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Lotus Engineering Study: Unsprung Mass Doesn't Much Matter

Not sure if this is the right discussion forum for this, but thought fellow Boss owners would be interested nonetheless...

Article on a thought provoking study by Lotus Engineering concerning the effects of a large increase in unsprung mass on vehicle handling dynamics. Study was done for a company, Protean Electric, which is marketing wheel hub-mounted 86HP electric motors to car manufacturers. The motors weight on the order of 30kg (~66lb) each.

http://www.thetruthaboutcars.com/2013/04/heresy-unsprung-lotus-engineering-unsprung-weight-doesnt-really-matter-much/

Article has links to Lotus' whitepaper, Youtube videos and a slide deck on the subject.
 

pufferfish

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those hub-mounted motors are a really cool idea. i often wondered how older cars would work when we shut off the gasoline. well there you go! i like the torque vectoring capabilities as well.

however, in the discussion of "unsprung mass doesn't much matter"...i beg to differ! they even pointed out that the added mass takes a class leading vehicle down to mid-class. that means a whole lot to me! also, the opposite must also be true then...reducing unsprung weight would take a mid-class car up to class leading. that's what we have all come to know and understand for decades now. its just spin doctoring to justify the ridiculous costs of doing the study to sell electric motors.

do i think unsprung mass is the holy grail of car performance? no. do i think its an obsolete and misconcieved notion? no. it does have quantifiable impact on handling performance. your suspension is only as good as its ability to react to the changing pavement and vehicle dynamics. every ounce that must move to compress or rebound the shocks is additional mass that carries inertia an and slows the shock's response. there is certainly more to the equation, but that is a fact of physics.
 

ArizonaBOSS

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Cliff's Notes: Unsprung weight "doesn't really matter much" if you're willing to rework your entire suspension to compensate, to get you back to where you would have been already with a lighter unsprung weight setup.

Ask any racer, any real racer... /vindiesel
 

pufferfish

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don't get me started on the Vin master. i learned to double clutch like i should right after i found out i never had him or my car. i am now also living my life a quarter mile at a time.
 
Oh it matters, take 40 lbs out of your wheels and see how much faster your car goes at the track. ( drag strip ) Not sure about you corner turning guys, but I am sure lighter parts make the suspension work less and handle better.
 
Handling would certainly suffer, plus you would have high voltage wires coming out of the body and attaching to a constantly moving suspension...that is going to need some serious armored conduit. BUT the extra mass to spin up/down argument might not be too valid for a street car, since that extra mass is actually generating torque to accelerate and decelerate. It isn't a static load. electric motors have insane torque across the entire operating rpm range, too. But you will still need real brakes.
 
WinterSucks said:
Handling would certainly suffer, plus you would have high voltage wires coming out of the body and attaching to a constantly moving suspension...that is going to need some serious armored conduit. BUT the extra mass to spin up/down argument might not be too valid for a street car, since that extra mass is actually generating torque to accelerate and decelerate. It isn't a static load. electric motors have insane torque across the entire operating rpm range, too. But you will still need real brakes.

Not sure on the dynamics of how it works but I believe they can use the electric motors for braking as well and do it quite efficiently.Something about regenerative braking. One of you electrical wizz kids correct me if I am wrong.

Didnt someone recently build a 4 engine electric super car ? Hate getting old, can never remember things like that.
 
Some of Porsche's first cars had electric motors at each wheel, he basically invented the electric hybrid. He also made tractors for farmers back in the day but that's a different story.
 
NewBossowner said:
Not sure on the dynamics of how it works but I believe they can use the electric motors for braking as well and do it quite efficiently.Something about regenerative braking. One of you electrical wizz kids correct me if I am wrong.

Didnt someone recently build a 4 engine electric super car ? Hate getting old, can never remember things like that.

I am an EE, so I have seen how awesome a well designed motor servo system can be. You would be surprised how well an electric brake can work. BUT all that energy has to go somewhere, and there is a limit to how much can be put back into the battery during braking since they have a max charge rate. You can use a capacitor to store that brief surge, but at the voltages needed you are talking about a lot of space and expense depending on how much capacitance you want. The only other way to get rid of the regenerated power is a high wattage resistor that would turn it into heat like normal brakes do. It would help longevity of your normal brakes, but they are still going to be needed for fast stops and safety, I think. I would not drive a car without a mechanical brake system.

One huge advantage with a true servo motor drive is you could accelerate as fast as possible without breaking traction. The torque can be easily managed and wheel slip can be detected quickly and managed. The system would even be able to characterize the tire grip (it knows how much torque is applied). Tire manufacturers would hate that :)

But for handling, you would end up with more rotating weight. If you have ever picked up a spinning gyroscope and tried to turn it on only one axis like a front wheel you will know what I am talking about. Adding more mass just makes the wheel/gyro resist you even more. I recently put on wheels that saved around 10lbs per corner and I could immediately feel the difference in feedback force on the steering wheel.
 
WinterSucks said:
I am an EE, so I have seen how awesome a well designed motor servo system can be. You would be surprised how well an electric brake can work. One huge advantage with a true servo motor drive is you could accelerate as fast as possible without breaking traction. The torque can be easily managed and wheel slip can be detected quickly and managed. The system would even be able to characterize the tire grip (it knows how much torque is applied). Tire manufacturers would hate that :)

But for handling, you would end up with more rotating weight. If you have ever picked up a spinning gyroscope and tried to turn it on only one axis like a front wheel you will know what I am talking about. Adding more mass just makes the wheel/gyro resist you even more. I recently put on wheels that saved around 10lbs per corner and I could immediately feel the difference in feedback force on the steering wheel.

Thanks Winter, I knew we had a smart kid here somewhere to answer that.

Oh I know rotational mass and unsprung weight make a huge difference in performance, the only way I know of to overcome it is massive amounts of horsepower and tires big enough to rotate the world. ;)
 
I really love having a big V8, but you can do some really cool things with electric motors (easily too, and with fewer parts). The biggest thing hampering electric vehicles right now is the batteries. Hopefully some new tech comes out that makes them more environmentally friendly and cheaper. Battery chemicals are nasty. I laugh at people being smug driving POS Prius'. They contribute more pollution than our Mustangs ever will. Carbon is the least of our pollution problems IMO.
 

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