|Breathe On The Medevac!|
The main purpose of this guide is to try and explain how all these parts are held together so that you can have some confidence in pulling them to bits. Before and after pictures are included so that you have a visual reference as a backup. I took them as I pulled it to bits and I certainly found myself having to refer to them when trying to put it back together again.This guide is intended for new flyers with no experience. I have not got any experience really so I am sure many readers will have better ways of doing things.
The aerial lead can be a real pain when working on the model, loop it up and secure with a rubber band and you will find it doesn’t get tangled around everything as you work.The guide is offered in order of the most common things your going to be doing. I won’t bother repeating what is already in the user manual.
You don’t have to remove the fitting from the rotor shaft. To remove the blades just take out the two screws as shown in Fig. 1. You then prize the lugs outwards and the blades come apart and then pull away from their fixing points on the rotor hub. Reverse the procedure to re-fit the new ones and wipe away a tear as you remember the £6 they cost you! (See Fig. 1 above).
Re-sticking the 4 on 1 receiver box
Even a badly smashed canopy can be repaired with sellotape. It may not look pretty however whilst your learning and still crashing you may prefer to use the old one until your skills improve. One tip I can offer is that you do not need to use the small screw. The canopy will actually just push on and remain in place during flight. The advantage is that if you crash it pops off and thus may avoid damage.
When it’s free, you can pull the undercarriage forwards to remove it from the rest of the model. Don’t pull it by the Canopy as you could break the plastic around the small screw. You may find it easier to twist it slightly as you pull it past the wires as that seems to help get the wires out better.
You now need to peel off the old fixing pad from the bottom of the receiver unit and fit a new one. When sticking it back see how you will have to off-set it a little to allow you to get the wires back into the canopy.
You will have to unwrap the aerial lead. The lead travels through a small clear plastic tube that can just be unclipped. (See Fig. 6 below).
Replacing the Inner Shaft
Next prize off the inner shaft gear. It’s a tight fit but it does just pull off. Note the hole in the drive cog shaft. When re-assembling, make sure one of the retaining screws locates in this lug and that it is properly aligned with the notch in the inner shaft. This makes sure that when tightened, the collar turns the inner shaft and does not just rotate. If your rotors don’t turn then this collar, or the one on the outer shaft have probably come loose.
Now you can pull out the inner shaft. (See Fig. 8 above). As you do you may see the BB collar come out of the BB holder. This can be slid off the inner shaft. You can now reverse the procedure if you’re fitting a new inner-shaft. Ensure the drive cog is properly engaged with the motor pinion and that the inner shaft is not protruding into the area where the battery fits otherwise you will find it snags on the battery once re-assembled.(See Fig. 9 below).
Replacing the Swashplate
If you fit the replacement alloy swashplate you may find that it’s quite hard to get it to slide over the main shaft. I had to put some lubricant (green slime) on it first and then brute force pushed it on. Once it’s on it will slide on and off again easily like the old one. Just be careful to support the model properly when your applying the force otherwise you could bend the shaft. (See Fig. 11 above).
The new swashplate fits both the Twister and the Medevac, because of the force needed to fit it I rang the model shop just to make sure I didn’t need to remove the brass collet. It’s needed so don’t be tempted to remove it. The old one was such a loose fit I thought maybe it was not needed on the Medevac. (See Fig.12 below).
Replacing the Outer Shaft
Take a second to see how they were fitted. There are two slots in them, one longer than the other. Fig 13 actually shows me holding it the wrong way round, the longer slot goes on the bottom when re-assembling.
There is no need to remove the lower blades. Unscrew the 4 retaining screws in the rotor hub. (See Fig. 14 above).These are very small so I recommend you don’t take them all the way out otherwise they are fiddly to get back in. Once they are out enough the rotor hub can be slid up the shaft. The BB holder just pulls off. (See Fig. 15 below).
Note the holes in the outer-shaft, Fig. 16. When re-fitting the rotor head ensure the top retaining screws locate in these holes. Screw these ones in first or your rotor head could be out of position. It is possible to seat the rotor head lower on the shaft without engaging the holes.
The model will still fly but will be out of trim and not be very responsive. Engaging into the holes ensures the swashplate has sufficient room to move.Next, unscrew the retaining collar that holds the outer-shaft in place.
This is where I ran into problems so be careful. The screw, which is smaller than in the inner shaft collar would not budge and I finally managed to damage the head. However, thanks to a loan of a set of jeweller’s pliers from Alan-G a member of the Flying Sites Forum I soon got it out.
Now I found that the outer shaft wouldn’t budge after I removed this screw. Being convinced that nothing else was holding it in place I decided to hit it with the Mark 1 hammer. This certainly dislodged it. Now I don’t know if this is normal, as I might have had a small bend in my outer shaft.
In the picture you can see the replacement outer shaft on the left and the old one on the right. (See Fig. 21 above). The new one is not supplied with a bearing so you have to use the one from the old shaft. I have found this very difficult to get out. I had to destroy the old cog with pliers to be able to hook it out. Re-assembly is of course just a reversal of what you have just done but without the hammer strike.
