powered, lightweight mower protoype

[Andy Carson]

@danielwinters 34833 wrote:

One option might be to build the cart assembly, then people could add an old cutter bar that they have restored and maybe supply a tongue, neck yoke and evener themselves.

Another option to consider would be to start with a 3 pt sickle bar mower for a tractor with a PTO. These are often very cheap. if you use one of these, all the engineering (IE bearings, balance, rpms, etc.) is done already and all you have to do is add a motor and a skid or cart. This is what I think I would do if I was making one of these. Not that there is anything wrong with what you are doing, Daniel, but if you want to make alot of these, it is something to think about.

[mitchmaine]

@danielwinters 34730 wrote:

I figured out the correct RPM for the crankwheel based on the dimensions of a #7 I had in the shop for restoration.

5,280 feet/mile x 12 inches in a foot = 63360 inches divided by 104″ (the circumference of a 32-inch steel wheel) = 609 wheel rotations per mile.
If I count the crankwheel turning 26 times for every drive wheel rotation, it turns 15834 times in a mile. Divide that by 60 minutes in an hour, and you get 294 RPMs at a speed of 1 MPH.
So, if an average team goes 2.5 MPH while mowing, the crankwheel’s optimum speed should be 659 RPMs.
If my small engine runs at 2200 RPM, a reasonable speed to reduce noise and stench, and the pulley reduces output 7:1, then my cranckwheel turns at 315 RPM, which should be fine, because the ponies shorter legs mean their gait is half the speed of a “real” horse.
I’m a newspaper reporter by trade, so my math is probably wrong. Anybody see mistakes in my figures?

Hey Daniel, I was checking out your math, and went out to the back of the barn and found our old Dearborn mower for the 8n. it powered a 8” pulley that drove a 5.5” pulley on the pitman flywheel driving the knife. Based on those numbers, it sped up the 540 pto to about 720 rpm’s or about 12 knife cycles per second. Holy smoke that can’t be right, can it? Sounds too fast. So I tried the number 7 mower. 2.5 miles per hour is 158400 inches per 3600 seconds. Divide the distance(158400 “) by 104” wheel circumference, and the drive wheel turns over 1523 times. Multiply that(1523) by the 26 knife cycles per wheel rev. and you get 39,600 knife cycles per hour . divide that by the 3600 seconds in the hour and its turning 11 times per second on the horse mower. Same crazy number (almost) so it must be so. More math says the horse mower at 2.5 mph is moving 44” per second, and cutting 11 knife cycles per second,four inches of forward motion per knife cycle, or two inches of forward motion per one close of the knife, and that starts to sound believable to me. Your math checks out, best of luck with your mower. mitch

[Jay]

Mitch, thanks for the perseverance to go through that figuring. Fascinating to see it all laid out like that with the comparisons too. Jay

[mitchmaine]

hi jay, when i came up with the twelve turns per second it sounded impossible. then i came up with it two ways and it sounded a little better. my math could be wrong as well. so any that want, double check the numbers. the horse mower is the best example. no matter what the ground speed, its the same two inches per cut. simple math. gotta love it. my team cuts about an acre per hour. but if you run the numbers, staying in grass all the time, and never resting, its only possible to cut 1.81 acres at 2.5 mph. so horses are fairly efficient allowing for the weather and bugs. i’ve always liked the sound of a horse mower. thanks jay, mitch

[near horse]

That’s why, as Jay says, it needs to “run like a sewing machine”. 😮

[Anonymous]

Thanks. I’ve been math challenged my entire life. My experience with my ponies hooked up to a #9 MCD with a 4 foot bar has shown that if the guards are set level and the knife is sharp, that sucker will still cut even at very low speeds — like when they are nearly pooped.
I saw on the internet that in the 70’s they made a riding mower that if I recall correctly used three huge six volt batteries and was reputed to be able to three acres on a single charge. That sounds unbelievable, but maybe it’s true. Then I see these electric wheelchairs hauling around really fat people that apparently use only a 250 watt DC motor. I think it might be doable. If I had the cash, I’d just buy a 500 watt DC motor and a couple golf cart batteries and give it a try.
I know where there’s a JD trailer mower that I can get cheap and so I thought about it the trailer mower idea, maybe permanently attached to a cart, but figured weight was my biggest concern and that my design would keep it to a minimum. For a bigger team, yes, the trailer outfit would be best.
But I also think that since the pony market is largely unserved by equipment makers, an upstart like me might have a better chance. One other thing, it’s an interesting challenge because you’re severely restricted by what they can pull, unlike a full-sized team where you can get away with a lot of overbuilding simply because they are so powerful.
Ponies are an interesting niche. If you only have 10-20 acres, you can’t afford much horsepower. I figure if a Honda civic can do the work, then you don’t need a Dodge dually one-ton, eh?

