Safety trim wiring in parallel

[Esser]

Why does the safety trim kit have two wires for everything? Going to the Servo motor I have 2 20awg wires supposed to hook up to a single 22 awg wire. Is there an advantage for this? What is the best way to butt slice two larger wires to one small?

Also, the kitfox wiring schematic has two 14awg wires from the alternator. Does it need it for load reasons and if so why not use a larger wire? Is it for redundancy? Is it really necessary?

[n85ae]

Makes no sense ... I've doubled up wiring when I needed a larger size, but
it doesn't really make sense to kit something like that. On the other hand
there's no harm in it it either ...

Jeff

[jiott]

Maybe I don't understand what you mean by "safety trim", but the pitch trim servo motor has 2 wires. The long wiring cable that comes in the kit also has 2 wires. Hook the two wires in the cable to the two wires from the motor. One will be power and the other ground, then vice-versa when you switch to reverse. This is too simple so I am sure I don't understand your question.

[Esser]

This is for the brand “safety trim”. It’s a controller that slows down the speed of the trim motor in faster flight. It also has runway protection etc. It’s wiring diagrams have a lot of the wires wired in parallel. So you would have two wires attach to the red and two to the black on the motor. And I’m not sure with a 18-22 butt splice if I can put two 20 gauge wires in One end.

[DesertFox4]

TCW Technologies, one of our great site sponsors, makes this safety device.
Learn more about it here:
http://www.tcwtech.com/safety_trim.html#features

[jiott]

OK, now I see what you are talking about.

[Danzer1]

Josh, What model trim contoller do you have? Sounds like you might have a dual axis controller and harness for single axis use. Should have 10 wires for single axis and 14 for dual axis - none doubled up.:confused:

On current single axis models - #3 (yellow) should go to red (+) on the servo and #4 (also yellow) should go to black (-) on the servo.

Greg

[Esser]

It is single axis model ST-1-12v-2sp-HD

Here are pictures of my install instructions from TCW and kiyfox. Note pins 4,12 3,11 7,15 1,9

I just noticed that there is s note that says these parallel connections are for servos rated for more than 5 Amps. So why is the Servo itself a 22awg wire?

[Esser]

I don’t know why my pictures are posting so small. Hope you can still see

[Danzer1]

Your servo is likely rated for way less than 5 amps, hence 22 ga wire. If so this is the wiring diagram currently being used:

http://www.tcwtech.com/Installation%20instructions%20model%20st-1-12v.pdf

Greg

[Danzer1]

Hold on - check with TCW 1st - sounds like the HD may stand for heavy duty which would be for a much more robust servo.

I'd ask if you can pin per the current diagram or "un-pin" the duplicates from your current harness. Assuming you have a servo of less than 5 amps draw (most are less than 1 amp for this application).

Greg

[Esser]

According to this thread Eddie talked to John M and John said it was 7A.

http://www.teamkitfox.com/Forums/showthread.php?t=8316&highlight=Trim+motor+draw


So what’s the best way to wire the two parallel to the trim motor? Shorten up the 22awg wires coming off the motor as short as possible?

[Danzer1]

I don't think that is correct. 7 amps at 12 volts would require a much larger wire size than 22 ga. for any distance. Maybe .7 amps? What is the brand and model # of the servo?

Greg

[efwd]

Not sure what the AWG is on mine but its bigger than 22. More like 18 or 16.
Eddie

[Esser]

I went into the garage and put a micrometer on the bare wire. Looks like .0415”. So I guess that would be 18AWG. My mistake. The wire seems smaller but I guess that’s due to a thinner casing

[Danzer1]

Thats part of why I'm confused. The kitfox diagram shows a 7.5 amp fuse - so a 7 amp draw would then make sense for a load. I know they use a more powerful motor for the tail trim than the Ray Allens. That would equal about a 1/10th HP at 12 v. Which would require a much larger wire for any significant length. So why would they put a 22 ga lead on it, which would then be the weak point when it's got to be wired 10 feet or even more that would dictate 14 ga. or maybe even 12 ga.

So Josh's question of why a 22 ga lead is valid and makes no sense to me either unless the amp draw is actually much less than the 7 amp answer given so far.

Greg

edit - forgot to add: And if the amp draw is less, I certainly wouldn't want to be protecting the circuit with a 7.5 amp fuse or breaker - it will never protect anything - especially a 22 ga wire sizzling! Further - if it really is a 7 amp draw - would you want to take a chance on a 22 ga lead sizzling?

Somethings not right here, still:confused:

[Esser]

Thats part of why I'm confused. The kitfox diagram shows a 7.5 amp fuse - so a 7 amp draw would then make sense for a load. I know they use a more powerful motor for the tail trim than the Ray Allens. That would equal about a 1/10th HP at 12 v. Which would require a much larger wire for any significant length. So why would they put a 22 ga lead on it, which would then be the weak point when it's got to be wired 10 feet or even more that would dictate 14 ga. or maybe even 12 ga.

