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HelicopterRadio - Servo - Gyro - Gov - Batt › 8717 as Tail Servo?
09-14-2007 05:00 PM  10 years agoPost 1
JKos

rrProfessor

Redondo Beach, CA

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Given the ultra high speed of the 8717 directly from a 2S pack (I've seen 0.4-0.5 quoted), could it be used as a tail servo? If so, it would be the first direct 2S qualified tail servo. Just throwing it out there.

- John

RR rules!

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09-14-2007 05:05 PM  10 years agoPost 2
DS 8717

rrProfessor

Here wishing i was somewhere else

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Wouldn't that be the ultimate TR servo,at 8 volts it would be the fastest TR servo with ungodly torque.You would have to make dam sure there is no binding at the end points with it.And it's cheaper than the 8900.Use one on the throttle also with the cyclics and you wouldn't need a voltage regulator,but you would need a high capacity battery for sure.How many volts will a JR gyro handle,you could snip the pos and neg wirs to the gain and use a small regultor for the gyro,also the governor might be a problem.

YOU ONLY LIVE ONCE..IF YOU LIVE IT RIGHT THATS ALL YOU NEED

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09-14-2007 05:21 PM  10 years agoPost 3
JKos

rrProfessor

Redondo Beach, CA

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I'm just wondering if there is a reason why it isn't being marketed as applicable for tail applications too. It would be so under worked versus capability it's not funny.

- John

RR rules!

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09-14-2007 05:57 PM  10 years agoPost 4
9387ASH

rrElite Veteran

UK

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Probably because the man at JR Radio in Japan says that they are only rated at 4.8V. They cannot guarantee performance above 6V MAXIMUM.

Personally I tend to go with what the manufacturers say rather than what a marketing and sales organisation says...

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09-14-2007 06:36 PM  10 years agoPost 5
AirWolfRC

rrProfessor

42½ N, 83½ W

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Servo update rate is a question also.

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09-14-2007 06:37 PM  10 years agoPost 6
jschenck

rrProfessor

La Vista, NE.

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Something else to consider is the electrical pull at a full stall. I think I read somewhere that these servos can pull 2.5A each on a hard stall... 5 * 2.5A = 12.5A, better have a strong electrical path, though I imagine this would only happen in a bad crash. But if there was a failure somewhere and the 2S lipo gets a direct short you may have a lithium fire take out your entire heli.

Perhaps an 10A fuse directly off the lipo is the way to go.

sure do like these 8717's - I think a bird flying all 5 servos on straight 2S power would be VERY nice.

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09-14-2007 06:41 PM  10 years agoPost 7
jschenck

rrProfessor

La Vista, NE.

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I did ask Danny about HH and JR's position with regards to 8V on the 8717's. It's not recommenced is the official line.

add this to the end of rcuniverse dot com

/forum/m_6275470/anchors_6365552/mpage_1/key_/anchor/tm.htm

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09-14-2007 07:19 PM  10 years agoPost 8
west-wot

rrApprentice

wales

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it is not recomended but many pilots such as curtis youngblood and the szabo brothers use these servos off a 2 cell lipo

also the reason they have not advertised it as a tail servo because of the centring apperently and you would have to male sure your gyro can handle 8v like a csm 720

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09-20-2007 05:30 PM  10 years agoPost 9
Joe90

rrApprentice

Quebec, Canada

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Update rate

The update rate for standard servo is 50Hz
For gyro servos it varies between 250 and 333Hz I think.

This is an important factor, so this is what we have to verify before appliying this one to tail.

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09-20-2007 05:43 PM  10 years agoPost 10
JKos

rrProfessor

Redondo Beach, CA

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> The update rate for standard servo is 50Hz

Most digital servos on the market are capable of handling a much higher rate than this.

- John

RR rules!

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