Blade mCP X known issues

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There are a number of known issues with the Blade mCP X, most of which are easily fixable. This page seeks to gather the prominent known issues in one place.

Main gear

The main gear is pushfit on the main shaft with a flat on the shaft and D-shaped hole in the gear to prevent it spinning in flight. This design allows the main gear to slip down the shaft in the event of a crash and absorb energy that might normally damage other components.

When the main gear slips down the shaft there is a significant amount of up and down slop in the shaft which results in a significant amount of negative pitch and vibrations in flight.

To check the main gear, apply up-and-down pressure on the main gear to see if the main shaft moves. If so:

  1. Hold the top of the main shaft.
  2. Rotate the main gear until the D-notch is aligned with the flat on the shaft.
  3. Push up on the main gear with two thumbs towards the center of the main gear while applying opposing pressure to the top of the shaft at the head.

Be careful not to break the main gear or landing gear because the gear will sometimes take effort to push into place. An empty pen tube can be used to push the main gear back in place to reduce stress on the gear and the main shaft.

If the gear comes loose in normal flying, you can tighten the fit by coating the end of the shaft in a thin layer of CA or nail polish and leaving it to set before refitting the gear. Do not glue the gear to the shaft—this will transfer the shock and could strip teeth from the main gear or split the main shaft.

Lost top links

Tethering the top links

The links between the swashplate and blade grips can fly off in a crash and are easily lost. There are spares in the box but you could tether them with strong thread, dental floss or fishing line.

Too much negative pitch

Some helicopters have the servo links set too short from the factory giving lots of negative pitch. Swing the blades so the tips are together and adjust the servo links until the blades tips are the same height when collective is at 50%.

New CP helicopter pilots are often confused by the behavior of the throttle. This heli is designed to fly at about 3/4 stick, unlike the mSR which flies at about half stick. Half stick is zero pitch and below half is negative pitch (for flying inverted). If you are not flying inverted, you can change the pitch and throttle curves so you use the whole stick travel but this will ultimately harm your progression when learning inverted flight.

Rear servo pushrod

DIY Rear pushrod
Made from an aileron pushrod

The front servo pushrods have a Z bends that allow a small amount of flex in a crash. The rear pushrod does not and as a result if the swashpate breaks in a crash, it's nearly always at the rear ball. A slight kink or a gentle S-bend in the rear pushrod will allow it to flex in a crash, reducing the shock to the swashplate and the servo.

The first photo shows a rather extreme bend, made from music wire soldered to the threaded end of the stock pushrod and probably has more flexibility that is necessary. The second shows a rear pushrod made from a spare aileron pushrod with 3 extra bends. Care should be taken to ensure the bends in the pushrod do not foul the frame.

Shake in flight

Any slop in the head or linkages can cause the heli to shake rapidly, in much the same way as the tail wags on a normal heli when the gyro gain is too high. Sometimes this is most noticable towards the end of a pack.

  • The main gear may have slipped down - see above.
  • One common cause is a split main shaft, which can be very hard to detect. Remove the head and put the screwdriver down the middle of the shaft/tube to open any crack. Glue it back together with a drop of CA or replace it.
  • Another common cause is slop at the top of the pushrod links. This can be eliminated with a small amount of pressure on the links. Common fixes are a rubber band around all three links (holding them in) or a spare canopy grommet behind the front balls. (the gromments are now standard on the V2 model)
  • Slop where the pushrods connect to the servos can be eliminated with a small drop of CA. This fills the hole around the wire pushrod. It doesn't matter if the pushrod breaks free of the glue, so long as the glue hardens before the rod is moved. Obviously you must be careful not to get glue in the servo.
  • Dirty servo tracks/conductors/"wipers". The tracks need regular maintenance/cleaning - they get dirty, just like slotcar racers. Remove the plastic part of the servo, clean the track on the circuit board with a pencil eraser and finish up with alcohol. Longitudinal shaking = clean elev servo, lateral shaking = clean front two servos. The shaking creeps in slowly making it difficult to diagnose if you don't already know what's happening

watch a how to on youtube:

Lack of tail authority (blowing out)

Collective management

Poor collective management can overpower the tail. The tail should hold reasonably well in a sudden full power climb from a hover but if you change from full positive to full negative pitch too quickly during a flip, the tail can be overwhelmed and blow out. Sometimes this triggers the over-current protection in the 3-in-1, and the heli will pirouette out of control.

Tail boom and motor customizations

  • Horizon is now shipping a redesigned v2 tail propeller (BLH3603), which is slightly larger and significantly improves tail authority.
  • KBDD sells a replacement tail blade which is more durable than the v2 prop and works better than the original propeller. Unfortunately, though more durable, it does not work as well as the v2 blade due to its higher moment of inertia. The range of available colors are excellent for tail visibility, however.
  • The most common improvement is replacing the stock 2mm tail boom with a longer boom to give the tail motor better leverage. An inch longer makes a noticeable improvement. It is necessary to unsolder the tail motor wires to remove them from the tail motor bracket, then the wires can either be wrapped around the boom, or run alongside the boom inside some shrink tube. 140mm of 2mm carbon rod is a popular replacement, as it is stronger than tube. Astroid Designs sells pre-cut booms in 125mm (stock length) and 140mm sizes in both tubes and rods.
  • A 3mm 120 SR tail boom is also an option for those with aftermarket frames.
  • The AeroAce/X-twin prop is slightly larger than the stock tail rotor, and should give more tail power.
  • If your tail can't cope with normal flight, the tail rotor blades can bend in a crash, leaving them with insufficient pitch. Twist a little more pitch into them, or replace the tail rotor to give it more power.

