[jocarp5281]

Hi guys,

I’ve recently graduated automotive engineering, unfortunately they don’t teach us much about electric power train systems. I’ve always been a fan of Ev’s and now I have the opportunity of building my own from scratch.

I want to build a ready to race electric offroad UTV (Side by Side) from scratch. I could go the traditional way and use only one motor couple with a gearbox and a transfer case but I’d love the possibility of using two motors, one on each axle.

Here are some Specs of IC UTV’s
Max Power 170 HP
Max Torque 120 Ft-Lbs
Weight 1500 Lb
Max Speed 80 MPH

Q1: a) is it feasible to use to motors, one on each axle with only one gear reduction?
b) What type of motor, AC vs Dc? Power? Other specs?

Q2: Battery- I don’t want to go to deep on this for now but, is it possible to do a 120 mile race on one go at racing speeds with a battery pack that “fits” a UTV?

I know it’s not much for now but I’m really in need of guidance.
Thank you,
João Carpinteiro

 

[brian_]

Q1: a) is it feasible to use to motors, one on each axle...

Yes, one motor per axle is feasible. Production EVs with all-wheel-drive (Tesla dual motor, etc) do not drive both axles from one motor, because the drivetrain to connect one motor to both axles effectively is unnecessarily complex and bulky.

Why stop there? You might want to consider using one motor per wheel, eliminating the differentials (but requiring twice as many inverters and transmissions). Tesla doesn't do that, but their mechanical design is over a decade old.

... with only one gear reduction?

What do you mean by "one gear reduction"?

If you mean a single ratio, rather than a multi-speed transmission: yes, that is normal practice in production EVs. It avoids the mechanical complication of shifting a transmission, and the control complexity of coordinating the power output of the two axles with separate transmissions. It assumes a motor with a broad enough power band; all production EVs use AC motors (mostly synchronous permanent magnet, although Tesla uses induction motors for the Model S and Model X).

If you mean a single stage of gear reduction - just one gear on the motor shaft driving one gear on the output shaft - then you'll probably find that a high enough reduction ratio leads to an excessively large output gear or an inadequately small input gear... unless you use an unusually high-torque and low-speed motor.

 

[brian_]

Here are some Specs of IC UTV’s
Max Power 170 HP
Max Torque 120 Ft-Lbs
Weight 1500 Lb
Max Speed 80 MPH
...
Q2: Battery- I don’t want to go to deep on this for now but, is it possible to do a 120 mile race on one go at racing speeds with a battery pack that “fits” a UTV?

You have information about the power used to drive the reference vehicle. I suggest estimating the power requirement of the proposed electric vehicle, and then the energy for a race, and so the volume and mass of the battery pack (by comparison with the batteries in current production EVs). You'll have your answer.

 

[dain254]

I was thinking about this exact type of build the other day - I really like the 100kw "Hyper 9" AC motor that is just coming out from Netgain, if a person could buy that motor with the auxiliary shaft a person could easily mount that motor center chassis under the two seats. In doing that, it would give the primary drive facing the rear where it could be reduced with a single ATV differential to the rear tires (4:1, 5:1), and another lighter differential up front (maybe with a lock/unlock if 4wd full time isn't desired) that would get power off of the auxiliary "front" motor shaft. While you lose the ability to differentiate between the front/rear you would save the weight of a transfer case. If this system was done with around 12kwh of lithium batteries (Chevy Volt you are looking at ~240lbs) I think some pretty amazing performance along with decent run time could be achieved. I've been watching for a sank Yamaha YXZ1000R or one that had an engine fire... something where the chassis is completely useable!

 

[dain254]

I also answered none of your questions with my post...

Q1 - Use 1 motor if you can. 1 motor = 1 controller = 1 precharge circuit = 1 contactor = 1 pain in the a$$ to program and operate. If you want a lot of power for cheap and don't care about brush maintenance and have some weight to spare a series wound DC would work fine. the Hyper 9 I mentioned is AC, it's lighter. PM VS Induction machine is another topic.

