Hello everybody,
I'm a first year engineering student and for the first semester design and process project,me and my group choose to create a automated scarecrow that is specifically designed scare birds in farmlands here in sri lanka.Its the second week,and the guy who is doing the electronic part suddenly got dengue fever and the rest of us know very little about this arduino platform.If there is anyone who likes to help us in this project we'll be very thankful.we have to finish this by tuesday.We have finish 75% of the mechanical part now.But electronic part is the problem now.About the electronic part,
Input will come from a PIR sensor.It's connected to a Arduino Micro. It will detect birds.
Signal will be transferred using RF 315/433 MHz Transmitter-receiver Module.
we used Arduino Uno for the scarecrow.and there will be three out puts.
1-it will make a noise to scare the birds.
2-It will move back and forth in a horizontal path
3-It will move its hands
There will be 2 separate power supplies.One for "PIR+Micro+transmitter" part.Its powered right now using a power bank.We'll latter use 5V battery. The Uno, Motors and the rest is powered using a 12v LiPO battery.
We(actually the one member who's sick now) have finish the the coding for Micro.Also in Uno,we finished coding for the first above mentioned 1st and 2nd out put.
Now,We have at least 3 big problems.Right now i will only mention the first one.
It seems when the distance between transmitter and receiver is like 3 feet or more this thing won't work.No response whatsoever.No sound from buzzer,no horizontal movement(no movement from gear motors)When receiver and transmitter are move closer, like 1ft distance,it works fine.
According to manuals, RF 315/433 module range can be up to 90m.
So what is the Problem here.?
Please,Can someone help us.?
If needed i can upload the photos and the codings for transmitter and receiver.
(PS-Thanks for even reading and thinking about this problem.)
I only can help you with the transmission range issue. The better the antenna, in detail at the sender side, the larger the transmission range. It may help to attach a straight wire to the antenna connector of each RF module, but only as a quick emergency hack. Try to find external antennas for your RF modules, or get modules that support the use of an external antenna at all.
My best wishes to your sick friend 
The RF sounds like an antenna issue indeed. That's all I can say about that.
The Uno: can't you power that off 5V, or at least a somewhat lower voltage? Powering it with 12V means you're putting the built in regulator really hard at work. It's got to dissipate quite some power to drop that 7V.
For more help: photos, wiring schematics, part numbers, code, description what it should do and what it actually does.
3 feet makes me think there isn't any antenna. Even a crappy PCB antenna not properly tuned should work further than that.
Some RF modules radiate better in some directions than others. try rotating the modules so they are facing each other of so that they are sideways to each other and all the combinations. Some might work better.
When you say 3 feet it is 3 empty feet, correct? there isn't any walls of material between them?
Does the RF transmitter have a power setting? Is the voltage supply sufficient?
What RF modules are you using? Pictures might be helpful.