Would like some feedback on my plan to electrify my reel mower

[electricreelmower]

Hello all! I have an old mclane reel mower that I plan on converting to electric. It has a 3 hp briggs and stratton motor in it. There are several conversions that have been on done on youtube that I'm following, but with some small adjustments.

I'd like to keep the operation of the mower as similar to stock as normal. How it works is there is a throttle lever, a dead mans lever, and drive system engagement. The drive system engagement will remain untouched. I'm trying to figure out how to maintain a throttle and dead mans lever style operation. So far I'm looking at scooter/go kart conversion kits like this. Obviously I won't use the pedal, and I'd prefer to not use the handle throttle.

For the throttle, my plan is to swap out the throttle in place for a simple potentiometer. I understand this should work with the controller, except that the motor will start up "late" (at maybe 10% on the pot?), and that the motor may cut off at 100%. This gets my throttle concern out of the way.

For the dead man's lever, I'm trying to find some sort of switch (like a momentary pull switch?) that the existing lever can actuate. The existing lever is a very simple design, it has a rod that when engaged pulls a belt tensioner into place, operating as a clutch. While I plan on removing the belt and clutch mechanism (just one more maintenance item that isn't really necessary with an electric set up - at least I think, let me know if you disagree). So in essence this lever operates like a normal throttle cable would, but it uses a hard rod instead of a flexible cable. What I'd like to do is have this lever engage a switch, and this switch is spliced into the throttle wiring. So if the dead man lever isn't engaged, then the signal wire from the throttle (pot) is open. One concern I have with this set up is how the controller will handle if the dead man lever is engaged when the pot has the throttle turned up already. Will it jolt forward and be rough on the motor/mechanics?

If I struggle to hook hook up a switch to the dead man lever, I can always just have a button I have to press on the handlebar, but I think that will be straining over time.

Regarding the motor, I'm aiming for a 60v 2000w motor. It should be slightly overkill, which I prefer. I'd like it to match the performance of the 3hp engine. These mowers actually have to do quite a bit of work since the reel is like a scissor (metal on metal), and sometimes you're cutting through very thick grass (scalping). Probably will use 60v greenworks batteries.

So yeah, that's everything! would love some feedback!

 

[amberwolf]

Not knowing how the orignal system is physically controlled, I can make some suggestions based on similar types of systems I *have* seen:

Most gas engine throttles are controlled by a cable. you can use COT Cable Operated Throttle either pot or hall type (whatever your electric motor controller requires) to preserve this system. If the pull range of the mechanics on the mower dont' match the pull range of the COT, you can change the gearing of the COT by using a different pulley. One of the motorcycle build threads in that forum has a recent post where they 3D printed a new pulley for this reason.


SInce the Deadman switch operates a "lever", you can use it to pull a springloaded swithc instead. That can be DIYed (ebike brake lever, etc) or you can find such switches online (mouser, digikey, etc, or possibly aliexpress, ebay, amazon, etc). Then the switch can be used as noted previosuly. Or you can mount the switch in a place it will be held engaged by the lever when "on", and use a Normally Open switch so when it is not engaged it is off. There are many kinds but the easiest to use are a lever-operated microswitch with a roller on it, like I use on my brake caliper to operate the brake lights on SB Cruiser.

The SB Cruiser : Amberwolf's 2WD Heavy Cargo Trike & Dog Carrier

I haven't used the electric braking on the "new" generic controller much due to the extreme excessive heating (goes up about 10 degrees C every time I use it...peaks have been nearly 70C even when starting at 8C on the last several cold mornings). I'm probably going to disconnect it from the...

endless-sphere.com

I changed it since the above post so the switch is on the ohter side fo the caliper and uses the other contact set, so it closes when the caliper pulls away from it, instead of when the caliper pulls toward it as the above post shows--it is much more reliable now.

EDIT: This part doesn't apply after re-reading your post
Most deadman switches just cut off the ignition / spark, or else the fuel supply. If yours is an ignition control, it's an electrical swithc, and youc an simply wire the throttle power supply thru that to kill the control signal to the controler and it will stop driving the motor without a command to do so. Or if the switch can handle the voltage of the controller / battery setup, you can use the swtich to turn off the KSI / keyswitch / ignition wire from battery to controller. Or you can use it to engage a brake signal, holding it high when on and bringing it low when off.



Regarding motor power, it is more about torque than power, at the specific RPM needed to drive the blades as they were before.

You'll need to choose a motor with the same loaded-down RPM at the voltage you will use it at that the engine has on it's output shaft under the same conditions

It also needs at least as much torque as the engine has at that RPM. That's partly determined by the currrent available to it from the controller. So you need a big enough controller (amps) to supply that.

Then the battery must supply all those amps (A) for the amount of time you need it to operate (Ah).

 

[glennb]

There's a bit to consider.

I've reasonable experience with mowers, but know little about reel mowers. (I do own one, but never use it, let alone customised it or measured RPM or power consumption). So, can probably only share my experience with throttle designs.

