Andrey_Rakhmanov's blog View Details
Posted by Andrey_Rakhmanov | Jun 20, 2020 @ 03:32 PM | 12,997 Views
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This article is final article of a long cycle (or the first article of a new cycle - who knows). Successor of Arlequin III, Arlequin IV is a very technological model made in the framework of the new technology. The model itself is made of a carbon frame to which volumetric parts of the model are cut from EPP. Unlike of the popular EPP models with carbon reinforcement, the role of carbon is higher here - in fact, the entire frame uses connected carbon parts. Some of the parts are cut by a CNC machine from 0.5 - 1.5 mm carbon sheets, and long carbon parts are standard carbon tubes and bars. A model of such complexity is almost impossible to manufacture without an CNC machine - but the availability of this technology has been growing and, I think, cutting of carbon fiber parts is no longer an unsolvable problem.

The main characteristics of the model:
Wingspan: 90 cm
Weight (without battery) 220 g.
(Other parameters you can see in Arlequin III description)

Why EPP and CNC-cut carbon?
This model is very light, durable and can withstand dozens of falls. Of course, one can think about film coatings and ultralight model like a balsa one, however, using a combination of EPP and carbon fiber makes the model durable and easy to repair. Broken carbon parts can be easily replaced or repaired - bandages can be attached to lengthy parts, cracks on the EPP can be easily sealed, and if EPP part damage is significant, it can be patched.
All my models made using this technology flew...Continue Reading
Posted by Andrey_Rakhmanov | Dec 18, 2019 @ 06:05 PM | 5,562 Views
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(this is the translation of my article written in Russian)

Summary: I like manufacture 2-engine aerobatic flying wings. Such models have a non-standard control scheme - due to the presence of 2 engines, they are close to quadcopters and need stabilizing gyroscopes. But the 2-motor models cannot be connected directly to the flight stabilizer, and for such models I created a separate signal mixer based on the Arduino Pro Micro (I have already written several articles about it). The latest version of the mixer uses the FrSky-S8R stabilizing receiver. Mixers of this type flew a few dozen hours on various 2-engine models and performed quite well. But at the same time, some shortcomings were found in the mixer:

- To set up the mixer, a relatively complicated calibration procedure is needed. He inherited this property from an older version of the mixed with semi-analog PWM signals. But FrSky-S8R generates digital SBUS signal which comes directly in digital form from the transmitter - why we need to calibrate it if all the parameters are stable and can be set in advance?

- Low accuracy. The mixer generates PWM signals for motors and servos. The fronts the PWM signals are generated by the ATmega32u4 processor with accuracy about 1-2% of the signals duration, although ATmega32u4 can produce precision digital PWM signals directly from the built-in timers.

- Not optimal signals mix for the elevons. In previous version I did analysis to find the optimal signal...Continue Reading
Posted by Andrey_Rakhmanov | Sep 13, 2019 @ 06:22 PM | 2,361 Views
For my pilotage 2-engine Arlequin I manufacturer square cockpit canopy. The canopy protects model electronics compartment from dust and moisture.
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It is quite easy to do, I briefly describe describe the process by several photographs.

First we need to prepare pressing form. I cut parts of the form from 4 mm polystyrene sheet.
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Posted by Andrey_Rakhmanov | Sep 10, 2019 @ 05:13 PM | 1,607 Views
Milling carbon fiber (3X speed) (2 min 1 sec)

I have a need to cut carbon parts for my airplane models and decided to create CNC capable to do carbon cutting.

Requirements for the machine:
  • Total price of components less than $300.
  • Weight less than 15 kg (30 pounds).
  • Should cut A4 size carbon sheet with precision about 0.1 mm.
  • Should be portable and environment friendly - designed to do cutting and to be stored in the apartment living room,

Finally I found cheap CNC ($125-$225) on banggood and re-designed it:
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Major improvements:
  • 500 Watts spindle ($50-$80).
  • Vacuum cleaner hose attached($10).
  • Bridge Cable Chain($10).
  • LED work zone light.($10)
  • New couplings and bearings($10-$20).
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Posted by Andrey_Rakhmanov | Jul 22, 2018 @ 05:14 PM | 3,709 Views
Previous stabilization scheme for the 2-engine Arlequin used Eagle Tree Guardian flight stabilizer. This stabilizer is quite old (more than 10 years) , so I decided to replace it with a more modern and popular one. It is not easy to do because very few stabilizer can match qualities of Guardian. Finally, the choice fell on a popular receiver with built-in stabilizer - FrSky S8R.

I tested FrSky S8R with classical scheme model, and what I found:
- Relative small price - $ 40 - $ 50 - 8 channels for a telemetry receiver with stabilizer isn't bad!
- It has telemetry channel - it is possible to measure the voltage of the battery.
- Can output data in SBUS format - allows to avoid PWM wires mess. Now receiver can be connected with one cable.
- An ability to do full configuration directly from the transmitter (Taranis + Lua scripts).
- A large number of flight modes (3D, horizontal stabilization, hover, knife).
- Active support from FrSky - new firmware releases, utilities, etc.
- Receiver configuration menu features minimum possible number of settings.
- Complex and unobvious processes of installation, configuration and calibration - for the understanding it's better to watch the video on YouTube.
- Support - only 3 basic types of plane models (classic, delta wing, v-tail) 'hover' and 'knife' flying mode aren't enabled for delta wing and V-tail type models.
- Not very obvious stabilization scheme. Impossibility to set the "general"...Continue Reading
Posted by Andrey_Rakhmanov | Jul 20, 2018 @ 04:47 PM | 3,195 Views
I usually write posts in Russian for Now I decided to start mirror publications in English here . I am placing below links to old rc-aviation articles - if someone needs to translate them in English - does good job here.

Arlequin IV -
Thermo-knife review -
Improved 2-engine signals mixer -
Easy way to make model canopy -
Home CNC for cutting carbon -
2-engine model flight stabilizer on base FrsSky S8R -
Arlequin III -
Previous version (review)-
Previous version (building) -
Previous version (pre-flight tuning)
2 engine signal mixer building and programming -