Getting the most from RevLock RL10 (or RL20 & RL30 without PC interface)

Download these technical FAQs as a Word document

Q. I am using RevLock RL10 in Manual mode so I don't have access to the Responsivity control. I find that the engine note warbles when I execute a violent manoeuvre. Your manual suggests lowering the Responsivity control to cure this but what can I do?

A. The throttle servo arm length and the responsivity of the governor are linked. Decreasing the servo arm length (and increasing the throttle ATVs to restore the correct throttle barrel movement) will act similarly to reducing the governor Responsivity. (Increasing the servo arm length acts to increase the responsivity). Remember that when you change the throttle ATVs you will need to tell RevLock about these changes by going through the Basic set-up procedure again. Note that when you do this RevLock's safety system will also zero all the Range values so you will need to restore these after the Basic set-up routine is completed.

Please note: With RL20 & RL30 you can adjust the responsivity for Manual mode using the PC interface.

Q. I run a two-speed set-up and want to get the absolute maximum performance from the governor at both headspeeds. Since there is only one Responsivity control on the unit how can I optimise the response at both head speeds.

A. It is possible to change the balance of the responsivity between low and high head speeds by offsetting the throttle linkage to introduce some 'exponential' into the system. If, for example, you find that a lower RevLock responsivity setting is needed at low head speeds than at high then you should offset the throttle linkage so that the barrel moves more slowly near the throttle closed position than it does near the fully open position. From our experience It is unlikely that you will want to operate with the linkage significantly offset the other way (i.e. with rapid barrel movement near the idle position) See diagram

Q. I want to have a convenient way of fine-tuning the RPM in flight. How can I do this?

A. If your transmitter has, say, a rotary control channel spare then you should mix this channel into the Governor's Remote channel. A 5% mix will give you a fine adjustment over the RPM with the full rotation of the control covering about 400 engine RPM (typically 50 rotor head RPM). A bigger mix percentage will cover a correspondingly wider RPM range. When setting this up check that the Mode LED on the governor stays on solidly over the full range of the rotary control. If at one end of the rotary control range the mode LED starts flashing then the governor will disengage at this point because the Remote channel signal has entered the dead-band between ModeA and ModeB. Unless you specifically want to use this as a way of disengaging the governor reduce the mix percentage until the Mode LED stays on solidly for the full adjustment range.

Q. I have recently changed my throttle servo. Having adjusted the throttle ATVs to suit I went through the Basic set-up procedure. However I now find that the governor will not engage. What's wrong?

A. To ensure that the RPM range setting is not overlooked, and to avoid first time users accidentally running RevLock with an inappropriately high RPM range selected, RevLock always defaults the Range values to zero whenever the basic set-up procedure is entered. In the interests of safety we hope users will accept the inconvenience that having to restore RPM range values under these circumstances causes. Note that since RPM offset values are set either by the RevLock's ADJUST control (manual mode) or by the transmitter Remote channel ATV values these are not affected by going through the basic set-up procedure.

Q. I notice that even when my helicopter is in a stationary hover the throttle servo arm is continually moving. What is wrong?

A. Probably nothing! The power output of a glow motor is subject to continuous slight fluctuations. RevLock is seeing the small changes in RPM that these cause and adjusting the throttle position to compensate. These servo movements generally increase as the mixture is richened so if you think the amount of servo movement is excessive you should try slightly leaning the mixture. Some people worry that this movement increases the throttle barrel wear however the wear of the throttle barrel is dominated by small vibration induced movements of the barrel. The servo movements will not significantly increase this.

Q. When I fit the magnet to the fan should I also fit a counter weight?

A. Although we make and sell counter weights for RevLock we don't often use them in-house and here's why. The weight added to the fan by fitting the magnet is about 150mg. The imbalance this causes is typically less than 5% of the out-of-balance of the single cylinder engine it's attached to so its effect will be slight. In fact most engines are less than optimally balanced anyway. There is not enough room in the crankcase unless a high density tungsten balance weight is employed which is unusual. If you bolt the fan on so that with the piston at top dead centre the magnet is furthest from the cylinder head the magnet will slightly increase the counter weight effect and may even improve the overall balance. If it's not possible to bolt up the fan like this or the fan is already drilled for a counterweight then its probably right to fit one.

