Long-term Memory

I got myself a new RC helicopter. It’s an electric one so I can fly indoors.

Here is the partlist and some basic specs:

• Thunder Tiger miniTitan E325
  624mm long, 120mm wide, 210mm heigh, 728mm main rotor diameter, 156mm tail rotor diameter, 750g weight
  manual [local copy]
• Thunder Tiger Ripper OBL Series Helicopter Brushless Motor 29/35-10H (mine came with the miniTitan kit)
  3500rpm/V, 20A continuous, 30A.60s burst, 12 stator windings, 8 permanent magnets on the (outrunner) rotor
• ACE R/C Brushless Motors Speed Control ESC BLC-40 (included in the kit as well)
  40A continuous, optional governor function
• 3x Hitec HS 65 MG (more detailed specs)
  4.8 – 6V input voltage, 60° in 0.14s (4.8V, no load), 1.8kg.cm stall torque
• Futaba S-9257 (more detailed specs)
  digital, 4.8V input voltage, 60° in 0.08s (no load), 2.0kg.cm stall torque
• R319DPS receiver – 35MHz band
  1024PCM receiver, 8 proportional channels, 1 digital channel
• Futabe GY401 Gyro
  Solid state gyroscope with Heading Hold (AVCS)
• FLIGHTPOWER 3s1p 25C 2500mA 11,1V
  Continuous discharge 25C/62.5A, Climbouts 35C/87.5A, Max burst 50C/125.0A
• Flightpower V-balancer
  LiPo balancer for up to 6s packs

The build

Some points to note during the build:

• page 8 of the manual – Main Rotor-3:
  The manual says to loctite the flybar in step 2 and add the paddles afterwards in step 3. I found it easier to add the paddles first and fix the flybar afterwards. It’s already difficult enough to get the paddles parallel to each other…
• page 15 of the manual – Main Frame Assembly-3:
  Since the Hitec servo’s are a little bigger than the “official” ACE servo’s, I had to file down the Servo Mounts to get them to fit. It’s a lot easier to do before they are mounted onto the frame. Beside the height of the servo’s being about 1mm larger, they are also a bit deeper. This isn’t a problem for the elevator-servo, but the two aileron-servo’s need this extra space. I solved this by adding plastic spacers which I cut from an old 3.5″ floppy disk:
  
• page 18 of the manual – Tail Unit Assembly-1:
  The manual simply states to “Insert the Tail Rotor Drive Belt through the Tail Boom”. The belt is made from a kind of rubber, so just pushing it through doesn’t work. What I did was to hang the belt from my Tx antenna, pull slightly on the belt so it’s stretched straight. Then just slide the Tail Boom over the antenna.
• page 24 of the manual – Tail Boom Bracket Set-2:
  The manual adds the Tail Boom Bracket first, than later (p25) adds the Rod Guides and Tail Servo Trays. I found it a lot easier to first slide those on and only then glue the Bracket. Be sure to slide on all 5 parts in the correct order (Rod Guide, Tail Support Bracket, Rod Guide, Servo Tray, Servo Tray).
• page 24 of the manual – Tail Boom Bracket Set-2:
  My kit didn’t have the correct parts. It should have had 2 Socket Screws M2x10; instead I got one M2x14 and one M2x10. I solved this by adding an extra nut to the head-side of the bolt. This effectively shortened the bolt enough to fit.
• I use the Futaba S-9257 as rudder servo. The servo horns that came with this servo have holes of 2mm in diameter. The screw that came with the mini Titan is only 1.5mm. I used a 2mm bolt to make the plastic threaded, then filled the (threaded) hole with epoxy and drilled out a 1.2mm hole.
• The battery connectors that came with the kit were close to useless. They are hard to get connected and almost impossible to get disconnected. Also, their gender (male- female+) was opposite of the gender of the balancer (female- male+). I de-soldered the connectors from the ESC and used decent ones.
• To get some extra protection from shorting out the battery, I use a wall plug of 7mm. This fits just over the male (negative) connector of the battery.

The setup

Once everything is build, it’s time to start tuning everything. First up was the ESC.

The Electronic Speed Controller is a piece of electronics that regulates the engine. The BLC-40 has a governor that can be enabled or not. Without governor, you basically control the power delivered to the engine; if you give more pitch, you’ll also need more power. Governor mode tries to keep the motor (and thus rotor) RPM at a constant value. In this mode, your throttle-curve is essentially a horizontal flat line.

The ESC has 5 settings. I configured it this way:

1. Battery protection: Light discharge protection for Li-Ion/Li-Po (1): This will decrease the RPM once the cell voltage drops below 3.2V and cut the engine completely when it drops below 2.9V
2. Motor timing: Auto timing (1): I don’t want to fiddle with this just yet
3. Brake Mode: No brake (1): Since the mini Titan has an autorotation one-way bearing, braking is not possible anyway
4. Throttle sensitivity: Standard throttle response (2): Won’t be of much use since governor mode is used and there is no change in throttle to react to
5. Flying mode: Helicopter mode with governor (2)

Next was the swashplate. First thing to note is that moving the swashplate down increases pitch. This doesn’t matter at all, but is a bit confusing in the beginning. The cyclic input is as one should expect and shows the direction the rotor will be tilted to.

