# How to build a EV mud buggy



## wildacres00 (Aug 20, 2010)

I travel in the everglades and am looking to build a EV mud Buggy. So far I want to use a 9" DC motor and 6 12 volt 150AH batteries. What I need is a vehicle that will travel slowly but will need torque for the mud and I must get at least 4 hours of travel. The weight is approx 3500lbs fully converted 4WD with 44" tall tractor tires. Please any suggestions would be welcomed since I am only a novice and have never built one before.


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## Guest (Aug 21, 2010)

> 4 hours of travel


 At what speed are you expecting with the small pak?


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## Guest (Aug 21, 2010)

Might get a half hour run time. You will suck up amps big time with that as you need to overcome a great resistance of the mud and weight of the vehicle. It will put a great strain on the controller and batteries but if you size it right you should be good to go. Time wise I doubt you will get 4 hours. Might just stick with diesel or bio in a case like yours. Your heavy and going to add even more weight of batteries and that does not seem like a good combination in the mud bogs of the everglades. 

But if you really want to do an electric mud buggy this is a good place. What kind of vehicle? The term buggy is too generic. 

Pete


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## wildacres00 (Aug 20, 2010)

The buggy is a old jeep frame with a typical running gear but has been converted to a platform swamp buggy. I was told by a friend that all i would need is high amp hour batteries with a voltage of 72v. I personally do not have much of an idea and am looking for suggestions to improve the idea. The only true part that i cannot change is the 4 hours needed to operate to get me to my camp where I can recharge. The top speed will only be possibly 10mph with varying levels of mud and water.


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## wildacres00 (Aug 20, 2010)

What do you guy's think would work?


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## madderscience (Jun 28, 2008)

something like this?








http://www.epa.gov/epahome/sciencenb/slideshow4/05%20RAM.jpg

One way to estimate how much battery you need is to make an educated guess based on the gas mileage of such a buggy and converting that to electrical efficiency. 

How much gasoline would it take to do the trip? Lets assume a gasoline powered swamp buggy being used on your trip gets 10mpg (meaning you will burn 4 gallons to do your trip of 4 hrs at 10mph)

One gallon of gasoline has 33.6kWh of energy stored, so four gallons has 135kWh or so (rounded off) However, you are lucky to get 20% overall efficiency with an internal combustion engine vehicle. So really about 26kwH actually went towards getting you there.

With an electric vehicle, you can get to about 80% overall drivetrain efficiency. so take that 26kwH, and divide by 0.8 to get 32.5kWh minimum usable pack size.

With lead acid, you want nominal (nameplate) capacity to be around 2x usable capacity to avoid over-discharge of the batteries. This would mean abaout a 60kWh pack. If this was a 72V lead acid pack, it would be about a 800Ah pack. It would weigh about 3000lbs, and might be comprised of three parallel strings of twelve trojan T-145's or equivalent. Way bigger than your initial estimate.

It doesn't look quite so bad with lithium. A realistic pack would be a something like a 640AH, 72V lithium pack. (four
parallel strings of twenty thunder sky 160Ah cells for example) this would weigh a bit under 1000lbs. 40kWh nominal but due to the better chemistry you don't need as much margin as with lead, and its lighter too. Very doable technically, but not cheap.

Anyway, in either case we are looking at a lot more battery I think than you hoped for.

FWIW a 32kWh usable capacity lithium battery pack if installed in my MR2 would give me about 150 miles of freeway range. 

Can you build a much smaller vehicle? Like perhaps an ATV, maybe with a powered trailer full of batteries? Could a boat make it?

Or take some notes from the kinetic sculpture crowd, and build something sort of like this: (I've seen this one in person, its really cool)








http://farm1.static.flickr.com/28/54635138_8509d6d89d.jpg

... which is human powered (one pedaller per wheel) and fully amphibious, and very light for its size. Use an etek motor on each axle, a much smaller lithium pack maybe 10kWh (since you are mostly floating and not plowing), throw about a kilowatt of solar on the roof for some extra kick and emergency recharging and maybe you'd have something interesting. Definitely would need to do your homework though.

or maybe I've been breathing too much swamp gas.


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## wildacres00 (Aug 20, 2010)

The first pic is exactly what I am doing. I believe that is a park ranger buggy but my buggy currently is built the same way with the same tires. I am pretty much locked into that design because of the space needed and the terrain. Is there a possibility to mechanically help the motor and batteries by using different gear boxes. As far mechanically speaking I can perform any task and also I can fabricate what I need the part I can't do is the electrical theory so thanks for the input. I have a friend who has built a electric truck and thats where I got the idea from.


