Week Seven – RC Plane Servo Setup
Having completed the covering I have to say, I am very pleased with the final appearance. I decided to pick out the main join lines between the Red and White with a black trim line and I think this works well. Here is a photo of the finished colour scheme standing proudly on its extended retracts.
The next job is to install the rest of the radio control gear, motor drive components and then carry out a complete rc plane servo setup. I intend to drive the motor via a 60 amp ESC with separate UBEC circuit and a four cell Lipo of around 3700 to 4000 maH.
Installing The Radio Control Receiver
I use Spektrum DX6i radio control gear and I have experimented using ‘Orange’ 6 channel receivers both with and without satellites. I have found these to be totally reliable and at a considerable cost saving over the original Spektrum receivers.
I am installing one such receiver with satellite in this model. This entails locating the main receiver in a convenient place to accommodate the bunch of servo cables and for ease of access for connecting and disconnecting the servos.
The latest six channel Orange receiver available here does not require a satellite.
There also has to be clearance for the short aerial that protrudes from the back of the receiver. This needs to be as far away from other signal carrying wires as possible.
The satellite receiver also has to be secured on a surface where the aerial is positioned at right angles to the main receiver aerial. Again this needs to be as far away from signal carrying wires as possible.
In order to protect the satellite receiver I wrap it in electrical insulation tape, without obscuring the LED that glows red when fully bound to the transmitter, so that it can then be secured to the chosen location using a spot of CA glue.
Aileron Control Surfaces to Servo Linkages
Being a frugal sort of guy I try to make my own components wherever possible. I know that moulded nylon control horns are relatively cheap but most involve a mounting plate and matching retaining plate that I find rather bulky and an unnecessary embellishment on the aileron surface.
The photo on the right shows the ones I have made for this model. These are cut from a scrap sheet of 1.5mm fibreglass PCB board.
These are let into slots cut into the aileron so that the pushrod connecting holes are directly in line with the hinge centres and secured using slow setting two part epoxy.
The two small holes in the lower stem ensure a good key for the adhesive. Once installed they look quite neat and there are no disruptions to the upper aileron surfaces. The sketch here on the right shows how they are installed into the Aileron.
Note how the linkage holes line up with the hinge point. This is very important.
Installing The ESC and UBEC
This model has a fairly narrow fuselage so fitting both the ESC and Lipo into the space available is quite a challenge. The swept back wing of this model necessitates the balance point being just in front of the point where the wing wheel legs exit the wing surface.
To get the balance point in the right place requires the Lipo battery to be as far back in the compartment as possible. There is just enough space in front of it to fit the ESC and UBEC (Universal Battery Elimination Circuit) right up against the side wall.
I prefer to use ESCs with a remote UBEC. I find that they are more reliable as there is no heat transfer from the ESC to the UBEC circuit. This keeps things more stable with less likelihood of heat induced failure.
Lipo Location & Access
The photo here on the right shows how the Lipo fits in close proximity to the ESC and UBEC and, as mentioned previously, needs to be in the most rearward position possible.
The Lipo is removed by sliding it forward and upward toward the front of the fuselage which in the photo is on the left. A ‘Velcro’ strap will retain it in position.
The forward base of this compartment (see photo above) is removable for access to the nose leg retract installation. Slots will be cut in this base to facilitate the installation of the retaining strap.
Receiver & Servo Wiring
There are six servos in this model for the following controls:
Ailerons – 2
Rudder – 1
Elevator – 1
Retracts – 2
Four of these are located in close proximity to the receiver so it is important for the leads to be organised and kept tidy. I use nylon ‘tie wraps’ to keep them neat.
The two aileron servos are connected through a ‘Y’ lead located within the wing. This then connects to a short extension lead that remains permanently connected to the aileron socket on the receiver. The ‘Y’ lead and the short extension are connected before fixing the wings to the fuselage.
A further ‘Y’ lead is required to connect together the fuselage mounted retract servo for the nose leg and the wing mounted retract servo for the two main legs. this then connects to the ‘Gear’ socket on the receiver. The connection from the receiver to the nose leg servo remain permanently attached whilst the link to the wing servo is disconnected each time the wings are removed.
So far, all testing for servo and control surface movement has been done using my trusty servo checker. The next step is to bind the receiver to the transmitter and check all control throws and make any necessary adjustments. This will then complete the rc plane servo setup necessary before committing her to flight.
Once this is done I will be testing the motor static thrust using different propellers. The total weight of the model with flight battery installed is approximately 5.5lbs (2.5kg). I am aiming for a maximum power to weight ratio of 11owatts for every one pound of model weight.
Using a four cell Lipo means that with an operating voltage of around 14 Volts, I will require a maximum current of 43 Amps. (Current = watts x weight/volts)
110 Watts x 5.5 lbs/14 Volts= 43.2 Amps
Based on this calculation I will be trying various propellers to find one that provides this power and current draw. The motor has a kV (revs per volt) rating of 900 so with a 14 volt input the maximum rpm will be close to 12600. This is quite high so the appropriate propeller will be a fairly small diameter and medium pitch.
Watch this space for the final details next time. If you have missed my previous build blog posts, the first one is here.
I hope you don’t mind me reminding you to visit my main website www.rookiercflyer.com, especially if you are new to the hobby.