Power issues

When the main motor is working hard, it can draw more power than the stock cell can handle, causing voltage to sag, reducing the power available to the tail motor. Switching to a higher C rated cell (like the Hyperion 250mAh) reduces this problem.


If your tail can't cope with normal flight, this is often due to a (user) error programming the transmitter—it is necessary to set the end points for both positive and negative pitch, and you need to move the collective stick to indicate which limit you are setting (this is fairly obvious on the DX7 but easily missed on the DX6i). The manual states 75%, but some people prefer 70%, sacrificing some power to reduce head load and torque on the tail.


If you have random intermittent tail blowout issues, it can be because the electronics is dying and/or the cables are damaged. In this case, insisting may result in the MOSFET components to burn out on the main board. When this happens, you will smell it and possibly see a white smoke. Then the tail motor will run continuously, even when the helicopter is not bound to any transmitter. It's usually possible to repair the board by replacing the MOSFET's.

If you repair or exchange the whole board, make sure you check the cable and tail motor before you fly again. If there is a short circuit, the MOSFET will burn out again.

See also:

Poor battery performance

The batteries supplied with the V1 model were not ideal, leading to frequenct tail blow-outs after the first minute or two. The V2 batteries are much better and there are many after-market alternatives that work well.

Rare issues

  • There have been some faulty 3-in-1 boards. Horizon Hobby have fixed these at no cost. Symptoms in one case were shut-down on throttle increase.
  • Some issues that looked like faulty boards have turned out to be incorrect Tx programming. Remember that CCPM is not required, set the Tx to '1-servo swashplate'
  • The brass bush in the servo has come loose for one person, resulting in slop and (thanks to the FBL gyro) a rapid shake, similar to tail wag in the cyclic. The brass ring can be repositioned by holding it with some needlenose pliers and spinning the shaft using the gear on the bottom until the the slop is gone.
  • If one of the three power transistor is destroyed(cable short-circuit or blocked rotor under power), it may be replaced by any P-chanel PowerMOSFET similar to the VISHAY SILICONIX SI2315BDS-T1-E3(this one works, proven). If one of the two transistors for the main engine has died, replace both.


  • The motor has strong 'cogging' making it much harder to turn by hand than the mSR and mCX. It also doesn't start turning until about 1/4 to 1/2 throttle. This is normal and not a problem—although it may worry people who are not used to it.
  • The linear servos jitter slightly at rest. This is normal.
  • The FBL system will not return the swashplate to level if the rotors are turning and the heli is on the ground (or otherwise held). This is because the helicopter is not responding as expected to course corrections from the 3-in-1. This is normal. When the motor is stopped, the FBL system will act normally.
  • The manual states that the swashplate will move up and down when the heli is bound in 'computer Tx' mode—this is incorrect.
  • The blade roots prevent the blades folding all the way back. You can carve/sand the blades so that they can fold back fully.

Obsolete issues

These issues have been fixed in later versions of the mCP X.

Thrown blades

Tethering the blade grips and top links

Early mCP X helicopters had issues with the blade grip bearing which could lead to separation of the bearings and ejection of the blades in flight. Some original grips are still flying so it's likely that the problem was due to a specific bad batch of bearings. No problems have been reported since the 'B' blade grips were issued.

Horizon issued a bulletin and modified the design of the blade grips. The new grips and will not leave the head and the heli is still controllable after a bearing failure. Existing owners could claim a new 'B' rotor head for free. These blade grips have a capital 'B' moulded into the top surface (not to be confused with the '1' and '2' which is simply to aid the factory in shipping balanced sets of blades).

A joint recall notice by the United States Consumer Product Safety Commission and Health Canada was issued on May 31, 2011.

  • The screw in the feathering shaft end has been loose in a few (early) cases, leading to some side-to-side slop on the blade grips. Some people haven't noticed this, and the screw has come undone in flight, leading the blades flying off. Ensure this screw is tight and consider a drop of (purple 222) Locktight. (Only the end with the cross-head is a screw, the other end is just sloted so you can hold it still while turning the screw)
  • The bearings in the blade grips have failed in a number of cases. They are 4mm outside diameter x 1.5mm ID x 1.12mm thick. Horizon now recommend the bearings should be fitted with their brass retaining ring on the outside. Both of these issues could result in the blades flying off at high speed and these blades are going fast enough to draw blood if they hit you. Wear eye protection when flying indoors.
  • Some people have tethered their blades (with kite string or fishing line), which should reduce the risk of injury.