Q. I have a glow powered heli and because of a previous governor installation the fan has two magnets already fitted. Can I leave these in place?

A. You will need to remove one of the magnets. RevLock will work with either the north or the south pole facing the sensor so it does not matter which magnet you remove. Stubborn magnets that have been glued in securely can usually be easily removed with the assistance of heat to soften the glue

Q. I am changing my previous governor for a RevLock. Can I use the sensor from my previous governor with RevLock?

A. No. Because of the unique way RevLock's sensor is arranged RevLock will not accept the signal from other types of sensor.

Q. My RevLock engages correctly in normal flight mode but I can not get it to fully engage in idle-up flight mode. I have set-up the rpm selection very carefully, but the throttle arm slowly goes to full power and stays at this position.

A. It is likely that your engine does not have enough power to reach the target speed and allow rev-lock to fully engage. This could be caused by the target speed being too high for the available engine power or the fuel mixture being too rich and causing a loss of power. Use the governor disable function to optimise the fuel mixture and if the problem persists, reduce the target speed to a level that the engine can sustain.

Q. My RevLock engages OK, but will not disengage at the end of the flight.

A. RevLock disengages once the throttle is brought below a point 15% above the normal idle position as programmed into the unit at stage 1 of the basic set-up procedure. It is possible that you have used too low a throttle position during the RevLock basic set-up. You should establish where your normal idle position is and re-do the basic set-up routine making sure that the throttle is at this idle position for stage 1 of the basic set-up. (Remember that after the basic set-up you will need to restore the RPM Ranges to the desired values)

Q. My RevLock works very well and the response from hover to full climb is excellent, but I can not eliminate an overspeed in long vertical descents.

A. This has two possible causes: -

Idle point is too high
RevLock uses the idle and full throttle position it has been given during basic set-up to determine the lowest usable throttle position for governor operation. A high tick-over position will mean a high minimum throttle point when governing. Check that you have not 'taught' RevLock an excessively high idle position as this will mean that RevLock may not be able to shut the throttle far enough to prevent overspeed in very low load situations. If needed re-do the Basic set-up with a revised (lower) idle position. (Remember that after the basic set-up you will need to restore the RPM Ranges to the desired values)

Mixture too lean
The very good throttle response indicates that the engine mixture is certainly not too rich and in fact it may be slightly too lean (not enough fuel). Refer to the engine manufacturers operating instructions and richen the slow running mixture slightly until a good compromise of response and reduced overspeed has been achieved. With some carburettors you may need a slight richening of both slow running and main mixture adjustments to obtain the desired results.

Q. I would like to run a very low head speed for slow 3-D aerobatics, but the RevLock unit hunts in dives.

A. There is a natural limit to any engine governing systems ability to provide smooth operation at very low rotor speeds. The limit is normally dictated by the cleanliness of the engine response and the overall set-up of engine, exhaust, blades, model weight etc. Firstly adjust the servo as highlighted in the earlier diagram to obtain finer control at low throttle openings and then find the lowest rotor speed you can run without problems. From here, slowly fine tune the engine and RevLock responsivity until you can lower the rotor speed further. In some cases, careful adjustments may allow the desired results, whilst other cases may dictate a compromise.

Q. I would like to upgrade from my standard non-digital throttle servo and money is no object. What is the best servo to buy?

A. RevLock senses changes in engine rpm so efficiently, that you are unlikely to see any distinct advantage from high speed / high frame-rate / high cost servos. The use of any good quality digital servo with an operating speed below 0.20 for 60 degrees will allow for a very well optimised arrangement.

Q. I have heard that it is important that my throttle is as least as fast as the collective servo. Is this true?

A. While this is a good principle the choice of servos is complicated by the very different loads the two servos carry. In the case of the throttle servo it drives a very light load with little friction and therefore operates at very close to its quoted (no-load) speed. The collective servo however is perhaps the most heavily loaded servo in the helicopter and as such may be moving very much slower than its rated speed. Remember that a 0.1s/60 deg servo running at half its rated torque will actually only be moving at about 0.2s/60 deg. In short, a 0.2s/60 deg throttle servo may well match a 0.1s/60 deg collective servo for speed under actual operating conditions.

