For 40Nm I would lean toward trying a TM motor and a DC drive, KB etc. Although the KB is analogue control, you could use a preset speed by relay output from your controller, Arduino or PLC etc.
As already covered, if the main rolling motor application requires low rpm some kind of gearing can involve a smaller, more economical solution.
I think after #120+ posts of advice you should have sufficient to obtain some kind of motors to at least test a prototype, after the first effort you can then refine it for the final versions.
Again, designing a machine from several thousands of miles away is difficult, and can only result in mainly general advice.
Max.

 

Lol, drill motors,window motors, stepper motors,treadmill motors,DC, bldc, servos, arduino, plc, I'm actually further behind than I was before 120 posts, is a treadmill motor reversible, highly accurate and programmable and powerfull enough?
Actually, I give up,
Thanks for your time guys