# hill climber



## Tesseract (Sep 27, 2008)

PHAT_pudding said:


> ...this is because i have a 3km (1.8 mile) hill to climb. the hill is almost a constant gradient of 6.3 degrees and the speed i wish to go up it is 80km/h (50mph). The car will weight approximately 1300kg (probably less) and i'm looking at running the motor through the gearbox without a clutch.


Okay... according to Uve's EV Calculator, it will take almost 7x as much power (~48hp) to drive up the 6.3% grade at 50mph than it would on level ground (~7hp). All of that extra power is, of course, in the form of more torque since the speed is the same (around 266 ft-lbs more torque, actually) _so that means you will need to push ~7x more current through the motor while going up that hill._

You will like be at least somewhat in the overheating region of the motor's operating curve - enough to consider adding the cover bands and a 200-400cfm blower motor to force cooling air through the motor. Try to keep the RPMs above 2000 as well.

One other thing to consider is that most controllers are rated by their peak current output and their continuous current rating is often shockingly lower. I would guess you'll need somewhere around 500A to go up that incline and 4 minutes is pretty much the same as "continuous duty". Make sure the controller you pick can deliver that amount of current for that amount of time otherwise you'll notice it start to "poop out" at some point along the drive up.

A 6.3%, ~2mi. incline is rather brutal - it would be nice to be able to recapture the energy it takes to go up that slope when going down it, but that would take a significantly more expensive AC drive at the moment...

OOPS! I just noticed you wrote a 6.3 _degree_ incline, not a 6.3%... To convert degrees of incline to percent grade you find the tangent and multiply by 100, so 6.3 degrees equals 11%. That would require *10x *more current. You will _need _either a Soliton1 or a Zilla _Z2K_ to go up that hill and a single WarP motor will be deep into the overload region and will definitely need forced air cooling. Frankly, this doesn't sound like good terrain for an EV.


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## PHAT_pudding (Oct 8, 2009)

Thanks for the quick reply, but i realised i stuffed up my time calculation. 
it takes 2 mins 30 secs (approx) so it's still up around the near continuous rating. also i had a look at the controller specs and it says 150kW peak power (at 1000A and 156V) 

it appears from the calculations you gave to me, i'll need 36kW over 0.04 hours which is 1.44kwh just for the hill alone! which is a lot! and that should be drawing 250 amps if i run with a 144V system. Looks like i will incorporate a liquid cooling system for the motor and controller to minimise the likelyhood of overheating the motor. 

also, thought i'd do a quick calc of the % of the battery pack required to go up the hill:
1.44kwh needed
available is 160AHA batteries x 3.2V nominal x 45 units = 23kWh total
70% useable = 16.13kWh
so the hill will use AT LEAST 9% of the total usable battery capacity. wow

considering work is 50km away, and i'll need 6kW to maintain 80km/h all the way thats 3.75kWh needed for the flats (with no points of acceleration and constantly flat ground)
leaves me with 10kWh left over! haha so i could actually go to work and back on one charge theoretically. 
madness

thanks for the help, and as you can see i have a long way to go yet. 
and i was looking at using AC, but i go down the hill to get to work, and back up it to come home. the regen brakes won't do bugger all as the hill is only 2km from my house


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## tomofreno (Mar 3, 2009)

> That would require *10x *more current.


 I believe it is around 4x more current. The sum of the hill climbing force (product of vehicle weight and sine of the angle), drag force, and rolling resistance force is about 4x the sum of just the drag and rolling resistance forces at 50 mph. So it should require about 4x torque and current at the same vehicle speed. Probably a bit more current since the efficiency is likely less at the higher torque. Rough numbers since I don't know the drag coeff. and vehicle cross sectional area.


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## PHAT_pudding (Oct 8, 2009)

tomofreno said:


> I believe it is around 4x more current. The sum of the hill climbing force (product of vehicle weight and sine of the angle), drag force, and rolling resistance force is about 4x the sum of just the drag and rolling resistance forces at 50 mph. So it should require about 4x torque and current at the same vehicle speed. Probably a bit more current since the efficiency is likely less at the higher torque. Rough numbers since I don't know the drag coeff. and vehicle cross sectional area.


yes this seems about right as going up the hill should require at least 250 amps, and the same speed on the flat requires around 45 amps. 

just have to talk to the motor guys about what is considered a safe amount of current to draw from the motor over 2 and a half minutes. luckily the cables i'll be using are rated to over 300A continuous so shouldn't have an issue there. might have to talk to the controller manufacturers also, but i figured the controller has a system where you can limit the amount of current drawn. otherwise you'd blow fuses left right and center! 

i'll conduct some more research and talk to some people in the area with electric cars to see if they can actually go up the hill.


