# Electric Motor Solution for Solar Car



## bigmotherwhale (Apr 15, 2011)

im no expert but i suggest you go for an inrunner or an axial flux design over an outrunner. 
I dont think i would use an outrunner unless i had to.


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## dcb (Dec 5, 2009)

just curious, have you accounted for the peak efficiency draw from the solar panels? It seems careful matching of the motor(s) to integrate them in to the MPPT strategy and reduce the power converting requirements might bear some fruit, since the motors and controllers are basically buck converters anyway, you might think in terms of maximum motor voltage (in relation to the expected solar power output under race conditions at MPP) and tweak the number of panels and motor selection from there.

I don't know exactly what it takes to be competitive in that event, I just know that I would dig deep as time/budget/knowledge allowed, and let the competition worry. It would involve careful analysis of everything from panels to wheels, to aero, motor and controller is only one piece of it. I'd look for losses and minimize/eliminate them.

Of course, my suggestion isn't original, they rarely are 
http://ieeexplore.ieee.org/xpl/logi...re.ieee.org/xpls/abs_all.jsp?arnumber=6924148

i.e. here is the efficiency graph for my leaf, it is not at max power when it is at max efficiency, and the controller (and the gearing, and aero and panel draw vs absorbed energy, and etc) all affect system efficiency, you want a motor at max efficiency along with everything else, for as much time/distance as possible:


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## SummerTime244 (Nov 5, 2015)

Thank you all for your answers, i'm currently looking into it.

How about using two motors, one in each wheel ?

Regarding electronic synchronization, is it similar, to small scale robotics, PID regulation ?


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## dcb (Dec 5, 2009)

SummerTime244 said:


> How about using two motors, one in each wheel ?


simplest for two motors is two controllers

Larger motors are typically more efficient.

it depends on how the motor will be used, lots of time at half throttle, there may be something in two motors (idling one), though it is dubious, and not likely how it will be used.

Look at the power efficiency graphs for the motors you are interested in and the anticipated loads and figure out which one works best.



SummerTime244 said:


> Regarding electronic synchronization, is it similar, to small scale robotics, PID regulation ?


w/two controllers, and a shared throttle, perhaps with one slaved via PID generated throttle signal to match the output of the master. And turning might be a challenge without some steering-torque override.

Also, if it is very hilly (or windy), you might want some gears to keep the motor at peak efficiency, at these power levels it isn't much beyond a derailleur, talk to the mechanical team, and talk to the aero team and whoever is in charge of analyzing the course (physics team?) and weather conditions (wind/clouds) and figure out the power demands and supply (and various losses), iteratively.

Otherwise it is pure speculation. You gotta start at the beginning if you want to be competitive.

edit: lots of info out there https://books.google.com/books?id=W...HDAA#v=onepage&q=solar car derailleur&f=false


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## SummerTime244 (Nov 5, 2015)

dcb said:


> simplest for two motors is two controllers


I know that in smaller applications like RC Car racing, you can find ESC's that are able to control two BLDC's at once.
I searched for such a controller for larger BLDC's but i couldn't find one?


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## dcb (Dec 5, 2009)

why is that important?!? 

Good luck morocco...


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## SummerTime244 (Nov 5, 2015)

dcb said:


> why is that important?!?


Well I guess it would be easier to plug two motors in one controller...


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## Karter2 (Nov 17, 2011)

SummerTime244 said:


> Well I guess it would be easier to plug two motors in one controller...


I would not "guess" like that at too many solutions !
First, do as suggested and confirm if 2 motors are benificial or not !
Otherwise you are just wasting time and effort.


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## RIPPERTON (Jan 26, 2010)

If you want 2 motors on different wheels you will need 2 ctlrs but you wont have to synchronize them. There also wont be any uncontrollable torque understeer.
Check out my Mira when it had 2 inboard hub motors to the front wheels
there was no steering feedback even when jumping on and off the throttle
in the middle of a corner. @1m58s
https://www.youtube.com/watch?v=28noTIX_ceo
https://www.youtube.com/watch?v=CfFK6b7812Y

University of Western Sydney (Kingswood) just made a 4 wheel solar-battery hybrid
with one motor in the right rear wheel, driver in the right pod and battery
ctlr in the left pod.
https://www.facebook.com/westsydusolarcarproject/


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## sirwattsalot (Aug 27, 2012)

I would think that using two 24 to 32 volt brushless DC motors wired in series would work well if you can eliminate the controller and simply use the peak available power to run the motors full out. You would not need to worry about synchronization. When turning a corner the wheel on the inside of the turn will be slower and the motor on that wheel will pass more current on to the faster motor and wheel on the outside of the turn. Try this with toy motors first to model any desired configuration. Loading one toy motor makes the other run faster. A solar car does not have much energy to work with and I can't imagine needing a controller to add weight or to slow it down much. I can be wrong though.


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## bigmotherwhale (Apr 15, 2011)

weight is your enemy 

i think having one motor would be more efficient than two, 

two motors mean two motor mounts two drivetrains two cables....etc
not to mention the increase in complexity.
you would be better off with one correctly sized motor. 

you should run the motor through a freewheel and run it intermittently at its peak efficiency range, this will help reduce drive train losses, (unless you need regen of course) moving a chain or belt or cog whehter its under load or not uses valuable power. 

find a motor with good copper fill, you dont want to much iron in the stator. 

use the highest voltage for all your systems as is practical in your design, the higher the voltage the less copper is needed. 

if you can afford a capacitor bank these are very useful for solar load leveling and have much better charge discharge efficiency than batteries and can be run down to zero (in some cases) without damage.

sirwattsalot
can you explain why you said brushless dc motors? or is that an error? i have actually experimented with BRUSHED dc motors in series driving front wheels in models many years ago, the E diff principle you speak of is exactly right, i remember trying to convince someone building an electric mini that having two motors wired in parallel on the front wheels was a bad idea but i believe they went ahead and did it anyway i never heard if it worked out ok or not.


