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Discussion Starter · #1 ·
Hey there, just introducing myself, I've been doing a ton of research as far as electrical/solar/inverters for my RV/Home for a while now, and am part of the diysolarforum.com that has help a ton. I'm in the process now of building my first 48v 272ah LiFePo4 pack, along with 6kw solar array and inverter system.

At heart, I'm an offroad enthusiast, and even have worked in the industry for a while as well, building simple bumpers for offroad cars/trucks, up to building full race trucks. I'm interested now in looking into making a sand car/rail powered by electricity alone. I haven't done a whole lot of research, but I can say it is obviously vastly different than a ICE.

I will be looking into these 3 questions first;

1) Is it feasible to have an electric powered sand car? The vehicle will weigh somewhere around 1500-2000lbs, have have roughly ~35" tall paddle tires that it will have to propel. We typically use anywhere from 500hp-1500hp in some of these cars, so I'm interested in finding out how that equates to an electric motor, as i'm finding 50-100hp motors much more common.

2) Is it feasible to charge this vehicle? We typically are in very remote locations when doing this with no access to grid power. I have an RV that will have 2500watts of solar available, and also a 5500 watt generator built in, but I would hate to be constantly running a huge generator just to get 50 miles out of it for a ride, especially if we want to do multiple rides in a day. Any insight to this?

3) One single large motor, with a transaxle and axle shafts out to the hubs? This seems the simplest way. Or can I get 4x of the In-Hub motors and have a functioning AWD car, with no moving parts other than whats at the hubs/motor? I really like the idea of the In-Hub motors, but I have no idea if they would be able to take the abuse and rough terrain, or if I can even get one that makes enough power?

Yes, I understand this will be expensive, and probably cost more than building one with an ICE, but I am interested and would like to see this through.

Looking forward to learning.
 

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Welcome!

In-wheel motors are a terrible idea for anything but a heavy-duty vehicle (such as a heavy highway truck or construction or mining equipment), or a vehicle so light that it doesn't have a suspension (a bicycle). You can use one motor per wheel to eliminate differentials and allow optimal drive torque distribution, but to be practical the motors still belong on the frame. The only extra mechanical parts are the axles shafts and joints, and they are well-proven, reliable, efficient, and cheap compared to wheel motors.

Battery capacity and charging are serious issues if you intend to use hundreds of kilowatts in a remote area for more than a few minutes per trip. Off-roading is one thing, but churning a lot of sand rapidly is not a good match to EV characteristics.
 

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Discussion Starter · #3 ·
Thanks for the welcome and info!

Is there a difference between a 500hp ICE and an electric motor? I guess I'm asking, is HP the same in both applications? Or does a 250hp electric motor do the same as a 500hp ICE? Any suggestions on what motors i should be looking at?

I'm curious on how I would even be able to calculate range or KW usage because of the difference in rolling resistance of being on sand compared to on pavement, should I just assume 600Wh/mile and shoot for big? It's probably safe to assume the car won't be cruising very much, and will constantly be at 1/2-3/4 throttle with short bursts of full throttle.

I'm not afraid of building an overly large battery pack, or even multiple and using it to balance out the car, I could see putting in 40kwh, which at 600Wh/mile would get me roughly 65 miles? How am I doing so far? Lol

Charging is going to be another challenge, but I don't think impossible. There's a guy that has done something similar to this, with tesla motors and I think chevy volt batteries, in an actual sand truck, and he uses 2x 7kw Generators to charge it quickly.
 

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Thanks for the welcome and info!

Is there a difference between a 500hp ICE and an electric motor? I guess I'm asking, is HP the same in both applications? Or does a 250hp electric motor do the same as a 500hp ICE? Any suggestions on what motors i should be looking at?

I'm curious on how I would even be able to calculate range or KW usage because of the difference in rolling resistance of being on sand compared to on pavement, should I just assume 600Wh/mile and shoot for big? It's probably safe to assume the car won't be cruising very much, and will constantly be at 1/2-3/4 throttle with short bursts of full throttle.

