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New zero-turn mower project - no hydrostats

12301 Views 27 Replies 8 Participants Last post by  dh1
hello all. apologies for the long post, I hope some have the patience to hear me out and offer ideas.

My name is Reid Allaway, I’m an organic vegetable farmer and tinkerer in les Cèdres Quebec, west of Montreal, and I’ve just joined DIY Electric Car to seek assistance with some new EV projects for our farm.

I’ve had only a few months experience with EVs since being infected with the bug by forum member Yabert who is a kindred spirit and great guy who helped me rebuild Bob, an old Taylor Dunn utility cart who is now in constant use for a multitude of tasks on our farm.

Success with Bob and the realization that the era of lead batteries is well and truly over has lit a figurative fire under my backside to do more of this wonderful work so I’m currently planning at least 3 conversions. This post is about converting my Toro Z500 commercial zero-turn mower to full electric.

I’ve read all the other posts here at DIY-EC pertaining to zero-turn mowers and I’ve learned a lot but I also think this is a different enough project to merit a new thread. My goal is to convert a large (550kg) commercial mower with 60" deck to a truly fantastic electric mower. Think "half as good as the $40K Green Machine on 1/10th the budget". At least I already own the mower :). And I de-ICED it last weekend. Anyone wanna buy a 20hp Kohler twin ICE?:D

Attached image is stock photos of Z500 machine factory config. Mine is much dirtier but also lighter and more svelte without engine, fuel tanks or hydraulic components. Of course it doesn't presently do anything but that will change.

So far the basic design of my mower conversion is governed by the following requirements - please disabuse me of any ideas that are wrong or concepts that are misunderstood:
• I want to abolish all hydraulic components and drive the wheels and mower with 3 separate motors
• each drive wheel (rears for this mower) requires independent control with perfectly fluid contactorless reversing (so sepex or PM motors only if I’ve understood correctly).
• drive wheels probably need only 1-2 kW apiece based on original config of 20hp engine + hydraulic effy losses + mower eating 3/4 or more of the power demand.
• a separate motor and controller, or perhaps simply a contactor, will be required to run the mower deck. Mower motor is probably 5-10kW, maybe even larger, and should be compound or shunt-wound if I want to belt-drive the unmodified deck.
• I want to keep the deck as-is and not mount individual motors for each blade because the existing spindles are super beefy commercial-grade units so I can’t imagine putting whimpy chinese PM motors in their stead and hoping for the best.
• my final product needs to be as easy to operate as original gas-powered version (easier if possible) so that farm employees who don't know !#$?-all about electric whatever can operate it safely and easily without doing the machine any harm.

So far I have two ideas in mind for the drive setup and I want input and suggestions. As for the mower motor I’m eager for ideas on where to source a used 5-10kW motor that can be used for a belt-drive application and which doesn’t weigh more than 150lbs.

My battery setup is flexible. I have a complete first gen Chevy Volt battery cut up in blocks waiting for this and other projects and I can allocate up to 4 of the 12S(48V 2kW) modules to this project. Hopefully that’ll give me an hour or more of mowing time?

DRIVE OPTION 1. twin sepex drives
Much of what I’ve learned about EVs, and especially sepex motors and controllers, comes from a very nice Crown electric pallet truck (jigger) which I bought at auction and fixed up. I love the fluidity of the drive and the way the sepex controller manages plug braking and super fluid transitions from forward to reverse. It can also move 2000kg with easy using a 1.6kW motor from AMD. There’s a nicely engineered oil-bath reduction gear unit, a Zapi SEM-zero controller and all the pots and whatsits to make a perfect drive system for one rear wheel. So if I can find a matched pair of identical pallet jiggers with Sepex motors going for less than $400 each I’m going to go that route. Of course, matched pairs of electric pallet jiggers aren’t something you find every day.

What’s wrong with this approach if I get lucky enough to find my donor machines?
24V is the only flaw I can see. Mower motor might want to be higher voltage to reduce wire gauges and resistance losses.

