FSAE EV Rules 2014 Questions

[uG]

Dear FSAEe colleagues,
Dear Tobias,

I have two questions so far on this year rules improvements. :-)

EV3.4.8: "[...] The contained energy of a stack is calculated by multiplying the maximum stack voltage with the nominal capacity of the used cell(s)."

- Why? Usually, energy is measured with nominal voltage. Maybe it refers to the way the 6 and 12 MJ limits have been decided?

EV8.3.3: "The charger must incorporate an interlock such that the connectors only become live if is correctly connected to the accumulator."

- We are using Brusa NLG5x3 chargers. They automatically detects when the output is disconnected, and it quickly (<0.1 sec) disables the HV output. The detection is made, I think, when it realizes that the current equals zero. Would this software interlock comply with the rule?

Kind regards,

P.S. As some of you might have notice, Tobias Michael decided to start a blog (http://tobiasmic.blogspot.de/).
P.S. #2: Is there a difference between a molten salt and a thermal battery?

[Adam Farabaugh]

3.4.8. makes sense, I think. They want to set a maximum energy within an un-separated segment. If nominal voltages were used, then at max charge the energy limit could be exceeded.

Where did you hear that energy is measured at nominal voltage? At 3.7V a li-po cell has less energy than at 4.2V...

[Francis Gagné]

Great to see that blog, it's a very good idea!


3.4.8. makes sense, I think. They want to set a maximum energy within an un-separated segment. If nominal voltages were used, then at max charge the energy limit could be exceeded.

Where did you hear that energy is measured at nominal voltage? At 3.7V a li-po cell has less energy than at 4.2V...

If you look at the following graph :

http://www.rctech.net/forum/attachments/electric-road/1104193d1377325541-benchmarking-best-2s-lipos-tp-extreme-5000-discharge-curve-graph.gif
The total available energy is the area under the curve (depends on your discharge rate). To estimate it, you use the Nominal voltage, which is approximately the mean voltage of the flat part of the curve times the capacity. If you use max voltage, you will overshoot the real energy capacity of the battery. In regard to the 3.4.8 rule, I think the use of the maximum voltage is playing it safe, which is alright with me.

[TMichaels]

Hey All,
if the contained energy is calculated with the nominal voltage then the result is the nominal energy, right? But the rules talk about maximum energy contained between firewalls for example, thus we have to calculate with the maximum energy. Yes, it is that easy :)

Regarding the interlock: Only hardware interlocks count, no software solutions, like more or less for everything safety-related in the rules.

Well, molten salt and thermal batteries is kind of redundant. We just wanted to make sure that nobody shows up with thermal batteries which are not made of molten salt.

[uG]

Haha. Thanks, as usual, Tobias.

[uG]

Dear FSAEe colleagues,
Dear Tobias,

Rule EV4.8.1 claims that: "The HVD must be above 350mm from the ground and easily visible when standing behind the vehicle."

Would it be allowed to have the HVD being made in two parts:
1) One part being hidden
2) One part (remote handle) being above 350mm off the ground and easily visible when standing behind the vehicle.

By the way: could "behind the vehicle" be "behind the vehicle, but slightly on the side"?

Also, EV8.3.5 stipulates that "When charging, the AMS must be live and must be able to turn off the charger in the event that a fault is detected." Is it enough to stop the charge (send a stop charge command to the charger) or it has to electrically disconnect the charger from its AC supply.

On a more general topic now, I'm wondering how suited do you think of the design points are split for electric cars. I think that the electrical design points should be worth more than what they are (around 25/150 @ FSAEe in Nebraska). Do you think we should even create an electrical design event (or regulate the amount of points the electric part of the design should be worth)? I also feel that the cost event is not well suited for electric cars, but I can't talk with experience on this :-).

Thanks, and regards.

[rz-jacks]

Dear FSAEE colleges, I'm currently working on the design of the battery pack and I have a question regarding the rules:

In EV3.3.3 is states that "The separation must affect both poles of the segment. This separation method must be used whenever the accumulator containers are opened for maintenance and whenever accumulator segments are removed from the container. Maintenance plugs requiring tools to separate the segments will not be accepted. Maintenance plugs must include a positive locking feature which prevents the plug from unintentionally becoming loose."

Q1: what do they mean by a maintenance plug? is this a specific type of connector they are referring to? and does the "tool-less" rule only apply to these?
Q2: Does this mean that whatever method we use to interconnect the segments needs to be tool-less? for example, couldn't we use a simple busbar arrangement in which the segment poles are bolted together? I must be missing something here because it wouldn't make sense to use 6 high current "tool-less" connectors (assuming you have 6 segments) that are going to be extremely expensive. I'm trying to understand what this rule is trying to safeguard against.