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## Amberwolf (May 29, 2009)

PHAT_pudding said:


> Looks like i will incorporate a liquid cooling system for the motor and controller to minimise the likelyhood of overheating the motor.


You can easily liquid cool most controllers (the Soliton1 already has this option built into it's heatsink). 

Liquid cooling a brushed DC motor isn't going to be that easy, though, and unless you custom-design and build it around that idea, not even practical to try, since you can't liquid cool the armature, rotor windings, and commutator, all of which is what gets the hottest and needs the cooling the most. 

You could probably reasonably easily cool the field windings down to superconductivity if you had the power to pump the heat out, and a place to dump it.  

Brushless motors, AC or "DC", permanent magnet or not, could be liquid cooled easily enough, because the part that needs to be cooled most will be stationary. The whole thing could be liquid cooled by pumping the liquid thru the entire motor casing, if it's sealed, since there are no brushes/commutator to keep from shorting or insulating with the chosen fluid. It would add some friction, partly via fluid turbulence and whatnot from the rotating parts shearing the fluid at the boundaries between rotating and nonrotating areas, but it would still work lots better than trying to do it in a brushed motor. 
________
Marijuana Dispensary Reseda And Hart


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## PHAT_pudding (Oct 8, 2009)

Amberwolf said:


> Brushless motors, AC or "DC", permanent magnet or not, could be liquid cooled easily enough, because the part that needs to be cooled most will be stationary. The whole thing could be liquid cooled by pumping the liquid thru the entire motor casing, if it's sealed, since there are no brushes/commutator to keep from shorting or insulating with the chosen fluid. It would add some friction, partly via fluid turbulence and whatnot from the rotating parts shearing the fluid at the boundaries between rotating and nonrotating areas, but it would still work lots better than trying to do it in a brushed motor.


not wanting to sound like a massive nerd. but couldn't you liquid cool a brushed DC motor in the same way by choosing a low viscosity non-conducting oil?

anyway doesn't matter because i'm not even gonna try and implement a liquid cooling system. The zilla controller will be liquid cooled with a pretty small radiator, and the motor will be cooled via dual blowers and filters. 

after reading a massive thread about thundersky battery balancing and low voltage protection... wow. soo much to think about yet! the motor is basically solved though, and the gears of the car can reduce the load on the motor by increasing the revs and lowering the speed. Still don't want it to overheat though. that'd be catastrophic!


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## Amberwolf (May 29, 2009)

PHAT_pudding said:


> not wanting to sound like a massive nerd. but couldn't you liquid cool a brushed DC motor in the same way by choosing a low viscosity non-conducting oil?


Right up until the carbon worn off the brushes and the metal worn off the comm segments pollutes the oil enough to begin causing conductivity.  Probably would take quite a while, but it is a potential problem. 

Another possible issue is the oil would get between the brushes and the comm faces, insulating them from each other. Perhaps only a bit, but that would increase the resistance, causing more heat/

I'm not a motor expert (barely even an amateur), so I could be very wrong. Major or some of the other motor experts on here would probably be better at answering this question.
________
WIKI VAPORIZER


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## PHAT_pudding (Oct 8, 2009)

yeah i wondered about the oil interacting with the brushes and causing issues. either way, a motor spinning at 5000 rpm with any kind of fluid in it is gonna cause issues from the viscosity. would be fun to try one day with a smaller, lower rpm motor.


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## Tesseract (Sep 27, 2008)

tomofreno said:


> I believe it is around 4x more current. The sum of the hill climbing force (product of vehicle weight and sine of the angle), drag force, and rolling resistance force is about 4x the sum of just the drag and rolling resistance forces at 50 mph.... .


I think we are both wrong! I see where I screwed up - I took tanΘ and multiplied it by 100 to get the percent incline, then went off on - literally - a wild tangent (ahem  ) from there...

So you are correct that it would be weight * sinΘ to find the _additional _tractive force needed - on top of what is already required, that is - to propel a vehicle up an incline of angle Θ, or an additional 143kg of tractive force in this particular instance.

However, subtracting out aerodynamic drag (which is not known here) one needs approximately 10x more power to go up an 11% grade, and if speed is constant then all of that increase must be in torque. So, pretty much 10x more current is required.

However, I readily admit to suffering from occasionally spottiness, to outright gaping holes, in my knowledge of mechanics... see above!


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