[Andy Carson]

About the battery, I do not think this a good application for electric power. I think batteries are great for if the power output is low and continuous, or high and periodic, but high and continuous is hard. Lets say your mower takes 1 horsepower to run. Horsepower = (Current x Voltage x Efficiency)/746. Let’s be very optimistic and say you can get 70% efficiency, that means you will be drawing about 89 amps (1 = (current x 12 x 0.7)/746). They make 200 amp hour batteries in lead-acid for golf carts and RVs and such. They weigh about 130 lbs and cost ~$500 each. You might think you could mow for two hours on this, and you likely could, but the battery life is very poor is you discarge the battery completely. You can get ~500 cycles out of the batteries if you only use half the charge. That means two hours of mowing will require about 260 lbs of batteries, with a cost of ~$1000 new. I think most people would want to have the capability to mow a little longer than that, though, which is only going to increase the weight and cost. I would probably use 3 big batteries, so you can undersell a little, and this would weigh ~400 lbs. You could go with a lithium battery, which is only 30% of the weight, but a 200 amp hour battery is going to run you $2000+, and you’ll need at least two (probably three). Few people are going to want to spend $6K on batteries…

I think from a design standpoint, you are underestimating your ponies a bit. They can pull alot when it’s on wheels. The rule of thumb is they can pull 15% of thier body weight (I think this is actually a bit conservative, esp with ponies). Even if they only weigh 500 lbs each, this is 150 lbs of draft (500+500 x 15%) to work with. Estimating the draft of a wheeled cart/wagon at 10% of the weight, this means they can pull a load weighing at least 1500 lbs (probably more). I doubt the batteries or a trailer sicklebar is going to come close to this. Not that there is anything wrong with making the design as light as it can be, just pointing out that you have some weight to play with.

[Anonymous]

I figured that the electric power idea would be tough. My house runs on a very minimal solar array, just 160 watts with four 6 volt batteries in two separate packs with inverters and charge controllers. It works fine and the batteries have been good for five years, even though they get badly deep cycled in the fall when the sun is scarce. But all they do is run the laptop, some lights and a DVD a couple times a month. Everything else runs on wood or propane.
The cost and weight of batteries is a killer, it’s true. Amazing that battery tech still sucks compared to gasoline, even after 100 years of throwing money at it. Like I said, though, if I had the cash I’d give it a try just to see for myself how viable it might be.
Those ponies are tough, and they can pull far above their weight, it’s true. I use them for hauling logs, firewood, manure and plowing gardens and they can do a good amount of work, but its the continuous burn of mowing that poops them out.
I built the ultralight mower as kind of an experiment to see just how light I could get it, and also because it seemed like nobody else had tried that tactic of putting a horse drawn cutter bar on a new chassis.
On that MCD #9 they were good for only about 90 minutes, even with lots of rest stops. I could maybe get two hours out of them if the cutting was lighter (last year the grass was super thick) and they were in better shape. A third pony would make all the difference in the world, but my old man still owns the farm and he hates ponies.

[Anonymous]

I figured that the electric power idea would be tough. My house runs on a very minimal solar array, just 160 watts with four 6 volt batteries in two separate packs with inverters and charge controllers. It works fine and the batteries have been good for five years, even though they get badly deep cycled in the fall when the sun is scarce. But all they do is run the laptop, some lights and a DVD a couple times a month. Everything else runs on wood or propane.
The cost and weight of batteries is a killer, it’s true. Amazing that battery tech still sucks compared to gasoline, even after 100 years of throwing money at it. Like I said, though, if I had the cash I’d give it a try just to see for myself how viable it might be.
Those ponies are tough, and they can pull far above their weight, it’s true. I use them for hauling logs, firewood, manure and plowing gardens and they can do a good amount of work, but its the continuous burn of mowing that poops them out.
I built the ultralight mower as kind of an experiment to see just how light I could get it, and also because it seemed like nobody else had tried that tactic of putting a horse drawn cutter bar on a new chassis.
On that MCD #9 they were good for only about 90 minutes, even with lots of rest stops. I could maybe get two hours out of them if the cutting was lighter (last year the grass was super thick) and they were in better shape. A third pony would make all the difference in the world, but my old man still owns the farm and he hates ponies.

[Author]

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