SGP Reactor & OMI OS91SZ
With the flying season around the corner and 3-D competitions soon to follow my son Colin and I have looked at ways to squeeze more performance from our current equipment. Looking at the new OS91SZ engine and the SGP Reactor seemed the logical and only real avenues remaining.
The OS91SZ has increased horsepower over the 91 C-Spec and a more stable carburetion. We’ve added a Cline regulator through the service of James Oneil of OMI to make sure top engine performance remains at any fuel level. The carb undergoes minor modifications at this time. Basically this engine simply puts one on par with other top flyers. Because the helicopter is maximized setup wise, tampering with the flybar and throws is unwise and not desired.
OS 91SZ engine with OMI modified fuel system.
The Revmax sensor needs to be relocated as the Cline regulator interferes with the mounting bracket. Monster engine power is handled by this rpm limiter as it is quite capable of pulling +11/-11 and 8 degrees of cyclic without overloading.
The Revmax assures the structural integrity of this engine by preventing damaging over-speeding when suddenly off loaded with low blade pitch angles. The regulator keeps engine runs consistent under all G loading and the special Cat’s Eye maintains clean cuts for autos, with excellent midrange transition and solid punch out. This is something you cannot always get off the OS shelf.
Revmax RPM limiter sensor has been moved to the hot side of the engine because the cline now resides on the cool side.
The Reactor is a product that allows for better radio performance in so far as controlling the helicopter goes. While this is our major point of interest other benefits such as reliability and fast charging parameters being part of the overall design will be explained. The unit is basically a dual voltage regulator designed for high power demands.
Reactor with included accessories
Powerful and fast digital servos are common these days but at the cost of a high electrical current consumption. Often servos are quoted at 4.8 and 6 volts for different speed and torque values. These quotes are of course valid only under ideal conditions. Because the model helicopter electrical system more often than not is less than ideal we are left with a lower performance level.
A comparison to an overly tasked RC system might be similar to if you hooked too many lights up to a single extension cord that caused reduced individual light bulb brightness. Faster servos will not change the maximum cyclic or collective rates however they will alter the control acceleration or general control feel. In some cases the servo speed may become so rapid that it is possible to get ahead of a manoeuvre and rotor response using very skillful fingers. At most times however there is a net benefit.
If we look at the sum of the electrical current consumed by all the servos we can exceed 3 amps quite easily depending on flying style and servo selection. With 3-D loading the total current may reach 8 amps peak. In analyzing the fast and strong digital servo we can see heavier wiring is employed to carry the larger electron flow when compared to conventional or moderately spec units. Since we have three servos installed on the swashplate we would expect to have a power supply using wiring capable of handling 3 times the electrical current.
If you look at electronic CCPM by nature it employs long servo horns functioning with reduced ATV causing the servo to be electrically tasked more than say using shorter arms with more servo rotation. While the control rod speed is notably higher, it comes at a cost. Some hard-core 3-D people running a conventional mechanical mix for swashplate control may use longer servo arms and reduced ATV to this same end thus resulting in a similar trade-off.
Usually receiver batteries come with wiring substantially heavier than that of a switch harness for a reason, however at best the OEM switch wiring is the same gage as the servo in many cases. The wire gage unfortunately is based upon the physical limitations of the electrical connector. At worst, during electrical peaks the power supply wire may heat slightly as the electrical resistance increases, however because the peaks are short in duration normally no adverse or permanent change in the wire occurs.
Both the switch connectors and the associated wire size may well become electrical bottle necks offering resistance to peak electrical power transfer. This will result in slower available maximum servo speed and torque when over tasked. The charge lead of the switch harness often will not handle a fast charge and so the battery needs to be disconnected and replenished directly.
Charge cable sizing from lightest to the very heavy duty.
Looking at the conventional electrical switch we can see that it uses sliding contacts. Common practice is to turn the transmitter on first and then followed by the receiver. If the servos are off position when this happens all will move at the same time just when the first part of the sliding contact makes with an initial reduced surface transfer connection.
This is where arching and pitting will be most pronounced. In the lifetime of the mechanical switch it is quite possible for the wear to move further along the contact as the previously damaged areas develop electrical resistance becoming somewhat non-conductive. Like it or not the mechanical switch will eventually wear out and this wear is accelerated by the size of the electrical current flow. The higher vibration level of the 90 machines will play a large role in switch wear and tear.