Q. How is my use of RevLock influenced by the exhaust system on the engine?

A. Tuned exhaust systems can have a very marked influence on the power output and throttling characteristics of the engine. By tightly controlling the engine rpm RevLock can help you to exploit the performance of very peaky tuned pipes. However this requires that you know the optimum operating speed for the engine/pipe combination you have. We suggest that you set RevLock to maintain the rpm at or just above the maximum power rpm for the engine and pipe. Often the throttle response can be quite poor below the peak power rpm and it is not advisable to try to govern the engine in this region.

If a two-speed set-up is required we recommend the use of a muffler which will generally provide good throttle response over a wide range of speeds. Some pipes may allow adequate throttling at speeds far below the resonance but some experimentation may be required to find what speeds can be used.

Q. What determines the optimum RevLock Responsivity setting for a given model?

A. There are many aspects that influence the optimum RevLock Responsivity setting for a model. The following factors tend to reduce the optimum responsivity setting: -

1) Increased engine power.
2) Lighter main blades.
3) Higher gear reduction ratio.
4) Lower drag blades.
5) Lower target rpm.
6) Longer throttle servo arm (with correspondingly reduced throttle channel ATVs)
7) Poor throttle response.

As you can see, many of these factors are positive or neutral attributes of the model and only one - poor throttle response - is a negative factor. So you should not take a low optimum responsivity setting as an indication of a problem with the model. Only where a low responsivity setting is accompanied by poor rpm control should you look for the cause of the poor throttle response.

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Getting the most from RevLock 20 & 30

RevLock 20 software

RevLock 30 software

In most cases, where the helicopter is well set up, the responsivity is all that will need to be adjusted (to avoid hunting at light loads). This guide is to help you optimise the governor's perfomance using the PC interface. Internal (PC access only) parameters are Integral Gain and Minimum Control Point.

Flight test: Engage the governor at the desired head speed (if you have set multiple head speeds, make the test for each speed, and adjust the parameter only for the relevant mode). With RevLock 30, the collective management should be inhibited for these first tests by setting the collective pull-off limit to zero and with the collective pitch range set to that which you would us with a conventional governo. Fly a series of full collective climbs followed by sustained steep descents of about 4 to 5 seconds. Fly the tests at a constant distance from you if possible, so as to be able to judge engine speed by ear without Doppler effects.

Using the table: Where there are multiple problems (eg hunting and underspeed), rectify them in the order they appear in the table (hunting first). Also check the possible causes in the order shown in the table (eg idle mixture before Minimum Control Point)

Note: If you need to alter the maximum collective pitch, then you may also need to alter the negative collective pitch. Ideally you could do this by repeating the flight tests inverted, but alternatively make an equal change.

Responsivity too high OR
Integral Gain too high

Idle mixture too lean
--------------------------------
Minimum Control Point too high

Lean idle mixture.
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Increase MCP by 5%

Main needle mixture too rich
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Max. collective pitch too high

Max. collective pitch too low

If responsivity below half then increase. Otherwise increase IG by 10%.
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If servo slower than 0.15s/60 deg., replace with faster servo

For RevLock 30:
Additional flight tests to assess Collective Management

Having performed the above tests with the Collective pull-off range set to zero, the same pattern of test flights should be flown with the Collctive pull-off range set to 25% and the Collective range increased by about 15% from that used with a conventional governor.

Engine overspeeds throughout sustained climb
(Collective Management active)

Advanced technical advice for RevLock 20 & 30

Download this advice as a pdf document

These instructions are intended primarily for those wishing to use RL20 for a non-standard application (e.g. gas turbine powered helicopters) but may be of interest to the contest pilot who wishes to establish the optimum performance from 'first principles'.

To avoid repeating the work the procedures outlined here should only be undertaken once the engine has been fully run-in and the mixture etc. has been set to provide a clean throttle response with minimal achievable lag both for increasing and decreasing power.

Start with the default settings but with the Integral Gain reduced to zero.

1. Test fly in a series of sustained climbs and descents and find the highest responsivity at which the engine does not hunt. Pay special attention to the light load situation in the descents. Note that with no integral gain set there will be some speed variation with load.

2. Re-test using acceleration gains above and below the default value (say 150% and 70%). Select the acceleration gain that allows the highest hunt-free responsivity to be used. The degree of fine-tuning you apply to this stage is a matter of personal preference.

