How to automatically deploy routers / industrial PC's I'm facing the problem, to setup Gateways and Industrial PC's (with SSH access) regularly. All have different default settings. Some have a default root password, some have a default user. Some have a initial fixed IP, some use DHCP.
Some are ARM architecture, some are MIPS. OS varies between Yocto, OpenWRT, Raspian, etc.

I'm looking for a way to somehow script the deployment and execute it automatically.

There are tools like Ansible, Puppet, Chef, etc. but I'm not sure which is best suited for my uscase described above or which isn't at all. In best case the tool has no requirements on the target device and works purely via SSH.
Regarding no requirements on the target device, of the tools you mention, only Ansible does not need an agent on the host. The minimal requirement to use Ansible modules is Python on the host you want to update. If you don't have Python on hosts you could even send raw commands to the hosts.

Wikipedia has a list comparing configuration management software, there you can find other agent-less tools.

Not listed on Wikipedia is Fabric, a simple Python library to execute remote shell commands. It is agent-less as well.