EV Challenge

[Seaniboi82]

Hi all. I'm a Design & Technology High School teacher with a background in carpentry (not engineering) and I've been given an engineering class called Electric Vehicle Challenge, where we make 3 wheeled EVs and race off against other schools. The vehicle that completes the most laps of a Kart track in an hour wins.

I used the EV from last yr as a starting point, which was primarily made out of cut up student desks and weighed in at +60kg. This year we used primarily aluminium and shaved off quite a bit of weight. We also ran the same hub motors (magic pie golden motor) and batteries (eagle electric 36V 10AH) as last yr. I'm told we were much more competitive this year (apparently we were at the back of the race last yr), but we were still slightly off the pace of the leaders.

How do I step it up again next yr? I'll definitely be purchasing new batteries, which are prescribed (36V10AH for the first race and 36V16AH for the 2nd) and I was also thinking of purchasing new motors. Should I just purchase another GM with the internal controller or go with something new? If I buy new should I go with a geared or gearless hub motor? I've read that geared is more efficient, but slower. How many amps should I be running?

I've always worked with timber, so this has been quite a stretch for me this yr. Any advice would be appreciated.

 

[Punx0r]

It sounds like your current setup is pretty simple and of modest output, so the good news is that you've potentially got plenty of scope for improvement. However, the first thing to understand is probably how constrained you are by any rules (max. voltage, power, battery capacity; battery type etc).

 

[Seaniboi82]

Regarding output the rules state we must use...
- A 36V10AH battery for the junior race, and a 36V16AH battery for the senior race,
- 1 x hub motor.

Not really sure where to go from here.

 

[Simonvtr]

Hi I would like to start off by asking how can I enroll in your class?
When I was in high school living in NYC we never did any cool projects like this.
The only group of class that did cool things were the AP class "Advance Placement".
But in a few projects the science teacher did let me join and so far I've won all 3 projects that I joined.
I remember there was a project where we only could use 8 sheets of normal printer paper to make a 4 stud foundation.
2nd place was 128lbs
Mine took first place at 971lbs.

My background is computer/ robotic engineer but I hope I can give you some idea.
If you are allow to use material outside of school and you have no welding skills then I would go with Aluminum Extrusions.
It wont be used as a bumper car so go light weight bare minimum frame. There are alot of plans on the internet using this stuff.

There are many options for cover.
You can go with just flaring for recumbent trike to reduce your wind resistance or full cover like the velomobile.

For motor I always thought gear motors have more resistance due to all the moving parts.
Compared to hub motor or direct drive belt motor going the same speed if both motors are the same spec.
Gear motors will have more weight to them due to the extra mechanic.
But my knowledge in these matters are limited.
I would think a DD motor will be better if you are on a GO-Kart track with no hills.
I wouldn't think you need anything that strong maybe 500watt?
All you need to do is get the vehicle up to speed and stay WOT "wide open throttle" till the 1hour is up.

You can go here to see which motor will give you the best speed/run time.
http://www.ebikes.ca/tools/simulator.html

For Wheels go light weight like single wall bicycle wheels tubeless.

Battery I would go lipo's. There are risk and you can do search on here and the internet to find all the risk involved in using lipo's.
But for the power density and weight nothing beats it.
Right now hobbyking.com has lipo 4s 5000mah battery for sell $14.99 west wearhouse.

Good luck and if you can please do post pictures of your class build.

Simon
.
.

 

[Simonvtr]

Maybe something like what is on the bottom of the image.

Simon
.

 

[Teh Stork]

Do not purchase Hobbyking RC lipo. Fragile in a crash and dangerous without a proper casing. Go for a ready made ebike or similar battery that can withstand some abuse.

Timber can be a good material for vehicles. The specific strength readily surpass aluminium and steel in beams. Furthermore, its cheap, fatigue resistant and lets you know before it failes catastrophically.

Geared motors do have merit, but it depends on the application. If the course is flat I'd stick with the direct drive motor.

 

[Simonvtr]

The lipo I link are in hardcase and if you want more protection seal them inside a ammo case or make a case from polycarbonate.
Many members on here run lipo's on ebike. There are risk with all type of battery.
When I did pro rc racing 4wd a 7cell nimh blew up during a charge before a race.

Is there a budget with this class project?

 

[Drunkskunk]

Were you able to drain your battery completely in the hour? Or was there power left over?


As I see it you need:
The most efficient vehicle possible for the conditions.
Proper telemetry so you can make the best use of the power you have.

On that first point, different tracks will have different needs. a smooth oval were the throttle can be held near constant would favor a direct drive motor like the GM Magic Pie you have now. However, a twisting road course with many throttle changes would favor some kind of geared hub motor.
In short, Direct drive is more efficient at constant speeds. Geared drive is more efficient at changing speeds.

The next part may be harder to do. You need a way to monitor the power being used each lap. then someone on the pit crew can do the math and figure out if the driver needs to go faster on the next lap, or slow down a bit and conserve power. the faster you go, the less efficient you are, but the more laps you'll get. So someone in the pits can figure out how to get the most laps out of the battery and relay that to the driver, leaving the driver free to concentrate on driving as smooth and efficiently as they can.