Since the miniTitan is an e-CCPM (electronic Collective Cyclic Pitch Mixing) helicopter, all three swash-servo’s need to cooperate for each of the possible actions. I configured the servo-arms to have a -10° to +10° collective pitch throw.

The tail servo is a digital one, so the delay-setting of the gyro is set to 0 and the DS dip-switch is set to on. The limit-value is set to around 120. At this point the servo was not binding yet, but the tail rotor did not change pitch anymore. My setup did not require reversing of the gyro.

Next I gave the battery an initial charge: 1457mAh.

The maiden flight

Finally I placed the mini Titan in the garden. I didn’t have the slightest idea what RPM was required to get this thing airborne. I set up the idle-up-3 to have a fixed pitch of roughly +5.5° and a linear throttle. Increasing power until the heli was very light on its skids. My RPM meter had a bit of a bad day, so I didn’t get the exact RPM (the reading was floating somewhere between 1800 and 2300, even though the rpm sounded very constant).

So I turned the procedure around: guess a (governed) throttle value of 50% and see at what pitch setting we leave the ground. Turns out 50% is a little on the low side; 60% worked better.

Next was trimming the gyro. In heading-hold mode it worked fine, but in normal mode I had some nice pirouettes. Adjusting the rudder trim to 92 right-ticks got him fairly stable.

Somehow I managed to get the tracking immediately right: I could not see any tracking, although I must admit that I needed most of my attention to keep the heli inside the garden.

The maiden flight was a success: no parts flew off, no crashes, no explosions; only the landing was a bit rough. The summary:

Place: Home garden
Batteries flown: guessing 0.7 or so
Time flown: not all flown, mostly setup, 1h37 (cumulative model timer: 1h37)
Time stolen: 0h13 from the Raptor 50 (its cumulative model timer: 30h05)
Rx battery recharged with: 1838 mAh
Tx battery recharged with: not recharged

The photo gallery of the build

The settings – transmitter side

Mostly for my own reference: here are the transmitter settings after the first flight.

Just for the record, here are all the settings:

• D/R,EXP
  • AILE
    • Switch: D
    • Up
      • D/R: 100%
      • EXP: -15%
    • Down
      • D/R: 100%
      • EXP: 0%
  • ELEV
    • Switch: D
    • Up
      • D/R: 100%
      • EXP: -15%
    • Down
      • D/R: 100%
      • EXP: 0%
  • RUDD
    • Switch: D
    • Up
      • D/R: 100%
      • EXP: 0%
    • Down
      • D/R: 100%
      • EXP: 0%
• END POINT
  • AIL: 100/100
  • ELE: 90/90
  • THR: 100/100
  • RUD: 100/100
  • GYR: 100/100
  • PIT: 100/100
  • AU1: 100/100
  • AU2: 100/100
• SUB-TRIM
  • AIL: 0
  • ELE:-32
  • THR: 0
  • RUD: 0
  • GYR: 0
  • PIT:+12
  • AU1: 0
  • AU2: 0
• REVERSE
  • AIL: Nor
  • ELE: Nor
  • THR: Rev
  • RUD: Rev
  • GYR: Nor
  • PIT: Rev
  • AU1: Nor
  • Au2: Nor
• TRIM
  • AILE: 0
  • ELEV: 0
  • THRO: 0
  • RUDD: > 92
• THR-CUT: INH
• SWASH AFR
  • RATE-AIL: +50%
  • RATE-ELE: -50%
  • RATE-PIT: +50%
• F/S
  • AIL: F/S -9%
  • ELE: F/S -14%
  • THR: F/S 15%
  • RUD: F/S -18%
  • GYR: F/S -51%
  • PIT: F/S +6%
  • AU1: NOR
  • AU2: NOR
• AUX-CH
  • CH5: NULL
  • CH7: NULL
  • CH8: NULL
  • CH9: Sw-A, NORM
• PARAMETER
  • TYPE: HELI (SR-3)
  • MODUL: PCM
  • ATL: OFF
• TIMER
  • <1>
    • TIME: 10:00
    • MODE: UP
    • SW: STk-THR
    • POSI: 19%
  • <2>
    • TIME: 10:00
    • MODE:DOWN
    • SW: STk-THR
    • POSI: 19%
  • <3>
    • MODE: MODEL
• TRAINER
  • INH
• THR-CURVE: see above
• PIT-CURVE: see above
• REVO MIX: INH
• GYRO SENS
  • MODE: GY
  • MIX: ACT
  • RATE-UP: AVC 60%
  • RATE-DOWN: NOR 60%
  • SW: B
• HOV-THR: INH
• HOV-PIT: INH
• HI/LO-PIT: MAN (disabled)
• THR-HOLD: see above
• RUD-OFST: INH
• OFFSET: INH
• DELAY: 0% everywhere
• GOVERNOR: INH
• THR->NEEDL: INH
• SWASH->THR: INH
• SW SELECT
  • IDL1/2: E
  • IDLE3: F
  • T-HOLD: G
• PROG MIX 1: INH
• PROG MIX 2: INH
• PMIX6 CURVE: INH