Thank you!
Rene.

[uG]

Hello Rene,

Q1: As far as I know, a maintenance plug is simply a connector that you disconnect when open the battery pack (when doing maintenance). No interlock is needed since the maintenance plug opens the series path in your battery pack (no electrical difference potential will come out of the battery pack).

Q2: You can use bolts as long as each separation has "a maximum static voltage of less than 120VDC and a maximum energy of 12MJ" (EV3.3.3). Note that it can be 6MJ if you use other chemistries than LiFePO4.

If you wonder why you need not to require tools to open the maintenance plugs, Tobias explained it well previously, on the FSG's forum (https://www.formulastudent.de/fsg/forums/?view=single_thread&cat_uid=8&conf_uid=12&thread_uid=695&page=2):

"The intention is, that the maintenance plugs shall always be removed whenever the accumulator container is opened. If you need tools for this, it may prevent you from following this approach, just because of lazyness or unavailability of the correct tool for example. The logic could be: "I am only working for 5mins at the accumulator container, I will not start searching for tool xyz now." This should not happen, if you could just unplug the connectors by hand."

P.S. You can also refer to what was discussed on the FSG's (https://www.formulastudent.de/fsg/forums/?view=single_thread&cat_uid=8&conf_uid=12&thread_uid=851) forum last year. Please note that there was no positive locking mechanism requirement at that time.

Regards,

[tobias.rheinlaender]

Hello everybody, hello Tobias,

I have a questions concerning the following rule:

EV2.1.2 Motors must be contained within a structural casing where the thickness is at least 3.0 mm (0.120 inch). The casing must use an Aluminum Alloy of at least 6061-T6 grade or better if a casing thickness of 3.0mm is used. If lower grade alloys are used then the material must be thicker to provide an equivalent strength.

Note: Use of a higher grade alloy does not enable a reduced thickness to be used.


At this point, I am not sure whether the rule refers to an additional housing or the motor case itself. (Although I must admit, I have yet to come up with a clear meaning for ‚structural casing‘ - perhaps this is crystal clear to native speakers…)

In Tobias Michaels blog, he states:
EV2.1.2:
Change: A minimum strength/thickness requirement for motor housings has been added.
Impact: Many teams may have to re-design their motor housings or at least check whether it fulfils the new requirements. This rule has been added due to lots of discussions this year at scrutineering about the necessary thickness of motor housings.

So, this sound promising, but it is not official, so...

We employ a rather sturdy motor out of a series-production vehicle that has a casing that might fulfill the material and thickness requirements. Would this be enough or is an additional casing mandatory?

In case the motor case is enough, what kind of documentation would be required and where would we put is? (SES, I assume)

Concerning the geometry of the case, if necessary: Since the new rule is akin to the scatter shield rule T8.4.4, we have been wondering if some kind of cylindrical case with open ends would be enough to comply with the rule (and contain exploding motors...) If not, how wide can openings for ventilation and such be and where should or could they be placed?

Thanks alot!

Kind regards,
Tobias R
Combined University Racing Berlin (CURB) - Germany

[Puneet Arora]

Hello Everyone,

I am not clear about this rule:

EV1.2.8 All components in the tractive system must be rated for the maximum tractive system voltage.

What rating is the rule talking about? The insulation rating? Or something else? Most components come with only insulation ratings and not supply ratings. They rather have current ratings. (e.g. fuse, wires, etc).

In particular, does this rule prohibit use of motors with maximum supply voltage greater than max accumulator voltage? (The motor has sufficient insulation rating).

Thanks for helping.




Puneet Arora
IIT Bombay Racing
Racing up the ladder!!

[tobias.rheinlaender]

Hi Puneet,

kind of slow going here...
Well, in my opinion, Rule EV1.2.8 talkes about isolation in case of wires (and perhaps sensors etc.), but basically about the specs for normal operation when it comes to fuses, relais, connector and everything else. Most components come with some kind of current AND voltage rating for normal operation and for the most part you should stick to that. Motors are the only exception i can think of right now. But he isolation rating is always the hard limit. But this is beyond your question anyways...

In case of your motor I do not see why there should be a problem. As long as all components in the tractive system are rated for equal or above the maximum tractive system voltage, there should not be a safety problem. Can you think of any safety issue when supplying the motor with a lower voltage?

