine exhaust servo since this servo resides under the tailpipe just aft of the wing trialing edge. I think when I reinstall I will move the servo to an area with no exposure to heat or perhaps try to insulate the servo in some way. These seem to me to be the two most likely causes of this servo failure.

I went through my loose/spare servo supply and did not find another JR 8411 and I do not have the a spektrum 6260 servo which is what BVM calls for on e-brake 2 . I did find in my drawer a JR 8611 which is the same physical size and will drop right in the mounting as it stands currently.

My questions are

Can a JR 8611 take 6.6 volts ?

What other servos are guys using in e brake one and two with 6.6volts ?

I am not opposed to buying a Spektrum 6260 if I have to but would prefer not to if my 8611 or some other servo will get the job done reliablably


PS Upon further inspection I see that the 8611 is a tiny bit longer and wider than the 8411 but would not require much effort to make it fit.

Last edited by turnnburn; 08-12-2017 at 02:26 PM.
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Old 08-12-2017, 02:41 PM
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BVM's e-brake is a cool little brake actuator, but I was never able to mount it close enough to make all the connections really short to work.

It needs a big servo to move it. I bet you burned up the poor (but very capable) 8411. The voltage didn't burn it up, being used where it was struggling to move its servo arm, "burned it. "

The spectrum as 271 oz/in torque at 6v. The 8611 has 260 oz/in.

I used a hitec 7955 (333 oz/in). I would say that the 8611 will likely work, but it will be still be a bit under powered.

Last edited by ravill; 08-14-2017 at 12:05 PM. Reason: Edit in underline
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Old 08-12-2017, 03:59 PM
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I run Life 6.6 with a mixture of JR servos and never burned one up yet so I doubt that was your problem. Good luck.
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Old 08-13-2017, 02:24 AM
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Check this out. http://www.promodeler.com
Very close in size to the popular JR 8411 and 8611, but much stronger in all ways.
I have one of their 470 in. oz. high voltage servos and will get more....they are a quality piece. Made locally in.cenral Florida. So far my only criticism is that they use a Futaba spline instead of JR........not a big deal, but I would prefer to keep only one brand of servo arm in stock.
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Old 08-13-2017, 02:29 PM
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I installed the JR 8611 this afternoon. Seems to work fine. Doesnt struggle like the 8411 did. Seems to work fine on 6.6 volts. Time will tell.
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Old 08-13-2017, 05:09 PM
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I am tempted to install one of these as it seems a simple and hassle free system, but I have one question.

If the brake is left fully applied for any length of time, does not mean that the servo is going to have to work very hard, just to hold position?
As I see it this will create a high draw from the flight battery, while the brake is in “park”. .

If so, it means you can’t really use it as a park brake, during engine start etc.
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Old 08-13-2017, 07:40 PM
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Default BVM E Brake ver-2

Hi Roger,

The great instructions with color photos included with the brake unit are very detailed and depict the servo arm at "top dead center" at max braking. Setting up the geometry as shown in the instructions should result in a minimal current draw. Do use the rec. brake line tubing. and short runs.
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Old 08-13-2017, 10:33 PM
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I guarantee you it wasn't a voltage problem. I flew 8411 and 8611 on unregulated Duralite Plus batteries for years and never had one fail.
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Old 08-14-2017, 12:03 PM
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I suppose, my reply could be taken wrong.

I doubt 6.6V would kill an 8411. Using it in a situation where it was underpowered killed it, ie "burned it up".

Roger, I tried using the e-brake in my 86, but I could not get the lines as "short as possible" because of where I wanted to place the thing. I went NUTS trying to find out why the brake wouldn't work, but alas, when I made EVERY connection uber short, it worked great.
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Old 08-14-2017, 03:26 PM
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Thanks Raff and Ad. I understand now. Set it up so that in the max brake or park position, the servo arm is in line with the push rod, which effectively unloads the servo.

I love the BVM pneumatic wheel brakes, but their sooth stop valve is just junk. The one in my Hun worked great for a dozen flights, and then one day at a rally it started loosing air, intermittently, with the predictable runway over shoot and busted nose gear rails.

The E brake looks to be such a simple and elegant solution with no on board tanks and no compressor required..

I might do some testing as I have one of the large cylinders to hand.
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Old 08-14-2017, 07:36 PM
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Default Separate Battery?

[QUOTE=roger.alli;12360138]Thanks Raff and Ad. I understand now. Set it up so that in the max brake or park position, the servo arm is in line with the push rod, which effectively unloads the servo.

I love the BVM pneumatic wheel brakes, but their sooth stop valve is just junk. The one in my Hun worked great for a dozen flights, and then one day at a rally it started loosing air, intermittently, with the predictable runway over shoot and busted nose gear rails.

The E brake looks to be such a simple and elegant solution with no on board tanks and no compressor required..

I might do some testing as I have one of the large cylinders to hand.[/Q
================================================== ==============
I tried this unit several years ago and wasn't successfull, probably my install. If I used it again I would probably put the brake servo on separate battery.
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Old 08-20-2017, 02:41 PM
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If you are worried about running a servo with 6.6v use this one. 277oz-in It won't burn up and will work for years.\

PowerHD LF-20MG Metal Gear Digital High Torque Servo | Value Hobby
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Old 08-20-2017, 02:42 PM
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[QUOTE=sidgates;12360201]
Quote:
Originally Posted by roger.alli View Post
Thanks Raff and Ad. I understand now. Set it up so that in the max brake or park position, the servo arm is in line with the push rod, which effectively unloads the servo.

I love the BVM pneumatic wheel brakes, but their sooth stop valve is just junk. The one in my Hun worked great for a dozen flights, and then one day at a rally it started loosing air, intermittently, with the predictable runway over shoot and busted nose gear rails.

The E brake looks to be such a simple and elegant solution with no on board tanks and no compressor required..

I might do some testing as I have one of the large cylinders to hand.[/Q
================================================== ==============
I tried this unit several years ago and wasn't successfull, probably my install. If I used it again I would probably put the brake servo on separate battery.
I had the same problem with one and the BVM grease never helped. I used some old kitchen faucet gasket grease I had laying around and never had another leak.
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Old 08-21-2017, 01:10 PM
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That e-brake is an awesome unit. But, and this cannot be stressed enough, EVERY connection has to be AS. SHORT. AS. POSSIBLE.

This does make mounting the thing a rather well thought out affair. I like to leave a touch of "extra" brake line "in case", but I could not get mine to work in my (BVM's) large F-86. My install was already done and I did not want to redo every system for it.

When I hooked it up separately to the wings with really short air tubing, it really did work nicely.

If you plan on using one, make sure you plan it out early in your install so that it'll work effectively.
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