Impact Attenuator for Over-sized Vehicle

[thomasg]

Hey guys, we are building a fully Electric Vehicle for competition and we are estimating that our weight will be around 800lb which I believe is above what is acceptable for the standard sized attenuator. Do any of you know where we could purchase a FSAE approved attenuator for competition or do we have to build and test it in house?

Thanks

[JulianH]

Sorry, but I would throw the concept away and start from scratch.

A 360+kg car has nothing to do with Formula SAE.

Rethink your concept and then go with the Standard IA.

Just for frame of reference: The first full electric car from Delft weighted in at 177kg (not even half of the limit!).

[thomasg]

@JulianH

We appreciate the feedback but our accumulators are what are making us so heavy, the rest of our vehicle is comparable to the standard EV car. We have 4 90lb accumulators that we have been constrained to use. Given this there is nothing we can do to redesign them this season. With this being in mind what recommendation would you have for the Impact Attenuator.

[JulianH]

Thomas,

how the .... did you end up at 360lb of accumulators? What kind of technology are you using there?
I really doubt that you get this car running ever.

From which university are you?
Have you reached out to other teams about this before deciding on the accumulators?

For the IA:
I'd buy the standard impact attenuator and test it with your car's weight. I am rather convinced that the Standard IA has a quite high safety margin so that you might be fine even with a higher car weight.
There is only one standard IA out there, so if that does not fit, you are forced to test it on your own.

If you are even above the safety margin of that part, you need to reinforce it even more...

Edit: Thanks Doug, I know read it also as 4 times 90... still waaay to much. Lead acid should not be in a FSAE car. That's like running a lawnmower engine in a combustion car.

[DougMilliken]

I read that as 4 x 90 pounds each. Assuming they are something fancier than lead-acid, why not use two of them instead of all four?

[Swiftus]

That's like running a lawnmower engine in a combustion car.

Eh, essentially guaranteed not to come in last if you do this. A 100% reliable car is likely to beat a large number of cars in the combustion competition simply by completing all of the dynamic events. So long as they don't run out of order in Endurance, they should be able to score the minimum value everywhere. Just as a reference, the Baja SAE car at Oregon State is faster than the slowest combustion cars in FSAE events. It has a lawnmower engine in it

[Bemo]

Just read the rules. The IA has to be tested with a vehicle weight of 300kg, regardless of the actual weight of the vehicle. One might argue that this does not make much sense. But it's clearly what the rule is saying.

Besides that I fully agree that there is no point in building such a heavy car.

[Claude Rouelle]

Formula Student is a DESIGN competition.

A 800 lbs car is not a car that was designed. It is a car that is assembled with parts thrown together as kids assembled a Lego with no or little engineering concept thoughts.

Electric or Combustion at over 450 lb, definitely 500 lbs you will already have design judges concerns. At 800 lbs you take the risk to have no attention at all. If you pass technical inspection;because at 800 lbs I guarantee many parts will show breaking potential.

F=MA. For the same lateral acceleration you will have more suspension elements load, therefore more compliance. One solution is to make the suspension elements stiffer ... which means more load. Vicious circle... The other, smarter, solution is to apply the form follows function method.

Formula Student is competition with serious challenges and it would be good we have serious people who try to compete

[FrederikWe]

I assume that they are a pretty new team, when they use the standard impact attenuator.

You all started somewhere right?

I don’t think they WANT to run lead acid by choice, if he writes that they are constrained to it.
Most comments made on this thread recently simply judged the whole car design by the weight of the accumulator, and declared the whole car as crap without even seeing it.
Pointing out that Delfts first e-car was 177 kg is ok for reference what can be achieved, but they also had some years of experience in building formula student cars at that point and they also are the benchmark for lightweight design, which should be kept in mind.
If I substract this whale of an accumulator (160 kg) and replace it with a common 50 kg version, the estimated car weight would be 250 kg

Weight of other first e-cars:

- Greenteam: 280 kg
- AMZ: 227 kg
- KA Raceing: 298 kg
- MunichMotorsports: 320 kg
- Running Snail: 218 Kg
- DHBW Engineering: 280 kg

So regarding their weight target of 360 kg they MUST do good structural engineering if they want a reasonably stiff car without mechanical failures.
So if you really can’t do anything about the accumulator weight, accept it and make the best out of it. You will learn plenty, gain experience and if this car will complete any endurance you did a great job. Reliability should be your biggest concern this year.
Next year you get lighter cells, so your can focus more on improving performance, whilst maintaining reliability.
You design doesn’t have to be crap if you are not as light as Delft and Rome also didn’t get build in one day.

Regarding your question, I think Bemo already gave the answer. Probably they didn’t expect such heavy cars when this rule was written.

[JulianH]

To be fair, Frederik, all those teams started with a 80kg rather than a "new standard" 50kg accu pack as well
At least our Furka packs from 2010 were like that

I agree with you, that we were maybe overreacting, but judging from experience, teams that "start like this" normally don't get to a running car by the time of the competition.