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F5K Motors & Parts: A Buyer’s Guide

An Ultimate F5K Parts Buyer’s Guide

F5K sailplanes is a relatively young class of competition RC gliders and a lot of people wonder about the gears they can and need to use. 

There is a lot of info around the web for the predecessor – F3K models and its gear as the last was around for a while. And considering that a lot of pilots and manufacturers make F5K models based and often from F3K ones, there is a lot of similarities. 

But, considering that F5K gliders have an electric motor in front, brings new changes for choosing the right gear.

So, we decided to help you choose the right components for your glider.  In this article, we covered different options and explained the pros and cons of using each of those. 

Hope you will find the information below useful and if so, we will appreciate your effort to share it with your friends or clubmates. 

And let’s dive in! 

Powertrains 

First things first, and since the main difference between F5K and F3K models is in the motor mounted in front, let’s see what options do you have. 

There are some plug-and-play options available, but below we’ll cover the components that you can use to create your own powertrain, tailored to your needs and flying style.

F5K Motors

Unlike F5J – the bigger brother, F5K gliders usually use Direct Drive drone outrunners. Their price is not breaking the bank, and there are a lot of options available from popular online retailers, local suppliers, and hobby shops. 

Plus, considering that it is drone gear, it’s capable of high loads and usually is quite power-efficient. 

Some good choices are the following:

Spinners & Props

Unlike the motors, there are not that many options available for spinners and folding props. As you need a folding prop, drone options aren’t applicable here. 

F5K gliders in the most are designed to use 25mm spinners, some of the recent ones like Yoda, are designed for 28mm ones.

The exclusive feature of these spinners is their comparability with threaded M5 shafts of drone motors. These items have a special nut that fixes a yoke and a plastic cone on the shaft directly, w/o any additional adapters needed.

The plastic cone then fixes 2mm prop blade shafts and keep them attached to the yoke securely.

All these makes a perfect combination, that is simple, reliable, lightweight, and easy to change if necessary.

So, there are just a few options by two main suppliers:

The same manufacturers offer folding prop blades to match the spinners above with 5mm yoke:

Having this selection in mind you can create different combinations based on the power and thrust you need.

Also, keep in mind that the CN-Models spinner is “shorter” and will require the motor to sit deeper in the fuse, compared to the VM spinner.

The yoke width of the first is ~2mm wider compared to VM one, so keep this in mind while choosing your parts.

Pro Tip – Lightweight Rubber O-Rings

Pilots who fly powered gliders know that sometimes the prop blades can hang out down from the fuse which created an extra drag. To prevent this, pilots flying F5J sailplanes made good use of rubber rings.  

However, the side of the blades on the F5K gliders are relatively small and it’s hard to find a good fitting and lightweight rubber ring. 

But there is a wide selection of orthodontal rubber rings which come in different sizes. So you could easily get a pack that will hold your blades aligned with the fuse for min drag. 

O-Ring Holding Folding Prop

Speed Controller Options (ESCs) 

With electric speed controllers, there are 2 completely different routes:

  • Go BEC-less, use HV servos, Rx, and 2S LiPo battery. The main benefit of this setup is a possibility of a proper onboard voltage telemetry. But using standard voltage LiPos is a must here. Another is a weight and size of the small drone ESCs w/o BEC – they are very tiny and light. 
  • On the other side, you can choose any ESC with BEC and expand the selection of batteries and servos to use for your glider. Rx voltage telemetry will be possible here as well, but will require some extra sensors and wiring that you will need to fit into a tiny glider pod. 

Considering that most of the recent micro receivers from major manufacturers are rated at 7.4v (8.4v) as well as good micro servos, I personally prefer the first option. 

Plus, HV-rated servos usually work better at 2S providing more speed and torque. 

So, the options for the BEC-less drone ESCs are the following, but note that some of these will not have a positive wire coming to the receiver and you might solder it on yourself: 

The selection of ESCs with BEC is also quite extensive, here are a few examples:

F5K Powertrain Combos

As an example, we used to offer plug-and-play power sets for F5K that used the following components:

Our thrust tests showed that this setup will provide over 500g of constant pull, tested with 450mAh 2S 70C LiPo. This is more than enough for the most F5K gliders over there.

The weight of this setup is just 29g, it’s pulling approximately 15A at full throttle, and can easily run on a full-throttle w/o cooling for 10 seconds.

This could be a good starting point for your experiments.

Also, if you need more data on various components, feel free to check this RCG tread with a bunch of test data. It covers a variety of props, motors, and batteries.

LiPo Batteries

A selection of batteries that will suit your F5K glider is big. There is a number of brands, and to get it right, you need to remember a few things. 

First, you need a high discharge rate. Usually around 70C or higher. 

People mostly use 350-600mAh batteries depending on the CG and desired AUW so to get a constant current close to 20A, you need high discharge rates. 

Second, most use 2S LiPo but rarely do 3S LiPos come in handy as well. 

As mentioned above, we recommend using 2S plugged into the receiver directly for the full power of HV servos and onboard voltage telemetry.

The last, be cautious with the size of your batteries. Since the modern F5K gliders have a tiny narrow fuse, you can’t stick just any battery in it. 

Instead, look for gum-stick style batteries which are long and narrow, something similar to the ones below: 

Servos

The next stop is the servos. 

In most cases, you will need something that will be small, robust, and reliable.

Luckily, there are a lot of options available in various budgets, both high voltage servos and also servos running at standard voltage, digital or analog.

Below, you will find a few we’ve tested and recommend: 

Final Thoughts

To sum up, all the information above is based on our personal tests and research.

Feel free to use these recommendations or choose similar gear that you find more suitable or preferred. Also, keep in mind that the availability of these parts may differ based on your region.

And ofc, if we are missing some great gear, please, mention it in the comment below!

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