As those who have been following along with our "minimum blimp" project to create the cheapest possible autonomous aerial robot (by adding an open source autopilot to a toy RC blimp), maintaining altitude in the face of air currents and temperature gradients has been a continuing challenge. The main problem with the toy RC blimps we start with is that they have a single tiny vertical motor and prop to control altitude, and unless you've trimmed the blimp exactly right and conditions don't change, that's not enough to reliably keep the blimp off the floor and away from the ceiling.

The best way to increase the vertical "authority" or control power is to get the two differential thrust props on each side to also do some vertical work, by tilting up or down along with their usual job of driving the blimp forward, back and right and left. Such tilting props are called "vectoring thrusters" and they're what the expensive blimps use. But on the cheap toy blimps that we start off with, the shaft that holds the two horizontal thrusters is glued and screwed into place.

No fear. Converting this shaft into one that can rotate is a simple matter of five pieces of Lego and a small RC servo. You can see it work in the video above, but here are some shots to show how to make it.

Before (typical toy blimp gondola, with RC equipment stripped out):


Parts needed (Lego Technic parts and one servo):


Cut the blimp motor shaft in half and insert the Lego rod, with the gear and two Lego beams on it. Cut out a bit more room in the gondola and glue the two beams in. The shaft can now rotate:


Now drill out the Lego gear to fit the servo shaft, screw it on, and then glue the servo on top of the Lego beams (depending on the size of your servo you might need a little plastic wedge to get the right spacing):


That's it! Needless to say in the autonomous version the onboard autopilot will drive that servo, not a RC transmitter. But you get the idea. If the two vectoring thruster do the trick of altitude hold, I may remove the vertical thuster entirely to save weight (and two I/O pins). If I need even more vertical control, I'll keep all three going.

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Comment by Howard Gordon on May 27, 2008 at 7:03am
Thrust vectoring is definitely the way to go, though I'll note that even with the rcguys 66" blimp kit, attaching the servo to the gondola was no simple matter. I had to first glue a block of wood to my servo and then shape the wood to match the gondola curves


before gluing the servo assembly to the gondola


3D Robotics
Comment by Chris Anderson on May 27, 2008 at 7:22am
Actually, those two Lego beams make a really stable servo mount (much better than the vacuum-formed gondola shell). I found hot glue was the best way to bridge any remaining gaps.

The remain question is whether to keep the vertical thruster, and if so how to use both of them. Vectoring thrusters for small altitude changes and then kicking in the vertical thruster for extra power when I get too far away from the target?
Comment by Howard Gordon on May 27, 2008 at 8:06am
Once you have added vectoring, the 3rd thruster adds no value. Because they are operating clear of the gondola, the vectored rotors provide much stronger vertical control than the fixed thruster, plus you have the thrust of 2 rotors rather than one.

You could move the 3rd thruster to one of the tail fins for stronger turn control - that's a fairly common configuration with larger blimps, though I haven't found a strong need for this.

3D Robotics
Comment by Chris Anderson on May 27, 2008 at 9:18am
Great advice. I'll drop the third and take the weight and power savings. Ideally, the two thrusters would be independently vectored, so they don't cancel each other out vertically in sharp turns (when one's going forwards and the other backwards), but I'll leave that to more advanced blimps. We can optimize this one in software for that case.
Comment by Howard Gordon on May 27, 2008 at 10:13am
I recently bought a larger blimp with independent vectors for its brushless motors, but it takes about 50 cu ft of helium to inflate, so I haven't done anything with it yet. Working out an autonomous control strategy for separate vectors will not be simple.

3D Robotics
Comment by Chris Anderson on May 27, 2008 at 12:20pm
Howard,

I'm thinking I may want to change the gear ratio to get a little more travel on the thrusters--I think I'm only getting about 100 degrees total. Can you estimate what the total angular range is of your RCGuys blimp thrusters?
Comment by Howard Gordon on May 27, 2008 at 12:32pm
I have 360-deg range via a 2:1 gear ratio (range of the servo is 180-deg). I currently only have access to 180-degrees because my servo pulse range is limited to between 1.0ms and 2.0ms, but if I expanded the pulse limits to 0.5ms and 2.5ms, I would pick up the rest of the range.

3D Robotics
Comment by Chris Anderson on May 27, 2008 at 7:47pm
Ah. My gear ratio is just 1.5:1. I'll switch to a larger main gear.
Comment by ovidio aza rojas on November 14, 2009 at 7:32pm
de que material esta echo el globo o zepeline y cuanto tienpo dura con el hidrogeno y cada cuanto se recarga
Comment by amy lingston on January 31, 2010 at 12:25pm
that is an amazing design! thrust vectoring in multiple vectors would really increase the stability and maneuverability of the blimp. I have been trying to do some major research on thrust vect. since I switched to a more reliable satellite high speed internet connection.

I am working on integrating thrust vectoring into my brushless motor fighter planes, but this is proving very difficult... That plane I used a motorcycle mount just to handle the weight. Hopefully this project won't require any precision machining.

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