Sunday, 2 October 2011

CCPM Mechanical Setup

CCPM Mechanical Setup





A good mechanical setup on the rotor head of a remote control helicopter, can be the difference between a model that almost flies itself, or one that is destined to hit the ground at high speed. OK, so they might be two extremes, but time invested now will be paid back ten fold. By the way, my blog will list the latest radio control helicopter guides and tutorials.

Radio Settings


First things first, start fresh on your transmitter, and select a brand new model channel, or if for some reason you don't have the luxury of multiple model memories, reset to factory defaults. This forces all trims to be reset, including the on stick ones, and sub-trims.

Some important tools for setting up the head on your rc helicopter
Go into your swash mix menu, and set the pitch, elevator and aileron to 50% swash mix. Set your swash type to 120 degree CCPM in the swash menu of the radio set (Yes, this "How to" is written for a 120 degree swash, from the swash up however, there are many similarities, so it will still be useful if you have a 90 degree swash). Lastly, make sure all other mix's are off, such as revo mix. Set all end points to 100% on the servo travel/end point menu.
Whilst setting up the helicopter head, we want linear throttle and pitch curves, so set these up now if this is not so. That is for the 5 stick points, 0%, 25%, 50%, 75% and 100% the throttle and pitch curves should match the stick values, going up linearly from 0% to 100%.

  Radio swash mix menu

Receiver and Servo Connections
Now, lets get everything connected. You may have all ready done this, but ill just skim over the essentials. I find it easier to use a standard receiver pack to power the servos and receiver whilst setting up. This saves having to incorporate the ESC and a LiPo. If you do choose the later option, ensure your motor wires are disconnected whilst working on the remote control helicopter. A good habit to get into, and essential for safety is to turn the transmitter on first, and then the receiver.
The servo towards the back of the swashplate is connected to the elevator channel on the receiver. The two forward servos can be connected to either the pitch or aileron channels on the receiver. Later mixing in the radio will sort out there orientations.

Servo Movement Directions
Now we need to get the servos and the swash moving in the rite direction. A modern RC helicopter CCPM swash is quite a complicated and confusing thing. But take some time and work carefully, and it most certainly isn't rocket science. The two tools we will be using are "servo reverse" and "swash mixing". The thing to remember is servo reversing works on only the servo in question. If you want to reverse multiple servo movements at the same time, you will need swash mixing.

Setup is based on servo horns being precisely aligned
The first thing to check is what happens when you move the control stick forwards on the cyclic. The swash plate should tilt forward. This means the elevator servo horn should rise. If it falls, and the helicopter swashplate tilts backwards, go into the reverse menu, and reverse the elevator channel. We want to do the same now for the left and right movement of the cyclic stick. It should tilt the swashplate left and right. As an example if we give full left cyclic on the remote control helicopter, the left hand servo horn should dip, and the right one rise, thereby tilting the swash to the left. If not, reverse the appropriate channels in the servo reversing menu.
Next, we want to see what happens when we increase the pitch, the whole swash should remain level (roughly, more on that later) and rise uniformly. If not, you will need to go into the swash mix menu, and reverse the value of the pitch entry, so if it is +50% change it to -50%. So to sum up, we need all 3 servo horns rising for up pitch, down for down pitch. Left cyclic should mean the left servo dropping and right rising, the opposite for right cyclic. Forwards elevator means the rear elevator servo will rise, and the forward pitch and aileron servos will fall.

CCPM setup, showing the alignment of the mixer arms on the helicopter
To correct a single servo use servo reversing, if all three are not moving in the correct order it can be corrected with swash mixing. We are now ready to move onto servo arm alignment on our remote control helicopter.

Helicopter Servo Arm Alignment 
Now it is essential to have followed the earlier instructions regarding correct initial radio setup. Make sure you have power to your servos, and the helicopter pitch/throttle is set to 50%, this needs to be as accurate as you can manage. You now need to get those servo horns on at 90 degrees. That is horizontal, or if you prefer, parallel to the ground. Now the grooves on these servo horns are not uniform, different horns, and different orientations will yield better results on your RC helicopters servos. Play around for a bit and get it as close as you possibly can.
Chances are you will have them nearly perfect, but not quite, that's OK, we can use sub-trims on the radio transmitter to correct for this. So head on in to the relevant section on your radio, and play around with the settings for each channel by a few notches until you can judge the arms to be at 90 degrees. A good tip is to line them up against the servo casing and use that to judge the alignment. Make sure to put the ball links on the inside of the servo horn, that is so the linkage will come between the servo horn and frame. Always remember to use loctite on these, as you don't want them coming loose during flight.

RC helicopter Swashplate leveling

Use the flybar cage to align the top seasaw mixer arms
Again, the pitch control should be at 50% for this step. I wont go into to much detail here, many people on many different remote control helicopters use different tools, tips, and techniques. Do whatever you feel is best. I do however recommend a swashplate levelling tool, they can be as cheap as a few pounds/dollars. The idea is, with the pitch at 50%, and all servo horns at 90 degrees, the swash should be perfectly level with the helicopter. If not use your tool, or judgment, and start adjusting the 3 push rods from the servos to the swash by a single turn, and re-measure. It is worth mentioning now always follow the manufactures instructions for the lengths of push rods as an initial starting point, some times they are spot on. Repeat this until the swash is completely level. You also now want to check that at 0% on the throttle/pitch stick on the transmitter the swash doesn't come down to far and hit the washout, also at bottom pitch, you should check the full range on the cyclic, as to make sure the swash doesn't hit the frame. If it does, raise the swash by turning all of the push rod linkages by the same amount, until these interactions are removed.
Now complete the construction of the rest of the head, as per the manufacturers instructions, up to but not including putting the blades on. Before moving on, you want a completely constructed head in order to set up precisely all the components. We will adjust out any irregularities.

