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Old Nov 06, 2012, 03:18 PM
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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.
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Old Nov 06, 2012, 04:41 PM
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Could try this, been using one on my 500 and it barely gets warm at 333hz and holds the tail like a robot.

http://www.hobbyking.com/hobbyking/s...dProduct=14831



This would be as large on a 450 as a 9257 is on a 250 though. But it's ridiculously fast and there's no pot to wear out over time.
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Old Nov 06, 2012, 05:01 PM
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Originally Posted by Harrow View Post
Yep, definitely want a different tail servo eventually. If you are only learning to hover, etc, it will not be a problem for you. But when you get to the level of mild 3D, (flips, etc.) you will want a better servo.
I guess I should have stated my intentions with this or what level I was at. Flown co-axles and fixed pitch (ie walkera u-fly, sub $100 airhogs etc) for far more years and far more models than I would like to admit to. Shy'd away from collective because I was warned it would be way too much money. Finally looked into prices a month ago and bought a MCP X (great heli) and have been flying the crap out of that ... 4-12 packs a day.

Now I am here wanting something bigger and that I can build up. I would consider it a trainer, that's why I went with a cheaper clone than the real thing.

With all that being said, I need to hit up a hobby store for connectors and what not because I simply ran into the weight limit for shipping (with-in 5 grams of being over weight). I will pick up a park size servo while there ... but it seems to me that the most important part is a sub .10 sec with lower being better. Also what torque should be a minimum?
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Old Nov 06, 2012, 05:16 PM
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Originally Posted by Atomic Skull View Post
Could try this, been using one on my 500 and it barely gets warm at 333hz and holds the tail like a robot.

http://www.hobbyking.com/hobbyking/s...dProduct=14831



This would be as large on a 450 as a 9257 is on a 250 though. But it's ridiculously fast and there's no pot to wear out over time.
I think it's aimed at 550/600 use, and they have an HV version that claims to be a touch faster. On the HK pages, someone has posted that all the Mi servos are only rated up to 280Hz, and references something on HF, but it's good to hear yours is fine at 333Hz. Pity they don't do a Park sized equivalent.
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Old Nov 06, 2012, 05:21 PM
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61g. Your 500 must fly with it's nose in the air lol!
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Old Nov 06, 2012, 05:28 PM
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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.
I just checked out the spec, and considering it's only running at 4.8v, they claim 0.05s and 3kgcm of torque, which compares to 0.07s and 3.8kgcm for the Fitec FS9357D at 6v. Have you tested the speed on a servo tester? (such as the CX or ZYX program box) If it performs close to the spec, it looks pretty good for the money. I think one more advantage of controllers such as the Robird over the CX/ZYX is that they give you more choice of cyclic and tail driving frequencies.
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Old Nov 06, 2012, 05:29 PM
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Originally Posted by 2Doggs View Post
I think it's aimed at 550/600 use, and they have an HV version that claims to be a touch faster. On the HK pages, someone has posted that all the Mi servos are only rated up to 280Hz, and references something on HF, but it's good to hear yours is fine at 333Hz. Pity they don't do a Park sized equivalent.
They do.

http://www.hobbyking.com/hobbyking/s...dProduct=14827

As I mentioned before these have about 0.3mm play in the output shaft (the recess for the top bearing has a little tolerance) but the Emax servo has this much worse and it doesn't seem to affect it's performance. Supposedly using a magnetic rotory encoder is more accurate than a pot but I think that there being no pot to wear out is the real advantage of this. I suspect the real reason for using it is that the magnetic sensor chip is cheaper than a quality pot.

I've been using the lower speed higher torque version of this as cyclic on my 500 and they have been running at 5v 333hz with the gyro gain turned fairly high without issues. The high speed version is only rated at 5v while the high torque version is rated at 6v. The only difference is the gears so I don't know why this is the case.

You can use the titanium gear replacement sets for these in your other 9257 and 9650 clones btw.

