RevMax by Model Avionics
review 11-21-2004

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So what is the RevMax and how is it different then a throttle governor? The RevMax takes over control of the throttle only when the rotor speed begins to get too high. A governor will take control of the throttle throughout the whole flight. So why wouldn't you want that? Well a governor such as the Throttle Jockey Pro does a great job, but if you are looking for the highest degree of constant rpm then the RevMax is the way to go. So what should you get, the TJPro or the RevMax? That depends on your skill level. The RevMax only engages when the headspeed gets high during the no-load sections of your routine. All other times you are in control of your throttle so you need to be proficient at setting up a good throttle curve and cyclic mixes. Okay now you're asking 'so it sounds easier to just use a governor, how much performance difference would the RevMax give?' Again this depends on how well you are at tuning the engine and how well your throttle curve and cyclic mixes are setup. With everything right it will remain locked in. With a governor there is some lag on quick maneuvers which results in less power at the points it is needed. With a cyclic mix the extra power is mixed instantly with the stick movement so you end up with a more constant rpm. While running a governor I found it worked great when doing individual tricks but I could keep a more consistent head speed throughout a routine with my own curve/mixes. However one thing I did miss was that the governor maintained a constant rpm during the no load sections of the routine. The RevMax solves this by having the advantages of manual curves/mixes as well as the governor mode during the no-load conditions. By it preventing the overspeed condition I can more concentrate on making the maneuver look symetrical and end up in the right place to flow into the next trick. For instance one trick I do is a tail stand take-off that levels out for a short distance into inverted tail-first then into a backwards outside loop followed by a backwards inside loop. Without a RevMax or governor I would have to really manage my collective when coming up to the top of the first loop. If I did not get out of the negative range and into the positive with the right timing and the right amount it would overspeed. And of course when you get an overspeed condition it does not return to normal quickly so it effects the next few maneuvers you do. Adding extra 'loading' to get the head speed down or to maintain rpm during things such as a power dive can be done by a combination of the collective and elevator. For example during a power dive you give positive collective while adding forward elevator to keep it going straight down. This does help to maintain the speed but at times it takes away from your accurancy in positioning. Also this loading move cannot always keep the rpm from going a little high. You have to work the next tricks in a way to load the engine and get the rpm down. I really like this RevMax, no loading maneuvers anymore, just concentrate on the routine.

