i love the system 88 aproach and want to make it work perfect with the FBL to achive the maximum resolution for F3C

The thing is, that in your aproach the links are going up at a angle.
that changes the geometrical issues on positive and negative giving a inlinearity.

the FBL Unit will correct for that, but i am still thinking of how to avoid that.

the B-Machine (my second Nova Cuatro) will be build in the next weeks (just HSC milled a new gearplate, little stiffer) and will first be tested with the flybar and the BD3SX to check the vibration levels with the Webra Engines.
Then i will convert to FBL (B-Machine) and then (if it is better) also the A-Machine.

in the conversion my goal is that the Head is maximal linear for the FBL unit, so we have the same ideas.

another question

Why do you connect the AIL and ROLL servos on the outside?
the building plan does not anything there

Hi RogerRabbit62,

Well, I'll have to examine the effect of that angle at the extremes of positive and negative collective but I don't think it's going to be different enough to be a problem because you just don't need massive movements with FBL since you're not sharing authority with a flybar.

I assume you're thinking you'll have less cyclic for a given swash tilt at high positive pitch than you will at high negative pitch? I'll look into this and check it with a pitch guage and measure the degrees of swash tilt but my thought is that whatever difference there may be just won't be enough to worry about. (there's always going to be some non-linearity at the extremes of pitch because of the nature of rotating servos.

I'm not sure what you mean about aileron and roll servos on the outside

Those Pictures where the servocases where connected where not from you, it was the last pic from "MARKUS" posts on the last page.
sorry for the confusion.

it would be nice if you post the results of your measurements on the pitch gauge.

another thing you might check is, if you induce delta.
I cant judge from the pic but it looks that the control point of the blade is not centered to the heads middle.

if you do it like that you induce delta.

That might be beneficiary or contraproductive. the FBL will take care anyway of that effect but - i am with you on that - it is better to have the fbl regulate away as few as possible.

Yeah, this is not a finished item with regard to the ball link on the grips, I just grabbed what I had lying around to get it close to where it should be. So it's a couple mm off from the centre but I will get it to where the link is centred and there will be no delta. But as I mentioned, I'll be looking for different grips anyway as I'd really like to get some metal grips on there so that the damping can be controlled without the element of flex in the grips. But if I don't find suitable metal grips I'm sure the plastic ones will work.

One thing I was going to mention regarding the rod to the grips being at an angle; Some of the JR and Kasama FBL rotorheads are done where they keep the upper mixer arm and this makes the link rod at an angle and I'm sure those guys would have changed that if it was a problem. I won't have time to sit down and take out the pitch guage till later but just looking at it I can see that the angle doesn't change when you move the swash up and down because you must remember that the grip arms are moving as well. Sooooo, if that angle doesn't change I don't think the geometry changes but I'll check it later using the full tilt of the swash at +/- 10 degrees.

Could you do measurements yet?

Hi Roger,

I'll do it today, I just keep getting distracted with other things.

--- I'll put up some pics tomorrow (Thursday) from my experiments today. It was more difficult than I thought to really measure accurately without servos connected but I think I can demonstrate the main points with some pics I shot.

Here's 12 degrees negative collective

12 degrees positive collective

As you can see, the swash doesn't really need to move as far as you might think for 24 degrees of pitch.

Here's the two overlayed. The important thing here is that the angle of the pitch rod to the grip remains the same. My pitch guage does not go high enough to measure the full cyclic range AND collective. So the best I could do here is see that the angle stays the same, so the change in geometry will be the same for pos and neg. With full tilt of the swash at mid stick I was seeing a LOT of cyclic. There's always going to be less cyclic at full positive or negative collective but it sure looks the same at both pos and neg.

Did you get to finish this conversion project as you have not updated the thread.

No, I didn't finish it I've been a real slacker on this one, which is not my usual style.

I keep putting other projects in front of it. I converted my Rave ENV to FBL and I'm now converting it to a Ballistic. I have also been building up a Knight 3D and spending time with a Kasama Faifa and Minicopter Triabolo.

I did think, just recently, that it would be nice to have an electric flybarless Robbe and that I should probably finish it. Sooooo, I'll give it some thought.

OK, I just ordered the frame stiffeners from rcmarket, which I only discovered they had a while back and thought I would have to get something fabricated (which wouldn't have been difficult in any case).

So I will really try to finish this conversion now.

Thinking about rotorheads / headblocks

Since ordering the frame stiffeners I have had a look again at the headblock and I have a few thoughts. First of all, I have no doubt that the stock Milli / Futura head will work just fine but ideally I'd like to lower the height of the grips just a little / effectively raise the C of G, and also I'd like a bit more engagement between the headblock and the main shaft (and if I'm making a wish list I'd also like metal grips).

One option that looks like it will work is an Outrage 50 rotorhead with FBL grip arms. It sits a little lower, has a little more overlap of the headblock onto the main shaft and has metal grips. So that's option 1.

Another possibility is to use a Beam Avantgarde headblock and main shaft which has a huge area of engagement. The shaft has to be used as well because the upper Jesus bolt sits way up there. It might bring the grips down a bit too low. I can't say for sure as I'm just making rough guesses until I actually do some measurements. I want the main blades to sit no lower than 160mm over the boom (I'm not totally sure what the lower limit is but that should be plenty safe with hard dampers).

The frame stiffeners arrived yesterday, so I'll revisit this project now and try to get the last bit of filing and trimming done, drill the holes for the front of the motor mount and then see about the head linkage.

