### Adding a horizontal motor/prop to drive a quad

When you command a quad to go forward, it tilts forward, and that creates a forward "thrust".
What would happen if I attached a horizontal motor/prop onto the quad, and provided a horizontal thrust that way? Would the quad maintain level?

#### Replies

• Probably not.

Think about thrust vectors and why the flight controller has to change the aircraft attitude to initiate flight.

If you want the aircraft to stay perfectly level in any flight mode other than loiter, you would need a minimum of 4 thrusters, mounted in opposition.  Two on the roll axis and two on the pitch axis.  Additionally each thruster pair would have to be in perfect alignment along their respective axis.

Now we have EIGHT things to control as opposed to just 4, and we haven't even discussed the code necessary to do this.

• That sounds complicated, Clif. I saw a video of a quad with a horizontal thruster maintaining level pretty well.

https://vimeo.com/144135616

• Exactly my point.  That scheme would insure the aircraft could move in any direction and the FC would keep the aircraft level.

I still don't get why you want to do this in the first place.

• I thought your point consisted of 8 motors, but maybe I'm misunderstanding you.

I'm thinking of using a quad to launch model planes of up to about 1kg. If it works, a lot of people would like something of that sort.

• I did say 8 motors.  4 motors for verticle lift and 4 motors for left, right, front,back.  Harrier jets use "puffers" to control yaw during verticle take off and landing.  The flight control system takes high pressure air from the turbine and uses it the much the same way the reaction control system on a space craft does.

OK, now you really have me puzzled...  Are we talking about a flying aircraft carrier?

• Randy, I have seen the first video but not the second one. In the second one I wonder why he mentioned that the pusher prop didn't help much. Does he mean that the quad can achieve the same speed without the additional prop?

With my idea of launching a plane from the quad, I would rather not have the quad tilt in order to achieve forward speed. I'd rather the plane be maintained level.

If a plane on top of the quad were to provide forward thrust, could the quad maintain level?

• Developer

Dan,

If the quad were in AltHold mode instead of Loiter it would stay level and not fight the forward motion (caused by the plane's motor).  It would be a bit manual though 'cuz the operator would have to then switch the copter back to RTL to make it come home.  It could be all done autonomously by either creating a new flight mode inside of copter or using a companion computer controlling the copter with guided mode (Guided mode has several sub-modes, one of them is the same as altitude hold).

• Randy, about the RTL control, I have an amateur idea how to accomplish that.

The quad Tx would be mounted on a board and placed on the ground. On the board there'd be a Rx and servo, controlled by the pilot. When the plane is separated from the quad, the pilot would hit a switch on their Tx and the servo would hit the RTL switch on the quad Tx.

• Randy, about the RTL control, I have a amateur idea how to accomplish that.

The quad Tx would be mounted on a board and placed on the ground. On the board there'd be a Rx and servo controlled by the pilot. When the plane is separated from the quad, the pilot would hit a switch on his/her Tx and the servo would hit the RTL switch on the quad Tx.

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