TRex 700 DIY Flybarless Conversion

[J-S-Q]

I converted my TRex 500 to flybarless a while ago and was extremely pleased with the result so I have decided to try a similar idea on my 700N. I've not seen any DIY rotor head conversions on the 700 so I really have no idea how well this will work but I thought it would be interesting to try it.

I will write some details of how I'm going about this in my next post but before I get to that I just want to say a very BIG thanks to Heliphil. He made some custom metal spacers for me that I realised I would need to make this work. I've never met Phil but he volunteered to make them for me after I posted about it on this site. Tried to bung him a few quid but he wouldn't have any of it! So, thanks very much Phil.

[J-S-Q]

First, here's a few photos of how I did the 500 conversion (all stock parts except the longer balls on the mixing arms, where the linkage comes up from the swash). It flies superbly (with a BeastX) although I have no point of reference because this is the only FBL setup I have ever flown.

[J-S-Q]

So, here's what I'm doing:

1. Remove the flybar, flybar cage, mixing arms and seesaw assemble so you are just left with the headblock and blade grips.

2. Heat the mixing arms in the oven and remove the bearings:




3. Replace the original bearings with MR74ZZ bearings which have a 4mmOD. Best to get the Align HS1222 as they also include a couple of washers that will come in handy. You will also need to find spacers that go between the two bearings. They will need to have an ID of 4mm, 1.5mm thickness and approximately 5mm OD. Here’s a picture of the original bearings/spacers (left) and the new ones (right):




4. Use an M4 x 12mm bolt to mount the mixing arms to the head block. You should use the washers that came with the bearings on the head end of the bolt. You should also use another spacer on the end nearest the head block. This will stop the arm rubbing against the head block. Here’s a photo without the mixing arm itself to show the order of assembly:




And here’s a photo with the arms actually in place:



That's it for now but more to follow pretty soon. I have a BeastX winging it's way to me as we speak and I am hoping to get this thing airborne some time in the next week or so.

[Paulo uk]

Nice one mate, been waiting for this.

Paul

[millerman]

looks interesting but surley the controls are all reversed as although you have got leading edge control at the head its being controled by the trailing edge on the swash im not sure thats a good thing really must confuse the crap out of the controller and an align flybarless head would cost around £80 odd and at least it would not be running the controller back to front

[J-S-Q]

looks interesting but surley the controls are all reversed as although you have got leading edge control at the head its being controled by the trailing edge on the swash im not sure thats a good thing really must confuse the crap out of the controller and an align flybarless head would cost around £80 odd and at least it would not be running the controller back to front

Doesn't confuse the controller at all. The swash movements are the same for cyclic control but reversed for collective control. All that means is that when you apply positive pitch the swash moves down instead of up but this creates no issues whatsoever -it's just 'different'.

Agreed, I could buy a ready made head for 80 quid or whatever but where's the fun in that?

In fact, I reckon I might well be buying the 3G washout base instead of adapting the stock parts although I haven't decided yet but will post when I figure it out.

[millerman]

thats ok then just looked confusing as i know how the controllers work but if it works then all good and as for the head parts what ever floats your boat mate personaly i like the correct parts but if you enjoy making them then thats cool too

[trillian]

That's cool. It's interesting you opted to use the flybar cage as mixer arms to tone down the input rather than go straight to the grips. Most FBL heads tend to extend the arms on the grips for this reason (to get a bit more movement and keep them from being too sensitive) so that's another way to approach it.

You have a bit of delta still with the links where they are on the grips but I'd guess that's pretty minor, especially with fairly stiff dampers.

I'm probably going to try a DIY approach with the Ely.Q and it should be really easy.

[J-S-Q]

You have a bit of delta still with the links where they are on the grips but I'd guess that's pretty minor, especially with fairly stiff dampers.

I read up a bit on delta before doing the 500 conversion. Some interesting stuff in this thread:
Positive / Negative / Neutral Delta - HeliFreak

There are some good arguments in that thread for having negative delta designed into a rotor head -hence the reason for using leading edge control.

[trillian]

I read up a bit on delta before doing the 500 conversion. Some interesting stuff in this thread:
Positive / Negative / Neutral Delta - HeliFreak

There are some good arguments in that thread for having negative delta designed into a rotor head -hence the reason for using leading edge control.

