[TheRedBaron]

Hey everyone:

I am looking at doing a zero turn radius riding mower conversion. However, as been mentioned in other posts, a hydrostatic transmission is inefficient when used with an electric motor. My idea is to use two hub motors, one for each drive tire, instead. Then I would use another electric motor for the operation of the blades.

This is 3 electric motors however, which adds a degree of complication to the design.

So my main question is if that is too complicated a set up?
Comments, Questions, and Concerns are more than welcome!

(basic mower stats: 16hp mower briggs and straton engine, 48" deck, zero turn steering)

 

[TheRedBaron]

Okay that makes sense! However, my greatest concern would be the independent wheel control. I would like to only have to buy one controller for both hub motors. However, I would have to have different power levels at times to each motor. Are there controllers that can accomplish this?

Oh and I am looking at using a brushless DC hub motors for the wheels.
An example of such a motor: http://www.hnmotors.de/product_info.php?language=en&products_id=42

Edit: From what I understand, you are not supposed tow with a zero turn radius lawn mower, however...I would like to plan on towing around at least 150-200lbs.

 

[TheRedBaron]

Hey Woody,

How about that sub forum for unusual vehicles, like karts, tractors, mowers, flying saucers, etc. Any progress?

major

First, an electric flying saucer would rock, but I'm unsure of the power requirements of such a thing. You perhaps would be better off w/ a fusion power plant instead of batteries but who knows?

Anyways, back to a less interesting project (we had wanted to do an electric ultralight but $$ is an issue there, I guess that is like a flying saucer).

The motor I have posted above I want to use as propulsion not for the blades; though hub motors may work for them too, hooked up to a simple switch. With a zero turn lawn mower, each handle would be hooked up to a hub motor and would allow independent operation.

Ziggythewiz, I don't know what your power rating on your blade mower was but I was looking at 1kw motors for the blades.

Also, anyone work with lithium batteries on an application like this or are the lead acids still the primary option here?

 

[TheRedBaron]

I don't know the actual efficiency losses of the hydrostatic setup but it certainly would be a lot easier and cheaper to use it than multiple motors and controllers. Efficiency losses could possibly be made up by just using an extra battery. Lithium would be neat but probably not cost effective.

Tried following your link but it appears to be broken . Anyway, the stuff I found on hydrostatics seemed to indicate to me that their inefficiency was sufficiently high (especially something in the lawn mowing range) to really start hampering an electric motor-hydrostatic transmission coupling.

I am also interested in the maintenance issue. With brushless electric motors, there would be few issues in that department. The system would also be more straightforward (battery->controller->motor->wheels) instead of (battery->controller->motor->transmission->wheels).

Plus transmissions take up space-> space I could use to add more batteries to the mower perhaps?

 

[TheRedBaron]

Thanks everyone for the information! The mower I have found to convert is a Dixon ZTR 4423.

42'' deck with 3 blades
no hydraulics
fiberglass body
Briggs & Stratton 16hp Engine
Chain drive

So hub motors for the wheels are probably out. Probably end up doing the single motor design. However, I am still thinking of doing 3 independent motors for the blades. Not only does that eliminate belt wear and tear, the overall efficiency of the system should go up as well. Also the system wouldn't need a really complicated controller.

On top of all that, it would make cleaning/removing the deck/changing the blades much simpler. The motors could be mounted to the deck. Add universal connectors to the wiring and that only leaves the mechanical structure to worry about.

Thoughts?

Side Note: anyone know what the torque of a lawnmower blade should be around? The rpm's should be around 3000 but the torque would vary depending on the motor used.

Side Note II: Though with the hub motors, while design maybe more challenging, since the power needed to the wheels is fairly small, the motors and controllers for that kind of set up would be much smaller hence less expensive.

 

[TheRedBaron]

Also, let me apologize to anyone who spent a lot of time looking into the issue of the hydrostatic drive efficiency. I was initially under the impression that the mower I was converting was a hydrostatic drive.

However, since I plan on performing more of these conversions, I probably will work on a mower with a hydrostatic drive so the information is still very much appreciated!

