Chemelc, Yes, this circuit is for a power steering assist and at rest and normal straight driving, the motor is turned into a dynamic brake to resist bump steering.
Another tidbit of information is probably of little concern is that when the FETs were destroyed, I was testing them to see if they would fail, the OHV has 4 wheel drive and the differentials can be locked and when turning, there is a terrific bind and this causes the steering to try to go straight and requires a lot of power to counter act. Turning the wheels to full left or right is virtually impossible on pavement, but on sand or dirt, just hard.
richardb, the 555 in the schematic is driven by the oscillator via the trigger input and out drives a boost circuit for 25v for the upper FETs, it has a feed back to CV to control the voltage.
While checking the spec sheets of the LM2901n and LT1017, I noticed this application,(see attached) and I will modify my circuit to include it.