Lama V3 Modification for Spektrum 2.4GHz
March 2009
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Recently I noticed that at various times I was starting to experience radio issues with the Lama V3, particularly where a number of other 35MHz users were around.
I put this down too poor selectivity of the receiver, either by poor design, or a fault. Either way I wanted to upgrade to 2.4GHz. Having experienced perfect service from my Spektrum DX6i with my Blade 400, I wanted to investigate how practical it would be to "hack" the Esky Lama to support Spektrum's 2.4GHz DSM2. |
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Sadly you cannot just bind your DX6i to an Esky 4-in-1, because the actual protocol used by Spektrum isn't compatible with the Esky 4-in-1. There are a number of possible solutions to this issue. Probably the most simple solution is to transplant an EFlite 4-in-1, which has a DSM2 receiver fitted. However with a AR6100 available, and a potentially faulty receiver embedded in an Esky 4-in-1, I opted to investigate interfacing the two.
Disassembling the 4-in-1
The Esky 4in1 lives in a lightweight plastic housing, and consists of two circuit boards. The first is a four channel receiver driving the two servos for aileron and elevator, and the remaining channels connect to the second circuit board for throttle and rudder.
The second circuit board is a mixer, gyro, and speed controller. It takes the throttle and rudder signals from the receiver and mixes the two to drive the contra-rotating motors.
Thankfully the two circuit boards can be separated quite easily, removing the receiver, and revealing the connections to the mixer/gyro/speed controller.
[Photo 1 - 4-in-1 initial disassembly]
[Photo 2 - The connections to the mixer/gyro/speed controller board]
Connecting the AR6100
The AR6100 at just over an inch long (30mm) is a nice fit, however in order to connect the 6100 to the Esky mixer/gyro/speed controller, we need to modify a couple of Futaba extention leads. The first modification is to remove the "sheath" from the male end of the extension lead. In some cases the sheath can be removed by inserting a small flat bladed screwdriver between the sheath and the plug, and with a gentle twist the sheath can be removed. In other cases the modification may require more extreme action. A second modification is also required to shorten the leads to around 1" (25mm).
[Photo 3 - Modifying the extension leads]
[Photo 4 - The AR6100 connected to the mixer/gyro/speed controller]
[Photo 5 - Mounted in the Lama]
Explanation of Programming The DX6i for the Lama
Under normal conditions the mixer/gyro would be connected to the throttle and the rudder on the receiver, to control the contra-rotating motors. However there appears to be a possible timing issue between the throttle and rudder channels of the AR6100 and the mixer/gyro board of the 4-in-1. There is a workaround, and it's a little bit complicated to understand, but actually quite easy to put into operation.
The solution to the initial timing issue is to use a different channel, and to this end we can mix 100% of the rudder to the gear channel, and use the gear channel for rudder control to get round the issue.
However this gives rise to another problem. Although we can mix rudder to the gear channel, the gear channel isn't fully proportional, as it's driven by the gear channel switch (front - top left switch on the tx), and the switch cannot be disabled (or rather inhibited). In fact you can visually see this from the DX6i's monitor function.
If you setup rudder to gear mixing, view the behaviour of the gear channel on the monitor screen. Here you can see that the rudder is indeed mixed to the gear channel, however the gear channel switch sets a +/-60% bias on the channel. So this means that there's a huge bias for the Lama to rotate right (or left) depending upon the position of the gear channel switch.
There is just enough adjustment if you use the trim, and sub-trim on the DX6i, and the proportional pot on the Esky mixer, to equal out the bias, but it's a very ineligent solution to the problem. Also should you flick the gear switch during flight, you'll probably lose control of the Lama all together! A better solution would be to use the second mix on the transmitter to mix -100% of the gear channel back to itself. In effect cancelling out the effect of the gear switch.
If you don't understand mixing, then all this may not make a whole lot of sense. In reality don't worry, just follow the instructions below...
DX6i Configuration
Select a free memory on the DX6i, and bind the AR6100 to the DX6i as usual
Configure Model Type as ACRO
Configure Mix1, and mix -100% of the gear channel to itself, as below, to cancel out the effect of the gear switch.
MIX 1
GEAR > GEAR ACT
RATE D -100% U -100%
SW ON TRIM INH
Using Mix2, mix the rudder to the gear channel at 100%.
MIX 2
RUDD > GEAR ACT
RATE D +100% U +100%
SW ON TRIM ACT
Note here that we're setting trim to ACT, to ensure that changes to the rudder trim follow through to the gear channel.
With the Lama safely secured, try gently increasing the throttle stick, and note which rotor blades start rotating first. Disconnect the battery from the Lama and using a small flat-blade screwdriver adjust the Proportional pot on the mixer anti-clockwise/clockwise. Connect the battery and re-test.