Many modelers will select a heavy-duty switch harness with the largest wire size available to extract a maximum lifespan. Presently of all radio manufacturers JR appear to have the best heavy duty mechanical switch assembly which I try to use on all our helicopters equipped with a mechanical switch. I feel this switch with its 22 gage wire, while being adequate is still subject to normal wear and tear.
Many modelers replace their switch on a routine basis before evidence of impending failure. When the mechanical switch fails you loose electrical power plain and simple. After market mechanical switch units are available with heavy contacts and large gage wire for addressing this. The limitation for electron flow now resides in the size of the connector pins.
Comparison of main power transfer wiring from the worst to the best.
The Reactor utilizes a slaved solid state switch with relay like attributes having no moving parts and specifically designed for a fail safe on. The normal OEM switch turns and maintains the reactor off using a very minute amount of electrical energy.
All servos and the receiver are fed electrical energy directly from the reactor that receives its energy from the battery through very heavy gage #16 wire. The unit has a regulated electrical bus for the swashplate servos and another regulated bus for the receiver operating at 5.6 and 5.2 respectively.
The lower receiver voltage is required to meet the restrictions of various gyro/servo combinations. These voltages are however maintained through the full operational discharge cycle of the battery and so a safe, constant and reliable supply of electricity is always available. The swashplate bus is rated at 7.5 amps while the receiver bus rates at 5 amps. There is no slow down of servo speed during all flights. We also tested the unit during winter and found the servos to stay fast and powerful due to the large voltage reserve present behind the regulators.
The voltage differential between the two buses is small enough that servo speed variance between the throttle and rotor control cannot be felt.
The throttle servo, gyro, tail servo and any accessories such as a governor all pull power from the receiver at 5.2 volts regulated. These are lightly tasked compared to the swashplate servos and this is the voltage value a fully charged 4 cell nicad battery operates at during the first flight or two. A qualified pilot using acceptable equipment can notice the reduction of voltage as the battery is depleted during flight.
Just as we try for a constant rotor speed for steady handling we do the same for the servo during both transient control acceleration and deceleration. We’ve tested it on both the Raptor 90SE and the JR Vibe with both exhibiting acceptable improvements for 3-D handling.
Many understand that with eCCPM any deviation in the swashplate support servos maximum speed will be translated into transient control cross couple or interaction. By having faster operating servos it is easier not to exceed or over run the weakest link.
The SGP Reactor comes with all connectors necessary to power a 3-servo swashplate control system. This leaves the older European 4 servo eCCPM unusable with the Reactor. Included is a jumper to adapt any conventional OEM switch for powering the system down. Charging and battery connection is through the heavy duty Reactor electrical cabling employing Dean’s Ultra connectors. Recommended battery is the 2 cell lipo/li-ion while 6 cell ni-cad or ni-mh may also be used. Packs from 2000-4000 mah are acceptable being dependent on flying time and electrical tasking.
Electrical current consumption while off is measured at 8ma so the Reactor should be unplugged from the battery during those inactive periods between weekend flying sessions. When using Futaba radio gear the plug index needs to be removed from the swashplate servos or the Reactor casing altered with notches cut.
The ACE DS-1211/1111 servos which we have preference to at this time have Futaba plugs. The mCCPM collective servo arm on the Raptor 90SE has been lengthened to boost speed further due to the Reactor’s consistent voltage and by application, unlimited current supply.While radio ATV is lower plenty of servo resolution still remains for precision control.
Raptor 90SE Reactor installation.
The Reactor is recommended in my opinion to modelers riding the edge of the helicopter flight envelope during 3-D flight, especially with the larger machines. Benefits are however still apparent with the highly stressed 50 size application. I can see large, expensive camera and turbine helicopters benefiting from this device solely from a reliability point of view.
The beginner and sport flyer has no need of such a device being unable to tap into the associated benefits. The Reactor offers through sound engineering design added performance and peace of mind. It definitely offers a competitive advantage for those pushing the limits. We purchased the OMI modified fuel system through East Coast Extreme Helis.