(ET) Reversing snowthrower motor

[Darryl McMahon <darryl econogics com>]

I have been using a spare ET snowthrower motor over the summer to power 
some test rig contraptions over the summer, and it's worked like a charm.

Last week, I was asked to try powering something new (possible 
amphibious drive 'tire'), but the new wrinkle is they want to be able to 
move forward and reverse.

As I understand it, the  snowthrower motors are compound wound - 
strongly series but with a weak shunt field to prevent motor speed 
runaway.  On the blowers and tillers, there are jumpers between what I 
expect are the 2 sets of field windings.  (I don't have a schematic for 
these motors.)  Which posts do what on these motors (there are six 
external connection posts).  For ET use, only two connections are used 
(pack positive and pack negative).

On a series motor, this can be done by reversing the field or armature 
connections (but not both).

I'm looking for guidance on the possibility of reversing one of these 
motors.  If that's doable and not going to damage the motor, I expect I 
would be putting a set of contactors in place to be able to do this 
conveniently and repeatedly.  I need the motor to survive so it can go 
back on a snowthrower in a couple of months.

Thanks in advance for any documentation or guidance,

Darryl

--
Darryl McMahon
Freelance Project Manager (sustainable systems)