Having the kids compete to drive the car using the fewest watt hours possible in the months leading up to the race could help them to understand more about what it will take to win.

And as a final thought, practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice practice.

 

[Seaniboi82]

Hopefully this image loads. This is what we were running this yr.

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Obviously I need to streamline next yr's vehicle better, but this was the simplest for this yr that I could get 13 - 15 yr old students to make that met all of the regulations of the race and also reduced the weight of last yr's vehicle.

The track contains a lot of corners and is on a very slight slope.
We ran out of power just before the end of the race, but our batteries are 2 - 3 yrs old and other teams who were running heavier and slower vehicles still had quite a bit of juice left in their vehicles at the end... so yeah new batteries next yr.

 

[Simonvtr]

Is the cover missing on that?
I think it needs a fairing for better aerodynamic.

I like how simple it is. I think with lipos to reduce weight a better hub motor if you have the budget and some fairing would be fine.

 

[Dauntless]

The problem with these kewl classes that these kids elsewhere wish they could take is that the kids who are there to take them aren't always so interested. You want to convince them that they're going to be building a really kewl, inspired vehicle. Think of a manga look. Sorry, but your pic just won't load for me, I have no idea what it looks like, or if it would remind the kids of flying up to battle Decepticons.

One old project that turned out nicely.

http://www.instructables.com/id/Build-an-Electric-Car-Powered-by-a-Bike-Motor/?ALLSTEPS

You might also think of some kewl, manga inspired team outfitting.

 

[Jonathan in Hiram]

At the speeds I suspect you are running the races the single thing that will help the most with your current setup is to put your Magic Pie motor in a smaller wheel like a 20". On the tight racetrack you are describing your motor is operating well off the peak of the efficiency curve, a smaller drive wheel will help that substantially for about the least cost, spokes, rim, tube and tire. To keep the vehicle at the same level the rear axle dropouts will have to be lowered of course.

There is a 16" Magic Pie kit available that would be even better for your purposes, that one the rim is built on to the edge of the motor with no spokes at all. http://www.goldenmotor.ca/products/Magic-Pie-4-(VECTOR)-16-Inch-Front-Conversion-Kit.html

A Cycle Analyst V3 set up for torque mode throttle would help too I think although a sharp eye on the ammeter and a practiced hand on the throttle can achieve the same ends of keeping current draw as low as possible. The CA V3 will also give you onboard readouts for various things like range, battery voltage, current, regen percentage and so on, useful data to help tune your driving in real time.

http://www.ebikes.ca/product-info/cycle-analyst-3.html




One natural way for a carpenter to make an aerodynamic shell would be with wooden canoe building techniques. A shell for an EV would be a lot simpler than a canoe since the rigidity and strength requirement would be less.

 

[Seaniboi82]

Thanks for the advice guys. Plenty to consider. Will update on any developments.

 

[ecycler]

Don't buy anything yet, except a cycle analyst and remote shunt. In order to manage the power, you first have to measure it. Give us some more details outlined below and we can help you CALCULATE what needs to be adjusted. This is an engineering class, right?!

0. After a lot of experience in racing of all different kinds I can tell you that nothing you do to the trike will make as big of a difference as practice.

1. Tell us a bit more about this track:
How long is a lap?
Can you be a little more specific about the minimum speed the trikes hit in the tightest turns?
Do the trikes lose much speed climbing the hill?
What is the top speed you estimate the winners hit on the straights?
How many laps did the winner get last year with the 10Ah battery?
How many laps did the winner get last year with the 16Ah battery?
Did the same team win both races?

2. Equipment
Do you currently have a regenerative braking setup?
Are the students able to drive in such a way that they can brake exclusively using regen?
What is your budget?
What tires are you running?
What is the race weight of trike + driver?
Do you think this is a competitive weight with the winners?

3. Can you post the regulations?

We can help you find the most efficient motor/controller combo based on the given load for the set amount of energy you are provided ( 360 and 576 watt-hours respectively) and average speeds you will be running for the 1 hour race. It is nice that two of the variables are set, energy and time, so it makes it easier to choose the proper equipment making a few assumptions.

 

[Gregory]

I believe he's talking about the EV Challenge in Western Australia.

View attachment 2015-rules-v1.3.pdf

 

[Samd]

Dropped you a pm Sean.
I believe a Mxus motor might offer a step in efficiency to the MP.
Cheers.

 

[ecycler]

Definitely. A higher efficiency leaf motor might be a good upgrade too. Another magic pie is likely not going to be the best option.

 

[Samd]

Leaf lacks the stator, temp sensor and custom winds but they do have thin lams.

 

[ecycler]

Gotta' give the students something to do, haha! Installing a temp sensor is no big deal. They should install one in the controller as well.