The first thing you do for installation is install the magnet(s). If you do have the stock plastic Raptor 30/50 fan then you will notice two places on the underside of the fan specifically made for the magnets. For other fans you will have to drill your own holes. Before you glue the magnet(s) in place you have a couple of questions to answer. Do you have a high point balancer to check the fan? And if you do then do you want to use one magnet or two?
Step A: No high point balancer. The engine spins at more then 10,000 rpm when running and any off balance will create a lot of vibration which can cause tuning problems, gyro problems, and decrease the life span of some components. I highly recommend balancing the fan after you install the magnets. Now if you do not have a friend with a high point balancer then you will need to install both magnets to try to keep the balance equal. You need to install them opposite polarity of each other. First test fit the magnet in the hole, it should have a close fit. So mix up some 30 minute epoxy and put a small amount in the hole in the fan. Do not put a lot otherwise you will not be able to get the maget in all the way. TIP: If you drill a small through hole in the magnet hole then the excess glue can come out as you push the magnet in. After you have one magnet installed you need to find the side of the 2nd magnet with opposite polarity. Place the magnet against the first one you installed. Find the orientation that causes the magnets to push away from each other. Then install the 2nd magnet with this orientation.
Step B: You have a high point balancer. Find out if your fan is currently unbalanced. If you do then install the magnet opposite of the heavy side. TIP: Be aware that the threads in the fan hub can offset the cones of the high point balancer. Rotate the fan hub 90 degrees and test again. If you come up with the same results then the threads are not interfering with the test. If you have a 2 stroke engine and choose to install only one magnet (like I did), then you first need to determine the correct direction to install it. Temporally hook up the RevMax. Unplug the throttle servo from the receiver. Take one of the extension cables and plug it into the throttle channel on the receiver. Connect the other end to the 'THR' plug on the governor. Next plug the sensor into the 'SENS' plug on the RevMax. Now hold one side of the magnet near the top of the sensor. This is the side with the slop (side facing the left of the picture shown here). When you have the correct side of the magnet facing the sensor you will see a red LED light up on the governor. Read the section in step A for tips on installing the magnet. Now check the balance of the fan. If the fan is not balanced you will need to do one of two things. Either install the second magnet or some other counterweight opposite of the heavy side. I chose to install a set screw in mine and keep the second magnet in case I needed to use the RevMax on another fan later on. If you do install the second magnet you have to make sure the polarity of the magnet is opposite of the other one. Now keep in mind this is unless this setup is installed on a four stroke engine. They run a lower speed and so both magnets need to be installed with the same polarity and exactly 180 degrees from each other.
Now that you have the magnet(s) installed and the fan is balanced then you need to determine which mounting bracket to use. On the Raptor 50/60 you use the larger of the two brackets. For the Raptor 30 you use the smaller one. Sit the sensor on the top of the bracket and gently bend the three legs down the side of the bracket. Make sure you get the slopped side of the sensor on the top. Place the heat shrink covering over the bracket and apply some heat to shrink it. I found the heat shrink that came in my kit was long enough that I cut it in two and just use half. Next with the sensor mounted flat on the top of the bracket apply some CA glue at the corner between the bracket and the sensor.
In the picture on the right you can see the bracket is installed under the two engine mount bolts. Also notice the bracket is installed on the opposite side of the muffler. Position the bracket so that the sensor is inline with the magnet under the fan. Rotate the fan a full turn to confirm you do have clearance from the sensor. You do want the sensor close, but not so close that it hits something under the fan.
Next you need to finish installing the electronics. Start by finding a good location to mount the RevMax. In the picture on the left you can see that I mounted mine under the battery tray. I used the foam tape that comes with it to stick it to the tray. Some people mount the RevMax on the top of the servo tray just in front of the pitch arm. In the event of a crash this might be a bad location (crashes have variable damage so this is just something to think about). The underside of the tray seems like a protected area so I chose this spot but wherever you pick just make sure the sensor wire is long enough to reach it. At this point plug the sensor wire into the 'SENS' plug of the RevMax. From a previous step you should already have one extension cable from the throttle channel of the receiver to the 'THR' plug on the governor. Next connect the throttle servo to the 'SRV' plug. Next run a wire from the 'AUX' plug to a spare channel on the receiver. If possible use a channel that is connected to a switch on the radio that you do not use. In my case with my Airtronics RD8000 channel 8 is connecte to the Aux2 switch. If you do not have a spare channel on your radio to control the RevMax (See Tip #1) then you will use the manual pot (labeled 'MAN'). However if you do have a spare channel then you can remotely turn the device on/off as well as set the target speed from the radio. Note: If you have all the receiver plugs filled up and you need a place to connect a battery monitor then connect it to the 'ACC' jack. Just do not use the extra jack that is unlabeld for battery monitor, it will not work.

At this stage you now have everything hooked up and you are ready for calibration. Where some people mess up here is with digital trim radios, you need to hold the throttle cut button/switch during the entire calibration process. The reason you hold the throttle cut during the calibration is to show it the entire range from engine off to engine full throttle. If you did not hold the throttle cut down then it would only see a range from 20% open to 100%. The other thing that people mess up on is with odd end points set for the throttle servo. If you have 150% on one side and 50% then it could cause problems. The end points need to be fairly close to equal and be no less then 80%. The manual wants you to have a setup of 100% both sides but I have ran it at just over 80% with no problems. BTW: If you had one end point at 150% then you were probably trying to keep the servo from binding with the cyclic mix, the best way to stop the binding is <this>. And one more thing people mess up on is not having the end points of the AUX channel set to 100% on both sides. Now with all of that in mind lets go through a setup. Turn the radio on and move the throttle stick all the way down. If you use a throttle cut switch/button to stop the engine then hold this when you get ready to toggle the switch. If you do not then make sure the mechanical throttle trim is all the way down. Now turn the receiver on and within three seconds toggle the switch for the RevMax twice. You should see the 'SET' light flash. Let go of the throttle cut button/switch and move the throttle stick all the way to the top (the LED will turn yellow) then all the way back down (the LED will turn green). Now toggle the switch twice to exit the calibration mode. I know... you thought there was more to it then that :) Quick and simple is better, I like it this way.

To set the AUX switch so you can disable the RevMax go to the end point menu in the radio and set one side to 5% or less.

Next is setting your target rpm. At this point after calibration your AUX channel is 100% for the 'on' side and 5% or less for the 'off' side. Make sure the switch is in the 'on' position then fly the helicopter and do a power dive at zero degrees collective. If you hear the rpm go high then lower the end point for the 'on' side a few percentage and try again. When I do not hear a change in rpm I know I have it right.

Tip #2: For convenience you can change the length of the sensor wire to a couple of inches then use an extension cable to connect it to the RevMax. This will allow easy removal of the engine without having to undo the cable routing to get the engine out.