Sea saw Mixer Arms
Some people think of this stage as being the hardest, but it is the simplest to be honest. Just take your time, and re-check your work. Essentially, all we are looking for is that the bottom and top sea saw mixer arms are nice and level when the swashplate is level and at 50% stick. To achieve this we need the flybar cage to be locked into position with an appropriate tool, an allen key as per Finless Bob, or judged bye. Arms needs to be straight and level with the bar of the flybar cage. This is achieved by adjusting the linkage rods going from the swashplate to the mixing arms at the top of the heli, lengthen or shorten to achieve the perfect balance.

The flybar paddles should be parallel to the edge of the flybar cage
Unlike the final push rods to the blade grip, these can be different lengths. It is an iterative procedure, where you adjust one set, see how it effects the sea saw arms, then re adjust. Each time getting smaller and smaller in adjustments until they are level. The top arms can be judged by lining them up with the flybar cage. The bottom ones by looking through the head to the arms on the other side, they should be parallel with each other and look at the alignment of the ball links on the mixer arms, repeat this on both sides.
The bottom sea saw arms can be adjusted uniformly by raising or lowering the swashplate linkage rods, applying the same amount of adjustments to them all at the same time, whilst the pitch is still at 50%.
Zero Pitch on Blade Grips
We would now like to achieve zero pitch in the blades at 50% throttle/pitch. This proceeds on the assumption your setup to this point is correct, including the aligned sea saw mixer arms. Put a set of blades on now. You will need to lock the flybar cage in position, check out Finless Bob's hack with an allen key to achieve this, or buy a tool, either way you need to have a steady and fixed flybar cage.

No pitch gauge? Easy, line it up by eye!
At this stage the blades should now have zero pitch, this can be measured with a pitch gauge, or judged by eye. If doing it by eye, and you have flat tops on the blade grips, you can line them up by eye, the flat edges of each blade grip being on the same plane as each other. You will need to take the button head of the top of the head. Another trick, is to take the blades of, and look at the bolt that goes through the blade grips that normally holds the blades on, this should be vertical.
If you have any pitch in the blades, adjust the very top most linkage rods to remove this, and re-measure. These rods should be identical in length, this is very important. So if one blade has more pitch than the other, something has gone wrong with your setup further down the head of the RC helicopter, so you will need to re-check this from the swash to the top mixing arms.

Checking Head Full Pitch Range
To do this put some blades onto the RC helicopter and measure the full pitch range over the full length of travel. Increase or decrease the pitch value on the swash mix. Taking note that the swash doesn't hit any of the other mechanics at the bottom or top of its travel. As we started with a swash mix of 50%, 70% should give roughly around 14 degrees of pitch. This will be a little to lively for a beginner. 60% swash gives about 11 degrees of pitch, which will be a good starting point for a RC helicopter pilot. As a reminder, when adjusting the full range travel on your helicopter, make sure the swash doesn't hit the washout or the frame during its travel. Similar to when we were adjusting our ranges in the sea saw mixer arm setup stage.

Another technique for getting zero pitch in the rotor blades

Flybar Paddles
I did notice when i was first starting out, that there wasn't much information on how the flybar paddles should be setup. Luckily, they are very simple. they should be of equal length from end to end on each side of the flybar cage. The leading edge pointing in the same direction as that of the blade (The paddles and blades should have there leading edger pointing in a clockwise direction by the way). Lastly they need to be flat and level, you can judge this by eye, line the paddle edge up with the top sea saw mixer arm, inside the flybar cage, they should be parallel to each other.

Checking for CCPM Interactions

It is best now to search for any CCPM interactions, this is due to not all servos moving the same amount, or linearly. This can be checked on the swash, but due to the mixing ratios, the paddles are much more sensitive to these interactions, so keep an eye on these while checking, you can use a small bubble level on one of them. Have the paddle perpendicular to the tail boom, and look for elevator interactions, do the same with it parallel to it to look for aileron interactions
When your pitch is at 50%, the helicopter blades should have zero pitch
If you spot any movements, go into end point adjustment section/travel adjustment section of your helicopters radio. So for instance if at full pitch the bubble moves backwards, apply an increase to the forward elevator end point in order to bring the bubble back to level, same goes for aileron interactions. You will still get in between CCPM interactions, but it is not overly important to fix these, getting full, bottom and centre the same is important, on digital servos we can get rid of this with P mixing but it is a task that is very time consuming.

Line the pitch gauge up with the helicopters flybar
The last step, reduce or increase pitch setting at max pitch in swash mix to get 11 degrees positive, if all links are correct at negative we should now have 11 degrees as well. This step is essential to finally check our setup. If more pitch is present in one direction, then something is wrong and we are getting some unwanted interactions, check and redo all of the links.

Cyclic Range
We are almost done now, and you will be able to breath easy. We want to adjust the amount of cyclic pitch available. Ideally we want 6 degrees in each direction, measured using a pitch gauge, the more pitch you have the faster the response of the model helicopter. As a beginner, you would be looking for a little less. As you have to add it to the total pitch of the blades in the first place.

Swashplate leveling tool
So if you have set your blade pitch range to +/- 11 degrees, you will now have a total pitch range of 17 degrees. Way to much for a beginner. As with this amount of pitch, collective management whilst flying will be a big thing. To adjust these ranges, use the radios swash mix, aileron and elevator mix to be precise, reducing the number reduces the throw of the swash, and the same for the opposite direction. You may have to experiment a little with this to get the right balance.
But if you have followed this guide word for word, you should now have a well set up, and ready to fly remote control helicopter. Good luck!


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