Leaf will do custom winds such as:
9 * 7T - 380RPM
10 * 6T - 480RPM
13 * 5T - 580RPM
16 * 4T - 680RPM

Sean, I think what we are both trying to say is that a well chosen Leaf or MXUS motor/wind (operating near their peak efficiency of ~90% for as much of the race as possible at the proper calculated speed for course and load) and efficient controller (with matched MOSFETS) for the power requirements will do much better than a randomly purchased Magic Pie with internal controller. That is really the key here. We need to help you establish how to define the requirements before jumping to equipment purchases if you want to win. 8)

 

[Jonathan in Hiram]

The OP probably doesn't have regular access to the track which might be in another city entirely. I wouldn't count on any measurements or practice on that particular track beyond what all teams get at the race event.

Running a tight cart track in something clearly not designed for cornering and with no front brakes they are spending a lot of battery charge accelerating out of slow corners in that vehicle, a smaller wheel on the same hub will decrease the amp draw and increase efficiency during low speed acceleration and increase regen on deceleration while cutting top speed a bit.

This is a vehicle being built by high school students led by someone admittedly unfamiliar with electrical systems, ebikes and this type of competition, let's keep it simple for them. Talking about MOSFETS and Leaf motors and thin laminations is only going to cause confusion at this point.

In order to finish first you first have to finish.

 

[ecycler]

I think you would be amazed what a few interested and dedicated highschoolers enrolled in an engineering class would be willing to learn and accomplish if pointed in the right direction with a small budget and a few nuggets to research and learn about. Why not give them more than enough to learn about?!?!

I am trying to help the teacher think critically so that he can teach them how to fish and not give them the fish. I have the utmost respect for teachers and firemen which is why I invested the time in the thread. If this school was anywhere near me I would be happy to help them in person with both knowledge and some resources. I love helping to bring the next generation of engineering professionals online.

 

[ecycler]

The OP probably doesn't have regular access to the track which might be in another city entirely. I wouldn't count on any measurements or practice on that particular track beyond what all teams get at the race event.

Possibly, but you would be amazed how accurately things can be measure from Google Earth with the measurement tool. Some of these pieces of information will be stats for the team mates (who are not driving the car, but worked to build it) to focus on next year during the race to actually learn how to compete as a race team.

Running a tight cart track in something clearly not designed for cornering and with no front brakes they are spending a lot of battery charge accelerating out of slow corners in that vehicle, a smaller wheel on the same hub will decrease the amp draw and increase efficiency during low speed acceleration and increase regen on deceleration while cutting top speed a bit.

Likely and agreed that their best option is a 90%+ efficient DD in a super small wheel, but why stab in the dark when we can help them calculate something? They are not going to be running nearly as high of speeds as the carts.

This is a vehicle being built by high school students led by someone admittedly unfamiliar with electrical systems, ebikes and this type of competition, let's keep it simple for them. Talking about MOSFETS and Leaf motors and thin laminations is only going to cause confusion at this point.

In order to finish first you first have to finish.

That is a bit insulting to their intelligence and capability. Clearly the teacher wants to learn and help them learn if he is coming here for advice and answers. Each class could be a new lesson on these individual components and related concepts, how they are designed, and what options and implementations might be best for their application. Why keep them in the dark? They can process as much as they want.

 

[Lurkin]

- weight. lighter, lighter, lighter. Might be worth contacting universities nearby and seeing if there's a design department willing to assist. Computer modelling these days is the way to go with this... I did something similar in high school and the local uni was of great assistance. Speed holes are your friend! I would be consider plastic panels where you can (obviously non structural guards to prevent debris entering the chassis)....

Your frame needs to have more function and less material that is unnecessary. The good news is there weight to be saved, bad news its tricky to accurately design a strong, safe frame without much material. This is where the uni design department could be handy. I also found the unis consider it a way to appeal/ promote to young students in order to inspire their attendance - it was really neat at that age to have an opening to check out what was on offer.

- motor and controller efficiency
Interesting there's been commentary on here about motor efficiency. Rather than insult the OPs intelligence, can anyone provide a factual summary/comparison for the OP?

- battery choice
Historically Lipo made sense - but 18650 technology and pricing has changed dramatically. I imagine a burnt kid would end this project - I would be steering clear of Lipo and designing a custom 18650 pack. There is another forum member selling spot welders for this purpose that are really affordable. This would be a great project with safety in mind and will provide for future pack building.

 

[ecycler]

- motor and controller efficiency
Interesting there's been commentary on here about motor efficiency. Rather than insult the OPs intelligence, can anyone provide a factual summary/comparison for the OP?

- battery choice
Historically Lipo made sense - but 18650 technology and pricing has changed dramatically. I imagine a burnt kid would end this project - I would be steering clear of Lipo and designing a custom 18650 pack. There is another forum member selling spot welders for this purpose that are really affordable. This would be a great project with safety in mind and will provide for future pack building.

There is no battery choice. There are 2 races and they are given a 10ah for the first and 16ah for the second. Before discussing the best motor options we need to know more about the course and competition. The two most efficient direct drive motors have already been recommended, the best winding choices will be calculated if he gives us more info. Controller options are budget dependent.

 

[MrDude_1]

I would run a phaserunner as they seem to be extremely efficent. I would only run regen braking. (aka not use normal brakes)
and build the damn thing like a racing kart.. none of this hokey stuff students slap together. They should be questioning where you purchased it, not looking at old desks or aluminum extrusions.