Replacing the Motors
Note how the wire looms are connected. Viewing the model from the front, both motors plug in on the right side of the 4 in 1 box. The left motor plugs into the top socket, the right into the bottom. Each motor has a black and pink wire; the black wires will be on the inside for both motors, i.e. next to the power lead. (See Fig. 23, 24 & 25).
If buying new motors, make sure you order the right ones. Motor A has its gear pinion flush with the motor and drives the lower rotors. Motor B has its pinion further out so as to engage with the top rotor cog.
First let’s note how the servos are wired up. When viewed from behind the model, the left servo plugs into the top socket on the right side of the 4 – 1 box. The right servo plugs into the socket underneath it. Black wires to the rear of the model. (See Fig. 26 & 27 above).
There are no catches on the plugs to secure them so they just pull out. If you ever replacing the right servo then you will have to completely remove the lower lug. Have a look at the old one for what needs to be done.
Your model probably had its wires secured together by a plastic tie. This cannot be reused and will have to be cut off carefully, I used a pair of scissors. You can see that I used a bit of green garden wire to do the same job.Ok, let’s take out the servos.
There are three screws holding them both in place. One screw is on the right (just visible in between the wires in Fig. 26 and two on the left. The servo wires unplug from the 4 – 1 box, not the servo itself.
When re-fitting the servos, note how the arm that you thread the aerial through engages with the lug on the right servo. The screw passes through the arm, through the servo lug, then screws into the frame. (See Fig. 29, 30 & 31).
If your replacing the rearmost servo you will need to cut a notch out of the bottom servo lug as shown on in Fig. 32. You don’t need to cut it as close to the hole as this one. If you offer it up first you will see how much you need to trim. This is so it sits flush enough to allow you to engage the lower retaining screw. A very sharp Stanley knife will cut this fairly easily.If it’s a new servo, then you will have to ensure the servo arm is properly set. Unscrew the small black screw holding the arm in place and remove the arm.
Now power up your heli as if your going to fly, i.e. with the transmitter on. Ensure all the trim tabs are in their centre positions on the transmitter. Be careful not to move the helicopter until you have the green light on the 4 – 1 box. This will set the servo to its neutral position. Now place the servo arm back in place as it should be when in the neutral position and secure with the screw. (See Fig.33 below).
Adjusting the Trim for a Hands-Off Hover
Looking at the Medevac from the rear you can see the two control rods that link the servos to the swashplate. Fig 34 above).The one on the left controls forwards and backwards flight. When the rod moves down the helicopter moves backwards and when it moves up it flys forwards.The rod on the right controls sideways movement. Down = fly right, up fly left. Remember this is when the helicopter is flying tail in to you.So
Now your model is properly trimmed. You can now use the trim tabs on the transmitter to make small adjustments for each flight as the center of gravity will change with each different battery.
See Fig. 16 and remember you need to screw the top part of the new rotor head into these holes in the main shaft. Before that slide the lower part of the rotor head into place above the swashplate. (See Fig. 35 above).Don’t tighten the lower screws yet.Now put the top part in place and tighten the screws so that they engage in the holes in the shaft. If you tighten them to a point where they just bite, you can feel when they have engaged. Now tighten them in place.
You can see in Fig. 36 (above) that the swashplate is sitting slightly above the collar that retains the outer shaft in place. This is important.Now turn the lower part of the rotor head so that the bars are 90 degrees to the rotor blade arms. It probably helps to attach the links at this point and then finally tighten the two retaining screws.
Fitting the Heatsink
There are four screws holding the motors in place. I did not need to remove the wires from the 4 – 1 box. Take care not to apply too much pressure to any of the solder joints. Once both motors are out you can clip the heatsink into place. The larger end goes in front of the motors next to the 4 – 1 box. It just clips around one motor and then you push the other motor into it. (See Fig. 27 & 38 above).
You can see how high it sits from the pictures. Re-locate the motors in position and apply some downwards pressure to ensure your screws can bite into them. Hey presto – heatsink installed. (See Fig. 39 & 40 below).
Curing Constant Yaw To The Right
Your going to make a sequence of small adjustments and then very short test flights to see if it’s cured. Make sure you do this using a well-charged battery.
Now, you will have noticed the screw marked GAIN. When adjusting your helicopter, don’t change more than one thing at a time before undertaking another short test hover to assess the change in behaviour.
The GAIN screw controls how much your gyro controls the tail as you fly. The more you turn the GAIN screw clockwise, the more the tail is controlled by the gyro. This leads to a more stable flight.
If the GAIN screw is turned anti-clockwise, then you will have to control the tail more by using the left stick. Whilst your learning, having a high (or maximum) GAIN setting is best. However, when you have become proficient, you can turn the GAIN down, or even completely off and you will find that the Medevac becomes much more responsive and agile. For normal flight, a good setting is to turn it to maximum, then turn it back about a quarter turn.
That’s all for now folks. Hope this has been of some use.