So Josh's question of why a 22 ga lead is valid and makes no sense to me either unless the amp draw is actually much less than the 7 amp answer given so far.

Greg

Hey Greg see my post above. I physically measured the wire and it is in fact 18amp. The casing on it is very thing and made me thing it was smaller. Sorry for all the confusion and thanks for all the help even though I was giving bad info!

[Danzer1]

My edit crossed your post;)

Still would be concerned. 18 ga is good for 5.37 feet. (2) 20 ga = 17 ga which is better than 18 ga but still only good for 7 feet or so. So if using 2 wires for say 10 feet that calculates to (1) 14 ga which in 2 wires = 17 ga each, which of course they don't make, so you would then go to (2) 16 ga which is effectively 13 ga and then good for up to 17.5 feet! Make sense?

(all calculated at 12v with 2% drop)

So in my mind, the wiring is fine from the controller to the servo if located within 5 feet or so of each other, but the power wiring from the controller to the fuse and the source may not be if also 20 ga.

How far is it from the controller to the buss? If more than 7 feet, may want to think about larger than (2) 20 ga wires. FWIW

Greg

[Esser]

I mounted the controller in the centre console so from the controller to the trim motor is probably about 10’. And about 5’ from the controller to the buss.

Maybe I will email kitfox and get the straight scoop on the trim motor. It’s installed and I can seem to get a make or model off of it.

[Danzer1]

Sounds like a plan. Looks like your wiring to the buss may be okay but to the motor might be iffy. I always use 2% drop but if calculating for say a 5% drop it would calculate okay with (2) 20 ga (then up to 17.3 feet). May not make a hill of beans difference but worth checking out!

Greg

[Esser]

Thanks for all your input Greg, it’s appreciated. Slowly starting to get my head around everything electrical.

[efwd]

Josh, the motor is unmarked. You will in fact need to ask John. Am I erroneously recalling that I got the electrical wire to that servo motor directly from Kitfox in the kit? I don't remember ever buying this gray cable. Let us know what John says if you don't mind.
Eddie

[Esser]

Josh, the motor is unmarked. You will in fact need to ask John. Am I erroneously recalling that I got the electrical wire to that servo motor directly from Kitfox in the kit? I don't remember ever buying this gray cable. Let us know what John says if you don't mind.
Eddie

Now that you mention it, I recall there being grey cable with multiple conductors in the casing. Is this for the trim motor? Noth8ng is said in the instructions. When I get home from work I’ll check it out

[jiott]

I am not going to get involved in this discussion because I only know enough to be dangerous. I just want to make one comment, and that is the wire gauge/amps/length tables are based on an allowable temp rise; so there are several tables depending on how much temp rise is allowable, usually based on the wires insulation type. I THINK Greg is quoting values based on a 10C temp rise which is very conservative for aircraft wiring with Tefzel insulation. Also remember this application is for very temporary duty-usually much less than 5 seconds on-time. IMHO the 18 ga. wire is just fine for 7 amps and 10'.

[Flybyjim]

I am about to start my panel layout, has anyone used a CAD type program that has the Kitfox panel available? I was looking at Solid Works as an EAA member but I am having trouble downloading onto my MAC.

[PapuaPilot]

Regarding using a Mac (I copied this from a website):

The simple answer is that SOLIDWORKS do not develop an Apple Mac version of the software, so we can’t install SOLIDWORKS natively.

We used to recommend the Bootcamp route, which involves installation of Bootcamp and then Microsoft Windows on the partition Bootcamp creates. The issue here is that if you need to access the Apple Mac Operating System (OS), you would need to shut down windows and boot up the Apple Mac OS, because they cannot be running simultaneously. This allows the full use of the hardware (RAM and graphics card) you have in your Apple Mac for Windows.

The alternative solution that we used to steer people away from is Parallels, a virtual machine software that allows you to run another OS inside the Mac OS (inside a window). The reason for not recommending this is that you are sharing the resource of the machine with two operating systems, thus not necessarily having the required resource to run a demanding program like SOLIDWORKS.

There were also historic problems with not being able to use the graphics card properly which would result in exceptionally slow performance when selecting things. This is due to most Macs not having certified graphics cards for SOLIDWORKS and parallels using a virtual graphics card driver or the default Windows driver. The virtual or generic drivers don’t offer the level of performance needed to run SOLIDWORKS correctly.

[Esser]

I used SketchUp. It’s a great program once you get past the learning curve. The catch is you need the professional version to export CAD files. You can down load the regular version, do all your design, and then get the professional 30 day trial and export the CAD file. Works great on Mac. This what I did for mine I just got a whole new panel cut for $100 instead of using the kitfox supplied one.

[jiott]

I made and still have AutoCad .dwg and .dxf files for my SS7 panel that I would be willing to share. If you have AutoCad you can erase my cutouts and put in your own. The exterior outline should be the same.

