# Mtd Novotrac singleblade mower convertion



## agniusm (Apr 30, 2012)

Blade is 26" long. I can set my motor from 1000 to 4000 rpm with battery voltage.
Reduction to blade is 1.78. What would be optimal rpm at motor shaft?


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## brian_ (Feb 7, 2017)

Small gas engines are typically designed to run at 3600 rpm for maximum power, and the same engine is typically run more slowly for better efficiency and life. This specific speed isn't random - it works well for use in generators, which need to run at 3600 rpm to produce 60 Hz from a two-pole generator.


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## agniusm (Apr 30, 2012)

brian_ said:


> Small gas engines are typically designed to run at 3600 rpm for maximum power, and the same engine is typically run more slowly for better efficiency and life. This specific speed isn't random - it works well for use in generators, which need to run at 3600 rpm to produce 60 Hz from a two-pole generator.


Its 10.5hp engine. I will try and calcutate blade tip speed if its something close to the legal limit.
Would 3600rpm be at the shaft?


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## agniusm (Apr 30, 2012)

Ok, so after 1.78 reduction blade gets 2023 rpm.
Blade circumference km times 60 minutes = 251kmh if my math is ok. A bit low as i find 210-230mph which is over 300kmh


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## brian_ (Feb 7, 2017)

agniusm said:


> brian_ said:
> 
> 
> > Small gas engines are typically designed to run at 3600 rpm ...
> ...


Yes, I was referring to the engine output shaft speed.


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## electro wrks (Mar 5, 2012)

I'm converting a riding mower similar to this one with a large, single center blade. Is your mower like this: https://www.motoruf.com/n/partslists.html?id=644464 ?
If so, the mower design has a separate gearbox driving, through a roller chain, a rear axle/differential . I would recommend you drive this axle/differential with a small electric motor and variable speed controller that replaces the gearbox. The chain drive makes it easy to position the motor in the body of the mower and change the drive ratio with different sized chain sprockets for optimum ground speed. This is a motor separate from the much larger motor needed to drive the cutting blade in the mower deck.

On the mower I'm converting, the large blade drive motor is going to be mounted on the cutting deck, driving the blade through a V-belt. This eliminates the undesirable variable angularity of the V-belt of a typical ICE drive set-up. The V-belt drive allows the motor to be positioned to clear the bodywork as the deck is moved up and down. Also, the blade drive ratio can be changed very easily by using different diameter pulleys and belts. And, the belt will reduce the shock loads on the motor and slips if the blade hits a large object.

It might be possible to have this cutting deck motor run at a fixed, constant speed. This would eliminate the need for an expensive electronic speed controller. Another possibility is to bring the cutting deck motor up to speed in steps to reduce the starting torque shock loads with the use of a large resistor bank, like the old electro-mechanical golf cart controllers. The resistance speed controllers are very inefficient, but they would only be used for few seconds as the motor is brought up to its fixed speed.


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## agniusm (Apr 30, 2012)

electro wrks said:


> I'm converting a riding mower similar to this one with a large, single center blade. Is your mower like this: https://www.motoruf.com/n/partslists.html?id=644464 ?
> If so, the mower design has a separate gearbox driving, through a roller chain, a rear axle/differential . I would recommend you drive this axle/differential with a small electric motor and variable speed controller that replaces the gearbox. The chain drive makes it easy to position the motor in the body of the mower and change the drive ratio with different sized chain sprockets for optimum ground speed. This is a motor separate from the much larger motor needed to drive the cutting blade in the mower deck.
> 
> On the mower I'm converting, the large blade drive motor is going to be mounted on the cutting deck, driving the blade through a V-belt. This eliminates the undesirable variable angularity of the V-belt of a typical ICE drive set-up. The V-belt drive allows the motor to be positioned to clear the bodywork as the deck is moved up and down. Also, the blade drive ratio can be changed very easily by using different diameter pulleys and belts. And, the belt will reduce the shock loads on the motor and slips if the blade hits a large object.
> ...


Yes, very similar tractor. 
I wont be using 2 motors and i will leave same setup. My motor is capable 13kW and stock is 6.9kW so i am well over to support both, blade and drive wheels. Less of messing about and i will still have my gearbox.
I am using Navitas TPM-400 controller with 400A peak. I will make 5k pot and connect it to excising throttle cable.
Easy peasy job.

I have found a sticker where it says it is 2900 min-1 so that must be motor rpm and at 48V i should be very close


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## agniusm (Apr 30, 2012)

Got motor plate made. I will mill old engine shaft to fit my motor and weld it into the pulley


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## electro wrks (Mar 5, 2012)

Do you have any photos of your motor? How about its output shaft length and diameter? Another advantage of the setup I described is that it can free up more room for batteries. Also another advantage with electric drives is that if your drive motor is large enough(usually it only needs to be 1-3kW if you're not towing a lot or pulling a tiller), and the right drive ratio can be set-up, a muliti-ratio transmission is not needed.


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## agniusm (Apr 30, 2012)

electro wrks said:


> Do you have any photos of your motor? How about its output shaft length and diameter? Another advantage of the setup I described is that it can free up more room for batteries. Also another advantage with electric drives is that if your drive motor is large enough(usually it only needs to be 1-3kW if you're not towing a lot or pulling a tiller), and the right drive ratio can be set-up, a muliti-ratio transmission is not needed.


I do have some photos but not uploaded yet. My motor dhaft is 19mm. I have cut off the engine shaft, lathed 19mm hole to fit my motor shaft, cut the keyway open and welded it to a dual pulley. I spaced the shaft with couple of washers as i needed 6mm to locate it properly. I still need to weld on. A ring so motor torque does not split open the insert i lathed. It all looks good atm and it was quick job.
What sort of battery capacity are you thinking? I will put some 2.7kWh for starters as this is what i have laying arround and see how that works out for me. I have calculated that my final rpm at nominal voltage(51.2V) will be 2833 vs 2900 on gas engine so pretty damn close.
I have mounted the motor and i have plenty of space under the hood for all electronics and battery. Ultimately i could go with 16 winston 130ah lifepo4 for total of 6.6kWh


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