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Old Apr 29, 2001, 08:50 PM
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Neil Morse's Avatar
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Calling all motor experts

OK, here's the question. I have a Lil Hornet with the stock power system which is called the "MMG-1." It uses a flat can motor with the name "Johnson" on it, and a home-made gear drive that uses a piece of square brass hollow stock, a piece of brass tube, a 4-40 shaft, and nylon gears. You solder the whole thing together, and it looks pretty funky but works great. I'm using it with the recommended 7X5.5 prop on 7X720 NiMH packs, and it flies the plane really well.

So what's the problem, you're wondering ... Well, after 20 or 30 flights, the brushes are sufficiently worn so performance drops below an acceptable level, and it's time to buy a new one. At $14 a pop, this doesn't seem like a great deal so I'd like to find something that will give me the same performance but last bit longer.

The TR-389 system has a flat can motor imported by Johnson that appears to be identical. Does anyone know if it's the same motor? Any other ideas for the Hornet?

Thanks for your help.

Neil
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Old Apr 29, 2001, 09:04 PM
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Toronto, Ontario, Canada
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I don't know if this applies directly to the motor you have, but the EDF guys have had a lot of trouble with the Johnson 180 motors burning up in the past. If the motor you are talking about is a 180, well it seems it's par for the course.

If it helps, they have found the DMC20BB motor, by Kyosho I believe, to be a more reliable replacement.

If you need further info in tracking down these motors, either ask here, or do a search for the DMC20BB motor in the EDF forum on Ezone.

Phil.
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Old Apr 29, 2001, 09:25 PM
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The MGK (or MMG-1) are very short lived on 7 cells, I don't even k ow why they recommend it. I guess because it will give you the power you need to fly the airplane but at the cost of short motor life. 5 cells they last and 6 is pushing the motor.

The TR-389 is a different motor in both size and power. I use 7 cells on my TR-389 motor all the time and it is still going strong.

Todd
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Old Apr 29, 2001, 10:15 PM
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Todd:

Thanks for the info. I will call you tomorrow to order a 389.

Neil
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Old Apr 29, 2001, 10:20 PM
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Order some more of just the MM1 motor from EMPS for $3 ?

Let us know how the TR-389 does on the Hornet, mine is almost complete, so I may be in the same boat soon...

Todd, are you selling replacement motors for the 389 if they are needed ?

[This message has been edited by radix2 (edited 04-29-2001).]
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Old Apr 30, 2001, 09:28 AM
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Radix:

What's EMPS? Thanks. I'll let everyone know how the Hornet does with the 389. I'll have to change the name from Lil Hornet to "Lil GTO." (Automotive reference that may be lost on the younger set.)

Neil
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Old Apr 30, 2001, 10:41 AM
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Neil,
http://www.empsinc.com/catalog.html
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Old Apr 30, 2001, 11:04 AM
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I emailed airplane planet who makes or distributes the geardrive some time ago asking if the motors could be purchased separately and I was told that I would not be able to remove the motor from the gearbox housing without destroying the housing.HMMMM.......... Best Regards
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Old Apr 30, 2001, 07:59 PM
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OK guys I did some digging and came up with some hard data on the TR389 compared to the MG-1 The TR389 has the same diameter as the MG-1 but it is 1/8 inch shorter. The TR389 also has only half the resistance as the MG-1 has. tested at a consant voltage the TR389 showed 2.5 amps locked and 1/4 amp free. The MG-1 showed 5 amps locked and 1/2 amp free. (thanks Bob)
This translates as that the TR389 will run better at a higher voltage than the MG-1. It will also be more effiecent at the higher voltage. It will however have a low RPM at the lower voltage.
Neil, Let us know how you like it in flight.
Also Neil, I was thinking about the props you were using you had increased the prop diameter on your Hornet, that may have contributed to your early motor failure. I will email you. JT
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Old Apr 30, 2001, 08:04 PM
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Quote:
Originally posted by Bleriot:
I emailed airplane planet who makes or distributes the geardrive some time ago asking if the motors could be purchased separately and I was told that I would not be able to remove the motor from the gearbox housing without destroying the housing.HMMMM.......... Best Regards
As I posted above, it seems like a better motor but it also seems like as steep price for a disposable setup. To be honest that is enough to discourage me from buying one. I have a drawer full of burnt out motors from one reason or an other. Thank god none of them have a thirty dollar gearbox attached to them. John Tracey

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Old Apr 30, 2001, 10:28 PM
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Is the MM1 the same motor that's in the Firebird? It's a flat can motor with Johnson on it like the one Neil described. If it is I'm going to get some of these for some projects. The Firebird has a good amount of thrust running on the little 4 cell nimh packs. As soon as my Pixie 7B arrives, I plan to use a firebird motor to power a Wattage B-2. I think it might turn the B-2 into a nice flying little plane, and still keep it fairly light.
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Old Apr 30, 2001, 11:01 PM
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Quote:
Originally posted by JTinCT:
OK guys I did some digging and came up with some hard data on the TR389 compared to the MG-1 The TR389 has the same diameter as the MG-1 but it is 1/8 inch shorter. The TR389 also has only half the resistance as the MG-1 has. tested at a consant voltage the TR389 showed 2.5 amps locked and 1/4 amp free. The MG-1 showed 5 amps locked and 1/2 amp free. (thanks Bob)
This translates as that the TR389 will run better at a higher voltage than the MG-1. It will also be more effiecent at the higher voltage. It will however have a low RPM at the lower voltage.
Neil, Let us know how you like it in flight.
Also Neil, I was thinking about the props you were using you had increased the prop diameter on your Hornet, that may have contributed to your early motor failure. I will email you. JT
There is alot of good info on Hornet improvements on the RadicalRC Webpage - http://members.aol.com/davthacker/lilhornetmods.htm

JT, can't follow your data here:
1. 389 is smaller
2. 389 has less resistance
3. 389 has lower stall current
4. 389 has a lower Kv

these can't all be true -

2,3 don't work at all toghether

if the 389 has a lower resistance, it would likely be due to lower turns =less reistance =higher Kv=higher efficiency=better for lower number of cells, not higher

or

if the 389 has a higher resistance, it would likely be due to higher turns =higher reistance =lower Kv=less efficiency=better for higher number of cells.

whatchathink?
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Old May 01, 2001, 05:49 PM
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Well, I think that you are probably right. The measurements that I got (and actually wrote down) were the both motors free running current and their locked up current. As far as the resistances go I didn't made a mistake on that and it all went down hill from there. I stand corrected.
John Tracey
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Old May 01, 2001, 06:22 PM
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John,

So I think your saying that the 389 is a higher turn/ lower speed motor - right ?

You know where this leaves us now? - Still waiting for Neil to tell us how it works !

Regards

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Old May 05, 2001, 10:14 PM
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I tried the TR-389 in my Lil Hornet today, and it works great. It flies the plane just as well on 7 cells as a fresh MMG-1, but is quieter, draws less current, and apparently will last a whole lot longer. Highly recommended.

Neil
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