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Hitec 5945 endpoint jitter???

Old 02-22-2004, 09:57 AM
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Steve
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Default Hitec 5945 endpoint jitter???

I have 3 brand new Hitec 5945 servos that I tested on my programmer and the neutral point is very solid, but the endpoints at both ends jitter alot with just a little presure. Is this normal for this servo or do I need to send them back? Thanks.

Steve
Old 02-22-2004, 10:57 AM
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Default RE: Hitec 5945 endpoint jitter???

The servo jitter as you note occurs with pressure applied, therefore it’s simply the servos response to maintain its commanded position. The jitter is a result of the high frequency of the digital amp pulsing power to the motor.

This is normal behavior of a digital servo.
Old 02-22-2004, 03:28 PM
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Default RE: Hitec 5945 endpoint jitter???

I also run several of the 5645 servos and none of them do what the 5945 does. I can put a fair amount of presure on the arm and they don't budge. These are my first coreless digitals and weather I use the Servo Programer or put it in the plane, endpoint jitter occurs, even just deflecting the elevator or rudder with the programer. Very strange to me.

Steve
Old 02-22-2004, 03:33 PM
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Default RE: Hitec 5945 endpoint jitter???

Steve,

Without going directly to Hitec for an answer, MGlavin is probably the most knowledgeable person that I know of regarding Hitec servos. You may want to contact him in a PM for more in depth answers to your questions. He's a very straight up person. It's possible that he may be willing to converse with you directly.

Pat
Old 02-22-2004, 08:49 PM
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Default RE: Hitec 5945 endpoint jitter???

ORIGINAL: Steve

I also run several of the 5645 servos and none of them do what the 5945 does. I can put a fair amount of presure on the arm and they don't budge.
The 5645's are as you note; standard 3 poled cored motors. They are less precise as a function of the three poles asscoicated with their armature. Cored motors stop and start in between the poles while corless motors are infinitely positionable.

Below is some basic information about or servos I provided for others, hope this helps.

Cored motors:

Cored electric motors are incredibly common; you'll see this design concept every time you turn around if you’re looking. Auto starters, power tools, RC car motors and lots more... The heavy rotating mass [core] of these electric motors known as an armature is comprised of metal plates [poles] sandwiched around a metal shaft, the metal shaft is supported at both ends by bearings, and each pole is wrapped with copper wire [windings]. More poles, equals more windings which in turn creates smoother less notchy operation. The armature spins at high rpm encompassed by a permanent hollow center magnet which is located within and lines the inside diameter of the metal can. The armature spins within the inside diameter of the magnet. Power is introduced to the windings, which in turn creates an electro-magnetic field. This field is opposed by the magnet which in turn causes the armature to rotate.

Coreless motors:

Coreless motors operate within the same design concepts, but are assembled in a different manner. The coreless armature is lightweight the windings are formed into a cylindrical shape [no metal plates or poles, typically a wire mesh screen]. The armature is fixed to a metal shaft at one extreme and the armature is supported at one end [imagine a hole saw with an arbor attached]. The armature rotates around the outside diameter of a permanent hollow center magnet within a space between the inside diameter of the metal can.

Coreless motors respond faster to the electro-magnetic field due to their light-weight. The coreless armatures accelerate and decelerate much faster and smoother resulting in less overshoot of the commanded position, cause and effect is more precession. Additionally more force is generated with like amounts of power, on a side by side comparison to a cored armature with a smaller diameter. The larger diameter coreless armature emulates a longer lever or arm when pushing the motor shaft, this equates to a higher torque rating. The lack of poles opposed by electro-motive force [EMF] allows the coreless armature to center more accurately while maintaining or holding position with increased authority [there is no space between poles, thus more positions to rest at].

Analog and digital servos share the same internal components less the servo amplifier [the device which commands the servos position].

Analog amplifiers interpret RX command and pulse power [on/off] to the armature at say 50 cycles per second, the space in between the on/off cycles is known as dead-band [db]. No power is consumed at idle. Power is delivered at full available voltage. The potentiometer [pot] feeds position info to the amplifier. If a signal is received from the RX or the servo arm is deflected the amplifier pulses power to either move too or resist the opposing force. The amplifier compares position to commands and reacts to the need by alternating the duration of the pulse to speed up or slow down the servo motor, thus moving too or holding the commanded position.

Digital amplifiers via the micro-processor interpret RX commands or signals and operate within fixed parameters; the preset commands together with commanded position are then delivered to the servo motor. Center, end points and maximum speed are preset parameters. The duration of the power pulse and the amount of power utilized to activate the servo motor varies dependent on the need. Servo performance is greatly enhanced with this method of motor control. Digital amp's also send power pulses to the servo motor at 300 cycles per second much more frequent than the analog amp [power is consumed at idle]. Known result [servo buzzing]... The increased pulse cycles command the servo motor to react and perform with more precision simply because of the increased pulse frequency or interval. Net results are faster response to control command signals, lower dead-band numbers, increased holding power and much better resolution.

Programmable Digital amplifiers, in addition to the aforementioned digital amplifier operating description have a programmable memory which can be altered via a programmer. The servo operation parameters therefore can be manipulated within programmable parameters to the user's individual needs. Center and end-point positions, speed, dead-band, rotation, failsafe and more are programmable.
Old 02-23-2004, 12:36 AM
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Steve
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Default RE: Hitec 5945 endpoint jitter???

Thanks for the info on the servos. I'm going to try and fully charge my battery and see if that may be the problem. As you said in your post, the coreless should hold better and be more precise, but that are acting just the opposite.

Steve
Old 02-23-2004, 01:18 AM
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Default RE: Hitec 5945 endpoint jitter???

Do the servos exhibit this behavior when the surface is disconnected? Is it possible you’re binding at the end of the travel arc? Turn down your ATV and try it. Did you program the servo and end-points? It really sounds like a setup problem or the typical jitter noise associated with digital servos. The coreless servo will be more audible as they try hard to find the commanded position. With more motor resolution they noise frequency is increased.
Old 02-24-2004, 09:17 PM
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Default RE: Hitec 5945 endpoint jitter???

Found the problem!! I charged the battery and it did help but then the Y'ed servos would quit working. I figured it was a power problem so I went throught the system. I found a bad extention on the switch harness that was the problem. Once I took the extention out, everystuff worked very well. These coreless digitals are much faster than the regular digitals. I put expo in to make them more to my ability. Flew the plane twice today and every thing woks great!! Thanks for all the help.

Steve

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