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## SummerTime244 (Nov 5, 2015)

bigmotherwhale said:


> weight is your enemy
> 
> i think having one motor would be more efficient than two,
> 
> ...


- First : how about a 6 phase controller to Control the 2 motors at once ? Are there any available on the market for BLDC hub motors ? 
- Second : Do you think the mechanical team would find problems finding the right weight distribution if we go with 1 motor on the Left Rear Wheel ?
- Third : In that case, would the non-motorized wheel be completely free?
- Fourth : Would we need to worry about extra friction on the motorized wheel ? => More losses ?


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## ken will (Dec 19, 2009)

If you drive 2 wheels, they should be equal distance from the center line of the vehicle.
If you drive 1 wheel it, should at the center line of the vehicle.


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## SummerTime244 (Nov 5, 2015)

ken will said:


> If you drive 2 wheels, they should be equal distance from the center line of the vehicle.
> If you drive 1 wheel it, should at the center line of the vehicle.


Yes but we want a 4-wheel vehicle, can't we drive one of the 2 rear wheels, and have the other Free ? That 4th wheel would just be there for stability.


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## dcb (Dec 5, 2009)

is it a round or oval track? If all the turns are in the same direction, you *might* get away with it on a low powered vehicle.


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## bigmotherwhale (Apr 15, 2011)

ive run one wheel drive on a go kart for many years, it works absolutely fine, there is no "getting away with it" it will work.


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## dcb (Dec 5, 2009)

that isn't terribly accurate, it depends on a lot of things like weight distribution/center of gravity. There are plenty of vehicles that will lift the inside rear tire completely off the ground in corners. That is not a formula for "competitive".

There are carts with differentials and solid axles as well, and appropriate techniques (aside from "coast until the drive wheel can make traction again").

"The lack of a differential means that one rear tire must slide while cornering. This is achieved by designing the chassis so that the inside rear tire lifts up slightly when the kart turns the corner. " 

And solar racers ars are "delicate" by kart standards. They have more weight and a much higher center of gravity, thinner taller wheels, batteries, panels.

Like I said, if all your turns are in the same direction, you *might* get away with it, or the competition might blow your doors off while you struggle with 1/2 the traction. But I have to think that something is horribly wrong if 1/2 traction isn't the limiting factor if you do have 1 wheel drive.


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## ken will (Dec 19, 2009)

SummerTime244 said:


> Yes but we want a 4-wheel vehicle,


I am slightly biased when it comes to Trikes.
This is one of my favorites


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## SummerTime244 (Nov 5, 2015)

dcb said:


> is it a round or oval track? If all the turns are in the same direction, you *might* get away with it on a low powered vehicle.


No track. It's National Two-way Road. The race happens in regular traffic. 
The Moroccan Race is 500km. 
World Solar challenge in Australia is 3000 Km. From Darwin to Adelaide.

I'm really just trying to weigh pros and cons of two very different solutions : 
*Two synchronized 1.5 Kw BLDC hub motors*
+ Better stability and weight distribution
+ Evenly distributed Traction Force on both rear tires
+ No uncontrollable Torque understeer

- Tuning the PID for synchronization is hard to get right
- In case of a breakdown, we would go at half speed.

*One 3 kw motor in only one of the rear wheels*
+ Easier to implement
+ More efficient than 2 motors
+ We could buy two 3kw motors and only use one : the 2nd would be there for counterweight and in case the first one breaks down

- The freewheel will slide during cornering
- Half-traction

Is there anything I haven't thought about ?


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## dcb (Dec 5, 2009)

you should see about getting this book or one similar, this is a niche, with lots of design compromises to be made.

https://books.google.com/books?id=W...yBDcQ6AEIHDAA#v=onepage&q=wheel motor&f=false

haven't looked at this one much, so far I like the level of detail in the above link.
http://www.amazon.com/The-Winning-Solar-Car-Design/dp/0768011310

edit, use google and READ, then read some more:
http://www.nerdgirls.org/Docs_files/
might be a little dated, refers to the "winning" doc.


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## Vanquizor (Nov 17, 2009)

Since you appear to have narrowed it down to hub motors why don't you play with the simulator at:

http://www.ebikes.ca/tools/simulator.html

It has a bunch of commonly available bike hub motors. I went to bike hub motors based on your vehicle being more of a heavy bike in load and available power than a car.


That being said I think it will be real tough to beat a purpose built motor (system efficiency mid to high 90's) unless you have ruled it out for budget or other reasons:

https://lati-solar-car.wikispaces.com/file/view/Solar+Car+Wheel+Motor+Information+Sheet.pdf

Failing that consider a higher efficiency motor and drive system- a lynch motor or even golden brush less motor on chain drive will still likely be more efficient (high 80's) than a hub motor (low 80's).

Regardless 2 hub motors putting out ~3kw at 80%+ efficiency is easily achievable on a modest budget with off the shelf parts.


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