# Electric-hybrid rough terrain vehicle



## Brett (Feb 17, 2013)

Hi everyone.

I have an exciting thesis project for my mechanical engineering degree.
I have to implement a hybrid electric drive train onto a Mini Baja vehicle (see attached image) 
The IC engine is 10HP Briggs&Stratton (assume 7.5 Kw of power)
After generator and any couplings we can assume 6 kW of electrical power.

I am thinking 2 3kW motors, one in each rear wheel. OR 4 1.5kW motors, one in each wheel.

If need be I can design any gear box to get a desired wheel rotational velocity of 410 RPM.

Any ideas on motors, batteries and generators will really help me. 

Nice bit is that it must be designed, implemented and tested by August this year.


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## PStechPaul (May 1, 2012)

You can get a 10kW generator head from Harbor Freight for about $300:
http://www.harborfreight.com/10000-watts-max-7200-watts-rated-belt-driven-generator-head-45416.html
Or a complete generator set for under $500:
http://www.harborfreight.com/420cc-6500-watts-max5500-watts-rated-portable-generator-68529-8560.html

You can use the 240 VAC output to provide a 300 VDC link for industrial VFDs for the electric motors. If only a limited range of speed is needed you might get by with a fixed reduction drive. Otherwise at least a two-speed transmission, which could be tricky for all-wheel-drive and motors on each wheel. For such low HP a variable speed belt drive might work.

2 HP three phase motors are inexpensive ($50 or so), and VFDs of similar power are also about $50. 

You should have a 300 VDC battery bank to provide surge current capacity for the motors so the M/G set won't have to respond to sudden load changes. You can get 3.5 kWh of SLAs for about $500 if you can handle 300 lb weight. Otherwise you might be able to put together a 1 kWh pack using R/C battery packs of about 3-5 Ah. Maybe 30 of these:
http://hobbyking.com/hobbyking/store/__9185__Turnigy_4000mAh_3S_20C_Lipo_Pack.html
That would be $750. 

That should give you some ideas. Good luck. This might be better in the non-road-going forum. It may be better to go all-electric.


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## Brett (Feb 17, 2013)

Thanks PStechPaul

That info is much appreciated. The vehicle need only reach 45km/h. Thus I will design a set ration gear box. ITO mechanical components I am fully competent, the electrical bit is my dilemma.

LiPo's are my favorite things on earth, I will definitely use them.

I have to go hybrid as per project description.

The power curve of the motors are also critical. More actually the torque curve.

Thanks


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## Ziggythewiz (May 16, 2010)

PStechPaul said:


> Otherwise you might be able to put together a 1 kWh pack using R/C battery packs of about 3-5 Ah. Maybe 30 of these:
> http://hobbyking.com/hobbyking/store/__9185__Turnigy_4000mAh_3S_20C_Lipo_Pack.html
> That would be $750.


I wouldn't recommend RC battery packs unless you're very experienced in using them and can manage 30 in series. Many EVs have burned using similar batteries.

LiFePO4 is much safer and will last far longer, though I recognize longevity may not be a significant goal in this project. That may also support your hub motors idea. In general it's best to just use one motor and a tranny or a diff, so the expensive motors and controllers aren't hitting every rock and pothole directly, but for a limited use vehicle it might work.


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## Brett (Feb 17, 2013)

Hi.

Yeah the whole purpose of my project is to gain capability and ditch inefficiencies. Using a single motor through a conventional diff and transmission leaves me with exactly with what I have now + a generator + motor + batt.

So either a motor in each wheel (major off road capability) or one in each rear.

We build and design our own hydro-pneumatic dampers thus I can account for any shock loads and impulse. We also use carbon fiber rims, thus very much shielded from foreign object damage.


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## tylerwatts (Feb 9, 2012)

Brett I'd say firstly with the large profile tyres of the ATV you're safe from harsh shocks. THese are bigger issues with low profile road tyres.

Secondly, 1,5kW hub motor is very feasible and very promissing. PSTechPaul has a thing for good hub motors so look up his threads and get his input, but you could design some fantastic hub motors. If you could build composite motors you'll be even better off! Maybe build the magnets into the composite rims and run high count light weight stators on the hub. a 12" stator diameter will provide very good torque for a 1,5kW power output!

Weight in the hub and wheel are your enemy, so composites are your friend. A low rotational mass will amplify acceleration as less of your power is consummed accelerating hulking great wheels, and lower unsprung mass will give the motor a better time, again composite will help a huge amount here.

PS, a cheat may be to use lower ply count tyres to save weight, but risk punctures. Will need weighing up or even testing maybe.

That's an awesome little buggy you show there, I had built on back in South Africa that got driven all over the place, awesome fun!


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## Brett (Feb 17, 2013)

TylerWatts

I could not agree more. Integrating the motors as part of the rim (ie making the rim the rotor of a huge outrunner) is very attractive. I must use a 10" rim so this make life a little harder. 
Based on the performance requirements I need a total force of 2400 Newtons.

The motors must provide enough torque such that the torque of the motor multiplied by the gear ratio is equal to the force needed (2400/# driven wheels [N]) plus the torque induced by accelerating (rotational) the wheels, hubs, and any gearing used. 
A planetary gear box has a huge moment of inertia but can act as a huge torque multiplier. 

I think I'll write a small program so we can stick in a motors torque curve, moment of inertia of wheels, rims, motor, and then allow for different gear boxes as well. 

A resultant plot of velocity against time will also determine if we meet specs.


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## Brett (Feb 17, 2013)

Hi everyone.

So much has happened since I last posted.

See attached image of hub motors + gear sets. Already under construction.
Motor is a Perm PMG 132 [48 Volt version]

Now I need to select a generator/alternator to be run by the 7.5kW four stroke ICE. The motors peak power is at 3600 RPM. 

I really need help selecting these components. I need DC to charge batteries and also power motors directly. 

Any help is appreciated.


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## PStechPaul (May 1, 2012)

It's probably best to run the wheel motors directly from the batteries (through controllers) and have the ICE run at optimum speed to keep the batteries fully charged. The maximum efficiency may or may not be at the maximum power point. The charging current should add to the battery current when running so you can probably get more power output with the ICE running.

You could get a DC generator for charging, but you may need to make a charger circuit or adjust the speed of the ICE to change the charging current. I found a suitable unit which provides about 60V and 6HP at 3600 RPM: http://www.ebay.com/itm/9-HP-PERMAN...-DC-MOTOR-EV-BOAT-CAR-GENERATOR-/170995740269

It may be easier to get a 120/240 VAC 10kW generator head for about $300-$400 and use an AC to DC switching type charger which can be obtained off-the-shelf from MeanWell or others.


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## Heavydutytech (May 9, 2013)

How bout using an electric motor to drive a hydraulic gear pump and have hydrostatic drives at each wheel..... Sounds like a better option for you and your limited space and weight requirements.


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## Heavydutytech (May 9, 2013)

I would suggest a pressurized hydraulic system with an accumulator, and with a variable displacement in line piston pump with a pressure limiting compensator, load sensing compensator, and torque limiting compensator to reduce kw requirement of electric motor and keep wasted power to a minimum, or maybe look into electrohydraulic compensators as well.


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