Long-term Memory

Place: Halle

Raptor
Tanks flown: 2
Time flown: 0h27 (cumulative model timer: 31h19)
Rx battery recharged with: mAh
Tx battery recharged with: 559 mAh
Glow heater battery recharged with: 1300 mAh
Starter battery recharged with: 1250 mAh

miniTitan
Flights: 2
Time flown: 0h21 (cumulative model timer: 3h17)
Heli battery recharged with: (1) balanced 1934 mAh; (2) balanced 2137 mAh;
Tx battery recharged with: see above

Comments:
Went flying after work. It was fairly windy, but the wind was fairly constant. I practiced the maneuvers I’ve been doing in the sim lately: autorotation and inverted flight, both successful!

Inverted flight worked out fairly well. I started by doing backflips. Next I stopped halfway through the backflip and tried to keep it stable. I only need to work on my reflexes to get me out of inverted trouble. Obviously pushing the throttle/pitch up is not the best idea… Luckily I had (just) enough height to correct my peculiar situation.

The miniTitan held up fairly well in the winds, although I was more busy fighting the wind than flying. I increased the CCMP-mixing from 50% to 75% on the elevator and ailerons. Now it is more vivid, just like my raptor. I tried some backflips as well, but the wind made this a challange.

Continue reading ‘Flight log – 2009-04-23’ »

Place: Halle
Tanks flown: 2
Time flown: 1h00 (cumulative model timer: 30h52)
Rx battery recharged with: 272+392+overnight trickle mAh (again)
Tx battery recharged with: 489+overnight trickle mAh
Glow heater battery recharged with: 1473 mAh
Starter battery recharged with: 498 mAh

Comment:
Before this flight, I adjusted the pitch and throttle curves and activated the IdleUp2 position. This is the updated table from before:

Today was the first day with reasonable weather. It was still windy, but almost no gusts.

Had some trouble starting the engine. Turns out there was some dirt in the needle of the carburator. Simply turning the needle a bit (5 ticks) open, starting the engine and returning the needle to its original position solved this issue (although it took me more than 30 minutes to figure it out).

No spectacular flight for this first time, just some hoovering in different directions. The second flight was a bit more entertaining: I rehearsed my stall-turns and tried some standard patterns, which was quite a challenge in these (cross)wind conditions.

Place: Sporthall Braillard, Ruisbroek
Flights: 2
Time flown: 0h19 (cumulative model timer: 2h56)
Heli battery recharged with: (1) 1639 mAh; (2) balanced 1896 mAh;
Tx battery recharged with: not recharged

Comments:
Indoor flying. The tail vibrations mentioned earlier are probably caused by some slop in the linkage. I tried various gyro-gain settings and the vibrations did not seem to be affected.

One of the things to pay attention to when building any RC vehicle is the setup of the servo’s. In (almost) all cases, the servo is connected to the controlled handle using linkages. One of the rules-of-thumb is that the servo, connecting rod and slave handle need to be at right (orthogonal) angles. Obviously I wanted to know WHY. John Vugts explains this in more detail, but I still wasn’t satisfied.

So I went through the math and ended up with a calculator to draw the curves on-demand. It’s a standalone JavaScript calculator, so it can be used offline. It uses Open Flash Chart to draw the graph.

Note that the angles are measured in the mathematical way: counterclockwise starting from the horizontal X-axis.

Place: Sporthall Braillard, Ruisbroek
Flights: 3
Time flown: 0h27 (cumulative model timer: 2h37)
Heli battery recharged with: (1) 1566 mAh; (2) 1844 mAh; (1) 1774 mAh
Tx battery recharged with: 607 mAh
Starter battery recharged with: 1187 mAh

Comments:
Indoor flying. Finally got the chance to properly trim my miniTitan. The gyro still needs some tuning: when I stop the rudder command, the tail overshoots, then comes back. Also sometimes I notice the tail vibrating left-right at around 3Hz. Unsure if this is a gyro problem or just a vibration problem.

I tried recharging my LiPo with the starter battery, but after 15′ (680mAh) of delivering 2.5A the charger reported that the source battery was too low… Luckily one of my friends had some spare 12V power.

On the third flight I tried getting some forward speed. Even though it was a big indoor hall, this machine wants more…

Place: Home garden
Flights: 1
Time flown: 0h25 (cumulative model timer: 2h10)
Heli battery recharged with: 1714 mAh
Tx battery recharged with: not recharged

Comments:
Demonstration for the family. Flew for 7 minutes or 68%, guestimating on the charged-in capacity.

Right after the flight, the battery was warm (I’d guess somewhere 35-40°C), the engine was fairly warm (around 50°C) and the ESC was hot (60-70°C). The temperatures are measured with my fingertips, so they are very accurate…

Since I’m a fairly curious and technical kind of person, I needed to know all the gory details of exactly how helicopters fly. Here is what I found out:

• Very nice series (part 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) by Colin Mill on different aspects of model helicopters. Subject goes from servo linkage through Bell-Hiller ratios. The articles are fairly old (1995-1996) but the physics are still the same!
  
• Dynamic Helicopter Aerodynamics describes all the aerodynamic effects on (real-size) helicopters. Most of these effects also apply to model helicopters, although some become less important. Covered topics go from basic airfoils to vortex ring state and dynamic rollover.
• The same site also has a Dynamic Flight Maneuvers section, bringing the aerodynamics into practical situations such as ridgeline landings or plain simple hoovers.

Place: Home garden
Flights: 1
Time flown: 0h08 (cumulative model timer: 1h45)
Heli battery recharged with: 1185 mAh
Tx battery recharged with: 1021 mAh

Comments:
First real flight. One of the things I need to calibrate is the flight duration of my battery. I flew 5m55s on this battery and it was recharged with 1158 mAh. Extrapolating this gives an max flight time of around 12 minutes and 28 seconds.

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

Continue reading ‘The new toy: mini Titan E325’ »

Place: Halle
Tanks flown: 3
Time flown: 0h56 (cumulative model timer: 29h52)
Rx battery recharged with: 728 mAh
Tx battery recharged with: not recharged
Glow heater battery recharged with: 462 mAh
Starter battery recharged with: 133 mAh

Comment:
Another beautiful autumn day (which are fairly rare in Belgium), although the sun was hanging low. Naturally, I was able to pilot my heli straight into the sun. Apart from the black spot in my vision the next 3 minutes, nothing got damaged in the process.

Tried and succeeded in a full auto-rotation with 0% engine power (previous attempts where with some power). Turns out that it isn’t too much different from 15%. Even at 15%, the engine is hardly engaging the clutch so it barely provides power.