Introduction: Nano Air Swimmer
Air Swimmers come cheap, but they are quite large compared to modern RC blimp standards, making them not very manoeuvrable in smaller rooms. So with Plantraco creating a new class of nano blimps I wanted to check how difficult it is to build an air swimmer in the nano blimp class, i.e. based on a 9" latex balloon.
Building a working Nano Air Swimmer proved to be quite simple (keeping it simple being the key). It's all in the tail: everything is done with just one servo. The servo combines propulsion and steering, as in commercial air swimmers.
While commercial air swimmers move their center of gravity back and forth to move up and down, I went for an even further simplification: the nano air swimmer is permanently pointing slightly up and moving forwards means moving up, stopping means moving down (a trick used in 2ch toy blimps).
Check out how it performs in this video:
Step 1: Materials and Tools
Used RC gear:
- An ultra micro receiver under 1g. I used my favourite 0.65g DelTang Rx33 DSM2 receiver. This is the most expensive part at around 30 EUR. With a slightly larger 11" balloon you can use the 2.2g OrangeRx R415 which can be found at 22 EUR to 10 USD, depending on the supplier.
- An ultra micro servo under 2g (a regular type, not a linear one). I used a so called 1.7 g servo, which actually weighs 1.9g with wires and connector. Make sure the connector is compatible with your receiver. Such a servo goes 12 EUR to 4 USD, depending on the supplier).
- A 1s LiPo battery around 2g. I used a Zippy 50mAh cell. With a fresh 9" balloon (carrying 8 g) or an 11" balloon I was also able to use a more common 2.5g 80mAh one. Such batteries should cost around 5 EUR or less. Obviously you will need a suitable charger (not shown).
- A 25cm battery extension lead to connect your battery to the receiver. A shorter lead works too, but it allows for less trimming the weight distribution. Specialist suppliers of micro RC gear can make that to order for under 4 EUR.
For the tail:
- Some EPP sheet (Expanded PolyPropylene), 3 mm thick. I used a triangle with two 16 cm long rectangular sides
- About 5cm of 0.8 to 1mm diameter carbon rod.
You can get all of te above at aether-sciences.
For assembly and trimming:
- Some sewing thread.
- Tape (scotch tape or selotape).
- A couple of grams of putty, to be used as trim ballast.
All this is added to a 9" latex balloon, inflated with helium (and treated with Hi-Float). You can get it at the balloon shop (1-2 EUR for one) or bring home a helium bottle (rented or bought, around 50 EUR for a canister + 50 balloons). Depending on temperature and moisture a latex balloon will last longer or shorter. The spare buoyancy needed for the nano air swimmer lasts roughly a day.
- A scale accurate to 0.1g
- A felt tip marker pen
Step 2: Making the Tail
The carbon rod is attached to the tail fin with some tape. Align carefully, so the fin will be perpendicular to the servo and fix in place with some drops of superglue where the rod protrudes from the tape.
Experimenting with shaping the tail fin showed it not to be very critical for good propulsion.
Step 3: Attaching to the Balloon
As the servo with the tail represents a large part of the weight, it is attached to the convex "top side" of the balloon (having the largest buoyancy).
Mark the middle of the "top" of the balloon. Tape the servo in place with its axle at the mark.
The servo and battery extension lead are inserted in the receiver and some tape is added to relieve any tension on the wires where they go into the connectors. The ultra micro connectors do not provide much of tension relief, making them rather fragile.
You can choose to put the servo on either the rudder or the aileron channel. Switch on the transmitter and the receiver to check. With the servo in neutral position, put the tail fin on the servo in the middle position. It proved not to be necessary to use the screw to keep the horn on the servo.
With the servo in a straight up position determine the underside of the air swimmer and tape the battery near the lowest position. Let the servo leads - receiver - battery extenson leads "chain" run along the belly of balloon, towards the battery. No switch is used, connecting the battery switches on. The battery lead end is taped to the balloon near the battery, to keep things in place when switched off.
Step 4: Trimming and Flying
Add putty to trim the buoyancy. The air swimmer should almost float neutrally, just sinking very slowly. I put the putty on the balloon's knot. Then I move and tape the battery more forwards or backwards till the nose is pointing up just slightly.
The air swimmer should slowly rise when moving forwards with some speed. If not, retrim. In any case a regular retrim will be needed as latex balloons lose helium noticeably in a matter of hours.
Flying is easy, real control takes just a little practice. The nano air swimmer is very suitable for kids and for anyone with a lively inner child. Moving forward is simply done by moving the transmitter's stick left and right with some vigour. Turning is done by restricting the movement of the stick/tail to one side or by keeping the tail to the left or right when coasting.
Obviously the air swimmer is only suitable for indoor use. In large rooms air currents and mainly rising air might prove troublesome, but actually the helium loss of a latex balloon is an advantage whenever it is gets stuck to ceiling.
As long as you keep doors and windows closed and there are no hot surfaces that can damage the balloon, nothing much can go wrong. Even when the balloon does breach the ultra light gear should survive the drop and you can simply replace the balloon and go flying again.
Flight times were easily over 20 minutes with a 80 mAh battery.