"Relays" is always a good topic for beginners. They do come in handy for controlling all sorts of things. There are basically two types of relays available to the hobbyist today: electro-mechanical and solid-state. These both come in a variety of
operating voltages used to actuate or energize the relay, a variety of
switching voltage capability and a variety of
switching current capability. In addition, electro-mechanical relays offer a variety of contact configurations. Solid-state relays typically only offer one switching configuration and one contact configuration.
The 4-channel Bluetooth remote-controlled relay module that
@Goldhelmeth has selected for this project uses four electro-mechanical relays, each independently actuated (energized) by means of a specific remote channel of a Bluetooth data communications radio-frequency link to either a four-button key-fob or another device (such as a cell phone) "paired" to the Bluetooth module. The details of how this works are complicated, but the knowledge required to use the module does not require knowing all about Bluetooth. All that is required is a cell phone with Bluetooth capability and an app (application program) that provides the user with a human-machine-interface (HMI) to the relay module.
Each relay on the module has one set of Form C contacts, the most common contact implementation. Form C contacts have a common contact that the electro-mechanical relay can physically move with an electromagnetic coil to close a conductive path between the common contact and one of the other two contacts. When the relay
is not actuated (energized), the moving contact rests on the normally closed or
NC contact. When the relay
is actuated (energized), the moving contact moves to rest on the normally open or
NO contact.
A circuit can be completed with either the moving contact and the normally-open contact (typical usage) or with the moving contact and the normally-closed contact. It is possible to connect both the NO and the NC contacts to separate circuits, but both cannot be closed simultaneously by the common moving contact, except in the special case of a relay constructed with "make before break" contacts, which is not the case here. I mention it only for completeness, and perhaps to forestall any comment by overly pedantic readers who might comment that I forgot about make before break relay contacts.
Relays have a long history with the switched telephone networks, sometimes affectionately called POTS (Plain Old Telephone System). Telephone relays typically have long, slender, electromagnetic coils that attract a moving armature when the coil is energized. The armature then simultaneously moves many thin, flat, conductive metal springs mounted adjacent to the coil with contacts attached to their ends, and sometimes with contacts attached at other places along the flat spring. It is the unique mechanical construction of this stack of flat springs and their contacts that allows some really strange contact behavior when the relay is energized and de-energized. We will not further discuss this here because such relays are obsolete and not used anywhere except in developing countries that cannot afford a POTS network with solid-state relays... and also maybe used by few die-hard electronics enthusiasts who just happen to like them and who, with the aid of steering diodes, managed to design and build complicated logic machines using diode-relay logic late in the previous century, before changing over to TTL, CMOS, and microprocessor designs.
So, your actuator will use one or more of the relays on your Bluetooth remote-operated relay module to connect to the battery that will supply power to the actuator. You could directly connect the two wires on the actuator to the two terminals of the battery and the actuator motor would run, but where is the fun in that? The actuator would extend (or retract) until it reached a mechanical limit, whereupon it would stop and the motor would stall, drawing its "locked rotor" current, which is generally much higher than the current required to move the actuator rod under its maximum-rated load. Some actuator circuits can sense the increase in current when their motor stalls and use this information to perform some corrective action, such as reversing the motor direction or shutting off current to the motor until its direction is reversed. Your actuator has a DC motor, likely a permanent magnet DC motor with brushes to carry current to its rotating armature. The motor is reversed by reversing the polarity of the voltage applied to the two motor leads by the battery. I don't see that you have purchased or specified any components that would allow you to sense actuator motor current or actuator limit positions, so you will just have to accept whatever consequences occur when the actuator reaches an extension or retraction mechanical limit stop.
There is a simple switching (relay) circuit that you can interpose between the battery power source and the motor leads to effect a polarity reversal when the relay changes state, from energized to de-energized or vice versa. Unfortunately this switching circuit requires
two sets of Form C contacts that operate in unison on a
single relay. I suspect your Bluetooth module cannot guarantee this will happen when two sets of Form C contacts on two separate relays are used. There will be a slight delay upon energizing or de-energizing the two relays, and one set of relay contacts will open or close before the other set. This could lead to a short-circuit of your battery and that is never a good idea.
So, the simple circuit probably won't work for you. However, since you have four independent Form C contacts available on four relays, it is a relatively trivial matter to connect the contacts in such a manner that energizing two relays in sequence will power the actuator in one direction, while de-energizing those two relays and energizing the other two relays in sequence will power the actuator in the opposite direction. Of course, all four relays are never actuated simultaneously. And when all four relays are de-actuated, power is completely removed from the motor and it stops.
Perhaps
@Goldhelmeth can draw and post a schematic of how this will work...
