Sir, In funjet you cannot put the motor as you are holding.....it has to have the shaft on other side and the motor fits to the motor mount of funjet.

Shaft which we put was a shaft used for ODIN motors from RCB.... 3.17mm with machined groove.


so far 3  shafts are Broken from the circlip groove.... see the motor Pic above ... when we put the prop it is pushing shaft inside motor and circlip is preventing that.

Entire thrust of motor is resting on circlip... cannot figure out is that force so high to break shaft???

or excessive heat at that point can help in breaking shaft since its the Circlip groove which gets heating and becomes the weak point??

Been looking at my motors. All have therove at one END. where there is not possibility of a bending load, and NOT BETWEEN motor and prop.

In your case the clip/groove is BETWEEN the motor and the prop.
This becomes a WEAK LINK.
Any vibration from the prop, however imperceptible, WILL lead to a fracture.

While reversing the shaft, did you use a different shaft?
Or did you grind a groove for the clip?

Not able to understand how you got a shaft with the groove between the motor and prop.

Should have put a washer and a collet. Doubt if even that needed.

Edit
"Entire thrust of motor is resting on circlip... cannot figure out is that force so high to break shaft???"
It is a bending load, not thrust load, that is breaking the shaft.

kindly see the pictures and advice.

These two motors saw two shafts sliced.

One motor where we reversed the shaft; I can understand that There may be a fracture because of the groove we created. Other motor has a factory fitted C clip with a washer on the shaft;

All those who use a funjet please advice; what could be the reason. I am down with 4 shafts. Planing an inrunner this time.

Just a thought ... Have you used the same prop adapter / spinner

@asinghatiya
The first pic is proof of what i said.

Regarding second pic, please post a pic of the other side of the motor too.
What motor is it?

Ctd.. With all the shafts ... If the adapter has some eccentricity the shaft is bound to fracture ...

If you carefully study the shaft break point, it is a metal fatigue failure

Arvind is correct, although he might not have framed it correctly

The motor thrust pushes the shaft. The side of the groove is subject to wear.

Then the shaft ''rebounds'' back. This cycle is repeated

This leads to a metal fatigue failure

Fatigue occurs when a material is subjected to repeated loading and unloading. If the loads are above a certain threshold, microscopic cracks will begin to form at the stress concentrators such as the surface, persistent slip bands (PSBs), and grain interfaces.[1] Eventually a crack will reach a critical size, the crack will propagate suddenly, and the structure will fracture.

When a new groove is cut in the shaft, by jugaad as there is no machining centre available, the edges of the groove are not properly rounded. These edges and corners act as stress concentration point

(3rd year Strength of Materials, IIT-B )

By using a sleeve, this could be avoided

Waste of time posting pics and debating. Arvind, try the collet/sleeve

@sanjayrai55
Sir,
With due respect, kindly see pm.

Dear Iyer Sir & Sanjay Sir, I guess the reasons you both mentioning is perfectly fine. SO should I use a inrunner now?? As in funjet ultra  an inrunner is recommended.

ummm.... a picture is worth a thousand words and usually saves times than typing a lengthy description.

placing a collar at the spot is not a good idea.  The collar would push against the washer or the bearing.

here's the back of my clone Funjet, a Hobbyking Rad 800.

As you can see, No c clip and no collar. All the force is on the short shaft.

@theleabres
Was wondering where you were.
Quote from my earlier post:

"Should have put a washer and a collet. Doubt if even that needed"

in your case, motor is mounted straight. If pushed by a propeller it wont get hurt;  in the case of funjet where the same motor is mounted in reversed position; in this case thrust is completely on a C-clip.  

Its a unique case and after lot of search on internet I found a funjet is recommended with an inrunner.

Okay, try an inrunner.  I have my speed measuring device on hand now.  Will your funjet be ready to fly next Sunday at 7:30 am?  If so, let's race the stock Skyfun and Radjet against it.

 > AWESOME, will let you know.

Today I did the maiden on my Hobbyking radjet (funjet clone).  The stock setup measured 52 mph.   I don't have the space to do a straight and level pass to get a more accurate reading.  It seems she is capable of 60+ mph.  I hope to get out to Gurgaon next Sunday to enot the field there.

Looking forward to your visit Lance....

This evening I clocked my RadJet 800 in 45 degree full throttle dive at 79 mph = 127 kilometers per hour.

Still planning to take it to Gurgaon after my friend returns from the U.S.