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Old Jan 09, 2004, 07:58 PM
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farmington, mn
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is it better to up size or downsize your prop when picking gearboxes

ok i'm having a hard time deciding on my gearbox, i have found two that are garanteed to be crash proof, which is what i need, one is 2.8 gearing which means that i have to go with an 8 inch prop and the other is a 4.1 gearing which i would have to run with the 12 inch prop. they both give me about the same power and amps. it is going on a gws pt-17 with a mega 16/7/7. don't know if bigger is better or not. i know that my idea gearbox is a 3.1 but i haven't found any that would survive a hard impact without cracking or bending ect... ect... so if someone does know of a 3.1 gearbox that can take a hard hit please let me know.
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Old Jan 09, 2004, 08:12 PM
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Gig Harbor, Washington, United States
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Guaranteed crash proof???

Which two?


Larry

Edit: As to your question on prop size - it depends on how you want to fly. The larger prop on higher gearing will have more thrust and lower speed (assuming the same aprox total power input). I don't know the plane you have so can't comment on it.
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Old Jan 09, 2004, 09:08 PM
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Chattanooga, Tennessee, United States
Joined May 2003
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Crash proof 3:1

Does the Mega have mounting hole spacing the same as a Speed 400? If it does, what you need is the ACC347 all metal gearbox for Speed 400's (comes with 3 pinions so you can go 2:1, 2.5:1 or 3:1) - Kirk Massey at www.newcreations-rc has them listed for $19.90:Maxx Products has them as ACC347 for $21.95:Hobby-Lobby has them, as MPY345, for $21.90.

They are very versatile, very strong, and not too heavy [22g] and I've used them on Speed 400's and my MiniAC 1215/20.

Here's a photo of one on the Mini AC.

Cheers, Phil
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Old Jan 10, 2004, 07:32 AM
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farmington, mn
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that does look like tough gearbox but the pinions are 2.3mm and i have a 3.2mm shaft. how many teeth are in a 3.1 and 4.1 pinion?
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Old Jan 10, 2004, 09:17 AM
KLH
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Hayward CA / Valley Springs CA USA
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Maxx Products has that same gearbox with a pinion for a 3.2 mm shaft part no. ACC387 $21.95, but it only comes with 2 pinions, 2:1 and 2.5:1.
Didn't check Kirk's site , but I'm sure he also has it, he's got to have one of the largest/diverse inventories in the business.

Kern
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Old Jan 10, 2004, 10:18 AM
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farmington, mn
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thanks i will look for that but i think i may have to just order a different pinion thats why i need to know how many teeth the 3.1 has
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Old Jan 10, 2004, 10:59 AM
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Concord, MA
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You could probably drill out the 3-1 pinion too. I have a GB that looks just like that I bought from Dymond Modelsports with a long can 480. I flew a 2 meter glider on 10 cells with it. I would say: 1: put it together with loctite, 2; I found a 2-1 ratio 3.2 pinion that was originally from a Master Airscrew speed 600 reduction drive that worked with the big gear (on my gb this was aluminum) 3; you need to set the gear lash on this type of GB. www.aircraft-world.com also sells an open frame speed 400 gearbox that fits a speed 400 so should fit the ac16-15 series, as well as the MPJET series oif palnetary or other wise, although the planetary aluminum ones are a little heavy.

Finally, why don't you just get a little outrunner??. MPJET also has a 2520 series with a gb that should work poifict on that plane and is only $60. look ay Hobby Lobby site for the ittle outrunners or this MPJEt motor.
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Old Jan 11, 2004, 01:18 PM
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East Anglia, UK
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Re: is it better to up size or downsize your prop when picking gearboxes

Quote:
Originally posted by jeff262
ok i'm having a hard time deciding on my gearbox, i have found two that are garanteed to be crash proof, which is what i need, one is 2.8 gearing which means that i have to go with an 8 inch prop and the other is a 4.1 gearing which i would have to run with the 12 inch prop. they both give me about the same power and amps. it is going on a gws pt-17 with a mega 16/7/7. don't know if bigger is better or not. i know that my idea gearbox is a 3.1 but i haven't found any that would survive a hard impact without cracking or bending ect... ect... so if someone does know of a 3.1 gearbox that can take a hard hit please let me know.
A deep ratio box on that motor will probably give you very good thrust but little pitch speed.

Fine for a glider, useless for a sport plane.

Use the lower ratio - 2.8:1 - its near enough the 3 that you want.
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