Building an Ultralight Racing Mini Quad

I recently built an ultralight racing drone – the lightest 5″ mini quad I have ever built, and it’s awesome! I want to share my experience on the advantages and limitations of ultralight racing drone when it comes to building and flying.

Further Reading: How to build a racing drone from scratch?

Racing is not my thing, and I mostly fly the more robust freestyle frames. But I have always been curious about the differences between a light-weight racing drone and a heavier freestyle quad, so I decided to build one and find out.

I have been flying mini quads for years, but even so, my skills are no where near a professional drone racer like Minchan Kim or Luke Bannister. Hopefully my years of flying experience will help me understand and explain the differences in performance from these very different styles of craft.

What is an Ultralight Racing Drone?

Every gram counts on a quadcopter.. An ultralight mini quad takes this rule to the extreme and remove all the dead weights to be as light as possible.

Generally, a 5″ freestyle mini quad, such as the ImpulseRC Reverb, weighs around 350g to 400g without the battery and GoPro (Dry Weight).

Freestyle FPV Mini Quad

Freestyle FPV Mini Quad – Reverb

An ultra-light racing drone, however, can be much lighter than that. The typical dry weight is only at around 180g to 220g. I am sure the weigh can go even lower on some extreme builds.

Ultralight Racing Drone

Ultralight Racing Drone

There are positives and negatives to almost any quadcopter, an ultralight racing drone is no different in this regard.

Pros:

  • Lighter = Faster (given the same hardware)
  • The lighter weight leads to higher efficiency and ultimately longer flight time (given the same power system)
  • Lighter = less inertia = a more agile and responsive aircraft
  • These properties combine to make an ideal craft for racing

Cons:

  • Lighter frames use less material and skinny arms which are easier to break
  • The space for components is usually very small, making building more difficult
  • Often the frame is incompatible with HD cameras such as the GoPro Session
  • Mounting the battery is limited to the bottom of the frame
  • Ultralight frames sacrifice protection of components in order to save weight

Light Quad vs Heavy Quad

The weight of a multirotor has a direct correlation to its responsiveness, and how immediate your stick movements affect the quadcopter.

A heavier quad has greater inertia, which means it takes more time and power to change its direction, and to accelerate and decelerate as well.

A heavier quad will carry more momentum in a crash, therefore things can break more easily. But that doesn’t mean ultralight racing drones are going to be more durable! In fact it’s the opposite due to the skinnier frames, they are probably even more vulnerable to crashes.

Heavier quads can offer more stability and smoother flight characteristics than a lighter quad, and is thus more suitable for freestyle.

More weight can help a quad to track better through the air, and the extra momentum improves ‘hang-time’ and hold inverted moves longer, making them look really effective.

A lighter quad is more easily affected by external forces. For example, wind will have a greater impact on performance, as well as vibrations from a bent or unbalanced prop or motor might cause more noticeable problems too.

A light quad simply maneuvers better on a racing track due to its lighter weight, cornering is instant and direct.

Flying a powerful ultra-light quad is an absolute blast! :D I’ve never felt faster or more nimble flying a 5″ quad!

Before you jump into building your own, you must understand that ultralight racers ARE NOT for everyone. Firstly the build process can be problematic due to the limited space, and unless you never crash, an ultralight frame will probably not last as long as you would hope.


Choosing Hardware for an Ultra-light Racing Drone

Lighter is always better…. ?

While this is generally true for anything that flies, there is often a trade-off between weight, performance and features. You will be forced to make a sacrifice, and where you choose to make those sacrifices comes down to your personal style and preference.

Frame

The first and most important aspect of an ultralight racing drone is the frame. You will find the majority of racing frames to have a minimalist design, with all the unnecessary material removed, sometimes that even includes “important protection” to the components. Like I said, it’s a compromise, so choose carefully.

Motor

Because the aim is to be as lightweight as possible, we can replace the powerful and heavy 2306 or 2207 motors with something smaller, such as 2205, 2204, or even 1806. You don’t want to put too much weight at the end of the arms which can also increase the inertia.

Some people even use tiny 1407 motors, but small motors like these generally have too little torque to swing 5″ props efficiently and you will have insufficient control and response.

ESC

I find 4in1 ESC a huge weight saver: you can save 5g to 10g easily by replacing standalone ESC’s with a 4in1 of the same current rating. Most 4in1 ESC’s these days come with current sensor, PDB capability and 5V BEC, which means you can save more weight by doing away with a separate PDB.

My First Attempt (31/01/2018)

  • BrotherHobby 2205 motors
  • DemonRC 5X Lite
  • Holybro Kakute V2 + TekkoS 4in1 ESC Combo
  • Runcam VTX200
  • R-XSR RX
  • Micro Swift
  • Dry weight: 212g

Build log: https://oscarliang.com/demonrc-fury-5x-lite-frame/

3 thoughts on “Building an Ultralight Racing Mini Quad

  1. Khan

    I fly a 210g dry weight 5″ low rider, with 2mm thick carbon arms (from a Diatone ET 200) and 1.5mm body plates. Durability is achieved using nylon screws to hold the arms. In case of a crash, the screws break, taking the energy away and protecting the carbon frame. Of course, you’re less likely start right away again after a crash, you have to pick up the quad and replace the broken screws, but that’s a cheap and quick process. Lightness and agility comes at a price :-)

    Reply
  2. zak

    another issue with super light builds is tuning out frame harmonics and tuning in general..
    its not as easy..

    I’m working through these issues right now on a 170g build
    rcgroups.com/forums/member.php?u=169763

    Reply
    1. Oscar Post author

      I don’t know about that, the Fury Lite I just build is flying beautifully even with stock settings.
      Maybe I just haven’t built enough to notice the problem…

      Reply

Leave a Reply

Your email address will not be published. Required fields are marked *

Are you Robot? *

I only check blog comments once or twice a week, if you want a quick reply you can post your question on this forum IntoFPV.com... You might get a faster response from me there (multirotor related only).