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## wildacres00 (Aug 20, 2010)

The amount of batteries you are speaking of is more weight than I can carry and going the lithium route is too expensive. I expected to draw approx 25amps while travelling. If I were to perform this project and found it just didn't I guess I could sell the batteries and parts on a EV community web page and have to take a minimal loss.


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## wildacres00 (Aug 20, 2010)

The overall distance I travel is only 16 miles but I used 10mph as the highest speed I travel while the lowest is really 3-4 mph due to the terrain. The trip takes me about 3 hours on average depending on the time of year.


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## Guest (Aug 21, 2010)

I'd think about going diesel and use bio diesel to be clean. You can have the torque you need and have a blast while being clean.  Way easier than converting such a vehicle to electric. It could be done but the distance is going to be difficult.


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## wildacres00 (Aug 20, 2010)

Looking for a challenge or a glutton for punishment. I've been in the everglades for 22 years and have a couple of different buggies and am ready to build another. The quietness and efficiency is what has me intrigued. 

Thanks Don


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## wildacres00 (Aug 20, 2010)

Also i am using 2 1/4 gallons an hour of fuel for around 9 gallons in a 4 hour trip. What would that equate to for batteries? Based on your math Major I came up with 19 kwh and doubled is 38 kwh needed.


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## madderscience (Jun 28, 2008)

Ouch. 9 gallons to do 16 miles. I knew it would be bad but I didn't expect less than 2mpg. Plowing through mud is hard work. ( I can attest, having found myself thoroughly bogged down a few times)

I assumed you were using about 4 gallons (distance or speed not really relevant since gallons used will be more or less directly proportional to battery size needed). You said you are actually using 9 gallons.

So you need to multiply my numbers by 9/4 or 2.25.

That would mean minimum usable pack size would be about 32 * 2.25 or about 70kWh which is bigger than a tesla pack. 

If it's not possible to build a smaller or lighter vehicle, then I think I agree with gottdi that a diesel would be the best approach in your case. 

sort academic at this point, but gearing down the motor would be a requirement of course since you'd probably want the motor spinning at around 3000 to 5000 rpm depending on the type. Nonetheless, watts are watts, horsepower is horsepower and the work required to get you there doesn't change so you still would need a big (er, huge) battery pack.

maybe build a hybrid design? so that at least you can sneak around quietly for shorter distances if you want, or run on electric over the not so gnarly sections of terrain, then fire up the diesel for longer hauls and muddy slogs?

A relationship to consider: one horsepower is 746 watts. one watt is 1 volt * amp.

You mentioned that you had assumed your motor would be pulling 25 amps at 72 volts. that is 72 * 25 or 1800 watts, or about 2.5 horsepower. 

Based on your fuel consumption (9 gallons) over the course of 3 hours and an assumption of 20% engine efficiency, I can compute your average horsepower needed.

9 gallons == 302kWh
divide by 3 hours to get 100kW
multiply by 0.2 to account for ICE efficiency to get 20kW shaft power
divide by 746 to get horsepower of 27

So if you are using a constant 27 horsepower (roughly the same oomph as it takes to maintain freeway speed in a full size pickup or van) then you probably would normally install a 100 horsepower rated engine (at least).

I've found many people (self included) when first learning about EVs don't realize just how much energy is in a gallon of gasoline, how that relates to stored electrical energy and how hard it is to replace one with the other. Petroleum is a great fuel, except of course for the pollution, all the various geopolitical issues, and the noisy, thrashing, steaming, reciprocating machines needed to utilize it.

good luck.


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## wildacres00 (Aug 20, 2010)

Thanks for the info. I may decide to do a small ev utv project until I learn more of the process. I am still going to build a new buggy but will probably go with a straight six jeep motor or with a diesel tractor engine depending on it I can find one or not. I already have the jeep engine. Thanks again


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## JRP3 (Mar 7, 2008)

You could try something like I did with my 6x6.


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## Tesseract (Sep 27, 2008)

Whoa, there, wildeacres... you may be getting such crappy fuel economy now because you are spending most of the time idling the engine! Moving at 3-4 mph, even in the mud, is not going to take a whole lot of power, but even if it took as much to drive at 55mph on the highway you might need, oh, 5-6kWh of battery capacity to go ~16 miles.

This seems like a perfectly reasonable project. You don't need much power, you don't even really need much range, you just need good endurance at slow speeds.

A fixed reduction drive should work fine here, too. I'd go with an HTD belt drive, myself, as it is low maintenance and easy to build (and no lubrication required - a definite plus in muddy/dirty environments). You want the motor to be spinning at somewhere around 2000 rpm when driving at your 3-4 mph speed, which will give you a realistic top speed of 10mph.

