Any one heard of Shell Eco Marathon Competition??

S

sheikhuu

10 mW
Joined
Jul 18, 2012
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34
Location
Pakistan
Hey folks! It's been a while since i've been gone from this forum. It's good to be back. :)

Has anyone ever heard about the competition, Shell Eco Marthon, which is held in 3 places around the world every year. Well I participated this summer in Shell Eco Marathon Asia held in Sepang F1, Malaysia. I went in the petrol-powered category along with my mates from University. Let's say we didn't do very well. Only 224km/liter next to the record of 2903km/liter.

In the summer of next year, I intend to go in the electric category and intend to use whatever i have learned from my experience with ebikes. A picture of my ebike is attached.

The objective is to create a three-wheeled prototype electric car that travels the maximum kilometers per kilowatt-hour (km/kWh). Each team is allowed only 4 attempts to acheive whatever mileage they are capable of. Each attempt is 4 laps of the Sepang F1 race circuit (north track) which equates to approximately 17kms. We also have to complete the attempt in 35mins. that is like an average speed of 30km/hr. So we are lookiong for a car that can go much faster than that. The tarck also has a steep incline.

We are going to modify our already existing car. A picture is attached.

I had a few ideas at first. We wanted to use Brushless hub motors. thinking of along the lines of Conhis motor or magic pie. But the problem is that for an application sth like this, they weight ******* alot. The Conhis 1000W weighs 6.4kg. Everything about this car is power-to-weight ratio. We need the lightest batteries that can last atleast 20kms.

My uncles, who are electronic engineers, suggested i look into R/C motors. I researched and came accross people who had used Turnigy 80-100 130KV in their ebikes. I really need help, people. Also regarding whether i should use Headway LiFePo4 or Li-po R/C batteries.

Looking forward to anyone's reply. :)
 

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Hub motors are great for simplicity, but common 3 phase ones like you mentioned are only around 80% efficent. Not bad, but they aren't likely to win. Some RC motors are in the mid 90s % range, and while there is some drivechain loss, they would likely be atleast 10% more efficent over all.

Good RC liCo weighs less and has lower internal resistance (so more efficent) than headway LiFePO4. But the usual turnagy RC has some saftey issues you need to account for.
 
Hey thanks Drunkskunk!

Hmmmm....if i had to go with R/C ones, which motors then? Something powerful enough to get a 90kg (included driver) car to speeds of around 40km/h. I didn't have a very good experience with chain drives this year. there were always alignment issues with the sprockets and the chain, as a result, would come off the sprockets at high speeds.

BTW, the rules say we can only use Li-ion batteries. So do Lipos count? i mean, what is lipo? Lithium Phosphate or Lithium polymer?
 
sheikhuu said:
Has anyone ever heard about the competition, Shell Eco Marthon,
Click to expand...
Several threads about it. ;)
http://www.endless-sphere.com/forums/search.php
 
sheikhuu said:
Let's say we didn't do very well. Only 224km/liter next to the record of 2903km/liter.
Click to expand...

Leaking gasoline or did you left the motor running all the time? :mrgreen:

sheikhuu said:
In the summer of next year, I intend to go in the electric category and intend to use whatever i have learned from my experience with ebikes. A picture of my ebike is attached.

The objective is to create a three-wheeled prototype electric car that travels the maximum kilometers per kilowatt-hour (km/kWh). Each team is allowed only 4 attempts to acheive whatever mileage they are capable of. Each attempt is 4 laps of the Sepang F1 race circuit (north track) which equates to approximately 17kms. We also have to complete the attempt in 35mins. that is like an average speed of 30km/hr. So we are lookiong for a car that can go much faster than that. The tarck also has a steep incline.

We are going to modify our already existing car. A picture is attached.

I had a few ideas at first. We wanted to use Brushless hub motors. thinking of along the lines of Conhis motor or magic pie. But the problem is that for an application sth like this, they weight ******* alot. The Conhis 1000W weighs 6.4kg. Everything about this car is power-to-weight ratio. We need the lightest batteries that can last atleast 20kms.

My uncles, who are electronic engineers, suggested i look into R/C motors. I researched and came accross people who had used Turnigy 80-100 130KV in their ebikes. I really need help, people. Also regarding whether i should use Headway LiFePo4 or Li-po R/C batteries.

Looking forward to anyone's reply. :)
Click to expand...

Buy this book, you'll learn like hell (like I did) about really high efficiency and lightweight electric drivetrains (>95%) not the inefficient and monster heavy "crap" of motors you suggested.