DRIVE OPTION 2. industrial PM motors and worm gear reducers
My second drive option is to use a pair of PM motors (either 90V industrial-type as I’ve already got a matched pair of 1hp) or maybe a pair of 2hp 24VDC motors that I’ve found on Kijiji if that pans out. I’ve been thinking of running them through a worm gear reducer for final drive and possibly mounting that reducer straight onto a bearing-supported stub axle to drive each hub. Using this approach the motors are easy to come by but I’ll have a hard time finding matched gear reducers used so I might have to spend money there and possibly pay more to get Al gearboxes with hollow output to save space in mounting.

If I go with PM motors will I have enough torque, even when multiplied through a worm gear reducer? My math and a quick verification with a torque wrench suggests that 50 lb-ft of torque will move the machine from a stop on flat ground and that 100 to 150 should be adequate for slopes but maybe I’m wrong. I don’t want to spend time and money on a drive system that won’t haul this 1200+ lb beast up a slight incline. I have NO big hills but I don’t want to put $1000 or more into whimp-ass drive setup.

I can assemble a 96-volt battery for the 90V industrial motors but then it’s callenging finding a controller. Roboteq seems to have an appropriate 2 channel controller though it’s far from free. At least I'd only have to buy one. Anybody used a robotics-oriented controller before? I like reading manuals at least:)

I don’t know much about PM motors, their torque at low RPM, and their capacity to tolerate plug braking and contactorless reversing control. Please advise.

I know that the worm-gear reducers will sap some energy and generate some heat and also spin to an immobilized halt almost immediately but I don’t think these are show-stoppers for a zero-turn mower. You never coast with a mower like this anyway, it’s always under power or braking or stopped. No need for a parking brake :)

Thanks to any and all who have the patience to read through and offer any insights.

~ reid

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Why worm gears? They can do a lot of speed reduction in one step, but they're not efficient compared to spur gears.

I'm no controller expert, and I'm sure that this has been addressed in the other zero-turn discussions mentioned, but the operator needs speed control to steer, not the usual torque control; that is, if I'm running the thing and I hold both levers forward the same amount (or whatever control action is equivalent in the scheme you choose), I need it to run both wheels at the same speed (not apply the same torque to both, as would be expected with the controller configuration of a typical car).
 

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Only problem that I know of with worm drive is that they tend to shear the teeth when the output shaft suddenly stops, like hitting a rock with the mower blade, ratios are really high, generally more than 20:1 so you need some monster motor rpm to get decent blade rpm.
As already mentioned, the worm drives are for the wheels, not the blades; see the first post. It is true that they don't coast, but I assume that would be handled by the controls (limiting the rate of speed change), as it presumably is in a power wheelchair... a common place to find worm gear drives.

This aspect of speed control is essentially the same for worm gear drives as it is for hydrostatic motors - you really don't want anything that allows an instantaneous drop to zero speed except as an emergency stop.


The blades do need brakes, presumably the same ones which are probably already part of the belt drive which is being retained, although the belt drive clutch is no longer needed. Whatever control is used to turn the mower on and off should both release the brakes and close the contactor for mower power, and vice versa.
 

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There's a few different meshes as well, presumably trading friction for durability.
I believe that the tradeoff is between manufacturing cost (lowest for non-enveloping), and all of the positive attributes (strength, durability, efficiency) which are better with single-enveloping and best with double-enveloping.
 

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I don't think he is going into the EV mower production business, but rather salvaging surplus, so manufacturing cost isn't gonna be all that relevant. I bring it up in case he is worried about stripping teeth and wants to take a look inside whatever he brings home. If I opened up my $20 worm gears and found double-enveloping I wouldn't be too worried. If I found neither enveloping, I would be more worried. If I found brass gears I wouldn't know what to think.
Sure, that all makes sense. It means that if given a choice of boxes to salvage, he should prefer ones with double-enveloping gears, and should expect to find crappy (less reliable, less durable, higher drag) non-enveloping gears in the cheapest (because they cost the least to make ;)) boxes.

My point was just that there seems to be no technical reason (such as friction) to choose the cheaper non-enveloping style.

Softer materials are normally used on the wheel than the worm, so while the worm should likely be steel, the wheel might reasonably be bronze or brass. These things slide on the contact face much more than other forms of gearing, so lubrication issues and corresponding material choices are not the same as a common spur gear. I don't know what to set as a minimum standard, either. :confused:
 
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