Finally, I'd personally consider an Alltrax controller running at 72V and maybe a 6.7" motor. A 9" series motor is just crazy big for this job. 

Geez - this is almost perfect application for electric drive. Get out there and do it, man!


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## JRP3 (Mar 7, 2008)

Have you ever driven through thick mud with over sized tires? Rolling Resistance is through the roof! You're usually using low range on the transfer case and low gearing, so motor RPMS's are not exactly idling.


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## Tesseract (Sep 27, 2008)

JRP3 said:


> Have you ever driven through thick mud with over sized tires? Rolling Resistance is through the roof! You're usually using low range on the transfer case and low gearing, so motor RPMS's are not exactly idling.


Nope... but I did stay in a Holiday Inn Express last night! 

First I will cheerfully admit that I didn't quite make the connection between 3-4mph, 4 hour run time and 16 miles of range. That does, indeed, imply that not a whole lot of time is spent idling. Like, none.

However, I did assume that driving through mud would require a lot more power for a given speed than on a paved road, which was I just took a WAG and figured it would be the same as driving at 55mph. Maybe that's completely off, dunno, but I didn't exactly come up with budget-busting numbers in the first place.

It would be a simple physics problem to solve if someone has good data on actual rolling resistance of mud tires in the mud.

When I plugged in the relevant numbers to this calculator, including rolling resistance of 0.3 and a 72V x 100Ah pack, I get a range of 4 miles at 4mph. So, quadruple the pack and you got it. Maybe. 

Would definitely help to lower the weight as much as possible in a vehicle like this because power to overcome rolling resistance is directly proportional to weight. This could be a case where lithium pays for itself immediately by requiring much less energy just to move the batteries around.


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## wildacres00 (Aug 20, 2010)

Actually quite a bit of time is spent idling. Most of the time I am idling or just a little higher than idle while in 1st or 2nd gear on low ratio in the transfer case. In my case the 3-4 hour limit is a must since my camp is that far of a drive,by buggy so endurance is definitely the key. A couple of the other members seem to make it near impossible based on the KWH calculations I have seen. My buddy is the one who told me that 72v 150ah would accomplish the task with a series wound DC motor. With the mud and water I would have thought that belt drive would be a negative but i dunno. Also I am not sure why the motor needs to be at 2000 rpm. I was under the belief that on a dc motor you get max torque from low rpm, so based on that why would I need to spin the motor up? Of course any input is greatly appreciated since I am still trying to figure it out.

Thanks Don


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## JRP3 (Mar 7, 2008)

There is also the actual viscosity and depth of mud to consider. Sometimes you can power through it with torque, sometimes you need to paddle through it with tire speed. If it's a few inches of mud and water that you don't sink into then it might not be that bad. I've spent a lot of time slogging through, and getting stuck in, the deep stuff. Some day I hope to do it again, in an EV, when I can afford the batteries and motor that I need to do it right.


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## JRP3 (Mar 7, 2008)

wildacres00 said:


> My buddy is the one who told me that 72v 150ah would accomplish the task with a series wound DC motor. With the mud and water I would have thought that belt drive would be a negative but i dunno. Also I am not sure why the motor needs to be at 2000 rpm. I was under the belief that on a dc motor you get max torque from low rpm, so based on that why would I need to spin the motor up? Of course any input is greatly appreciated since I am still trying to figure it out.
> 
> Thanks Don


You want to spin the motor up for better cooling and lower amp draw. All that low end torque at low RPMs means you're pulling more amps from the battery. You'll also have to figure out how to waterproof the motor while still allowing for cooling since it's an air cooled motor. Water cooled BLDC or AC motor would be better in that respect but much more expensive.
If you really are mostly idling along most of the time then your power requirements are much lower than what I was thinking.


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## JRP3 (Mar 7, 2008)

I've been imagining something like this:










But maybe you're dealing with something more like this:


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## wildacres00 (Aug 20, 2010)

JRP3
What do you think it would take to make it work. The vehicle weight pretty much prevents it from paddling through the mud but I rarely get stuck knock on wood. Most of the time the mud is 1 to 2 feet thick but the viscosity changes greatly depending on the water present and time of year.


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## JRP3 (Mar 7, 2008)

If we could figure out the actual HP you are using that would give us a better idea. A HP curve for the motor you normally use would tell us what we need to know.


