Is it still possible to do cpu mining for experimenting?
Yes it is technically feasible to solo mine with a rpi3. The 'fastest' miner you could run would be minerd. However, there is a slim-to-none chance you will ever mine a block on the bitcoin mainnet, but there is still a chance! I would save the trouble of building minerd and use bitcoind's build in block generator

bitcoin-cli setgenerate true 1

You don't need to worry about crashing other bitcoin nodes, they will validate if your newly mined block is valid. 

If you are looking to have some fun with mining on the rpi take a look at bitcoind's regtest mode. Regtest mode lowers the mining difficulty to the absolute minimum level of difficulty. This means you can mine 1000's of your own blocks per hour on a rpi3.