You can put worse things in the field box. When a servo acts up this little instrument
could save the day, and your plane.
Text, photos and video by Tom Hintz
Posted - 11-6-2014
Digital servos were a natural part of the computer radio evolution and now we are able to take even more control over how these digital wonders work. The Hitec HFP-25 Digital Servo Programmer & Tester lets us fine tune our servos to more closely fit our needs and those of the plane. I recently used the Hitec HFP-25 Digital Servo Programmer & Tester to set up servos to allow the use of a Y-cord to connect upper and lower ailerons on one side of a bi plane which meant that I didn’t have to buy a bigger receiver or an in-line accessory to do essentially the same thing. That one use saved me more than the cost of the Hitec HFP-25 Digital Servo Programmer & Tester!
The Hitec HFP-25 Digital Servo Programmer & Tester is a 6” by 2-7/8” by 1-1/4” bit of electronic wizardry that lets us program Hitec's HS-5XXX and HS-7XXX series of servos in the shop or at the field. The Hitec HFP-25 Digital Servo Programmer & Tester comes with a 4.8V NiMh 1300mAh rechargeable pack that you have to charge out of the unit using virtually any peak charger with NiMh capability. (That covers virtually all modern chargers) It has an easy-to-read LCD screen, low battery warning, manual and automatic testing capabilities along with an impressive list of programming features.
The Hitec HFP-25 Digital Servo Programmer & Tester allows us to reset a servo to factory defaults which is very handy if you get lost while learning to use this unit. We can also fine tune the center and end points individually on each servo. This is a huge benefit in that you can essentially match ailerons so they both have the same deflection with a precision not easily achieved with linkages and transmitter programming. We can also reverse rotation directions with the Hitec HFP-25 Digital Servo Programmer & Tester.
I see lots of servos that have a buzz or slight shudder at rest and the Hitec HFP-25 Digital Servo Programmer & Tester gives us a way to fix that by adjusting the width of the dead band. The manufacturers try to bulls eye the dead band at the factory but now you can tweak that as needed to get individual servos to settle down.
The instructions walk you through the
many tests this unit can do.
Other programming capabilities include setting a Failsafe Point to which the servo will return if the signal is lost. In addition to returning a servo to neutral this programming could be handy for setting a bit of rudder deflection so a signal-lost plane doesn’t just fly straight away. We can reduce the speed of servos from their default highest setting. This can be nice for taming a normally twitchy plane or an unusually sensitive control surface.
The Hitec HFP-25 Digital Servo Programmer & Tester will configure an Overload Protection in HS-50XX & HS-7XXX Series only. This is a kind of safety for when the servo encounters excessive resistance it reduces the torque being applied by 10% to 50%. You can turn this feature On or Off also.
With Hitec HS-7XXX Series only we can change the resolution. This essentially lets us choose between the high setting of a 120-degree range of movement and the Normal of 180-degrees. This can be handy with planes that have large throw capabilities where a precise touch is less important than achieving maximum deflection.
The Hitec HFP-25 Digital Servo Programmer & Tester has four buttons and a dial that control all of the programming functions. You get an illustrated instruction sheet that does a good job of guiding you through the processes so keep it handy!
Though you can do the programming with the servo in or out of the plane I most often tweak their programming in the plane so I can set Center with the surface in its neutral position. (I zero out the transmitter settings prior to using the Hitec HFP-25 Digital Servo Programmer & Tester on installed servos.) This also lets me identify the limits of a set of control surfaces. Like with ailerons, I can find the lowest up and down capability and set both ailerons to that exact throw so one is not fighting the other when I do a roll. You can also set up identical differential in control surfaces when needed on planes like a Cub with the Hitec HFP-25 Digital Servo Programmer & Tester.
I once had a plane nearly crash when one of the elevator servo leads had the signal wire worn through on a former in the tail section. When it lost signal it stayed at near full deflection. I was able to control the crash into some tall grass and save the plane but with the Hitec HFP-25 Digital Servo Programmer & Tester I always program these types of servos with a neutral failsafe point. That can make an otherwise fatal crash situation much easier to control and land without damage.
After programming the servos with the Hitec HFP-25 Digital Servo Programmer & Tester I have had to make tiny adjustments to the Sub Trim in the radio a few times but most often the plane flew with the servos as I programmed them. Keep I mind that we set the end points with the Hitec HFP-25 Digital Servo Programmer & Tester and can then dial in dual rates and expo through the transmitter that work better because of the precision we can achieve matching throws.
The Hitec HFP-25 Digital Servo Programmer & Tester certainly is not for everyone because of the limited servo series it works with. However, those servos are very popular, particularly with larger planes. The amount of versatility and safety that can be programmed into our servos with the Hitec HFP-25 Digital Servo Programmer & Tester make its $69.00 (11-6-2014) street price attractively low. In addition to the safety we can program in with the Hitec HFP-25 Digital Servo Programmer & Tester it can help refine the way the plane flies when we match throws so accurately.
If you fly the Hitec's HS-5XXX and HS-7XXX series servos you need to take a hard look at the Hitec HFP-25 Digital Servo Programmer & Tester. It is deceptively easy to use but gives us extensive capabilities that can directly save a plane plus make it easier to fly.
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