What prop for a 2.3mm shaft w/ prop saver - RC Groups
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Feb 26, 2010, 11:03 PM
Scratch building addict
rotagen's Avatar

What prop for a 2.3mm shaft w/ prop saver

Hey all, this is the first time I have made a model with a 2.3mm high KV (2250kv) motor, its the aurora 300df. I've calculated that a 5x3 or 5x4 prop should work well as direct drive, so I ordered some (I think they are GWS direct drive props)..

Long story short I had to drill the prop hole larger to keep the prop from bending around the conical saver so easily, and the o-ring is too lose for my liking as well.

So what prop brand and type do you think would be good for this motor?

I'm new to jets and high kv planes.

Also, anyone have any data or experience with this motor from justgofly.com?

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Feb 26, 2010, 11:10 PM
Suspended Account
I'm really confused here. How does a prop bend around a prop saver????
Feb 26, 2010, 11:32 PM
Scratch building addict
rotagen's Avatar
Basically due to the relatively small hole in the prop, and the larger conical shape of the prop saver, the prop was not stable on the saver.

As in it could be easily moved from side to side with my fingers.
Feb 27, 2010, 12:01 AM
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Dr Kiwi's Avatar
Don't use a prop saver on a 300DF motor (far too dangerous on such a high Kv motor)... get a Graupner CAM 4x3 or 4.7x4.7 and a 3.2mm collet prop adapter. I never dared run my test motor (MTM 300DF) on 3s in direct drive, but if you do, you'll be around 20,000rpm... remember that motor is rated for maybe 7A max [http://ecsvr.com/RC-Direct/shopexd.asp?id=955].... a 4x3 may take it to 10A+, and a 4.7x4.7 may have it at 13A or so.

If I misunderstood and you are using 2s, then a Graupner 4.7x4.7 might be okay.
Last edited by Dr Kiwi; Feb 27, 2010 at 12:14 AM.
Feb 27, 2010, 01:04 AM
Scratch building addict
rotagen's Avatar
According to justgofly they run them direct drive all the time ?

They have some charts there with prop sizes and amps, most are under 10 amps even 5.5 x 4.5 or so ranges.

I guess I'll give them a call and see what they suggest, I also bought a gws type adapter regular screw on type...colette adapters are not for me, talk about a dangerous mechanism.!

guess I'll stick to drilling for now, remember, with small props even though the kv is a little high, the amps will be lower.
Feb 27, 2010, 10:14 AM
Registered User
Dr Kiwi's Avatar
Here is what Vinnie has to say: the amp limit has been raised to 10A, so it looks as if a 4.75x4.5 might be okay on 3s if you are looking for good pitch speed. That RPM at only 66% of Kv x V is an indicator that the motor is somewhat over-loaded (75% is the typical target)... and obviously anything bigger (5.5x4.5) would NOT be suitable.

On smooth shafts, collet adapters are far more secure than the set-screw type! The set-screw type are okay if the shaft has a flat on it, but even then I don't trust them very much.
Last edited by Dr Kiwi; Feb 27, 2010 at 10:21 AM.
Feb 27, 2010, 02:29 PM
Scratch building addict
rotagen's Avatar
Yeah thats the chart I was using. I'm hoping my model is light enough to just use the gws 5x3 props, if not I will switch to 5x4 (my pusher model design doesnt allow anything larger than 5 diameter anyways).

Funny, I have had the opposite experience at least with GWS props, had a collette adapter fall off repeatedly until I switched to the dual screw prop savers. I just dont think you get near enough pressure clamping the collette down.

Thanks for your help, my model should be around 9 oz with 2s or 10 ounces with 3s. I want only medium speed (which will still be fast for this little jet), so I'm hoping 5x3 will work for this size model.
Feb 27, 2010, 07:54 PM
Registered User
Dr Kiwi's Avatar
5x3 GWS HD will be okay at the 2s rpm, but on 3s it might be at its rpm limit.
Last edited by Dr Kiwi; Feb 28, 2010 at 06:55 PM.
Feb 28, 2010, 05:12 PM
Rochester, NY
JustGoFly's Avatar
Prop Savers are not healthy on the high rpm 300DF. I used them for a while and ran two small bands cut from silicon tubes, but started running prop adapters after I threw a bunch of props. The high RPM will still shatter the prop on a full throttle prop strike - even with a prop adapter. And flying props at over 20,000 RPM could be very harmful to you and your co-flyers.

The benefit of the prop saver is it may keep the tiny shaft from snapping. Use two or more bands to hold on the prop. Make sure it seats well and doesn't make a high noise or your unbalanced. Imbalance can toss props or even wreck mounts. Never run up the prop when someone is standing behind the blade - even the side of the motor is not safe - so clear the rear of the plane totally.

Feb 28, 2010, 06:57 PM
Registered User
Dr Kiwi's Avatar
I just don't think you get near enough pressure clamping the collet down.

Here is how to get plenty of pressure on a collet adapter!
Mar 01, 2010, 12:03 AM
Scratch building addict
rotagen's Avatar
cool, thanks for your help guys

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