I have some Align DS610 servos I can use and a spare Total-G. I'll see about having this Align 700M motor rewound as I have another one that is working really well.

Looking forward to seeing the finished work, if you want the head lowered can you use the fly bar bearing for the J bolt and the bottom stock J bolt clamped down with a swash driver block. if i do get mine converted i will post a photo.

Hi IYKIST,

Yeah I thought about moving the Jesus bolt to where the flybar carrier used to go and then what I'd do is find a locking collar that would fit over the lower part of the headblock and clamp it securely against the main shaft.

I have to finish the fitment of the motor mount first anyway so I'll have a think about it. I need to buy a new drillbit as the one I have has become too worn to bite properly.

--- OK, after a few minutes with the file it all fits together as it should now. Here's a pic with the frame stiffener in place.

progress

Well a month went by that I didn't do anything but today I drilled the front motor mount holes and have bolted it all together now. So from here on I truly will make much quicker progress as all the difficult stuff is done and now it's the fun stuff.

I just need to round up some servos and decide where to physically mount the electrics.

It will have a Total-G FBL unit and for now I'm using the Outrage rotorhead. Hopefully I won't have any problems getting enough pitch.

I got a 700MX 470KV motor and was pleasantly surprised to find that it is shorter and lighter than the 700M.

Provisional layout

In order to figure out where the LiPos can go and where the C of G would be I put the tail on and played around with the placement of the electrics.

There's bags of space under the motor but I want the C of G as high as possible so this is what I came up with. I the servos just sitting there along with the RX, FBL unit and regulator just to get the weight on for finding the balance. With these 4300mah packs the balance is just right and there will still be another 150 grams or so in front with a 2 cell RX pack and there will be 50 grams or so in back when the tail servo is mounted. So it looks really good as far as the weight distribution.

Total ready to fly weight should be a bit under 5kg with those packs, which is not bad at all.

One really nice touch is that the frame stiffeners have threaded metal inserts on one side so that the frame bolts just thread right into them.

I do not yet have an upper pinion support in place but that's really easy. It is probably not needed but couldn't hurt.

Anyway I'm a little ways off just yet as I need to get another DS620 servo and I'll need to fashion some plates with velcro for the batteries to strap onto and stuff like that but it's definitely a reality now!

Looks good.

I bought a setup off here and it had a RJX head on it and I'm pretty impressed with the quality for the price. Just one thing to think about is that Robbe had a problem with taking the boom off with the blades and this was a problem found when 3D was just beginning. I personally wouldn't drop the height of the blade grips much.

Also you might be better off rotating your swash follower so that the rods are straight and using a 45 degree mixing in your gyro. I've got mine set up on a GY750 and its perfect and originally my heli was done using a Vbar so it works well.

I just installed the RJX head on a Cuatro turbine and used a longer shaft that Robbe has, its 10mm longer than standard but I don't know the part number sorry.

Mick.

Robbe & Futaba.

Hi Sparkhead,

Things have come a long way since the Robbes were in fashion and one thing that has generally changed is that rotorheads use much harder dampers now for FBL setups.

The original Robbe heads had just a single o-ring per side and then with the SE there is a metal insert and a few variations to allow more o-rings.

Anyway, the point being there's nothing special about Robbes when it comes to the potential to boomstrike, any helicopter can do that if the damping is soft enough and there's enough teeter angle. Plus, blades are much stiffer these days than some of the blades being used in the early 2000s.

But I'm not even using the Robbe rotorhead on this one at the moment anyway, it's an Outrage head with metal grips and very hard dampers.
Right now the clearance is approx 160mm which is only about 10mm or so lower than the Robbe head. I think it's a safe margin but I've got a ways to go yet before it's ready to fly so I'll double check that it's not getting into the danger zone.

---just to add here - I just read on another forum in a Goblin thread that they consider the minimum safe distance on the Goblin 700 is 145mm. One thing I could easily do with the Robbe is angle the boom down slightly, just a very small angle would result in a considerable extra space toward the blade tips. I think the Kasamas have this kind of thing happening where the boom is at a slight angle relative to the main shaft. So just a tiny bit of slotting of the rearmost frame bolt holes where the boom mounts would be all it would take.

Regarding the 45 degree swash. That's part of the whole exercise. I can't imagine essentially working against the system 88 mechanics. I know it can be made to work by changing the phase in the FBL unit but for me that would totally defeat a big part of it. I want to keep the separate servo movements, or certainly at least try it.

Sounds like you have done your research, good luck with it. Are you going to run the same sort of HS as the Goblin?

Where did you get that canopy? Looks good. Was it made for the Robbe or is it a retro fit?

Mick.

Robbe & Futaba.

That is a Synergy N-9 canopy. It has to be cut a bit at the bottom to fit but otherwise the proportions are pretty much right. I also have a stock plastic Milli canopy.

Not sure on the HS just yet, I'll have to see what works best. My flying is smooth 'big air' and FAI type stuff so I generally don't need really high headspeeds these days.

--- Just to add, today I slotted the holes just enough for the boom to angle down ever so slightly, about .5 of a degree results in just over 1cm. So it went from a blade to boom distance of 160mm up to about 173mm. (that's measured from the underside of the blade, in reality it would be the tip that would strike the boom and the tip sits in the center of the blade at zero pitch so it's potentially closer or further away depending on the pitch)

Looking very good, it looks almost finished, i just like robbe mechanics they are robust and versatile.