# MSOE SAE Formula Hybrid build help



## arbartz (Sep 27, 2013)

Okay guys, I've posted here before, but that was all when I had pretty much no experience in this sort of thing. I've been doing a lot of research and I am trying to put together a design proposal so I can convince the team of Mechanical Engineers and the department that full EV would be the way to go next year. 

We need to design a whole new chassis next year anyways, so I figured it's the perfect time to plan for a kick-ass electric system! I would like to make this as fast as possible as almost every other car at the competition struggles to just go up the hill at the track. 

My main constraints are:

Fully charged battery voltage <= 300VDC
Total battery capacity <= 5,561.25Wh
Prefer gear-boxless motors, i.e. directly coupled to the wheel.

Weight and size are also a concern, but since I don't know what I can get my hands on yet I don't have any hard constraints on it. So I'll be looking for motor with a really good power/weight ratio. 

For batteries I'm planning on creating my own pack with 5Ah 40C LiPo cells since I can get them for really cheap and they have insane power density. As of right now with the two main constraints I have figured a 70S4P LiPo pack is my best bet. That would provide me with 259Vnom, 800Acont, and 5180Wh.

For motors I would like to use twin Emrax 268 MV's, each directly coupled to the rear wheels. I figure a top speed of around 140MPH with our 20" wheels and a maximum 284HP to the wheels. Considering that our whole vehicle with driver will be well under 1000Lbs, I think this could be quite the rocket!

For the controller I'm thinking a Sevcon Gen 4 Size 8 would do just fine for us, but I'm honestly not too sure.

This will all depend heavily on what we can get for sponsors and funding. 

I'm only a sophomore EE and pretty much the only active EE on the team, so I may need a bit of help from you guys in figuring this all out.

With that being said, any comments, questions, advice, etc is more than welcome!

Oh, and here is our team's website: http://fh.msoesae.org/


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## Tomdb (Jan 28, 2013)

Why in the world would you need two ermax 268's?

I would look at how wining European teams are doing it. 
TUdelft
University of Stuttgart
ETH Zurich


One big thing is that power is not everything. European formula student is limited to 80 Kw draw from the batteries. 

A few points that will become important;
Traction, hence almost all top teams run AWD
Weight, Most cars dip below 200kg 440lb
Money/sponsor, with out these you are not going anywhere.


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## arbartz (Sep 27, 2013)

Tomdb said:


> Why in the world would you need two ermax 268's?
> 
> I would look at how wining European teams are doing it.
> TUdelft
> ...


We probably don't need twin 268's, but I'd like to do that because it's the best way I see to run then without any gearing down. Running a 268MV with a 300V system allows for a 140MPH top speed. That's faster than we'd probably ever go on the track, but it's the slowest top speed when comparing all the emrax motor configurations in direct drive with 300V. 

I have looked at the AMZ team in the past, but I was having trouble finding useful information other than their motor power output.

Luckily Formula Hybrid doesn't have an energy draw limit, just a capacity and voltage limit.

Our vehicle will likely be all wheel drive, just not right away. I would like to run two 208's up front with a gear reduction.

For weight we've always been the heaviest team, and sadly I don't see that changing too much. Last year our vehicle weighed in at 900Lbs.

Sponsorship is a huge thing that we need to focus on, historically we've had trouble getting sponsors because our school has to approve of who we are going to talk to before we ever make contact with them.


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## RIPPERTON (Jan 26, 2010)

What kind of track do you FSEA guys race on ?
don't you do car parks and Kart racks ?
then your 140mph and 280hp is a bit overkill isn't it.
Also what is your rear wheels rolling circumference ?


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## dcb (Dec 5, 2009)

arbartz said:


> Fully charged battery voltage <= 300VDC
> Total battery capacity <= 5,561.25Wh
> Prefer gear-boxless motors, i.e. directly coupled to the wheel.
> ...
> As of right now with the two main constraints I have figured a 70S4P LiPo pack is my best bet. That would provide me with 259Vnom, *800Acont*, and 5180Wh.


5561/300=18.5ah
800/18.5=43C
You have <20ah batteries that can do *45C* discharge continuous?!?  (and you don't mind fully depleteing the pack in under 1.3 minutes?)

you might consider belt if not chain reduction, shouldn't be too hard to step it down with the smaller wheels. Also, if you limit discharge to a more reasonable but still pushy 10c (not continuous) the absolute most you can get from a 5.6kwk 300v pack is 74hp, divide that by the number of motors to determine appropriate motor size (1 per wheel=18.6 peak hp/wheel (14kw)) and you can only get that 74hp out of the battery for 6 minutes or until something melts, whichever comes first.

you might have to put a lot more thought into how long the race is and what sort of power demands you will need vs what you can expect from a battery.


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## browncamaroz28 (May 14, 2014)

900lbs? Light and nimble is the way to go in fsae. That's not to say you should be making it with 5/16" diameter tube a-arms but this is really a case of less being more. The car we built weighed in at 457lbs and it was a pig.


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## coleasterling (Feb 29, 2012)

My FH car was 441lbs ready to rock and roll at competition. Seems like with sponsorship issues, you'd want to keep the car as simple and cheap as possible...Add in the fact that you weigh 900lbs and it sounds like you guys need a diet. A minimal accumulator gives you more gas, lets you go faster in AX, and with some planning, will still get you all the way through Endurance. My ideal car these days would be a single EMRAX 208 coupled to the rear through the diff with a sprotor on the engine side, and around 120V of 5Ah, 100C LiPo cells in a single string. Engine-wise, Yamaha or KTM 250. Parallel hybrid, so no generator necessary.


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