I'm not afraid of building an overly large battery pack, or even multiple and using it to balance out the car, I could see putting in 40kwh, which at 600Wh/mile would get me roughly 65 miles? How am I doing so far? Lol

Charging is going to be another challenge, but I don't think impossible. There's a guy that has done something similar to this, with tesla motors and I think chevy volt batteries, in an actual sand truck, and he uses 2x 7kw Generators to charge it quickly.
Electric motors will feel much more powerful than a gas engine with a similar HP rating off the line because electric motors have the maximum torque from 0 RPM. At higher speeds, the difference isn't as significant since you're working in an ICE's powerband of around 3000 RPM. For your goals (which I assume a quick acceleration is far more important than a high top speed), you probably wouldn't want more than 250hp.

You have the right idea with those battery numbers. 600Wh/mile might be a bit of a pessimistic estimate, but if you assume that's what's needed, its always better to be pleasantly surprised than disappointed in your final range.

For this type of project, you might want to consider a DC motor. No regenerative braking (which you probably wouldn't want for a sand and you can push crazy amperage thru them for a short time. DC motors are a popular choice for track cars. Look into the Netgain Warp 9 or Warp 11. Weak on paper but people have pushed well over 1000 amps thru them. I'd be interested to hear what brian thinks about a motor choice.
 

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You have the right idea with those battery numbers. 600Wh/mile might be a bit of a pessimistic estimate, but if you assume that's what's needed, its always better to be pleasantly surprised than disappointed in your final range.
I think 600wh/mile is optimistic on paddles.

122062


Compare, say 0.015 vs. 0.40. It's 26x as much rolling resistance.

He's off the end of the scale here, that's car tires on loose sand, he's using 35" paddle tires.

This of course depends on speed. At highway speed on sand, he'll quite possibly be using 30-40x as much energy fighting rolling resistance as a normal tire on pavement. Car tire on pavement is 25-50% of your power requirements. Well, multiply that 50% by 30 and now you've got like, 3% of your power from fighting air resistance, and 97% from fighting the sand. It's a pretty massive power requirement, which does not surprise me then that sand rails are 500-1500 horsepower.

I'm not afraid of building an overly large battery pack, or even multiple and using it to balance out the car, I could see putting in 40kwh, which at 600Wh/mile would get me roughly 65 miles? How am I doing so far? Lol
If those were the numbers, that's fine.

Charging is going to be another challenge, but I don't think impossible. There's a guy that has done something similar to this, with tesla motors and I think chevy volt batteries, in an actual sand truck, and he uses 2x 7kw Generators to charge it quickly.
The fastest way to charge is to ask one of your buddies to tow you around in circles for half your time while you flatline the regen paddle.

More batteries doesn't really help, since, presumably you're racing with these? Batteries are heavy. Also, weight is proportional to rolling resistance.

2500 watts of solar ain't gonna do shit. They'll provide, in peak sun, 2500 watt-hours per hour, obviously. On a 40kwh pack, that's 16 hours of noon-sun to recharge.

You might have to give up on some of your requirements.
 

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Discussion Starter · #6 ·
Thanks for the info, THIS is the link for that Tesla Sand Truck, you can see he’s got 22kwh of batteries (which he has recently upgraded to a larger Chevy volt pack) and he gets around 25 miles, so figure 1kw/mile then, as that’s a more realistic figure. He charges it with a single 7kw generator, not 2 like I thought, and it charges in roughly 2 hours, which isn’t bad for me, even if I get a 40-50kwh battery and it charges in 5-6hrs, I could probably get a couple rides out of a single charge, even with a slower charger in between rides or overnight.

I don’t think charging is the problem.

The only difference is he is using a ludacris Tesla motor out of a model S, at 1600amps and I think I read somewhere else at 396v. The Warp 11 motor obviously can’t compete with something like that, can it? Is the Tesla motor something I should be looking into, or is there another motor that can compete?
 

