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Discussion Starter · #1 ·
I want to build a mower unlike any I've ever seen. You may have seen Swisher "Big Mow" and "Ride King" 3-wheel front-steer-&-propel mowers. They are the ONLY 3-wheel front-steer-&-propel mowers I've ever seen. I feel that 60-year-old design did some things exceptionally well but included a nearly-fatal flaw. The only true Zero Turning Radius mowers I've seen which neither need nor include a power-dividing differential, which trouble-prone and expensive-to-repair mechanical section is the most common cause for ZTR mowers going to salvage, are single-wheel steer-&-propel configurations. To me, rear-wheel single-wheel-steer-&-propel is inferior to front-wheel single-wheel-steer-&-propel because the rear must swing sharply out in the opposite direction from the direction of a new abrupt turn. So if you're brushing along a wall or fence and then need to steer abruptly away from that fence, the rear wheel steer version can't do it due to rear swing-out required to turn.

So I want to explore the front-wheel drive and steer version. To get a good ground grip, the fewer wheels propelling your mower, the larger they SHOULD be. Yet Swisher's front-steer-&-propel mowers skimped on its one and only driving tire's size. If they'd upgraded that tiny tire to a big studded snow tire of that 1950's era, with a more robust drive system, it's updated more powerful versions with a better drive might be commanding a big market share today.

I'm looking at automotive-sized snow tires which rotate about 900 times per mile. So for each mile per hour speed it must spin 900/60 = 15 rpm.
It would be nice for it to be able to travel up to 8 mph, which would be 120 rpm, but it definitely MUST be able to sustain at least 4 mph, which would be 60 rpm.

I'd like to find a 90-degree electric gearmotor capable of delivering enough torque to directly-couple to this big front wheel's axle. If the gearmotor's lubricant-filled transmission directly couples to the front axle, no gears, chains or other abrading components will be exposed to the mower's contaminated environment. That configuration would be hard to wear out.

Power allocation models suggest that commonly, about 95% of mower power propels blade(s) while about 5% propels tires. So I expect this gearmotor's average power demand will be well under 1hp, perhaps 1/4 hp would sustain 4 mph rolling. If a human can even briefly push an out-of-gear mower to a useful mowing speed, that indicates that not much actual power is required.

I know it will disappoint some readers, but I expect to power the blade from an internal combustion engine which engine will also drive an alternator or generator to electrically drive the front-wheel's gearmotor.

Does anyone have opinions about what are likely to be the least-cost candidate gearmotors for this experiment? Recycling parts from existing parts donors would be best. I'd prefer to stay with 12V DC gear motors, but if necessary, I can use alternator 3-phase output before it passes through its bridge rectifier. I'm not eager to have this system carry more than one 12V battery.

Steering that big front tire pumped up to only 6 psi to ANY direction including 90-degree side turns should be easy if its drive link is all electric. Try to get a tire that big and soft to slip or get stuck or fail to easily roll over ground depressions which might almost stop midget-sized tires. Sounds like fun.

Much of our aesthetic taste about what appears "right" is developed by previous experience. Even if a new design at first appears strange, if it outperforms existing designs, people soon learn to like it. I expect people would not instantly like how this new big front-wheel-steer-&-propel mower appears. But if in prototype testing trials, it
turns out to be a champ, "truth will out." Rear wheel steering is less directionally stable than front wheel steering, so rear-steer machines need more frequent steering input corrections to maintain a straight course. I have a rear-steer mower and that built-in feature is unpleasantly noticeable. Big tall soft tires roll easily giving cushioned rides. Its passively-steered smaller rear tires will be suspended to minimize shocks.

I need gearmotor candidate suggestions. Help. Maybe somebody reading this will have something that's been sitting around waiting to be reused.
John
 

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have you thought of using a Starter generator off a old golf car they run as a starter untill they hit around 800 rpm most are 3/4 hp 12 volts
 

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Discussion Starter · #3 · (Edited)
Hi Dale,
Thanks for your reply. I think your newer shorter Electro-Snapper version is a HUGE improvement over your first version with 4 rear wheels and probable minimum turning diameter somewhat like an extended wheelbase pickup truck. Your new weather-proof box seems like a good solution too.

I've just spent a few hours trying to determine energy conversion efficiency ranges for various electric motors rated up to no more than 1 horsepower. Most of them apparently convert MOST electric power input into them to waste heat. The Torqueedo high technology high-priced brand of electric outboard motors posted some claims about their motors' energy conversion efficiencies in a chart comparing some of their products to some of their competitors. The most efficient of their own charted models appear to convert, at their most efficient point on their efficiency curve, 44% input power to mechanical power and 56% into waste heat. While that doesn't sound great, the best of their competitors on that chart was only able to convert 32% into mechanical power and 68% into waste heat. Typical competitor model efficiencies were closer to 20% with 80% going to waste heat! Sounds like motors created by Fred Flintstone, yet they are sold today.

I have not yet found any efficiency information about these large heavy golf-cart electric motors and motor-generators. I understand that some new switching power supply controllers used with them are highly efficient and very expensive. Some old variable-speed golf-cart motor power supplies converted a lot of power into waste heat.

I'm still collecting information about used golf-cart electric motors. Some of them are certainly large, heavy and impressive. But I didn't find any with 90-degree gearboxes built onto their motor frames. So I'd need to find and integrate a separate 90-degree gear box with a reduction ratio around 6 or 7 to 1 to knock that 800 rpm down to my target 120 rpm needed to go 8 mph top speed.

