hello flyers during the COVID lockdown, I have built a rc blimp. It took me a lot of searching and research to find the materials and technique to build and fly. there are very few post on blimps so thought my post would be helpful to the enthusiasts.
Specifications:
Android App based transmitter
Nodemcu receiver
DRV8833 motor driver
Coreless motors
1200mah li-ion
1.6mts long (parabolic ends and cylindrical mid)
Solar energy powered (capable not tested)
1hr of endurance without solar
20+hrs with solar (theoretical)(1.6mt)
materials used:
18micron met Bopp-envelop material
balsa wood- construction of gondola
coreless motors 720
6.5mm prop
node MCU – receiver
drv8833- motor driver
li-ion battery 18650 4amp conti discharge
li-ion charger and discharge module
wires
HD foam (optional)-gondola
envelop
envelop is key in building a blimp. before going to the material i used ill talk a little on my research.
Some of the common choices one would think would be latex, foilballoon or mylar.
I have tried out latex,foil balloon and mylar(emergency blankets). One would want to use latex balloons because of its easy availability, but latex is fragile to burst and it easily loses helium or hydrogen I no time. Some of the methods to extend its float time is to use “hi-float” or fevicol. I have tested fevicol and it extends the float time significantly, apply a generous amount of fevicol in the inside of the balloon enough to layer the inside of the balloon. Foil balloons float a long time but the shapes are limited and the material is also relatively heavier than mylar or BoPP. Another test I did was on emergency blankets(mylar), I saw this video on YouTube(
) where contact cement was used to glue emergency blankets to make an envelope. So I got my hands on emergency blankets and I used fevibond to stick it. These blankets are very think about 12 microns. I made a small envelope in the beginnings and it had leaks. The main reason to have leaks where because while sticking the material was wrinkling and you couldn’t undo it because fevibond once contacted would not lift off. Fevibond is a rubber based adhesive and is thick so might be that a thinner contact adhesive could be effective.
Finally I used met BoPP, fascinatingly mylar is a commercial name of BoPET (Biaxially-oriented polyethylene terephthalate) finding a dealer of BoPET was rare so I looked up at alternatives and found BoPP to be similar. BoPP is the material used in packaging. Metalized BoPP is the one to use, this is commonly used in chips packets and is an excellent gas barrier. The most important part of the material is that its heat sellable. BoPP comes in various thickness from 3microns onwards. I have used 18 microns for a 1mts blimp and a fell that its too thin, I would recommend going with min 20 microns for a 1mts blimp. Sometimes the BoPP depending on your manufacture the heat sealable plastic side is only on one side of the material so you’ll have to fuse the plastic sides together for the best bond. Though BoPP is easy to find on indiamart convincing the manufacturer to give you 1kg of material is hard. I got mine from a local supplier, I had bought 2kg 18microns for 400rs and 32gms of material is used to make one blimp.
There is no specific measures on the envelop design that I followed however elliptical shapes are preferred to lower the cross section.
Gondola:
Used balsa to make a light weight structure. The entire power train and controllers are attached to one gondola. The main reason I did this is so that i could test the different types of envelops and also its difficult to harvest the fins from one blimp to another. The gondola would be attached to the envelop with a generous length of double sided foam tape.
Electronics :
All my electronics were stuck at the university so I had to buy everything once again so most of the electronics would be project specific however alternatives could be used just make sure that they are light weight.
I didn’t have my transmitter receiver so I found the nodemcu to be useful for rx and I controlled the blimp with an app I made. Since I used a nodemcu a little bit of programming Is involved. For the best flight experience one should use the tx rx as you don’t get the gimbal feel in an app.
I deliberately used a li-ion battery even if its heavier than a lipo, because I had this li-ion charger module that was convenient for charging and discharging, it had a low voltage and high current protection and I could charge mid-flight if I had attached solar panels which was a further idea.
The total weight of the gondola setup is 39gms without battery and 79gms with battery. If i used a lipo of 500mah with 12 gms the total weight could be 51gms+evnelop.
This helps calculate the volume of lifting gas needed
https://www.omnicalculator.com/everyday-life/helium-balloonsCircuit
Lifting gas:
The most confusing part lifting gas…https://en.wikipedia.org/wiki/Lifting_gas refer the link for all the possibilities of lifting gas. The two viable options would be hydrogen and helium. But
• Hydrogen is highly flammable
• Helium is expensive
Technically helium and hydrogen have nearly the same lifting capacity(hydrogen with 17% greater than helium) however hydrogen is explosive so helium is more preferred. However in some cases if you are operating in an open wide areas far from population you could use hydrogen** with highest caution and safety. If you are using hydrogen, it should not be stored in the blimp, the blimp should be deflated(hydrogen) immediately after use. Its not advised to use hydrogen.
Helium is mostly available in balloon shops or you could find helium dealers on indiamart. If you want to buy helium from suppliers they only deal with the cylinder, one cylinder of 1cu mts cost around 10k. instead you could buy the helium form the balloon shop on a cylinder return basis.
Happy flying
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