Q2 - If you are a bad racing driver and aren't very fast you could possibly go "your" race speeds and 120 miles... but you likely won't ever meet your weight goals if you have 120 miles of range and drive it like I would. Also depends on if you are trudging through deep sand or on hard packed trails with a lot of half throttling... need your duty cycle for an accurate prediction! Off the cuff guess is you'd need 40kwh-50kwh to do a UTV race 120 miles in a 1500lb machine. For reference, the 60kwh Chevy Bolt battery pack weighs 960lbs... So you are looking at 700lbs of battery.

 

[brian_]

... if a person could buy that motor with the auxiliary shaft a person could easily mount that motor center chassis under the two seats. In doing that, it would give the primary drive facing the rear where it could be reduced with a single ATV differential to the rear tires (4:1, 5:1), and another lighter differential up front (maybe with a lock/unlock if 4wd full time isn't desired) that would get power off of the auxiliary "front" motor shaft. While you lose the ability to differentiate between the front/rear you would save the weight of a transfer case.

That's a good point: the drivelines of these vehicles are remarkably crude, and so do not normally have a centre differential, so driving both axles with one motor isn't as complex as it is for a reasonable road vehicle.

This emphasizes the importance of understanding the requirements of the vehicle... down to the level of whether or not differentiation between axles is needed, and if so what degree of control is required. As soon as you need anything more than locked together (or front disconnected), the mechanical complexity of doing it with one motor escalates.

 

[Duncan]

Q2: Battery- I don’t want to go to deep on this for now but, is it possible to do a 120 mile race on one go at racing speeds with a battery pack that “fits” a UTV?

Hi Joao
i don't think that there is a single EV anywhere on the planet that can do 120 miles at "racing speeds"

 

[jocarp5281]

Brian two motors are definitely my maximum.. I did a two year project on an RC car with one motor per wheel, it was a lot of fun implementing torque vectoring and Stability control and all other possible kinds of control but it really is a pain in the ass implementing everything.
Yes I meant single ratio, sorry my English is kind of rusty hehe.
You are right, estimating the power requirement taking into account the mass of battery and other accessories is the right way. My problem is to find the equivalence between a IC engine with multi/speed transmission and a electric power train. Two 50 KW electric motors with a single ratio have the same performance of an IC engine with multi speed transmission?
Dain254 from what I found on the internet every electric race car had an DC motor as you say. But usually those cars don-t need a huge range, just enough for a drag race or a drift race. As far as I know only AC motors allow regenerative braking, with is something important since while racing you are either pushing the throttle or the brakes but never coasting, meaning that you probably will take advantage of regenerative braking.
Duncun Acciona 100% is a car that raced in Dakar it has a 120 to 180 mile range while racing but then again it is a much bigger vehicle with a 250 KW motor.
So, let’s assume the two motors architecture. Taking into account regenerative braking and racing conditions (Off Road, heat, etc), which is better AC or DC motor?

 

[Duncan]

Hi Joao
You will have to give more data than that about that car - I simply don't believe it

A Tesla cannot sustain full power and even at it's down-powered state cannot run for more than about 50 miles at "racing speeds"
The Bike guys do the Isle of Man TT race - but they do one lap - 38 miles - and even then they have to slow down and not use full power

120 miles means a very slow race - NOT really racing -

As far as DC v AC and re-gen braking - most cheap and cheerful (and powerful) DC systems use series wound motors -
These cannot be used for re-gen braking as you can't stably control the amount of braking

 

[jocarp5281]

Duncan in truth your right, even the example I gave, acciona 100%, their main goal was to finish the race that’s it. Perhaps it’s too soon to have EVs competing with IC on long races.
EV racing is on its first steps and that means that they can only truly compete with each other.
That is a big problem when you are not a big brand that can create out of nothing an exclusive EV championship. For “small” guys like me, the only chance of getting an EV into competitions is to sign in as an open category mixed with IC vehicles. To accomplish that you have to at least be able to finish the race and be competitive if possible.
That would be my main goal.

 

[Duncan]

Hi Joao

I use my car competitively (the slowest part is nut behind the wheel) and there are a number of other people who do the same

http://www.diyelectriccar.com/forum...dubious-device-44370p15.html?highlight=duncan

Can you find some shorter events? - EV's are very competitive in short events

Then design your machine around a sensible race distance

 

[brian_]

My problem is to find the equivalence between a IC engine with multi/speed transmission and a electric power train. Two 50 KW electric motors with a single ratio have the same performance of an IC engine with multi speed transmission?

