How much shorter should the TT be than the boom?

[curmudgeon]

On my E7SE, the boom is 813mm long and the TT is 802mm.  So the boom is 11mm longer than the TT.

On the E5s conversion kit, it is my understanding that the boom is 710mm and the TT is 700mm.  So the boom would be 10mm longer than the TT.

On my E5, the boom is 640mm, and the TT is 632.5mm.  The the boom is 7.5mm longer than the TT.

Should I shorten the E5 TT from 632.5mm down to 630mm to avoid too much pressure against the TT gears?

[Rodney Kirstine]

You have way more than 2.5mm of adjustment by moving the boom in the boom clamps  and/or moving the tail box on the boom to account for that difference. Unless you have access to machine tools, you aren't going to be able to accurately cut 2.5mm from the TT, anyway.

[Jason Cummings]

A miter saw could very cleanly and accurately trim 2.5 mm if you needed to imho. We trim aluminum at work this way all the time.

[Jason Cummings]

Don't forget safety glasses!

[curmudgeon]

So, if I understand you guys correctly, you suggest I cut the TT so it is 10mm to 11mm shorter than the boom?

[Rodney Kirstine]

You also need to drill a new hole for the screw that holds in the TT end, otherwise, you've effectively done nothing to shorten the TT.  Unless you have a drill press and the right kind of jaws for your vise, it's going to be pretty hard to put the hole in the right location.  The TT is pretty small diameter and the drill bit is going to want to walk off the tube, even if you do center punch it first.  I'm not saying it's impossible but my main point was that, for that small of a difference in length, the alternatives to just adjusting the boom position in the boom clamps are kind of a PITA.  I have access to a full machine shop and I'd still go the adjustment route, not the modification route, but that's just my opinion.

[curmudgeon]

I cut the E6 boom and TT to 700mm and 689mm, respectively for the E5s.  I managed to make the TT end holes with a Drill.  I admit it was tedious, but I can do it.

My question relates to whether other E5 owners have had to shorten the stock 632.5mm TT to play well with the stock 640mm boom?

[Rodney Kirstine]

No. I'm guessing the percentage of people who just assembled it, as is, would probably be pretty high but that's just a guess.

[Rodney Kirstine]

What i meant was... I have a few hundred flights on mine with the stock length parts and the only time I've had issues with the TT gears is when I broke them in a crash.

[curmudgeon]

I wanted to share some of my findings on the boom to TT length difference on my new E5 build.

First of all, I inserted the boom into the boom clamp (305-111) so that the boom edge is flush with front boom clamp (page 36).  I inserted the tail box assembly (page 39) all the way into the boom.  With the stock 640mm boom and 632.5mm TT (7.5mm difference between the two), either the boom is 0.5mm too short or the TT is 0.5mm too long.  Since one cannot make the boom longer, the only choice is make the TT shorter.  At 632mm (8mm difference), the TT would be flush.  I is my understanding that the TT works best when is "floats" on either end, so I am going to cut it down to 630mm (10mm difference).  Since the TT end (320-502) flat part is 15mm long (or 30mm between the two ends), 2mm of float should be fine.

[Rodney Kirstine]

I'm just curious why, with that tiny bit of a difference, you wouldn't just either pull the boom back 2mm in the front clamp or pull the tail box back 2mm?  Or, split the 2mm between the two and adjust it 1mm at each end?  You seem really bent on wanting to make a lot of work for yourself that's probably not necessary.  If you enjoy the challenge of trying to get every little thing as exact as possible, then, more power to you. The tolerance stack up of the whole TT transmission and tail boom assembly consists of the hole locations in the frame where the TT transmission mounts, the tail boom mount mounting hole locations, the transmission parts, the tail boom mount thicknesses, the tail boom length, the TT length, the TT end lengths, the hole locations in the TT end and the TT, and the tail box parts.  I haven't asked Matt, to be sure, but I'm pretty sure that's one of the reasons the tail boom clamps and the tail box mount the way they do, so you have some adjustment.  There are threaded holes provided in the boom clamps and the tail box so that you can get it adjusted to where you have your gear clearances and then mark that location, drill your holes, and pin the boom.

Also, what kind of metrology are you using to measure the length of these parts?  Do you have an instrument that's truly capable of accurately measuring the length of these parts with sub-mm precision?  Come to think of it, without having a print to look at or talking to Matt, we don't even know what kind of tolerances he has on the overall length of the TT and the hole placements.  These are the reasons I'm asking, I'm not trying to be critical of what you're wanting to do.  I'm just interested in your point of view and I'm also trying to save you some time and hassle for something that's so far up the slope of diminishing returns that it's just barely a blip on the chart.

[curmudgeon]

Consistency.  I now have 3 Synergy kits with similar boom and TT mechanics.  It just makes it easier for me to annotate this information for whenever I have fix any of the helis or buy another Synergy heli.

All Synergy manuals recommend keeping the boom edge flush with the front boom clamp.  On the other end of the boom it make sense to me to insert the tail assembly all the way into the boom.  It makes it easier for me to just adjust the TT length to match the rest of the system than to try pulling back on the boom from the front boom clamp and/or pull back the tail assembly from the boom.  Just easier for my brain.  Either way, I removed the excess 2.5mm off the TT with a pipe cutter and drilled holes on the TT so the TT ends sit flush on the TT.  I really don't expect to log tail vibrations related to the TT.

What's my methodology?  I used two methods.

Method #1:  Boom inserted flush with front boom clamp.  TT inserted into boom.  Tail assembly inserted into boom as far in as it will go.  Mark the edge where the tail assembly and boom meet.  Then, remove tail assembly, remove TT from boom, reinsert tail assembly all the way in, and mark edge where the tail assembly and boom meet.  There was a 0.5mm difference.

Method #2:  Boom inserted flush with front boom clamp.  No TT used.  Tail assembly inserted into boom as far in as it will go.  Annotate length from rear boom clamp to edge of tail assembly (540mm in my case).  Then, remove boom.  Just used TT inserted into from drive and tail assembly.  Length from rear boom clamp to tail assembly was 540.5mm.

Both methods agreed that the TT was 0.5mm too long relative to the boom (or boom 0.5mm too short relative to TT).  I figured that instead of eyeballing pulling back the boom from the boom clamps and/or pulling back on the tail assembly, it was just easier for me to just cut the TT to appropriate length.

[Rodney Kirstine]

I said metrology, not methodology:

Metrology -  The science of measurement. Metrology includes all theoretical and practical aspects of measurement.