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He charges it with a single 7kw generator, not 2 like I thought, and it charges in roughly 2 hours
If by "roughly 2" you mean 3+, then yes. 7kw * 3h = 21kwh.

At 1600amps and I think I read somewhere else at 396v. The Warp 11 motor obviously can’t compete with something like that, can it?
Duncan uses an old forklift motor (basically a Warp 11, that only costs $200 in scrap) on his drag racer, and I think he pulls 1200 amps at 400v. And his setup is nothing special, cheap budget build.

Obviously it can't sustain that load for long, let alone that the motor would melt without significant air cooling, but, his battery pack would be empty in about 90 seconds anyway. He does some autocross in it too.

It depends on your preferences. If you want a cheap fun budget build now, and a fancy build later when you learn what you need, you can get a build going for decently cheap.
 

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If by "roughly 2" you mean 3+, then yes. 7kw * 3h = 21kwh.
And charging rate decreases as the battery nears fully charged, so it's more likely that this person is using 80% or less of the battery charge, then spending hours to recharge at 7 kW peak, but a lower power near the end of the charge, and never full recharging.
 

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Discussion Starter · #10 ·
Hmm, is there a way to attach 2x forklift, or cheaper DC motors, to one differential? That way I don't push a single motor way too hard and can split the load between them?
 

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Hmm, is there a way to attach 2x forklift, or cheaper DC motors, to one differential? That way I don't push a single motor way too hard and can split the load between them?
Sure, 2 mechanical ways, either series or parallel. (Electircally series or parallel is a different set of choices).

Series is just picking a motor with a through-shaft and coupling it to the motor behind them, so you sort of have one motor that's twice as long.

Here are some series:

122070





Parallel is using gears or usually belts, two motors side-by-side, that drive a common prop shaft (one directly, one via toothed pulley).

Here are some in parallel (including one used on a sand rail, that was for sale on these forums):


122071


122068


122069




You may want to search for offroad EVs, I think there's a specific race series for them.
 

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As far as battery and range requirements are concerned - how much petrol would you use??

Very very roughly you will need 10 kwh of battery for every gallon that a petrol vehicle would have used

So if an event would have used four gallons - you would need 40 kwh
 

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Discussion Starter · #13 ·
Hey guys, sorry I sort of fell off the map on this, I got a little busy with some other things. But im back to thinking about this.

I just got back from a desert trip, and we took our Turbo RZR on a few rides, the longest one being 65 miles averaging 25mph and topped out at 65mph through the trails. I used roughly 6 gallons, so using @Duncan formula, safe to say I would need 60kwh, and using an extremely conservative 1kWh/mile, I come up with 65kwh of battery. So now I have a number to shoot for.

I'm really interested in using these 280AH LiFePo4 cells to make the pack, as they are large capacity and much more affordable. Only downside is they don't have a high discharge rate, which is just 1C, and a peak 3C for 10 seconds.

Here's what I'm thinking. Getting 90 cells all in series makes 288v Nominal, with 78kw of Capacity, which is above my 60-65kw number, and I would rather have extra range than not enough. Also with 288v X 280 amps (1C discharge rate) i could consistently make a little over 100hp continuous. And with short bursts of 840 amps (3C peak), it would make a little more than 300hp, which I feel like is more than enough and would make a very fun car.

90 Cells is just over 1000lbs, and I can make them 48v Nominal packs that I can wire in series and they would be a little more manageable to move around if I need to.

As far as charging, I'm fine with just 1 ride a day, as we already rarely ride more than once a day, so im thinking even if i get a 6-8kw generator to charge with at 240v, its only around 8 hours depending on DoD. And if sometime in the future, I want to charge faster, I can look into getting a 2nd generator to run in parallel, or split the battery packs to charge separately. Also thinking about making replaceable packs that I can leave in the trailer to charge while I ride, then swap out when I get back.

Thoughts/ questions/ concerns? Tell me if I'm dumb!
 

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Super cool project! I want to also build an electric side by side or buggy type vehicle. I think electric RZRs would be awesome, super fun to drive, and also VERY QUIET!