3. Now set the integral gain to 40% and re-test. To avoid hunting a very small reduction in the responsivity relative to the no integral term case may be needed. In exceptional circumstances a large loss of responsivity may occur at 40% Integral Gain in which case an even lower value may need to be adopted.

4. At this stage the minimum control point can be set. Try descending the model steeply for several seconds with the governor engaged (e.g. in idle up). Set the minimum control point to the highest value that does not cause the engine to over speed in the descents. Where a multi speed setup is being used do this test at the lowest required headspeed.

5. Now the correct level of integral gain can be established. Fly with successively higher integral gain values, say 50%, 75%, 100%, and 125%. If little or no reduction in responsivity is needed to prevent hunting try increasing the integral gain further. If however a large reduction in responsivity is needed the integral gain is now too high and should be reduced again. As with the acceleration gain setting the degree of fine tuning you apply to this adjustment is a matter of personal preference.

The following adjustments of acceleration limit and acceleration threshold have only very slight effects in normal operation and the default values can be used in the majority of cases. However the following procedures are given for completeness.

Acceleration Limit
To find the best acceleration limit try a climb-out with the collective pitch just a little too high for the engine to maintain speed. Listen to the recovery of the headspeed at the top of the climb and reduce the acceleration limit to quicken recovery to normal engine speed. Don't reduce the acceleration limit so far that it starts to introduce hunting in light load situations.

Acceleration threshold
This reduces small amplitude servo activity that occurs if the engine does not run very consistently causing the speed to fluctuate a small amount from stroke to stroke. These movements can usually be reduced to low levels by the correct choice of plug and fuel together with correct mixture settings. In situations where a tuned exhaust is being used it may be necessary to reduce the compression ratio by increasing the shimming under the cylinder head of the engine. However, where the amount of servo activity remains high regardless of engine tuning an increase in the acceleration deadband can be used at some cost to the tightness of the rpm control to reduce the wear on the servo.

Sub-responsivities
The internal sub-responsivity values allow independent responsivity adjustment for each mode. In remote operation the sub-responsivities for Modes A and B act in conjunction with the master responsivity controlled by the 'Adjust' pot. The overall responsivity of Mode A, for example, depends both on the pot position and the internal Mode A sub-responsivity. If, for example you find that the engine tends, at a given 'adjust' position, to hunt in Mode A but not in Mode B then the internal responsivity of Mode A can be reduced to correct this until the onset of hunting occurs at the same adjust position for both modes. In general, where a tuned exhaust is employed, higher RPMs are more easily stabilised and can sustain higher responsivity than lower RPM settings.

Note that in manual operation The 'Adjust' pot is used for rpm setting so the internal Manual Mode responsivity value is the only way of adjusting the overall responsivity.

Full-Throttle throw limiter operation
By default the unit has this set to "all the time" and prevents the throttle servo being driven beyond the programmed full throttle point even when cyclic to throttle mixing is used on a transmitter that does not prevent overtravel of the throttle channel. Where specialist applications require it the "only while governor active" option turns off the limiter function when the governor is inactive.

Setting a mode to operate as an RPM limiter (RL20 only)
If you want RevLock to operate simply as an RPM limiter this is done by selecting the "RPM limiter only" option under the "RPM control action" heading for the mode or modes required.

Note that the integral term is not used for limiter operation. When using one of the modes for RPM limiter action you should adjust the proportional term gain to set the sharpness of the limiter action. Generally the proportional term gain will need to be increased from the default value for governor action. A proportional gain of 130 is a reasonable starting point and the responsivity should be adjusted so that under light load conditions (where the limiter will be active) the RPM are steady. An excess of responsivity will give rise to fairly rapid fluctuations in the engine RPM.

RevLock 30 only:

Stick gain
This parameter sets the degree to which the governor makes use of the incoming throttle signal to assist in the control of the throttle. There are a two main considerations when setting this parameter:-
The higher the governor responsivity being used the lower the Stick gain should be set.
In the more violent 3D type of flying the incoming throttle signal is often not a good indicator of likely load and the governor becomes more accurate when lower Stick gain values are used.
Where you are using a crisp throttling engine (and consequently a high governor responsivity) and where you are doing hard 3D manoeuvres consider turning the Stick gain to zero.