Rather than looking for some equivalence formula - which will apply properly to only one specific combination of engine and motor - why not take it in two steps?

The transmission is used to keep the engine in the desired speed range, which in racing would be the best power range (not the way you drive on the street, or even recreationally). The spacing between gears is narrower in higher gears, so there's no single answer, but if you averaged the available horsepower (as shown on whatever power curve you can find online for one of these engines) over the range from whatever speed provides peak power down to whatever speed you would get when you upshifted from the peak power point, you would have an approximate available power. If you can't find gear ratios, I would roughly guess that the power after upshifting between upper gears might be 3/4 of the peak power, so the average could be 7/8 of the peak... so 150 hp or 110 kW. But use a real power curve for a specific engine and real transmission ratios to get a better idea.

The chosen motor must deliver this power over the operating speed range, not just at one optimal point. Ideally a PM AC or induction motor can run at the same maximum continuous output over a very broad range, so with the gear ratio chosen to put the maximum ground speed just within the motor's upper speed, the continuous motor rating is the available power at any race speed (less for the lowest speeds, where the motor is torque-limited). A brushed DC motor will have a much "peakier" power versus speed characteristic, so you can use a multi-speed transmission, or expect to run well off of peak power at most ground speeds.

Production EV motors are commonly rated at 80 kW to 100 kW, with some (for the lightest and/or cheapest cars) rated substantially lower. I suspect that you're looking to have more power than the typical (not Tesla) EV in a vehicle half the weight, with a substantially greater expectation of range... which won't likely add up. But that's why some real numbers are needed.

Remember that if your electric powertrain (including battery) is heavier than the gasoline powertrain (including fuel tank), you will need more power roughly in proportion to mass.

 

[brian_]

... from what I found on the internet every electric race car had an DC motor as you say.

Since most electric race cars are essentially do-it-yourself projects, they have tended to use modestly priced and available components... which means the brushed DC motors which are used in essentially nothing of any significant power which is currently commercially produced.

Still, this forum has one thread about a Tesla powered (so induction motor) Cobra road race car, and of course Formula E uses AC motors (presumably PM, but I haven't found any details). ELMOFO built an electric version of a Radical sports racer with an AC PM motor.

And of course Formula E (and Formula 1, which is hybrid rather pure battery-electric but has a substantial electric motor) use regenerative braking, although braking events are very short in duration and very small fraction of the running time.

 

[brian_]

... Acciona 100% is a car that raced in Dakar it has a 120 to 180 mile range while racing but then again it is a much bigger vehicle with a 250 KW motor.

You will have to give more data than that about that car - I simply don't believe it

I assume this is the ACCIONA 100% EcoPowered Dakar machine. According to a December 2016 article by Acciona, it has a synchronous AC motor (from AM Racing) and still uses a 6-speed gearbox. If the AM Racing motors look familiar, it may be because they are built from Remy HVH cartridges (or they may be complete Remy motors). A motor of the same product line (a PM unit; they are available both PM and induction) is used by ELMOFO's electric Radical sports racer.

I haven't found a good online description of the car, but an article suggests 150 kWh battery built of cylindrical cells and 200 km racing range, so 750 Wh/km. The pack will weigh about 50% more than a Tesla 100 kWh pack (using the same cells). Unless that 200 km takes 36 minutes (for a ridiculous 333 km/h), it obviously isn't running at anything close to full power continuously, but that makes sense due to ground conditions; perhaps it's averaging around half power?

It looks like the offroad racing UTV would have perhaps half the power of this Dakar racer, with half the weight or more.

 

[dain254]

One other elephant in the room that no likes to discuss right up front is budget. In all honesty to build the vehicle correctly FROM SCRATCH you are looking at $40-50k. Were I building the vehicle - I'd start with a rolling chassis Yamaha YXZ1000R - source a Netgain Hyper 9 and place it at the center, complete Volt battery for 1200 bucks to make a 36S2P 12kw pack... I'd expect my range to be 15-50 miles depending on what terrain... if I"m cruising down the road I'll get 50 miles - ripping on a sand or mud trail hard probably closer to 15! All in all that build would cost me around $10k.