Is it more about the project? Or more about the mowing? Because there's plenty of decent electric mowers available. Selling it and reinvesting the money in an electric mower is not appealing? Is it for commercial or home use?

 

[electricreelmower]

Regarding motor power, it is more about torque than power, at the specific RPM needed to drive the blades as they were before.

You'll need to choose a motor with the same loaded-down RPM at the voltage you will use it at that the engine has on it's output shaft under the same conditions

It also needs at least as much torque as the engine has at that RPM. That's partly determined by the currrent available to it from the controller. So you need a big enough controller (amps) to supply that.

Then the battery must supply all those amps (A) for the amount of time you need it to operate (Ah).

Hmm this is good info, thanks. So far I was just trying to match the RPM. I'm not sure how to find the loaded RPM though. The engine supposedly idles at ~1700 RPM and goes up to 3200-3600 RPM. From what I've seen, a 2000w 60v motor has a "cruise speed" of 4250RPM. That's too much, but I planned on using the speed settings. Is it safe to assume the motor will have enough torque, given motors have more torque at the low end, and I'm likely going to be running it in the slower settings?


Regarding the battery. I was thinking a 60v greenworks 5aH battery. They don't say what the peak amps it can support though, but 5aH should be enough based on other conversions I've seen online. I have a fairly small lawn.

 

[electricreelmower]

There's a bit to consider.

I've reasonable experience with mowers, but know little about reel mowers. (I do own one, but never use it, let alone customised it or measured RPM or power consumption). So, can probably only share my experience with throttle designs.

Is it more about the project? Or more about the mowing? Because there's plenty of decent electric mowers available. Selling it and reinvesting the money in an electric mower is not appealing? Is it for commercial or home use?

The only electric reel mowers are very expensive, starting at over two grand, otherwise yes I'd buy one of them.

Luckily with the mclane mower the reel speed is matched with the drive speed, so as long as I can get the drive speed in a good range (medium paced walking), then the reel is guaranteed to be going the correct speed. It's just a matter of if the motor will have enough torque I suppose.

Most people online are converting manual reels to electric with 1000w brushed motors. These just make the reel motorized, but they do not have drive wheels (not self propelled). That's why I plan on "rounding up" to 2000w. Also using the 3hp motor as a figure to try to match.

 

[amberwolf]

From what I've seen, a 2000w 60v motor has a "cruise speed" of 4250RPM.

Every motor has a kV, or RPM per volt. The voltage of a motor isn't related to it's RPM other than that (and the wattage isn't related at all).

So to know how fast a motor will spin, if you don't already have a specification for it that states how fast it spins at a specific voltage, or that states it's kV, you'd have to actually spin it up at the voltage you'll run it at, and measure the RPM.

Some motors you can make a guess, like hubmotors that say they go 20mph in a 36v system and are in a 26" wheel, for instance, you can use all those things to find out what the RPM of the motor itself is, then divide that by the votlage to get the kV and use that to guesstimate how fast it will spin in your own system.

With any standalone (chain, belt, etc drive) motor you don't have that way of oding it, so you have to either have a spec giving it to you or test for it, if you want to actually know the RPM.

YOu can just build it and test it and see if it works...but it's usually less costly and time consuming to figure out the bits beforehand and buy the right stuff.

If you are using a chain/belt system, then you can also change the system RPM by changing the sprocket sizes on input and output; this also inversely changes the amoutn of torque you get.

Regarding the battery. I was thinking a 60v greenworks 5aH battery. They don't say what the peak amps it can support though, but 5aH should be enough based on other conversions I've seen online. I have a fairly small lawn.

Keep in mind that capacity (Ah) sn't related to current capablitly (A) even though they both have A (amp) in them.

You have to use a battery capable of delivering the current (A) the system needs, with as little voltage sag as is acceptable (because that slows the motor down).

 

[electricreelmower]

Keep in mind that capacity (Ah) sn't related to current capablitly (A) even though they both have A (amp) in them.

You have to use a battery capable of delivering the current (A) the system needs, with as little voltage sag as is acceptable (because that slows the motor down).

understood. I meant to say if it can handle the peak amp load, then it should have enough juice to mow the entire lawn.

Every motor has a kV, or RPM per volt. The voltage of a motor isn't related to it's RPM other than that (and the wattage isn't related at all).

So to know how fast a motor will spin, if you don't already have a specification for it that states how fast it spins at a specific voltage, or that states it's kV, you'd have to actually spin it up at the voltage you'll run it at, and measure the RPM.

Some motors you can make a guess, like hubmotors that say they go 20mph in a 36v system and are in a 26" wheel, for instance, you can use all those things to find out what the RPM of the motor itself is, then divide that by the votlage to get the kV and use that to guesstimate how fast it will spin in your own system.

This is unloaded RPM per volt, right? I think I can figure out unloaded figures to match.

 

[amberwolf]

This is unloaded RPM per volt, right? I think I can figure out unloaded figures to match.

The kV rating is usually unloaded.

The hubmotor thing is usually loaded.

A good guesstimate is that loaded = around 80% of unloaded RPM for a given controller output/motor/etc.