Not sure if you can buy a metal gear set for that servo or not.
Rob - The hitec website will take you through all the differences of Digital vs. non. digi. From the 10 times greater speed, to the strength etc. They also point out the fact that they are power hogs. With some centerless servos or coreless servos, you can spin the spline all the way around. Then, when you turn it on, its already centerred (until you turn your radio on etc etc). The key bennefit is so you dont run into 'flat spots' as I call them. A common problem is a servo will not return to center after extended use. This is due to it being a 'fixed' center set by the pot which limits travel one way or the other. With no centerring pot, you will not run into this issue.
Here are some excerpts from HiTec's site:
Unbreakable MP Gear™
The heart of our unbreakable geartrain is the MP Gear. The MP Gear is made utilizing a revolutionary production technique that injects a high impact plastic around a metal pinion gear to form an unbreakable first gear. By utilizing this gear Hitec has succesfully reduced the amount of drive train noise that is common in metal gear servos and at the same time added considerable strength to the geartrain.
The HS-645MG represents the latest generation of Hitec servos. With a custom designed programmabledigital circuit and our unique Alumite/ MP gear train technology the
HS-5645MG has our infamous un-breakable gear train. The powerful
HS-5645MG is perfect for those applications that demand a high torque servo.
Q. Do I need to program my Hitec digital servo before I use it?
A. No. The Hitec digital servos can be run "out of the box" and will perform just like a "normal" servo.
Q. How do I program my Hitec digital servo?
Using Hitec's proprietary programmer and servo tester device, model HFP-10, Hitec digital servos can be programmed for, direction of rotation, center and end points, failsafe option, speed and dead bandwidth adjustment. This is great for matching sets of servos for deadband width, center and end points in giant scale aircraft applications and for reversing a digital servo when two or more are used on a "Y" harness.
Q. What is the difference between an analog and digital servo?
A. The motor of a analog servo receives a signal from the servo amplifier 30 times a second. This signal tells the servo motor what to do and when to do it. Digital servos use a high frequency amplifier that sends a signal to the servo motor 300 times a second. Wow, this is 10 times "more frequent" than an analog amplifier, so a digital servo's motor is really working hard! This 300 times a second refresh rate delivers the full torque value of the servo right off the centerpoint and gives the servo a tighter deadband and thus, better centering ability and massive holding power.
Q. What are the advantages of digital servos ?
A-1. Instantaneous response
The digital micro processor is 10 times faster than an analog servo, this results in much quicker response "off the line" with the servo developing all the rated torque 1 degree off of the center point.
A-2. Programmability
Using Hitec's proprietary programmer and servo test device, model HFP-10, Hitec digital servos can be programmed for, direction of rotation, center and end points, failsafe option, speed and dead bandwidth adjustment. This is great for matching sets of servos for deadband width, center and end points in giant scale aircraft applications and for reversing a digital servo when two or more are used on a "Y" harness.
A-3. Enormous Standing Torque
The standing torque of the digital servos is 3 times that of the analog counterpart. Check it out, try moving the transmitter stick or wheel and at the same time hold the servo horn to keep it from twisting. You will not be able to prevent the horn from turning.
Q. Are there disadvantages to digital servos?
A. Digital servos use more power than an analog servo. Power is not free. They produce more power, so they take more power. Modern digital servos have impressive torque values, this takes a lot of power. Receivers are capable of delivering only so much power to the servos plugged into it before the voltage draw down caused by the servo power consumption falls below what the receiver requires to "hear" the signal from the transmitter. When this occurs a "glitch" will result from loss of signal to the receiver. Large aircraft can easily use 6 or more powerful servos with some 1/3rd scale and larger planes having multiple servos per control surface. There are several answers to this issue. Many modelers choose to use two receivers and others power the servos with a separate battery from that of the receiver. The point here is to be cautious when "Y" harnessing or "ganging" powerful servos together. Using larger capacity Nicad batteries as well as Heavy Duty switch harnesses are highly recommended in these applications.
Hope this helps!
