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HiTec HS-7954SH Coreless Premium Digital Servo
High voltage, high torque and steel gears for the BIG planes
Text, photos and video by Tom Hintz
Flight video by G. Jawhar
Posted – 1-27-2015
The HiTec HS-7954SH Premium Digital Servos don’t look much different outwardly but what they have inside is what counts. They are actually economical for a high voltage, high torque, coreless servo with steel gears. They generate 403 inch ounces of torque when fed 7.4 volts. (333 inch ounces on 6.0V) They also deliver that power with a quick 0.12 second transit time also on 7.4V. That kind of power and speed will obviously generate some heat so HiTec uses a heavy-duty case with an aluminum heat sink built in. Despite the power and speed the HiTec HS-7954SH Premium Digital Servos have a trim 1.57 x 0.78 x 1.45-inch size and weigh 2.30-ounces each.
The HiTec HS-7954SH Premium Digital Servos feature hardened steel gears and oversized steel gear pins. Because this much power would kill bushings in short order the HiTec HS-7954SH Premium Digital Servos have two ball bearings supporting the output shaft.
The HiTec HS-7954SH Premium Digital Servos are also programmable a feature I essentially disregarded when I put them in my Aeroworks 60cc Freestyle Extra 260 QB-L. But when I built my Aeroworks 50cc Pitts Python having four aileron servos made programming a big deal so ordered a HFP-25 Digital Servo Programmer & Tester and strongly suggest you get one as well if you use programmable servos.
All servos come with an accessory bag that contains the rubber isolators, brass inserts and mounting screws. You also normally get a small selection of servo arms and wheels that are often tossed because they appear suitable for light duty only and are usually too short for many big throw applications.
The HiTec HS-7954SH Premium Digital Servos come with large, heavy-duty arms that let you take advantage of the available power without worry about the arms distorting or breaking. I was surprised to see two heavy-duty pull-pull style arms, one with a 2” spread and the other 2-1/2”. These arms will accommodate many larger pull-pull systems and of course the spline on the output gear that fits the larger after-market aluminum arms so many use in giant scale models.
In the Air
I am the poster boy for maximum servo power in my planes. When I want full aileron or elevator deflection I want all of it and I want it now. My Aeroworks 60cc Freestyle Extra 260 QB-L and Aeroworks 50cc Pitts Python ARF-QB planes both have HiTec HS-7954SH Premium Digital Servos everywhere but the throttle. Both of these planes have above average engine power, remarkably large control surfaces and both have an all-up flight weight right at 18 pounds. Cheap servos just were not going to make the cut. And to be sure the HiTec HS-7954SH Premium Digital Servos get the power they need to put out the 400 inches of torque both planes have the Smart-Fly PowerExpander Sport Plus systems driven by a pair of 7.4V, 5000mAh battery packs.
From the maiden flight of my Aeroworks 60cc Freestyle Extra 260 QB-L it was obvious that I have chosen the right servos. The HiTec HS-7954SH Premium Digital Servos allowed me to take advantage of the almost unbelievable aerobatic capabilities of this plane. One of my favorite things to do with the Aeroworks 60cc Freestyle Extra 260 QB-L is to point it up at speed and tumble it. The other favorite is knife edge spins. Both of these and any other maneuver I can think of come off fast and clean because the HiTec HS-7954SH Premium Digital Servos thrust he control surfaces into the air and keep them at the deflection I want. The servos simply do not stall on my planes which means that big things happen predictably when I go full-throw.
People are often amazed to see the speed and violence with which the Aeroworks 60cc Freestyle Extra 260 QB-L will perform maneuvers in the air, especially when I bring it back in for a landing and they see how big the plane actually is. It is the HiTec HS-7954SH Premium Digital Servos driving the control surfaces that let me take full advantage of this planes capabilities.
When I put HiTec HS-7954SH Premium Digital Servos in my Aeroworks 50cc Pitts Python ARF-QB and put one of the on each aileron some thought I was nuts. Then on the maiden flight when I took the Aeroworks 50cc Pitts Python ARF-QB up to speed and hammered the ailerons, the roll rate shocked everyone, including me. Coming out of a full-throw roll right side up with the HiTec HS-7954SH Premium Digital Servos is usually more luck than coordination.
If you have an airplane with big control surfaces the HiTec HS-7954SH Premium Digital Servos are a must see. I occasionally find the HiTec HS-7954SH Premium Digital Servos for $90 to $100 each (1-26-2015) which is short money for the performance and durability these servos offer. (See Anderson RC in the sources below)
Nothing worth a dam comes cheap in the RC world but the good stuff, such as these HiTec HS-7954SH Premium Digital Servos can last through several planes barring the wildest of crashes. That durability and their built-in versatility make the HiTec HS-7954SH Premium Digital Servos a very good long-term investment.
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