I was starting to get excited about the electromagnetic slip clutches but then reality kicked in. They present the same old problems I wanted to avoid: expensive, complicated, heavy, mfr. only specialty parts, can't repair out in the world if at all.
On the non-electric slip clutch models I saw most had very low input power ratings, like for small garden tractor engines/drives. When sizing one would have to consider engine's torque rating plus the multiplication factor of transmission and final drive ratios.