Multiple Mavlink devices on the same serial connector

I would like to connect sik radio, osd and storm32 gimbal on the same serial connector by using mavlink 1 protocol

It can work if I use the same baudrate, different system and component ID… ?

It could work, as long as there is only one transmit-line to the flight controller.
The Sik radio needs transmit and receive, but the storm gimbal and the osd could work if the only received signals…

so I have to only connect rx to sikradio tx pin… ? when I tested the gimbal the result was that control xan only work when emit heartbeat gimbal option is activated, so gimbal needs of transmit data… ?

Indeed, all Mavlink devices must identify themselves by emiting heartbeat.
Without heartbeat nobody will know that the device is available.

Possible to set arducopter to send frames at 1hz even if no heartbeat received… ?

nope, it will not send gimbal commands out. So you have to look for gimbal commands from the ground, and osd data from the flight controller.

What are you meaning ? I can control gimbal with pwm but I prefer serial…

All other serials connectors are used by other components (gps, camera, escs telemetry…)

I must connect osd, sik radio and gimbal on the same connector…

With Mavlink you can control the gimbal directly from the GCS as well.
The control Mavlink commands (serial) are sent to port where the flight controller detects the gimbal. No heartbeat, no gimbal.

OSD is fine because it can use the telemetry data which is sent back to the ground station.

flight controller can detect the gimbal without heartbeat ?

AFAIK no. A heartbeat is a must.

so how gimbal can receive commands… ? I must control gimbal with rc radio (by using flight controller)

If I use same system and component id for all devices, frame sent by FC in answer of the heartbeat sent by sik radio will be received by all other devices… ?

Take a look at how mavlink routing works

To make it work, the gimbal must have its own component id, but for that it have to connect to a separated serial port and emit heartbeat.

Why separate id ? Data needed by components are included in a single frame.

If Gimbal,osd, sik radio has the same system, component id; Heartbeat sent by sik radio will produce mavlink frame which can be used by all devices ?

Nope, FC identifies the gimbal by the heartbeat MAV_TYPE field, which should be GIMBAL.

OSD, is the only capable device (from those you mentioned, or a flir camera) that can be used with a Y cable on TX line of a serial cable, since they dont need to send mav type back to FC. the only get data.

on the other hand most FCs have atleast 5 serial ports and if you have a CAN enabled one, you can save 2 more (i.e GPS).
Another more complicated but still doable way is to deploy a Companion with mav router and start connecting new non-critical periferals to the companion like the Gimbal.

And another upcoming way is to use the can node, which you can have more traditional serial devices with one can port

Its possible to use an Y cable splitter to share sbus output from rc receiver between flight controller and an arduino nano embedded board ?

I’m planning to control gimbal with mavlink protocol on software serial and read rc input on hardware serial0…

You can share SBUS. I do it all the time.