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Gearbox Help

Old 03-02-2007, 12:55 AM
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Default Gearbox Help

I need some help with how to choose what gearbox/ gear ratio to use.
I have a Himaxx 2815-3000 kv brushless inrunner that I had on an F-27 Stryker for some time. I am replacing it with another setup and now have this motor with no home.
I do not know how to figure out what gear ratio/box and prop would give me different #'s for pitch speed, thrust, amp draw and so forth. (at least not without buying a bunch of gearboxes and props and use the watt meter)
I have alot of planes for the 5 oz range to 80 oz. All are direct drive (either inrunner outrunner) so I could be flexible with what this would go on.
I am hoping someone has had this motor on a gearbox and could post their results for me or at least show me to the Gearboxes for Dummies section.

Thanks for any help here.
A link to the motor

http://www.maxxprod.com/pdf/HB2815-xx00.pdf
Old 03-02-2007, 11:45 PM
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Default RE: Gearbox Help

I got my answer
Old 03-12-2007, 07:18 AM
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Default RE: Gearbox Help

I would also like to know how to choose a gearbox and why I should. Care to share what you found out?
Old 03-13-2007, 05:38 PM
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Default RE: Gearbox Help

Simark, I got an answer from Dr. Kiwi about that Himax motor and what gear to use.
This is what he told me,
With the relatively low Kv you will need fairly high gearing unless you want to
run an enormous prop. For example 6.6:1 would be ridiculous unless you need a
20" prop! But 4.43:1 lets you spin a 13x8, and so increasing to 3.5:1 or 3:1 in
say a Cobri box might be the way to go if you want to run a 10"-11" prop.

I'll toss in some Motocalc simulations here: I don't guarantee their absolute
accuracy but they should be in the ballpark.
Motor: HiMaxx HA2815-3000; 3059rpm/V; 1.8A no-load; 0.035 Ohms.
Battery: Thunder Power TP2100 (ProLite); 3 cells; 2100mAh @ 3.7V; 0.018
Ohms/cell.
Speed Control: Castle Creations Phoenix 45; 0.0026 Ohms; High rate.
Drive System: 10x7 (Pconst=1.16; Tconst=1) geared 3:1 (Eff=80%).
Airframe: Anything you want.
Conditions: 600ft above Sea Level, 29.92inHg, 68°F

Motor Amps = 29.0
Motor Volts = 9.5
Input (W) = 274.2
Motor RPM = 25194
Prop RPM = 8398
Thrust (oz) = 34.8
PSpd (mph) = 55.7


As much as I would like to tell you what I have learned, I learned nothing on how to chose a gearbox or gear ratio and why. I am still clueless.

However, I did learn if you ask a very detailed question, with very detailed specs on what you have and what you would like to do, you MAY get some help.

This post has been up since 3/2 and you see what answers are here. I was hoping to get enlightend just the same as you.
Old 03-14-2007, 08:22 AM
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Default RE: Gearbox Help

BgCatfish1

Ok thanks.

I'm just getting into this electric stuff and am bewildered with the methodology that is used to properly select a power system for a plane. I've got down the battery technology, esc, Becs etc. but the choice of motor/ motor configuration seems to be a crap shoot, compounded by lack of a common motor size naming convention.

If you ever do find out the secret, please let me know.

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