Someone already mentioned early that weight is the big factor... If you make your vehicle 1000lbs instead of 1500, you can use smaller motors, smaller battery and achieve the same performance for significantly less cost. Motenergy makes an ME1616 motor where if 2 were used you could get somewhere around 80kw peak power. Optimize your chassis HIGHLY and then source 5 tesla model S modules in series for 25kwh and 110 120V? I only suggest those because I think they are the most energy dense. Again, take a look at your budget and you will find out quickly what you can/can't do.

YOU ALSO may want to simply look at the Nikola Motors UTV. Take a HUGE shortcut - buy one of those and put it on a diet. Lots of room to lighten that thing if you have unlimited budget - it has up to 100kwh pack and something like 500hp?

 

[brian_]

YOU ALSO may want to simply look at the Nikola Motors UTV. Take a HUGE shortcut - buy one of those and put it on a diet. Lots of room to lighten that thing if you have unlimited budget - it has up to 100kwh pack and something like 500hp?

I assume that the Nikola Motors UTV (the Zero) is as fictional as their truck, presented to attract media attention and capital. I don't think they even have a prototype (since their website shows only digital renderings, and low quality at that), but maybe they will build them someday; for now they're just collecting reservation deposits and promising production next year.

To underline how far Nikola Motors is from being a company with any product, their truck went from turbine hybrid to hydrogen fuel cell between two press releases - obviously it is nowhere near production.

On the other hand, it would be interesting to look at their design choices. That is, if they described it...

• It has 10:1 gear reduction, but the only information about the drive layout is that it is 4WD.
• It is listed as having 555 horsepower, but there is no other description of the motor(s).
• Battery capacities are listed (75 kWh , 100 kWh or 125 kWh), but there is no indication of battery type or location.
• It appears to be a substantial four-seater, but no dimensions (linear or mass) are given.
• An acceleration number is provided, but no top speed or range.

 

[nucleus]

The Netgain Hyper9 is fictional so far too. From what I can tell the cooling looks suspect, so until these are in the field, no telling what kind of power they can sustain.

Netgain's dyno is limited to something stupid like 30HP if I recall.

There should be a way to upgrade the cooling on the Tesla units.

 

[dain254]

Given what crowd funding has done to new products lately, it can be hard to differentiate fictional from non fictional products. Since Netgain is a well established company with a product line that is widely known, I wouldn't call the hyper 9 fictional at all - just in prototype phase and given that nothing is actually new technology they are doing with it I would certainly expect them to follow through with a finished product.

Nikola on the other hand, has definitely been all over the place with their claims on the electric turbine fuel cell Mr. Fusion flux capacitor semi. My prediction is that they actually will build a couple dozen of their electric UTV's (highly doubtful they will perform as advertised, but should still be fast and have decently high battery capacity) but will run out of funding after a while trying to build their electric semi and will eventually fizzle.

 

[CFECO]

If this Race is a current event, I'd find put what the current vehicles weigh, their top speed, and how much fuel they use. From their fuel usage, you can determine how much battery the same vehicle would need. If the required battery is too big, make it so you can quickly change batteries at a pit stop. And above all, weight is your Enemy, I'd look at carbon fiber or fiberglass pultruded tube, or aluminum monocoque construction. I am building a 2 seat UTV, not for racing and the goal is < 1,000lbs with both occupiants. What about having two motors and only using one when cruising and both only when needed for 4x4?

 

[GoElectric]

Lots of comments here! I think this is possible.

I would say use a single AC motor, and bolt it onto a 4wd drive train with gears. I don't think the Hyper9 is at all necessary, that thing will launch a 3000lb car in third gear. Gears mean you don't have to have 100kW, more like a 30kW PM motor. And you can keep the motor in a somewhat optimal efficiency range.

If you are going for range, the best choice is Tesla modules. They are 50lbs/25 volts. So, if you are going to build your o wn chassis, you can design it to take enough batteries to run a 300V motor. Check-out EV Drive for some pretty nice ones. Then you would have 12x5.5kW. I think you could finish the race with that. I also think you wouldn't have to cool them, as current draw would be only 100 amps or so. Hmmm, might have to cool the motor though, whereas maybe not if you use an induction motor.

My 2 cents - what do you think? Wedded to the idea of 2 motors Then go for it, but I don't think you need 100kW. You might not have to cool them. I get that you have all the skills to take advantage....