RL30 Collective management
Collective management is a technique to allow a greater collective pitch range (or longer or broader chord blades) to be used without the pilot having to consciously limit the amount of collective used in order to prevent excessive loss of engine RPM in certain flight situations. The maximum collective pitch that can be sustained depends on the flight situation. In straight, fast forward flight for example higher collective pitch can be employed than in high g manoeuvres. Indeed maximum forward speed and maximum climb speeds are usually obtained by increasing the collective pitch to the point that the engine, even at full throttle is loaded to a point towards the bottom of its power band. Although this causes slightly less power to be produced the reduced blade speed causes less power to be expended overcoming the drag of the blades leaving a greater proportion to propel the helicopter forwards or upwards. The low g-loading on the blades in these situations mean that the loss of maximum lift capability is not significant. Neither is the slight reduction cyclic authority noticed. In aerobatic manoeuvres the maintenance of head speed is more important as reduced headspeed leads to a reduction in available thrust for high g as well as a reduction in the speed and crispness of the cyclic response. It is important to realise that the maximum thrust of the rotor falls off very rapidly with falling headspeed so higher g values are maintained by sacrificing small amounts of pitch in order to keep the speed up. It is this trade-off that RL30 manages for the pilot.

By relying on the inertia of the blades it is possible to make good momentary use of very high collective pitch angles. However, There is usually not enough power available to sustain these in high g situations beyond a fraction of a second without significant loss of headspeed.

RL30, when engaged, controls the throttle to ensure the engine RPM are maintained within a tight tolerance of the target RPM. However, once the throttle has been opened to the maximum no further power increase is possible and it is then only possible to manage the RPM by unloading the engine in a controlled manner to prevent the RPM dropping outside the power band of the engine. For each of its modes RL30 has 3 internal parameters which set how the unit acts on the collective during periods of reduced RPM. The following diagram shows how these parameters control the way RL30 reduces the maximum collective pitch when the RPM drop below the target value.

Collective pull-off gain
The higher the value of this gain the faster the maximum collective pitch will be reduced as the RPM falls and the faster the maximum collective pitch will be restored as the RPM recover towards the target value.

Collective pull-off limit
This sets the degree to which the collective pitch can be reduced. The default value of 25% means that if the maximum collective pitch is set to 12 degrees then RL30 will be allowed to reduce this by up to 25% or 3 degrees leaving at least 9 degrees of collective pitch even with large RPM loss. Note that during autorotations RevLock is disengaged and does not modify the collective pitch in any way.

Pull-off dead band
This parameter allows for a small RPM loss before any reduction of collective is applied. This allows for the brief use of the maximum collective pitch in manoeuvres such as tick-tocks where the inertia of the blades can be relied on to provide the extra energy needed during very short high g situations. The value displayed in the PC interface is the percentage of the target RPM by which the engine speed can fall before any collective reduction occurs.

Notes on adjusting the collective management parameters of RL30.
The default setup of the RL30 collective management system is applicable for the majority of models: we would recommend adjusting them only after significant flight testing has suggested an improvement is possible.

Climb speed and forward flight speed.
If the engine power output is high and the available collective pitch range is somewhat restricted so that it has not been possible to significantly increase the collective pitch when installing RL30 it may be that the collective management adversely affects these areas of performance. In these situations consider if it is possible to fit longer main blades without danger of a main-tail blade clash. Failing this a change of gear ratio to allow slightly higher headspeeds may also be of benefit. Failing all these options you may wish to modify the Collective management response of RL30 by reducing the collective pull-off range and/or reducing the collective pull-off gain.

Sustained high g manoeuvres
In sustained high g manoeuvres such as pie dishes RL30 should, where needed back off the collective in order to keep the engine speed in the power band. If the loss of head speed is too great in these situations then try slightly increasing the collective pull-off gain. If you find that there is something of a compromise between the ideal setup for climb and fast flight and high g situations consider the possibility of using RL30 in, say mode A for aerobatics and Mode B for fast forward flight and using different Collective management setups in each mode. This should not be needed so long as sufficient collective pitch range is available.

Transient high g manoeuvres.
In short-term high g situations such as tick tocks collective pitch reductions can usefully be delayed to allow extra thrust from the rotor disk to be used while absorbing inertia from the rotor disk. If you find that the headspeed is excessively low out of these 'punched' high g manoeuvres then try reducing the pull-off deadband. Generally, large models with heavy blades will accept larger value for the pull-off deadband than a small model with light blades.

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