[Photo 6 - Adjusting the Proportional pot]
With both pairs of blades starting to rotate at the same throttle setting, try increasing the throttle further and check for any notable tail-wag. If tail-way is seen then reduce the gain of the gyro, followed by disconnecting and reconnecting the battery. Also don't forget to check that the aileron and elevator servos are configured correctly.
Try a couple of hops and check that the Lama behaves. If all looks in order, take a test flight. To minimise trim and sub-trim on the DX6i, you can use the proportional pot to assist with getting the Lama to fly straight, and you may well need a tweak of the gyro gain to help with stability.
Disassembling the 4-in-1
The Esky 4in1 lives in a lightweight plastic housing, and consists of two circuit boards. The first is a four channel receiver driving the two servos for aileron and elevator, and the remaining channels connect to the second circuit board for throttle and rudder.
The second circuit board is a mixer, gyro, and speed controller. It takes the throttle and rudder signals from the receiver and mixes the two to drive the contra-rotating motors.
Thankfully the two circuit boards can be separated quite easily, removing the receiver, and revealing the connections to the mixer/gyro/speed controller.
[Photo 1 - 4-in-1 initial disassembly]
[Photo 2 - The connections to the mixer/gyro/speed controller board]
Connecting the AR6100
The AR6100 at just over an inch long (30mm) is a nice fit, however in order to connect the 6100 to the Esky mixer/gyro/speed controller, we need to modify a couple of Futaba extention leads. The first modification is to remove the "sheath" from the male end of the extension lead. In some cases the sheath can be removed by inserting a small flat bladed screwdriver between the sheath and the plug, and with a gentle twist the sheath can be removed. In other cases the modification may require more extreme action. A second modification is also required to shorten the leads to around 1" (25mm).
[Photo 3 - Modifying the extension leads]
[Photo 4 - The AR6100 connected to the mixer/gyro/speed controller]
[Photo 5 - Mounted in the Lama]
Explanation of Programming The DX6i for the Lama
Under normal conditions the mixer/gyro would be connected to the throttle and the rudder on the receiver, to control the contra-rotating motors. However there appears to be a possible timing issue between the throttle and rudder channels of the AR6100 and the mixer/gyro board of the 4-in-1. There is a workaround, and it's a little bit complicated to understand, but actually quite easy to put into operation.
The solution to the initial timing issue is to use a different channel, and to this end we can mix 100% of the rudder to the gear channel, and use the gear channel for rudder control to get round the issue.
However this gives rise to another problem. Although we can mix rudder to the gear channel, the gear channel isn't fully proportional, as it's driven by the gear channel switch (front - top left switch on the tx), and the switch cannot be disabled (or rather inhibited). In fact you can visually see this from the DX6i's monitor function.
If you setup rudder to gear mixing, view the behaviour of the gear channel on the monitor screen. Here you can see that the rudder is indeed mixed to the gear channel, however the gear channel switch sets a +/-60% bias on the channel. So this means that there's a huge bias for the Lama to rotate right (or left) depending upon the position of the gear channel switch.
There is just enough adjustment if you use the trim, and sub-trim on the DX6i, and the proportional pot on the Esky mixer, to equal out the bias, but it's a very ineligent solution to the problem. Also should you flick the gear switch during flight, you'll probably lose control of the Lama all together! A better solution would be to use the second mix on the transmitter to mix -100% of the gear channel back to itself. In effect cancelling out the effect of the gear switch.
If you don't understand mixing, then all this may not make a whole lot of sense. In reality don't worry, just follow the instructions below...
DX6i Configuration
Select a free memory on the DX6i, and bind the AR6100 to the DX6i as usual
Configure Model Type as ACRO
Configure Mix1, and mix -100% of the gear channel to itself, as below, to cancel out the effect of the gear switch.
MIX 1
GEAR > GEAR ACT
RATE D -100% U -100%
SW ON TRIM INH
Using Mix2, mix the rudder to the gear channel at 100%.
MIX 2
RUDD > GEAR ACT
RATE D +100% U +100%
SW ON TRIM ACT
Note here that we're setting trim to ACT, to ensure that changes to the rudder trim follow through to the gear channel.
With the Lama safely secured, try gently increasing the throttle stick, and note which rotor blades start rotating first. Disconnect the battery from the Lama and using a small flat-blade screwdriver adjust the Proportional pot on the mixer anti-clockwise/clockwise. Connect the battery and re-test.
[Photo 6 - Adjusting the Proportional pot]
With both pairs of blades starting to rotate at the same throttle setting, try increasing the throttle further and check for any notable tail-wag. If tail-way is seen then reduce the gain of the gyro, followed by disconnecting and reconnecting the battery. Also don't forget to check that the aileron and elevator servos are configured correctly.
Try a couple of hops and check that the Lama behaves. If all looks in order, take a test flight. To minimise trim and sub-trim on the DX6i, you can use the proportional pot to assist with getting the Lama to fly straight, and you may well need a tweak of the gyro gain to help with stability.
