Why?

This project started when we decided to design a Bo 105 fuselage. Initially, everything was based on the OMP M2 chassis. However, since our scale builds had specific requirements, we introduced several modifications to the M2. As the number of changes grew, we aimed to make the chassis easily adjustable to ensure the best fit for our scale projects.

For doing a scale build you end up replacing the motor, the rotor head, and sometimes the main shaft. Additionally, you need to modify the M2 frame to be able to mount it in a fuelage and to fit the T-Motor MN4006. Doing all these modifications and putting some components on the shelf we decided to design a 3D printed frame that can be built from scratch to meet the needs of a scale heli.

Since we already had a CAD model of the fuselage, we started creating a 3D-printable chassis based on the M2. The initial versions only introduced slight modifications, but this has been the basis for adjustments here and there. So, currently, this chassis is not suitable for hard 3D flying but works quite well for smooth scale flying and light aerobatics. Some of the M2 parts can be used if needed. But you can choose from several options
When we came across Roforflight and got involved there, we also started developing an RF-compatible FBL with a dual ESC to complete the entire project, the Racoon FBL.

  • lower KV motor for 4 blade heads (T-Motor MN4006)
  • mounting points for the PTK servos
  • M2 threads for mounting the chassis into the fuselage
  • different main shaft lengths
  • different swashplate guide lengths
  • modifiable battery tray for adjusting the COG

Servos

PTK Servos

Compared to the M2 Evo servos, the PTK offer higher build quality and slightly better specs. The specs do not really matter for a scale helicopter, but this needs to be mentioned for the sake of completeness. They come with a standard servo connector and therefore need to be converted to JST Pico Blade connectors. the PTK servos can be used up to 8.4v input vvoltage for even more torque and higher speeds.

OMP M2 Servos

You can either go for the DS2710 or DS2710MG. The MG offer aluminum housing and metal gears, but are a bit more pricey. Quality is comparable to the the PTK servos.

PTK Servos: Mounting Points

The PTK servos have mounting points in slightly different positions than the M2 ones, so the PTK servos need to be moved a little closer to the main shaft for optimal linkage geometry.

OMP M2 Servos: Mounting Points

The OMP Servos are slightly thicker and require a different servo support bracket.

Motor

T-Motor MN4006

Using the T-Motor requires some effort to remove its main shaft. It is intended to be used on drones so it comes with a very short shaft and no connectors. The motor is 380kV, which is optimal for running a 4-blade setup. It offers enough torque and keeps the heli quiet and efficient for scale flying. We suggest using the flanged main shaft for the T-Motor.

OMP M2 Motor

When going for a 2-blade setup the OMP motors are better choices over the T-Motor. The offer something in the range of 700kV and therefore higher headspeeds. For 4-blade setups these motors are not recommended, since they run hut due to no being able to provide the required torque for such setups.

The different M2 motor options slightly differ in kV and torque. This does not matter too much when building a scale helicopter. What matters more is the mounting mechanism of the main shaft.

There are multiple versions:

  • SunnySky R40S-3 (V2)
  • SunnySky R40-3 (Explore/Evo)

Todo: We need to clarify the difference between the motors here. The main shafts also differ in terms of length and mounting to the motor. What is the deal of the performance upgrade shaft?

Our main frame offers mounting options for both motor setups. Due to space limitations, the T-Motor is mounted with 2xM3 screws, whereas for the M2 motor 3xM2.5 are to be used.

Main Shaft

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Flybarless

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Tail

Tail

The chassis is dully compatible with the OMP M2 tail section. The tail can be used for convenient testing and tuning, before mounting the chassis in a fuselage.

Landing Gear

A scale chassis does not need a landing gear (obviously!). But for testing, this might come in handy, especially when you don’t have a spare M2 landing gear at hand. The landing gear is entirely 3D-printables and only requires a few 1.6mm screws for assembly.

Using the Chassis for you own Fuselage

For fixing the chassis to the fuselage a flat surface and 4 holes for the screws are required. You may have a look at the dimensions below to make your fuselage ready of this chassis.
The image below shows an example of how the chassis may be integrated into a fuselage. For our Bo-105 we chose to design 2 mounting brackets to align the main shaft position and angle. Assembling the fuselage is as easy as possible: disconnect the tail motor (which remains in the fuselage) and unscrew the 4 chassis screws.

Future Plans

Currently, this is still a draft and under development. But as the title may suggest we are planning on open-sourcing the design to establish a platform for building 200 size scale helicopters. There are quite a few 3D printable fuselages out there and this chassis can be used to make those fly.

We will also be offering the entire chassis for download. So you can incorporate it into your designs and print the parts yourself.