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## wildacres00 (Aug 20, 2010)

The bottom pic is exactly what I have. In that pic the terrain is mostly water and rock because of the cypress it is in. The 3 types of terrain is cypress (wet and muddy with rock potholes), pine which is dry, and open prairie grass which is where people usually get stuck.
I have already put some thought into cooling and waterproofing. I was going to enclose the motor and run 2 air ducts 1 for suction and the other will have a fan drawing the hot air from the box.


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## wildacres00 (Aug 20, 2010)

I was just researching the torque curve. The motor I run now is a 258 ci jeep straight six and I figure that I run around 1500 to 2000 rpm normally. The book said that at 3000 rpm the motor put's out 210 ft/lb of torque.


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## Tesseract (Sep 27, 2008)

wildacres00 said:


> ...My buddy is the one who told me that 72v 150ah would accomplish the task with a series wound DC motor.


I think your buddy isn't too far off the mark. That would be ~9kWh of usable power. This is all strictly seat of the pants, though and the amount of energy required (kWh) will depend greatly on the tire rolling resistance, which itself will depend greatly on the terrain (like how much of the route is through grassland, swamp, hardpan, sand, mud, etc.)



wildacres00 said:


> With the mud and water I would have thought that belt drive would be a negative but i dunno.


A totally sealed gearbox would be best, sure, but that's a lot more expensive unless the vehicle you want to convert already has a 4WD transfer case and low-range gearing. If not then the belt drive is a "low maintenance" (not "no maintenance") alternative that lets you raise the motor away from the mud and water. Try to keep the single stage reduction to 10:1 or less for best belt life and efficiency.



wildacres00 said:


> Also I am not sure why the motor needs to be at 2000 rpm. I was under the belief that on a dc motor you get max torque from low rpm, so based on that why would I need to spin the motor up?


I'm not going to do motors 101, ok, but you need horsepower to drive at a certain speed and:

Hp = (rpm * lb-ft)/5252

Let's say you need 5000 lb-ft of torque at the wheels and 10 rpm to do 4 mph. That's less than 10hp but I sure wouldn't want to try to do this with direct drive. One drag racer has reported that the WarP 9 will deliver 625 lb-ft of torque at 2000A... and you need 8x more torque. That ain't gonna happen.

If you spin the motor at 2000 rpm, though, you only need 25 lb-ft of torque. Your motor will need significantly less current and you won't need to add an external blower to keep it cool (might want to do that to keep sand and water out of it, though).

If you mostly idle the engine to drive your route now then it is likely you are running at 750-850 rpm. You could probably get away with bolting the motor to the transmission without any additional speed reduction but then I would definitely add external cooling as the internal fan won't be turning fast enough to keep the motor cool (we know this from experience, btw).


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## wildacres00 (Aug 20, 2010)

The buggy is already a fully funtional machine and is close to the bottom pic in the above reply. The 4WD system is in place and I was planning on for going the transmission but plan on keeping the transfer case. If I need to couple up to the transmission I will especially if it reduces the power needed. The idle is advanced so I don't have to touch the foot pedal. I had planned on a external cooling system.


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## JRP3 (Mar 7, 2008)

I'd think bolting the motor to the stock transmission would be the best way to go. That coupled with the transfer case would give you a nice way to optimize motor speed for the conditions, and you don't have to deal with belts or chains. Since you don't have to deal with wind resistance it's very possible that you're using less than 500 watt hours per mile even in the mud, which would give you your 16 mile range with a 72 volt 150ah pack of lead. Personally I would start with a controller with a higher peak voltage as that would allow you to add a few more batteries if you need them.


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## Woodsmith (Jun 5, 2008)

Here's a thought for getting the motor out of the wet.
Mount an angle drive gear box on the front of the trans and then have a prop shaft vertically upwards and then mount the motor on top. It can be as high as you like out of the way.
The angle drive box could then have whatever gearing you may need to do what you want.

No doubt you could make something up with a diff or a transaxle for more gear ratios. Just be careful of the lubrication.


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## wildacres00 (Aug 20, 2010)

Alot of the controllers and motors I have been considering are from 72v as the low end and I think go up in the 120v range. I thought of going with a Curtis controller.


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## wildacres00 (Aug 20, 2010)

Thats a good idea woodsmith. I thought of mounting the motor at a angle in the front of the buggy with a CV universal joint and then have it meet up to the transfer case with another CV u-joint.


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## JRP3 (Mar 7, 2008)

wildacres00 said:


> Alot of the controllers and motors I have been considering are from 72v as the low end and I think go up in the 120v range. I thought of going with a Curtis controller.


To contradict myself, a 72 volt Alltrax is relatively cheap and you could always sell it later at a mild discount if you want to increase the voltage. Sometimes they show up on Ebay, and Carl at EVdrives.com has them used once in a while.


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