Plus other people get to use it as well!

 

[TheRedBaron]

Here's a deck I did a while back

That is a pretty nice set-up. Interesting idea to mount the deck in the front. Have any performance issues due to that? Also, is that the motor situated under the seat? I would then guess that the batteries are under the hood.

@ruckus -> I will post pics as soon as I can

 

[TheRedBaron]

After looking at a couple of threads it looks like using one motor for the blades is more efficient than using three separate ones for each individual blade.

It also looks like having the belt system in place is still a good idea though that reduces efficiency so that the blade system can deal with individual blades slowing down.

Any idea on the efficiency of a belt system or where I can look that up?

Also, what is a good place to look for motors? I am trying to find one in the 3.5 HP or 2.25kW range and haven't been happy with the selections.

Thanks!

 

[TheRedBaron]

Hey Guys:

Here are some pics of the lawnmower. We have already removed the engine and if anyone is interested in a 16hp Vangard Briggs and Stratton (still runs) shoot me an email ([email protected]). (I don't know why you would be interested considering the forum we are on but....)

Anyway the transmission of the thing is all jacked up. The engine runs and the blades will turn on but the mower doesn't actually move. This inclines us to think we should just rip everything out and go with a motor for each wheel running off the chain final drive rather than try to fix up the transmission. I have also read a couple articles describing the issues these cone drives had so going with a technology proven to go bad doesn't give me a good feeling.

On the battery front, it looks like we will probably go with a thundersky or HiPower 100ah LiFeSO4 battery

 

[TheRedBaron]

Oh my gosh, it's an old cone drive. What a blast from the past! I remember helping my boss put one of these on display 36 years ago when the technology was brand spanking new and I was working as a bicycle repairer at a lawnmower sales & fixit place....

Wow! Dinosaurs ran on cone drives? Who knew?

 

[TheRedBaron]

Update on the lawnmower's status. We currently have both of the wheel motors working! That just shows us testing one of them, but we did the other one as well.

Below is a picture of the current status of the mower. As you can see the new drive system of the mower is a lot different than the old cone drive. We are using a BLDC 500 Watt, 1000 rpm motor for each of the wheels. For the blade motor we will be running a 8 hp, 16 hp continuous brushed dc motor.

Our current issue is figuring out how to set up the control sticks. The controllers for the drive motors accept 0-5 volts. However, trying to get that sort of behavior mounted to the sticks is an issue because we still want to be able to have the reverse capability of the zero turn. The controllers have a switch that must be enabled in order to reverse the motor.

In other words we want some sort of functionality that looks like this:
+5v (full forward) ---- 0 Volts (stationary) ----- +5v (full reverse)

We were planning on using some sort of potentiometer set up but nothing we can think of would allow us to map this sort of behavior. If anyone has any ideas, that would be awesome because we are a bit stuck on this issue!

 

[TheRedBaron]

Greetings to all. this is my first post here on the site.

By a strange coincidence, I am a mower mechanic for the local school district. I keep up a fleet of 20 riding mowers of all sizes and types. But, 14 are the zero turn type. 10 are the Hustler 72" Super-Z and 4 are the 64" John Deere Z-Trak type.

Both types use individual fixed displacement hydraulic wheel motors, but one has a unified double pump and the other has two/single pumps.

Not to start any bad feelings, but either would be easy to do a single DC motor to drive the hydraulic pumps and mower deck, (which is direct-belt driven).

The hydrostatic pumps are of the positive displacement, variable volume type with a swash plate to adjust the output. There is no torque converters or slippage involved. they would be a great match for DC power.

The electric motor would need to be RPM controlled automatically by the controller. The deck is always an electric clutch. the variable displacement pumps would take care of for/rev and speed settings.

Turn on the key, and the DC motor starts at a set RPM. drive off trailer to mowing location. start the deck with a toggle switch. A sensor would be needed to throttle up and down with load to stop over speeding when suddenly unloaded.

Oh, well , just dreaming.

