Recently someone suggested the model airship’s rear control surfaces would not work very well without any prop wash flowing over them. I had thought about that before, and have been wanting to design a system to gimbal the motors to provide some thrust vectoring and better control.
So I have begun working with ideas to move the two rear engines to help control the ship. The two forward engines will remain stationary and will only provide forward propulsion.
This is proving to be quite a challenge. I want to move both rear engines up/down and left/right, using only one actuator for up/down and one actuator for left/right, and keep the whole system extremely light weight. I’m not sure if I will be able to make it work using only two actuators, but that’s the plan for now. I’ll post some drawings once I come up with a workable idea, hopefully soon!
So after designing the engine cars it’s time time to mount them on the airfship. So I copied and pasted my engine car model into the main airship Sketchup file and spent some time mounting them to the airframe.
I am fairly certain that I will use either 1/16″ balsa or spruce sticks to mount the engine cars to the airframe, but I have also been thinking about using extruded square carbon tubes, or maybe even some small diameter carbon rod, for the extra strength. Some good 2-part epoxy would probably bond those together, and to the airframe, pretty well. I’ll have to think about it though, and maybe I will try both on the test section once I get it built.
The engines will mount to the 13th and 15th rings near the tail so that the center of each propeller is 1 1/4″ from the ring it is attached to at a 45° angle. Since the propellers are 2 1/2″ in diameter this allows them around 1 inch of clearance from the airship.
Previously I had been thinking about designing a way to gimbal the motors to allow for some thrust vectoring to assist with the control system. For now I have opted to go for the simpler option, but may revisit the gimbal mount idea later on in the project. Stay tuned..
A couple of small motors and propellers I recently ordered from MicroFlight.com showed up in the mail today!
The plan is to run three of these small motors on the airship, and the radio kit I plan to buy already comes with one. Now that I have a couple to work with I can see how they look next to the test frame I’ve been messing with lately. So far I think they are the perfect size, I just hope the ~11 grams of thrust each one puts out will be enough to get the big ship moving. :)
I started shopping around online for radio gear, servos, motors and propellers recently. The whole thing can get a little confusing and over-whelming trying to match all these different components together, from different suppliers, and trying find stuff small enough and light enough..
So I think I have decided to go with the Plantraco “Deluxe Starter Set #3” from MicroFlight.com for $100. I also want to buy 2 more motors (I want to run 3 total), but I also need to figure out how, and if, I can wire up 3 motors with this system.. I don’t want to overload anything. I’ll keep you posted on what I find.
Anyway.. This system looks great, and everything is really light. The components it comes with, in addition the transmitter (which also charges the batteries!), are
This little receiver weights just 0.9 grams. They say only 0.5 grams if you remove the connectors (but I think the solder welds needed might negate any benefit to removing them). It’s also pretty dang small too, at 14mm x 16.5mm x 5mm.
You can connect 1 motor and 2 actuators to it, via these tiny plug-in connectors on the board. A tiny 3.7 volt LiPo battery is easily attached via 2 magnet connections.
MiniAct Magnetic 1.1g Actuators ($14.99/ea)
These 2 little actuators only weigh 1.1 grams each. Servos weigh quite a lot more, and my airship doesn’t need the range of a servo. All I need to do is kick the rudder to one side or the other every once in a while, and the same with the elevator.
I’ve been trying to figure out how to link things up so I can just use 2 actuators (1 for rudder and 1 for elevator). But due to the tail gas bag hogging the inside space all the way to the back I may end up using 4 actuators (1 for each fin control surface), in which case I may opt for the smaller 0.4 gram actuator instead.
LP90-FR Bahoma Cell with 10mm Bahoma ($12.99/ea)
This tiny battery is just 14.5mm x 23mm x 4.8mm, and weighs 3.0 grams. It’s a 3.7v single-cell LiPo battery, and it connects to the receiver via two small magnetic connectors.
The kit I’m gonna order comes with 2 of these, and they get charged on the transmitter.
7mm x 16.5mm 2.9g Motor ($4.29)
This small electric (brushed) motor is 7mm x 16.5mm and weighs 2.9 grams. It connects directly to the receiver via a nanoconnector socket. When used with the 65mm propeller (below) it should generate ~11 grams of thrust. I plan to run 3 of these on the airship, of which one in the rear may be steerable.
65mm 0.05g Propeller ($3.25/ea)
Small 65mm (~2½ in) propeller with a 1mm bore, which should fit the 7mm motor (above) perfectly.
Three of these with the above motors should generate around ~33 grams of thrust total. Being a lighter-than-air craft, I think this should get the airship moving.. I will be testing them on the test section once I finish building it to see how they do.
So at this point it is looking like the entire propulsion and control system might weigh only 14.95 grams total! There will of course be a few additional grams of carbon rod control links and several feet of wire, but the whole thing should still remain very light. :)
†Note: This post is not an ad, and I haven’t bought anything from them just yet. So I am not even sure if this is even good stuff at this point. I will post more information and photos once I have ordered my stuff from them..