I think your battery size sounds about right, especially if you have a heavy right foot or go in sand and mud. Luckily you can regen with an EV whereas in ICE that's just wasted. Off-road there is tons of regen opportunity and minimal wind resistance so possibly you can get more than the equivalent 10kwh per 1 gallon. That's my hope at least for my own project.

Either way I think your newer idea of a RZR conversion is a way better plan than a sand rail. Like you say a sand rail isn't really a sand rail without tons of horsepower and that means $$$$. A RZR will hit a very similar level of fun for way less and probably more practical also (more range less trailering).
 

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Discussion Starter · #16 ·
I realized my math was wrong and would need 96 cells if I wanted to break them out into 48v packs, which just means more capacity and higher voltage!

Am I wrong to think that the ~100hp Electric motor is equivalent to a much higher HP ICE? This thing might be capable of 330hp for 10 seconds, but we might knock on that door quite often out in the sand dunes, im not sure lol.

I guess chassis design is going to have to be first. I wonder if I could actually get a RZR chassis or something of that nature and retrofit it all. That way suspension is completely done, and a lot of the guess work is already done. Granted, adding 1100lbs in batteries to a RZR makes me cringe a little. The car only weighs 1500lbs with the ICE in it.
 

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I'm really interested in using these 280AH LiFePo4 cells to make the pack...

Here's what I'm thinking. Getting 90 cells all in series makes 288v Nominal, with 78kw of Capacity...

90 Cells is just over 1000lbs, and I can make them 48v Nominal packs that I can wire in series and they would be a little more manageable to move around if I need to.
For LiFePO4, the nominal voltage is 3.2 V/cell, so the 90 cells in series would be 288 V nominal. Multiply that by 280 Ah and that's 80 kWh.

48 V nominal) modules would have 15 cells each (15 * 3.2 V = 48 V); six would be required.

I realized my math was wrong and would need 96 cells if I wanted to break them out into 48v packs, which just means more capacity and higher voltage!
Why would you need 96 cells? If you are you thinking that you need 16 cells per module (pack), you would have 51.2 V (nominal) modules (packs). You can do that if you want, but not if you want 48 V (nom) modules.
 

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Discussion Starter · #18 ·
Well because 4x 3.2v cells make a 12.8v battery, so multiply that by 4x to make a 48v Nominal does make 51.2v but Im coming from Solar storage, where absolutely nobody makes 15 cell LIFEPO4 packs because the usable voltage is too low for any 48v inverter. Hence why I wanted 96 cells and to charge with a 48v LIFEPO4 charger.
 

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Well because 4x 3.2v cells make a 12.8v battery, so multiply that by 4x to make a 48v Nominal does make 51.2v but Im coming from Solar storage, where absolutely nobody makes 15 cell LIFEPO4 packs because the usable voltage is too low for any 48v inverter. Hence why I wanted 96 cells and to charge with a 48v LIFEPO4 charger.
Right... 15 times 3.2 is the 48 V that you said you wanted; 16 times 3.2 is 51.2 V. If you really want the higher nominal voltage, you want the higher number of cells. 48 V nominal in lead acid does not have quite the same voltage range as 48 V nominal in LiFePO4... so if you state your voltage requirement in terms of actual maximum charging voltage (to match a charger) and actual minimum discharge voltage (determined by the inverter in your solar application, and by the motor in your vehicle), you can get the right number of cells.
 

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Granted, adding 1100lbs in batteries to a RZR makes me cringe a little. The car only weighs 1500lbs with the ICE in it.
Now you know why I decided to start with a 5000lbs vehicle for my project :)

That's the challenge of EV conversions on lightweight vehicles; they don't end up so lightweight or they don't go very far.

I still think your idea is a great one, just maybe a bit too ambitious. I am building an electric off-roader, but I am not selling my current off-roader. I am building a prototype that I can wheel around and have fun with and learn what it will do and how to make it better. Maybe one day it will be just as good as my ICE but likely not anytime soon.
 
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