I'll have a look at that article as well. I was recently reading another one, I think on RR, about the idea behind correcting or non-correcting by using positive or negative delta etc. Just for grins I have setup for zero delta on one of my 450s but have not flown it yet to see if it makes much difference.

[ddracer]

Guys call me stupid but there looks to be very little delta if any at all. The link from the swash to the mixer looks to be vertical (perpendicular to the swash). Then the link from the other end of the mixing arm is also vertical (perpendicular to the grip), OK its not in the center of the mainshaft but that really doesn't matter as long as the link is vertical. The link leaning out from the mainshaft wll not effect delta only amplify control movement.

eg. if the lenghend the grip ball link and the mixer ball link so it was in the middle of the main shaft it would still have no delta.

[J-S-Q]

Guys call me stupid but there looks to be very little delta if any at all. The link from the swash to the mixer looks to be vertical (perpendicular to the swash). Then the link from the other end of the mixing arm is also vertical (perpendicular to the grip), OK its not in the center of the mainshaft but that really doesn't matter as long as the link is vertical. The link leaning out from the mainshaft wll not effect delta only amplify control movement.

Assuming that we are referring to the 500 head in my second post…

There IS negative delta in that setup. That is because the ball link on the blade grip is off centre from the main shaft so when the grip moves up or down (because the feathering shaft moves around in the dampers) the pitch of the blade will be altered (because the other end of the linkage is attached to the mixing arm which does not move).

eg. if the lenghend the grip ball link and the mixer ball link so it was in the middle of the main shaft it would still have no delta.

If you lengthened the blade grip ball so that it was in the middle of the main shaft then there would be no delta. The length of the mixer ball will not have any effect on delta.

[ddracer]

Right I get it. So with the ball extended to the center of the mainshaft the ball will stay at the same hight just rotate slightly with the movement of the blade.

Nice one thank you.

[J-S-Q]

A quick update:

I received my Beast X yesterday and set up the head. You can use the stock linkage rods without a problem and they only require a turn or two to make them the right length. I was pleased to find that the Beast X showed a blue light at 6 degrees cyclic during the setup process indicating 'correct geometry' for a flybarless head. I have set up for +/- 11.5 degrees collective (although there is room for more) and +/- 11.5 on cyclic.

I decided to buy the Align 3G mixing base assembly because the stock ones are a bit short for this purpose and result in some fairly sharp angles at extreme collective/cyclic pitch so I'd be worried that the links might come off the balls in flight. I am currently using the original mixing base (drilled and tapped for a grub screw to secure it to the main shaft) but with the longer 3G arms bolted to it. You can't use the 3G base because the anti rotation pins on the head block would obstruct it although If I'm happy after test flights I will probably dremel off the anti rotation pins and use the 3G mixing base.

Depending on work and the weather I hope to test fly later this week so I will report back on how it goes.

[J-S-Q]

I got three test flights in today and it's working very well. It flies much like my TRex 500 FBL i.e. extremely stable, very agile, tracks straight as an arrow. So the early verdict is very positive although I have to give the usual disclaimer that I don't fly proper 3D, just sport/aerobatic flying so I don't know how it would perform if pushed harder.

The downside to this conversion is that unlike the TRex 500, I had to spend about thirty quid (for bearings and anti rotation arms) and use custom spacers (thanks to Heliphil) so it's not quite as straightforward to do as the 500. The geometry also does not work out quite as well as the 500 in that the links are not as close to being parallel to the main shaft (although frankly from what I can tell from photos, the Align 3G head does not have parallel links anyway so the geometry on that head is certainly not perfect).

The upside? Well, it's cheap, it works great (at least for sport flight), and it's 'different'! I personally prefer the look of it compared to the 3G head but that's just me. I have also heard it claimed that this kind of lever arrangement offers some additional protection to the servos in the event of a crash. I don't fully understand the reasons why but interestingly enough, I had a pretty bad crash on my 500 (broken frames, bottom plate, landing gear, blades, snapped boom, smashed canopy etc.) and none of the plastic servo gears were stripped. Make of that what you will.