"Crap" that I'll be putting on my bike because I want POWER! That's something you'll not need much...


Do not forget the first rule of energy efficiency: Don't use what you don't need! Example: If you use the best tires (for low rolling resistance like the MicroJoule uses), that's energy you'll not use to push the car, resulting in less powerful motor and less batteries (less weight). Weight is of extreme importance in this competition!

best of luck!!!
 
Ehh, lighter is always better, but for such a low average speed, the amount of energy burned in slowing for corners and re-accelerating will be quite low. Power to weight is the massive factor for acceleration, but not quite such a big factor in energy efficiency when compared with aero drag. Design for the lowest rolling resistance tires that can still make the corners at design speeds so you won't need to brake or accelerate during the race, just maintain your design speed.

I would think a velomobile that was modified to allow the front wheel to have enough turning range to make all the corners of the track (I don't know if it has hairpins etc) would be about ideal. The motor powering it should be fairly wimpy, but efficient, and capable of coasting with no motor drag if the track has down-hill sections. I would personally avoid needing any more than a single stage reduction in the drivetrain for reliability and simplicity and optimal mechanical efficiency. A good hubmotor is actually temping for this.
 
I agree with you Luke.

But in this particular competition, there is no braking involved. Only after the finish line.
Engine ON is normally only going up.

Untitled.jpg

That formula plus the force needed to accelerate rotating parts.
That's mass written 3 times...

To give examples of how "small" things can have huge effects on the final result.
we've gained 50km/l by modifying the std freewheel on our back wheel.
By removing the chain tensioner from the ICE transmission, we've gained 80km/l.
And from our calcs and tests, a reduction of 1kg in our car equated to 10km/l improvement.
A less then perfectly tuned centrifugal clutch was more than 150km/l...

This competition is about insane and obsessive attention to detail.

A hub motor, not providing power, would have either losses: freewheel or iron losses. A transmission setup like a starter motor, that only engages when power is needed, is the best i've seen so far. Also electric motor "like rpms" to get good efficiency. Not forgetting that, for the same power, a faster motor is lighter than a slower one.
 
Thank you everyone for your support! :)

So R/C motors with a high reduction ratio and a single speed is the best? Remember, There is also a steep incline on the track. But before that incline, there is a slight downhill as well,. (medium gradient). Many teams make use of Regen and supercapacitors in that length of the track. Oh and we are also allowed to integrate solar panels. The maximum permitted area isn't large though. Only 0.17meters.squared. Some of my professors are insisting on using the topology of the track to our advantage. Use the solar panels for ONLY coasting. Use regen with supercapacitors for initial acceleration and battery for everything "in-between".

Another confusion i have is related to the power equation. P=VI. For a given power, the current drawn by the powertrain should be as small as possible, right? (to lower wire and copper and iron losses in the motor)? So, shouldn't i have a system that operates at the max permissible voltage i.e 48V? There are few R/C motors that operate at that voltage. ALSO, how i can regen from an R/C motor? Can i Use the same controllers for hub motors to power R/C motors? (my conscious says, no?). I'm personally inclined to use R/C motors cuz hub motors weigh SHIT!

Once again, Thank you all for your help!! :) (Sorry for late reply btw. University workload :( )
 
Inrunner or outrunner, low or high voltage, the right person to answer that is LFP (liveforphysics) and others...

But a rewound low kv, wye connected, high voltage RC motor seems a good place to start. 8)
 
I can't imagine a situation where regen on the down hill and then using the power on the up hill would be better than just conserving momentum by coasting down the hill. you have losses converting energy from one form to another, then more losses converting it back

And Super capacitors are fairly super, for a capacitor. But as a Battery they are shit. Heavy And very low energy density. And because of the voltage gradient, you need a DC/DC converter to get power out of them, intruducing more loss to the system. Better just to use a High C rate battery, but unless the track has tight curves that you'll need to slow down for, I can't see where regen would ever be used.Anytime you do any kind of breaking, you're throwing away energy. regen just makes it suck a little less.

If you're going to carry the weight of a solar pannel, there's no point in not letting it add power all the time. Otherwise itsw just dead weight and wasted power.
 
Drunkskunk said:
I can't imagine a situation where regen on the down hill and then using the power on the up hill would be better than just conserving momentum by coasting down the hill.
Click to expand...
When there is a traffic control stop at the bottom of the hill? ;)

(or other situation too dangerous to go right thru without slowing or stopping)
 
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