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Re: (ET) Ariens AMP Mower

David Roden wrote:
Not here! My property is hilly, uneven, and broken up in to little islands of grass. I appreciate being able to creep the machine at times. Am I typical? Probably not, but I'm sure I'm also not the only one.

Really? My yard is somewhat hilly and the shunt motor with cruise control (full armature, full field) is the only way to go. If I go up hill, it maintains speed as the motor pulls more amps. When I go down hill it maintains speed as the motor *pushes* the amps into the pack in regen. In all cases the tractor keeps a steady speed, switching speeds is what de-stabilizes your tractor's traction.

When you're designing an electric tractor from the ground up, I agree that the cheap way to go is to bolt the motor into an existing design. There are advantages to using mass-produced, proven components.

Sure. Put a shunt motor in a Chaftsman tractor, gear it to run the motor full speed/power, then belt it to the blades and transmission.

However, an electronic motor controller is effectively a continuously variable transmission without the inefficiency of hydro drive. The cost of a small DC motor controller adequate for a garden tractor is certainly not prohibitive, and much less today than it was 30-35 years ago.

Sure. However for most mowing you really need a few speeds. Use the transmission for that. Yes you will lose a bit of efficiency, but it's just not worth adding hundreds to the cost of the tractor to squeeze a bit more out of your T105's. The perfect *is* the enemy of the good.

I don't understand why you suggest this. Reversing the low current field in a shunt motor is almost a trivial task, requiring only a small relay or small semiconductors. It makes much more sense to reverse the field than to reverse the armature. This is one of the advantages of a shunt or sep-ex motor over a PM or series motor.

Um. Yes. However when you go from forward to reverse while the tractor is still moving forward, it will beat the daylights out of that little relay since it will get a very high voltage spike as it goes from F to R. This will destroy a varistor quickly too.

If you could ensure that the motor stops every time or use a nice big contactor pair to switch the field then this would be fine. However if you use a little relay it's going to get beaten up.

This is what GE did with the E15 and one of the main reasons why it is so bad. The E20 switched the armature and it's much more reliable and tolerant of going from F to R.

An even better solution though might be to forget motor reverse and just use the reverse gear on the transmission. Every transmission has it, so it's not like you're saving money. Do what everyone else does.