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HomeRC & Power✈️Aircraft🚁HelicopterRadio - Servo - Gyro - Gov - Batt › Are 8717HV Servos as good as it gets?
05-11-2013 05:14 PM  6 years ago
rexxigpilot

rrProfessor

rexxig2@comcast.net

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Regardless of gear slop, a brushless servo has a much faster response time (time from start of input signal to when the servo first starts to move, not 0-60° time) than a brushed motor servo. Brushless also has a quicker time to full holding power. These elements are more critical to smooth and accurate control, particularly on a FBL setup, than 0-60° time.

I fail to understand why we allow servo manufacturers to continue selling us brushed motor servos nowadays when brushless motors are ubiquitous. The extra cost of manufacturing the brushless servo is well worth the cost to manufacture and price to purchase. How many are still running brushed motors on the aircraft propulsion system!?
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06-20-2013 06:21 PM  6 years ago
Zaneman007

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Texas - USA

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I agree HV brushless servos are at the top of the "servo" chain, but they come with a price, exclusive of there availability.

Not everyone flys the same heli, so why would they fly they go "all" brushless?
Old Guys Rule!
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07-04-2013 03:24 PM  6 years ago
ssrobzoom

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Tn

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Can you replace the JR's 8717 gears with the 8917HV gears?
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02-23-2014 06:51 PM  6 years ago
richord

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JAX, FL

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I know this thread is months old...

A poster above states that brushless servos respond quicker than a brushed motor servo. I have actually heard the exact opposite from 2 different pro pilots. While they did say that brushless runs cooler and is more energy efficient, they also said that coreless (brushed) motor servos have a quicker response around center. Anyone else have knowledge and experience with this.

I'm on the fence with choosing th JR 8717 HV (coreless) and the Torq 9180 which is brushless.

I heard about the gear slop on the LV 8717 but not the 8717 HV. Anyone flown the HV 8717 fairly hard with over 100 flights, please provide gear slop feedback.

I think the torq has a full metal gear train. JR has a sacrificial gear, but doesn't necessarily break in a crash. Either way, I was told not to use alum servo arms, but to use plastic or carbon so they break instead of the servo gears.

I will be purchasing these for a Goblin 630 - 700 build.
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02-23-2014 09:12 PM  6 years ago
rexxigpilot

rrProfessor

rexxig2@comcast.net

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Coreless motors are quicker than cored motors of equal rotor size (diameter). The rotors of all brushless motors are "coreless." Brushless servos use inrunner motors which use lightweight cores or hollow cylinders instead of heavy ferrous metal cores. The "coreless" rotor of an outrunner is the motor housing with magnets attached to the inside. Lower polar inertial is a big reason why the coreless is faster than the metal cored motor. A stronger magnetic field is another reason.

The quickness or faster response time of the brushless servo is due to not having a mechanical commutator in the motor as does the brushed motor. An electrical device like an ESC is used instead to control motor start on a brushless motor. The slower response of a brushed commutator is because the alternation of the magnetic push-pull fields are slaved to the rotational speed of the rotor, which is initially zero. This is not the case with a brushless motor.
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HomeRC & Power✈️Aircraft🚁HelicopterRadio - Servo - Gyro - Gov - Batt › Are 8717HV Servos as good as it gets?
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