[Flybyjim]

Thank you for the suggestions, if you would like to send the files that would be great.

[jiott]

Send me a PM and give me your email address. This forum doesn't allow posting files of this type.

[dcsfoto]

TCW has a new box It will hookup to the Garmin autopilot without the need for relays or interface between the trim switch and trim motor

just put one in works great


they have two wires , small servos = 1 wire large (5 amp) like Kitfox need two wires

David Kelm
7SS 912iS

[Flybyjim]

Hi Dave,

I am going to use the Garmin G3X with auto-pilot also, I am not sure what the need for the relays are or the trim interconnect, could you explain. I am not up to speed with the wiring as I am going to have SteinAir make the harnesses for my setup.

[efwd]

I just spoke on the phone today with TCW. They told me that the schematic that is delivered with the unit is as easy as it gets. I was informed that if I had trouble figuring it out I better get help. By the end, what he explained was pretty straight forward. When you have two wires treat them as one. The 7amp trim motor will require two wire on each lead. He said this design was done on the request of Garmin. I think I will still get a little assistance but I am a bit more clear on the installation.. I think. :rolleyes:
Eddie

[Rob3782]

I believe the trim motor from Kitfox will draw only a little over 5 amps when running and 7 amps for a very short time when possibly starting or at the end of the cycle. It is very common for electrical manufacturers to under size their lead wires. 18 awg is large enough. Safety trim module is designed for more than just Kitfox’s trim motor. John McBean went through a lot to get them to redesign this for us.

[Flybyjim]

Is this trim module for a speed change in the trim motor depending on the speed of the aircraft? Is this in the build manual somewhere?

[Rob3782]

The Garmin servo has the speed reduction control built into it. It reduces the speed of the trim motors at higher flight speeds. Unfortunately Garmin tells you in their installation manual that the servo can only handle a one amp load. TCW has been building a safety module that prevents you from running your trim motor continually after it reaches the extent of its travel. So John McBean got TCW to build a module that would handle the higher amperage we need for our trim motor and lets Garmin control the speed reduction and has the safety circuit built in also. Some of this can be done with relays. It is a small compact module. I thought it was worth it. 14925

[Flybyjim]

I see, are most trim motors used in aircraft of this high amp draw? I have a Ray Allen servo mounted in the horazonal stab of my Rans S7 for my pitch control and I believe it is a much lower amp draw, there is no need for a speed reduction in operation at any airspeed.
Thank you for this explanation, Is there a need to have the speed reduction on the SS7 Kitfox screwjack for pitch control.

[Rob3782]

From what I have read on the forum in the past there was a few discussions on how to slow the trim speed while at higher speeds. It must be a common thing because Garmin built it into their system.

[Esser]

It’s described as quick but manageable with quick blips instead of holding a switch down above 60mph without it. Not required but a nice feature since you can reverse polarity if you need to and has a feature to stop a runway condition.

[jiott]

IMHO the trim speed reduction option is one of those nice to have items, especially for pilots new to the Kitfox, but certainly not necessary. I quickly got used to quick blips of the trim switch, rather than pushing the switch. After 10 or so hours I felt just fine with the simple stock system.

As a pilot gains experience you figure out ways to reduce your workload and be lazy. The Kitfox SS7 takes off perfectly with 1/2 flaps and the trim set at cruise trim with no flaps. So once you figure out this sweet position for trim, just set it there prior to T/O, then when your T/O climb is done and you retract flaps, you will find that the trim is already set for cruise. You hardly have to touch it except for maybe a quick blip to fine tune it. Yes, if you are doing a long climb to higher altitude you may want to reset the trim for cruise-climb then level cruise. Normally at the altitudes I usually fly at, I just hold a little stick back pressure and a little more throttle till I'm up to 1500-2000' and then just release the back pressure and throttle and wa-la I'm level cruising. Never touched the trim switch (OK maybe a quick fine tune blip). Lazy flying-works for me.

The better option to spend your money on I think is the trim position indicator. Then it is easier to preset your trim at that sweet spot I spoke of above.

[Flybyjim]

How does a servo know the speed you are flying and how would a servo be able to adjust your trim? The servo is connected directly to the push/pull control rod.
Perhaps I have a lot to learn here?

[efwd]

First, the Garmin Auto Pilot servos are connected to your Garmin G3X, (in my case). The G3X receives all the Pitot Data, so the computer knows your airspeed. It is the Auto Pilot servo (receiving info from the G3X) that is connected to the push pull tube of the elevator. As for the Trim Servo, It is in fact connected to the bottom of the horizontal Stabilizer, raising and lowering the leading edge of that wing. That trim switch is wired into the Garmin system so that the Garmin can adjust trim to lighten the load on the AP servos. All this, I am sure, applies to any of the Glass Panels. That function works with or without an Auto Pilot if I am not mistaken.
Eddie

[Flybyjim]

Okay, good to know

Thanks