Espritmodel.com Telemetry Radio
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Old Nov 06, 2012, 06:15 PM
AMA# 548800
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Originally Posted by mhills51 View Post
I just got a emax tail servo and it says everywhere only 4.8v. I must say it is incredibly fast and at 5v 280hz it gets warm.
Yes it does . I put a diode on my bec on the red wire to the Protos . I have all Emaxx 9258 mg servos all around . Even on max load with all the servos moving it drops to 4.8v from 4.9v .
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Old Nov 06, 2012, 10:22 PM
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Originally Posted by beenflying View Post
That's what I meant. They don't need a stop for the sensor they are using. When the magnet is aligned above the chip with the north pole at one end of the chip it will output half vcc, like a pot, as it move clockwise the output voltage increased. As it move anti clockwise the output voltage decreases. My understanding is that the device is analog, using induction coils and op-amps.

Edit: I'm told it uses multiple hall effects to work out the position of the magnet, not induction coils, as mentioned above. The resolution is 4096 steps for 360 degrees.
Where did you get this information? I would bet that they have multiple hall effect sensors on a single chip similar to how they put multiple MEMS gyros on a single chip. On the 280xxx servos the chip is on a little daughterboard soldered to the mainboard. I wonder if maybe they made the daughterboard to output position voltage like a pot so they could just drop it into existing designs?


4096 steps is insanely high resolution for a radio control servo, even high end servos have a few hundred steps at most. I would guess that the servo electronics that drive the motor probably don't come close to the full resolution of the position sensing device.


If it's as cheap as it seems it would be (mass produced chips would be cheaper than pots and last longer even if the performance is the same) then I wonder why Blue Arrow is the only company doing this.
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Old Nov 06, 2012, 11:11 PM
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Yes, it is a single chip solution. This one here:


My head of hardware design knows of these chips. He says they are commonly used for car throttle position sensing.

Blue arrow's site says the minimum resolution of the Mi servos is 0.088° (rounded up) and the sensor works over 360°.

There appears to be 6 connections to the magnetic sensor, as opposed to 3 for the pot, but there may still only be 3 connections. The extra pins may be there to support the board.


My guess is they have a patent on the method that may be slowing down others from using it.
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Old Nov 07, 2012, 02:41 AM
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Originally Posted by Atomic Skull View Post

4096 steps is insanely high resolution for a radio control servo, even high end servos have a few hundred steps at most. I would guess that the servo electronics that drive the motor probably don't come close to the full resolution of the position sensing device.
FWIW, JR servos have 1 usec resolution, 5900steps for120 degrees of travel:

http://www.jrradios.com/Products/Def...odID=JRPSDS368
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Old Nov 07, 2012, 07:06 AM
just gotta mess with it!
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Dumb thumbs...

Quote:
Originally Posted by pmackenzie View Post
FWIW, JR servos have 1 usec resolution, 5900steps for120 degrees of travel:
My thumbs have about 100 steps of resolution - on a good day!
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Old Nov 07, 2012, 01:04 PM
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Originally Posted by pmackenzie View Post
FWIW, JR servos have 1 usec resolution, 5900steps for120 degrees of travel:

http://www.jrradios.com/Products/Def...odID=JRPSDS368
Complete overkill for a radio control servo, assuming it actually does have 5900 steps of real world output, which it may not.
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Old Nov 07, 2012, 01:11 PM
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Originally Posted by beenflying View Post

There appears to be 6 connections to the magnetic sensor, as opposed to 3 for the pot, but there may still only be 3 connections. The extra pins may be there to support the board.
My thought was that maybe they designed the daughtercard to output position voltage like a pot and then just stuck it into existing designs to simplify development. But if it has 6 pins than this obviously isn't the case because even if three pins are only there for support you couldn't just drop it into a board that was designed for a pot.
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Old Nov 07, 2012, 01:17 PM
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Originally Posted by beenflying View Post
My guess is they have a patent on the method that may be slowing down others from using it.
If these kinds of chips are already used elsewhere to sense rotational movement then I can't see how they could be covered by a patent for use in servos. Unless it's the design of the chip itself i.e. it's something that Blue Arrow designed themselves and not something off the shelf.

