Thread: Mini-HowTo VTOL-Trainer Build Thread
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Old Jan 27, 2013, 10:55 AM
Ran D. St. Clair is offline
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Originally Posted by leadfeather View Post
There are details in the jump jet thread. The purpose of the jump jet build/experiment was to see if a standard quad FCB and programming would work for VTOL no mods to the quad code. It worked very well...much better than I expected. The tilt servo was hooked directly to the Rx with a servo slower device.

I think the spars I used for the fans in the jump jet were a stout 6mm. The motors are pretty protected by their location being nested in the airframe...less vulnerable to impact than plain quad. A single flush mounted servo in the fuselage tilted the fans.

I think tilting all 4 fans is probably better for a quad VTOL. As all 4 motors approach full forward tilt they will have little effect on forward flight control.

For the Bixler project I would suggest:
  • Beefing up main spar in wing...the spar that came with my Bixler was pretty wimpy. Also fans mounted on wings may cause wing twist with yaw inputs in hover.
  • Quad with all 4 fans tilting together
  • Tilt input direct from Rx with adjustable rate servo slower
  • Standard quad programing at first
  • After all else is working good make minor tweaks to programming such as turning off gyro to fans at full forward tilt.

I read your jump jet thread. Great stuff! It's clear you have been there and done that and that you know what you are talking about. Of course, I alredy knew that because your advice was so sound.

Speaking of advice, your list above is/was very much exactly what I had planned. I am waiting for parts now, so once I get the Bixler in hand I will be better able to see what I need to do.

My origional plan was to just glue the wings in and then add support struts from the motor pods to a flat plate on the bottom of the fuselage. That would solve both the wimpy spar problem and the torsional rigidity problem. Then I got to thinking about the disassembly for transport issue and now I am concerned about adequate access to the fuselage internals. A removable wing complicates the structure but could improve access. Everything is a tradeoff. If I were designing this thing to be productized (and I am not) I would want to mold in a large diameter wing tube and forgoe the drag and complexity of the external wing struts.

Speaking of productizing, I think you have proven that there are several variants on these concepts that are ready for prime time. I think they would be very marketable. I am not necessarily suggesting that you would want to do it. I gather that you, like me, have a "real job", and I think being a hobby toy designer is a very hard life for all but the special few. I do think you will see most of your designs available in an RTF version in just the next few years. It's just too cool and works too well for it not to happen.

Back to specifics... Can I assume your standard quad programming includes tuning for zero "I" and only "P"? I am concerned that any significan "I" at all would fight the plane hard in forward flight mode and probably cause all sorts of ugly side effects. On the other hand, without the "I" hovering is still entirely possible, and even relatively easy for an experienced quad pilot, but it is not the almost hands off "full training wheels" of a true auto level mode. As always, I am interested in your wisdom.

I am using the slow function in the TX instead of a servo slower, but I think it is the same concept. I would prefer to have the motor tilt on a pot rather than on the flap switch, but my DX7 doesn't support it. It has a pot of course, but it is not readily accessable without taking my hands off the sticks. Neither is the flap switch but at least it is a quick flip and back to the sticks. Some higher end transmitters have better ergonomics in this regard.

I will start with the KK2 standard programming, and the Guardian, since I already know how to make that all work. it would be better to have just one flight controller but in the short term I need the "I" (auto level) and the "tail following" mode in the Guardian. Both of these could be programmed into the flight controller but I haven't gotten there yet.

Your input is always appreciated.
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