MIZ

That may be more practical idea than you think. Considering the price of gasoline and where that is headed, starting to convert some of those mowers (both zero turn and standard) to electric may not be that bad of an idea. Considering the amount of mowers you have to maintain, do you live in a more populated area? I ask because if there is a decent college nearby you might be able to get a class full of engineers interested in doing such conversions. Plus with college funding you might even be able to get the entire thing paid for.

I say this due to direct knowledge. I am a Senior in a Big 10 school in the electrical engineering department and we are currently converting this lawn mower to electric drive for the city's maintenance department. As a community outreach program, we have received quite a bit of school funding that has allowed us to pretty much pay for the entire project ourselves.

In any case, I wish we had gotten a hydraulic system instead of a cone drive. The drive system setup would have been a lot less difficult though the hydraulic system may not have been as efficient as the direct chain drive we are using now.

As of now, we may just mount multiple over sized pots to give us the functionality we need instead of some sort of wig-wag pot. We have also thought about using string pots to map the behavior as well. If I have time, Ill post a drawing of what we are thinking about doing.

 

[TheRedBaron]

That might be a good application for a swappable pack so you don't carry around excessive amount of batteries. How many gallons of gas does a mower use in three hours? That should give you an idea of the kwhs you need in a pack.

We actually did think about doing a hot-swappable pack. Lithium batteries where out of our price range and lead acids for us to get the projected run time were too heavy/big for the lawn mower. However, we were able to find a compromise in the middle that should allow us to run for about 1-1.5 hours.

When we calculated the battery pack size for the mower, we hit a fairly high number even for only the two hours we budgeted to run it. Our calculations showed for a two hour run time on a 30 degree slope going 5 mph we would need a battery pack size of roughly 8.5 kwhrs. This of course was for only a like 44 inch deck, not one of the massive 72" ones. The plus side of course is having a bigger mower means that it can support more battery weight.

I use 20 pc TS90ah in my mower and 1-1.5 hour is no problem

The mower: http://www.automek.com/evrider.php?page=1v

Nice! Those batteries must have cost something crazy though. At least the quote we got on them would have been more than the entire rest of the project. Also: BMS...ERRRRG!

 

[TheRedBaron]

Here is a copy of the calculations that we used to determine the amount of kwhrs we would need. Most of the numbers could easily be swapped for a different mower. However, you would still have to find how much power the blades alone would require to drive.

Or not.....

True! It is nice to have a system that prevents your lithiums from exploding!

 

[TheRedBaron]

How do you then prevent under/over charging on the lithiums or a voltage imbalance on one cell compared to another? From my understanding of the situation, have over/under charged lithiums in series with each other can cause battery lifetime issues along with the potential to really screw up a battery(explosion may be a bit of a harsh term).

However, as a college student, I would say my hands on experience here is lacking. This is just what I have learned in the classroom and in research/talking with those who have dealt with lithium technology before.

So please, expand on this subject if you would! (why the electrical engineering department here does not have course on batteries is beyond me)

 

[TheRedBaron]

If you are still looking for a solution to your 5v-0v-5v potentiometer issue look for some concentric shaft potentiometers here is a couple of links one to digikey and the other is a datasheet from farnell they make linear taper pots for guitar amps. You didnt say what resistance range you needed but farnell makes most standard ranges. If you use a concentric shaft pot you can wire one pot channel to vary resistance one way and the second channel the other direction and then use a SPDT relay connected to your reverse switch to change which pot channel has the input voltage. If you have any questions i can draw up a wiring diagram just let me know.
http://www.newark.com/jsp/search/browse.jsp?N=1001531+5094071&No=0&getResults=true&appliedparametrics=true&locale=en_US&divisionLocale=en_US&catalogId=&prevNValues=1001531&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D1001531%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_US%26divisionLocale%3Den_US%26catalogId%3D%26prevNValues%3D1001531

http://www.farnell.com/datasheets/576650.pdf

Thanks for the links, we have hit a dead end with the string potentiometers. We were looking at a couple small ones (1.5" draw, 5kohm) and they had a price tag of $325 - $365. Which is so far out of our budget it isn't funny. So I'll look into what you suggested and perhaps some of the linear actuating ones.