These servos do "chatter" quite a bit while holding position without a load on the output shaft. My 500 sounds like a geiger counter powered up on the bench.
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Old Nov 06, 2012, 05:35 PM
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Resolution

How is the resolution? I can see that the magnetic encoder is more reliable than a pot, but if they keep costs down by limiting the resolution it might make the servo a bit jerky. I have to say I've not read of anyone complaining about lack of resolution with the Mi servos, but you might be able to do some meaningful tests on a servo tester - though it's clear that you're happy with yours and that it's doing a good job on your 500 tail.
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Old Nov 06, 2012, 05:41 PM
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Originally Posted by 2Doggs View Post
How is the resolution? I can see that the magnetic encoder is more reliable than a pot, but if they keep costs down by limiting the resolution it might make the servo a bit jerky. I have to say I've not read of anyone complaining about lack of resolution with the Mi servos, but you might be able to do some meaningful tests on a servo tester - though it's clear that you're happy with yours and that it's doing a good job on your 500 tail.
The resolution is very good. It's not actually a magnetic encoder. Magnetic encoders have the issue of not knowing where center is when they lose power, and have to drive to a stop or some other known point. They also usually require a gearbox to get a high resolution.

The Mi servos use the magnet like a compass. The chip can sense when the magnet is aligned north to south above the chip and then gives an analog voltage change as the magnet moves away from this point.
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Old Nov 06, 2012, 05:49 PM
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Originally Posted by 2Doggs View Post
How is the resolution? I can see that the magnetic encoder is more reliable than a pot, but if they keep costs down by limiting the resolution it might make the servo a bit jerky. I have to say I've not read of anyone complaining about lack of resolution with the Mi servos, but you might be able to do some meaningful tests on a servo tester - though it's clear that you're happy with yours and that it's doing a good job on your 500 tail.
They don't have "resolution" in the same way that a pot does, that's in the electronics not in the chip. They don't work anything like a pot at all. There would be no money saved by reducing the resolution of the encoder down to where it would actually become a performance issue in a radio control model.

http://en.wikipedia.org/wiki/Resolver_%28electrical%29

They're really Blue Arrow servos not HK, they're just relabeled. Resolution and centering seems pretty good. They've worked great on the Robird with the gyro gain set fairly high (I didn't touch the gyro gain pots when I moved it from the 450 that was running Ino Labs servos). One telltale sign of poor servo resolution and centering is that you have to keep the gains low or the helicopter gets the shakes.
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Old Nov 06, 2012, 05:49 PM
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Originally Posted by beenflying View Post
The resolution is very good. It's not actually a magnetic encoder. Magnetic encoders have the issue of not knowing where center is when they lose power, and have to drive to a stop or some other known point. They also usually require a gearbox to get a high resolution.

The Mi servos use the magnet like a compass. The chip can sense when the magnet is aligned north to south above the chip and then gives an analog voltage change as the magnet moves away from this point.
interesting
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Old Nov 06, 2012, 05:50 PM
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Originally Posted by beenflying View Post
The resolution is very good. It's not actually a magnetic encoder. Magnetic encoders have the issue of not knowing where center is when they lose power, and have to drive to a stop or some other known point. They also usually require a gearbox to get a high resolution.

The Mi servos use the magnet like a compass. The chip can sense when the magnet is aligned north to south above the chip and then gives an analog voltage change as the magnet moves away from this point.
The gear doesn't even have a stop. have to be careful with the servo horn positions when you power it up for that reason or it might go the wrong way to center.

Are you sure it's actually analog?
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Old Nov 06, 2012, 05:56 PM
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That does not sound very accurate to me. Where does the MI name come from then? a compass sensor is not based upon magnetic induction, right?
Also, what happens when you hold a magnet close to this servo?
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Old Nov 06, 2012, 06:00 PM
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That does not sound very accurate to me. Where does the MI name come from then? a compass sensor is not based upon magnetic induction, right?
After some reading on the subject I believe it's some kind of hall effect sensor now. Mi means Magnetic Induction, which i what a hall effect sensor is.

Quote:
Also, what happens when you hold a magnet close to this servo?
If it encounters a magnetic field strong enough to affect the servo's rotation sensor while it's in the air it means that nuclear war has just broken out and you've got much bigger things right to worry about right then than your helicopter crashing.
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Old Nov 06, 2012, 06:27 PM
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Originally Posted by Atomic Skull View Post
The gear doesn't even have a stop. have to be careful with the servo horn positions when you power it up for that reason or it might go the wrong way to center.

Are you sure it's actually analog?
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.
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