Is it possible to take out a loan against a solo 401k the same as you would with an employer type 401k, and use that loan to do the OP's cabin idea?

Hello All,Does anyone know of a bank that does Co-op loans for a property I would live in , not invest?

I think a security camera and coin-op laundry is your better bet.

Commercial coin-ops are bulletproof, bypass the pay system. 

Not enough information here to determine appropriate tax treatment for the OP.And OP is out of his depth because he isn't familiar with the volumes of case law on what constitutes a trade or business and what may be one-off occurrence that is neither considerable, continuous nor regular, and the resulting treatment of a myriad of fact patterns under Sec 162, so he must rely on the posters here who are all talking at once from a half dozen different directions.One flip cannot be examined in a vacuum. 

The OPs first step should be to determine whether this is in fact short.

Therefore, we provide washers, dryers with a coin-op conversion along with a coin changer for the tenants to use.

There is a bigger company, Payrange, that provides an app solution for coin op machines (but not for residential machines) with no upfront equipment cost.

Back to the OP, I am assuming the 2nd unit is an ADU because you indicated it was Single Family.  

Most likely a court would find the whole thing a sham under the "sham transaction doctrine" based on what you've laid out in your OP.