EDIT: JR is already doing this, they call them linear hall sensing servos. They used to have a standard high torque and high speed regular servos that use this that which were discontinued. The "high speed for gyro" version is still being made. They also recently came out with HV brushless hall effect sensing servos. It appears that JR reserves this technology for their high end servos only.
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Old Nov 07, 2012, 10:45 PM
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Blade 450 style pitch slider for 450 Pro/Sport.

http://www.hawk-rc.com/index.php?rou...roduct_id=1932

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Old Nov 10, 2012, 11:56 AM
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Need Suggestion on HK 450

Hello,
I am an intermediate flyer and I presently fly the Eflite Mcpx heli ....set in the normal setting on my DX7 it seems to fly like my Sr120 which was also a FP. I am wanting to build a hobbyking 450.Do you guys recommend the 450 TT Flybarless from
hobbyking. Since this is my first build would you recommend the flybarless or one of the other ones. I have built a lot of airplane kits but want to get into helis without breaking the bank. I do not plan to do any 3D .....just lots of sport flying. I do want to go with the 450 size.

Richard
Wichita KS
USA
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Old Nov 10, 2012, 12:05 PM
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Originally Posted by rnorth View Post
Hello,
I am an intermediate flyer and I presently fly the Eflite Mcpx heli ....set in the normal setting on my DX7 it seems to fly like my Sr120 which was also a FP. I am wanting to build a hobbyking 450.Do you guys recommend the 450 TT Flybarless from
hobbyking. Since this is my first build would you recommend the flybarless or one of the other ones. I have built a lot of airplane kits but want to get into helis without breaking the bank. I do not plan to do any 3D .....just lots of sport flying. I do want to go with the 450 size.

Richard
Wichita KS
USA
Well flybarless certainly seems very popular at the moment. I have the HK450 TT FBL and It's not a bad little heli. It certainly performs very similar to my T-Rex 450 Pro. However even though FBL helis are mechanically much simpler, they do require the same if not more care during set up. Even then the FBL unit requires some know how to get the best out of it, whether that be 3D or general sport flying. Each type of head has pro's and con's. In reality the decision is only yours to make and you shouldn't rely on anybody else to make the choice for you. Everybody will offer a different opinion. Personally I like FBL, others don't as they say it feels too "synthetic" if you know what I mean.

I'd go for it if I were you, better still, because the HK helis are so cheap, just buy both.

Paul
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Old Nov 10, 2012, 12:35 PM
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Paul,
Thanks for your input. I do like my flybarless Mcpx....so that's why I'm sort of leaning that way.
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Old Nov 10, 2012, 12:52 PM
just gotta mess with it!
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Belt up!

My principal reservation would be with the torque tube tail - it's a shame HK don't do a belt tail FBL 450 - and 550, for that matter - since belt tails are so much more forgiving in any sort of tail strike. Be prepared to have lots of spare tail gears to hand if you're just starting out.
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Old Nov 10, 2012, 01:05 PM
just gotta mess with it!
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Originally Posted by Atomic Skull View Post
Blade 450 style pitch slider for 450 Pro/Sport.

http://www.hawk-rc.com/index.php?rou...roduct_id=1932

I like the look of that - though I wonder about using the two bolts to fix it to the tail gearbox arm. Seems like the arm isn't thick enough to have a bolt only going to half depth from each side.

I'm currently trying out the cheaper Tarot TL 1200-02 tail mechanism.



The arm and part of the slider are plastic, but it seems to have taken out a fair bit of slop in my HK 450 Pro tail. My Gotek tail servo seems to run about 10f cooler as a result, maybe it's not having to work so hard with less slop. The only bad thing is the arm has too much of a crank in it, so my tail linkage rod now has a bit of a bend in it. Could do with slightly longer rod guides, since there's a similar bend at the servo end. It also seems to use a riveted-in slider bush - though I reckon I could make a hybrid slider using some HK bits and some of the Tarot bits.
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Old Nov 10, 2012, 01:08 PM
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Quote:
Originally Posted by 2Doggs View Post
My principal reservation would be with the torque tube tail - it's a shame HK don't do a belt tail FBL 450 - and 550, for that matter - since belt tails are so much more forgiving in any sort of tail strike. Be prepared to have lots of spare tail gears to hand if you're just starting out.
I second that. I bought the belt drive hk450 pro and then converted the head to flybarless myself, just so I could have the belt drive tail.
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