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-balloons
Circuit


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
 
       

app and nodemcu code

https://drive.google.com/drive/folders/1tK9aMINwJpHT3Z-Kuro_UtJ3L2CilbGr?usp=sharing

switch on the wifi hotspot on your phone
update the creds in the arduino code
upload the code to the nodeMCU
open the serial port to get the IP address
copy paste the IP address in the app
wait for the wifi connection
and your ready to fly.

envelop cap and heat seal

gondola and BoPP roll

envelop
this is a naive envelop with no beautyification. the seams are visible and are outward so that in case of a tear it would be easy to fix. the blimp is made of 2 sheets rather than many ellipsis(to reduce complexity).     

 

Interesting

Finally someone working on a blimp project! I remember some folks showed interest on blimps few years back but dont recall anyone showing as much progress as yours!

You've done your research very well!

i had tried making one long back (2016),got inspired by one flitetest episode where they showed a huge blimp for advertisement purpose,

For 1st attempt,I had purchased latex balloons (36inch ones) around 30 of them (MOQs)! i know i would have gone bankrupt on purchasing helium ! Got in touch with a balloon shop down on infantry road they filled one up with 'HI-FLOAT' and helium, was a pain to get it back home! unfortunately it didn't reach home! lesson learned never travel on a two wheeler with a balloon.
So overall all i didnt pursue with the latex balloons!

2nd attempt, i bought a pack of those heat sealable food packets! had this smart idea to cut them and make the envelope out of those small food packets sheets.  Used an iron to heat seal but couldn't get to work! this method is highly inefficient and prone to a lot of failures!

3rd attempt, Bought Mylar foils (space blankets) to make the envelope, but quickly ran into issue of sealing it! space blankets dont have heat activated adhesive so you cant seal them! CA would make it brittle and epoxy would make it heavy! So went to SP road and got 3M Super 77 spray, it does stick the foil but not airtight seal!

overall after spending alot of money and losing hope (seeing helium prices) abandoned the project.

i do recall there are few folks down at peenya who sell Helium gas, they charge you for the gas and a refundable fee on the cylinder! Gas welders will know where to get helium! Also remember you need extra precaution while using the cylinder, youll need proper regulators to regulate the pressure.

But i see, you are going on the right path! All the best and good luck for this project!

thank you
currently in lockdown so waiting to get helium to fly and will post flight video

I think this page has everything to make airship or blimp
http://silent-runner.net/index.php?title=Main_Page

Helium is notoriously difficult to seal! In fact, pressure vessels for critical uses (like in nuclear reactors) have their welds tested with a helium leak detector test! This is a fascinating project, and I certainly wish you all the best for it.