Another potential electric motor source I'm exploring is high-tech motors designed to power bicycles and scooters. Claims about the Currie Technology's integrated electric motor and electronic controller package seem amazingly high. Some articles mentioned figures that seem to be knocking on heaven's doors, like around 90% efficiency! I don't know why Currie isn't competing with Torqueedo. Granted, boats and bikes are different markets, but their required efficiency, weight minimalization and a durability seem to be virtually identical targets.

Right-angle gear boxes capable of sustaining up to 1hp throughput in various ratios are plentiful and have good energy conversion efficiency. Really efficient spur gears near 1:1 ratio only convert about 1.5% of input power to waste heat. As the ratio goes up, efficiency goes down. Bevel gears have lower efficiency ratios than spur gears. But I don't think a single-step right-angle gear box will convert more than 5% of input power to waste heat, so neither gear box heat rejection nor power loss should not be an important issue. If a really efficient electric motor's top speed is close to 3000 rpm, my 120 rpm front tire target top rpm can be obtained by selecting a suitable right-angle ratio conversion gear box. I don't mind complexity at the design level. But I expect final designs to comply with that complexity in very simple packages. The simpler the more elegant.

Converting engine shaft power to electric power is no free lunch either. Typical "claw pole" automotive alternators are only about 50% efficient, converting half their input mechnical power to waste heat. Brushless alternators like those recently produced by Neihoff and competitors for long-duty-cycle users like over-the-road trucks can run up to about 70% efficiency. The rather elegant "Polar Power" alternators have show efficiencies between 85% and 90% in US Military tests. But trying to buy one of them would probably through a wrench in the budget. It's not hard to see how system power throughput efficiency can end up being 10% when you multiply a typical claw-pole alternator's efficiency times some low-tech brute-force motor's poor efficiency. Making system component selections without doing lots of research doesn't align with my problem solving approach.

If you have or find any efficiency curves on what you think may be suitable electric motor candidates, let me know how I can access that information. I'd be interested to know how efficient typical electric motors are in existing electric mowers. Aren't you guys interested in that too? If much more efficient motors have been developed since some of these decades-old electric mowers were designed, shouldn't you at least consider moving over to a motor+controller package that might double your mower's efficiency?

John
 

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Much of the differences in efficiency that you are seeing are because they are lower voltage motors. General rule with electric motors is the lower the voltage the lower the efficiency. What are those electric trolling motors? 12v 24v? get into the scooter motors and they are 36 or 48v
 

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trying for that low of a rpm maybe a old wheel chair/ elec scooter motor one that look somethong like this it a 0 to 140 rpm
http://www.alibaba.com/product-gs/50777324/wheelchair_motor/showimage.html
there lot of old wheel chair around so you should be able to keep cost down and get the contor off it
you could get it real cheap hang around a old person home dump one out and run
it is in the name of science you know. smile
Help I cant get up
 

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the motors from a mobility scooter such as what a hoover round or scooters like that would work for what you are trying to do.. they very reliable well built and are work horses.. and they 12volt motors..
 

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Why not use a shaft drive motorcycle swing arm and mount your motor on the shaft end ??? This way you would have your wheel forks and gearbox all in one...
Or.... Mount you motor right inside the front wheel doing away with a gearbox...
 

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Discussion Starter · #9 ·
My failure to update this discussion thread does not reflect lack of attention. To the contrary, I'm dealing with temporary information overload. Like a dog chewing on a good bone, I'll work on this and expect to improve my position.

I searched through my electric motor collection and found one 90VDC 3/4HP Permanent Magnet 1725 rpm-rated motor connected to a 40:1 ratio 90-degree gear box. While its capable of drawing a lot of current, a tiny 12VDC battery spins it at its designed RPM/volt with very little load. I suppose I could trick out the regulator control section on an externally-regulated alternator so this motor would see variable voltage depending on my throttle position which would control the regulator's control target voltage. That's one alternative design strategy.

Second alternative is a newly-purchased but not yet received pair of 3/4HP 36VDC motors removed from a Tennant brand floor-maintenance machine. I'll have them in hand for inspection and testing within a week's time. They have no attached gear boxes. I believe, but am not certain that they are permanent magnet-type motors.

I'm about to collect a 24VDC Invacare brand joy-stick controlled electric wheel chair propelled by two small 90-degree gearmotors. The price was right. Its two 12V batteries can no longer accept a charge and when provided with 24VDC an electrical/electronic defect is causing it to only drive one of its two wheel gearmotors. Invacare sold wheelchairs with both brush-type and brushless motors. Until I can pull it apart, I'll not know how its drive system is configured.

I started writing a response citing each of the received suggestions. Excellent leads and lots of time is required to get up to speed on the issues those suggestions provided.

But I was including in that response some comments about how a single front-wheel steer & drive vehicle's caster-trail dimension affects its tricycle-type steering behavior. During that writing I discovered that I was making a wrong assumption and had to abandon the wrong assertions I intended to state. I will rewrite that and post it here, but the good news is that adding caster-trail to enable self-centering steering can be worked out with much better grace than I formerly thought possible.

My most likely "snow tire" candidate is a brand new aggressively-treaded 28"-tall tire that came as a new pair with my Kubota tractor. I calculate that will rotate 720 revolutions per mile. So its ground speed per rpm would be 1mph/12rpm.

I've mowed at 8 mph and it was very unpleasant. While the mowing performance was good, I'd need a really-effective seat suspension system to prevent making that experience unacceptable. That's another project, but I'm expecting usual mowing speeds to be more like 3-4 mph until an effective seat-isolating system can be included.

So, thanks for all your helpful suggestions. I'll report back when I can provide a more useful response.
John
 
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