Thorp Air Command - T18.net

Bob and I are currently rebuilding a T-18 and some have asked about our trim system. It is my belief that a vernier or the MAC trim are NO NO for this application. I've yet to see a trim system use anything other than a "screw Jack" for this application. Look at Bob's photo album and you will see our system. It consists of a Grainger gear motor (2L009), Traxxas driveshaft (5451X) available at a hobby shop, Traxxas yokes joint (5458X) a couple of micos switches, a double pole momentary on, center off, momentary on switch, and couple of 5amp 50piv diodes (radio shack)

Very nice! Thanks for the pictures.

Bill, I'm building up my trim system similar to yours and have several questions: Do you have a P/N for the Micro Switch and where did you get it from and do you have a wiring diagram. Thanks

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Stephen R. Peirce
S/N#078 Ph 256-461-0233
Rocket City
Huntsville, Alabama

I'll get the info this evening

*** admin posted for Bill Williams ***

Here's the wiring diagram;

Image Insert:

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Forum Administrator

I have been doing some work on an electric trim setup. I am trying to keep the weight down so came up with this set up. The motor is a 28mm Brushed Planetary Motor that does 12 RPM and weighs 260grams (9.2 ounces) it is held on by 4* M3 hi tensile (~172,000PSI)machine cap screws, they seem tiny. I haven't decided yet if the extra support bracket is actually needed, but some sort of additional support would add confidence.
I anticipate using that same Traxxas drive shaft setup to the jack screw.
Stuart

That really looks good! I put an access panel on top of the fuselage under the fin to help retrieve the motor in case I ever needed to remove it.

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Bob Highley
N711SH
SN 835
KLAL

Bill, what gauge wires are you running back to the trim?

I used 18 gauge, you can use 20 ga. as the 1L2009 motor draws 1.4 amps.

ok, thank you

Has anyone using the Granger motor, managed to incorporate a position feedback sensor? I am trying to figure out how one could be included but so far haven't yet come up with a neat solution.

Stuart,
It would be easy enough to implement, the two limits can be caught by the limit micro switches and a few intermediate points could be trapped similarly. However, I think you will find that it's really not necessary. The plane is controllable in either extreme and you'll figure it out pretty quick if you forget to set the trim for T/O which is the only time you really care about it. Basically as soon as the tail starts getting some airflow over it the stick will run fore or aft.

The stop to stop travel time on mine is around 11 seconds, I just run it full forward and then run it back with a 5 count. I just retrofitted Wendell's airplane with electric trim and he initially asked about a position indicator, I told him to just go fly, he did and has never said a word about it again.

I guess this really didn't answer your question maybe I'm just trying to say don't sweat it, you really don't need it.

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Lee Walton
Houston, TX
N51863,N118LW
KEFD

I put a small indicator lite next to my rudder trim switch to show when the tab is centered (lite ON). Nothing more than a small button micro switch epoxyed to the bottom of the rudder rib and a small tab on the servo arm to actuated the "button switch." I also have a RAC LED indicator for the elevator trim. As LEE has said it's nice to know where that trim is set for T/O !

RB

Although not a must have item some sort of indicator even if it was just a single light activated by an a micro switch when trim is set to the take off position would be nice confirmation. It would be simple enough to build it that way but when the 5 count count works so well it might just be an unnecessary complication.

Fraser had the same method on MLM (full forward trim, then come back for a count of 5) and he was happy with it. That's the simplest way to go.

When I rebuilt the as per the Bill-Bob pics, I was going to make one small addition... a red alignment mark on the side of the fuse for the proper trim location. The idea was to make it a pre-flight item.

Now that MLM has become MLMP, and I am fixing things that aren't broke, I went all fancy schmancy on the trim system. (Why simplicate when you can complicate?) I figure the only time you might want to know where the mechanism is set is for the T/O. Any other time, who cares? You just set it by feel. So,
I mounted a small magnet to the trip lever, and mounted a reed switch to the bracket. When the mechanism is in the correct T/O position, the magnet is aligned with the reed switch, closing the contacts, thus causing a green LED in the panel to light up.

Works great in the garage.

d

I think a ten turn pot. and a couple of gears and a meter would work. Mount the gears on the jack shaft and pot. using a meter as the voltage changes the meter wouln indicate the trim position. Go figure!