Please correct me if I am wrong. Thx!

Kind regards,
Tobias R
Combined University Racing Berlin (CURB) - Germany

[uG]

Hello Tobias,

I don't have anything official for you, however I got told that "teams started showing up with carbon fiber housings or very thin aluminium housings". Organizers were "afraid that if a part comes loose inside the motor, it might penetrate the wall and hit someone especially with the high revving motors".

In short, if your motor comes from a series-production vehicle, I'm expecting you won't require a beefier case.

For the geometry of the case, it should be meet the T8.4.6 regulation, even if it does not spin at rest (FAQ#107).

Regards,

[tobias.rheinlaender]

Hello Hugues,

thank you for your reply.
I find your argument very logical so at this point I will tell my guys to proceed without the extra case until I hear anything different. It is a risk I am willing to take.

You also mention T8.4.6 and a FAQ. The rule is about finger protection and I am yet to find the mentioned FAQ. Can you elaborate please? Thanks alot!

Kind regards,
Tobias R
Combined University Racing Berlin (CURB) - Germany

[Puneet Arora]

Hi Tobias,

Thanks for the reply.

I made a big error which I realised only after reading your reply. Very Sorry for that. I wanted to ask if we could use motors with rated voltage less than the maximum tractive system voltage. But your reply answers the question to some level.

In components like fuses and AIRs, the rule makes a lot of sense. In these components the Voltage rating is absolutely essential to their tasks. But I feel it is an overkill for components like motors. Especially with all safety compliances in the motor controllers as well.

In fact we asked this doubt to the rulebook committe (particuarly for motors) and their reply was : "Yes this is correct. If this is not complied with then it will be possible to provide a voltage to the motor that is too high and it could fail" So I guess motors too need to follow the rule.


Puneet Arora
IIT Bombay Racing
Racing up the ladder!!

[uG]

The rule is about finger protection and I am yet to find the mentioned FAQ. Can you elaborate please?

Hi Tobias,

Yes. You go to: "http://fsaeonline.com/". You login. You click on "Browse All Rules FAQs", then on "#107". Here's what you should be able to read.

"Per T8.4.1, "Exposed high-speed final drivetrain equipment such as ... electric motors, must be fitted with scatter shields in case of failure." (You are of course still required to use the steel material as the chain scatter shield.) For the shield around the motor housing, we will allow you to use 'mesh' or expanded sheet metal (aluminum or steel), as long as it meets or exceeds the perforation size requirement at T8.4.6 "must prevent the passage of a 12 mm (1/2 inch) diameter object through the guard." I realize the other language at section T8.4.6 regards 'parts that spin while the car is stationary,' but after discussing we request that you use the perforation details stated there, as a minimum specification."

Regards,

[Puneet Arora]

Hi Tobias and Hughes,

We have a similar problem with the casing too. We are using a stock motor for our car, which already has an external casing which is 1.2 mm thick. So we'll need to replace this or add another one above it.

Also, what is the purpose of the finger guard if the casing is now present? It itself performs the function of the finger guard, thus making the finger guard rule redundant.

Finally, if an external casing is required for motors, are perforations allowed on the casing?

Thanks a lot.

Puneet Arora
IIT Bombay Racing
Racing up the ladder!!

[tobias.rheinlaender]

Yes. You go to: "http://fsaeonline.com/". You login. You click on "Browse All Rules FAQs", then on "#107". Here's what you should be able to read.


Thanks for the info. I guess I have to be a 'Team-Member' to see those. Well, just more hoops...

@Webmasters: Please keep in mind that the FSAE-Rules are the basic rules for all the events. (okay, at least for FSG) Looks like I need to get a Team-Captain register a team before I can become a legit team-member so I am able to see the FAQ. As I am from a smaller German team that is not going to leave continental Europe any time soon (not with an electric car anyways...) this is for the most part a waste of time and database storage. Please consider streamlining that process.
Btw: There are way to many questions answered in the FSG-Forum that should be discussed here nowadays. Please consider contacting your colleagues and have them ban or at least discourage general FSAE rules question from the local forums so there is one place to go for these.... Thanks!!



"Per T8.4.1, "Exposed high-speed final drivetrain equipment such as ... electric motors, must be fitted with scatter shields in case of failure." (You are of course still required to use the steel material as the chain scatter shield.) For the shield around the motor housing, we will allow you to use 'mesh' or expanded sheet metal (aluminum or steel), as long as it meets or exceeds the perforation size requirement at T8.4.6 "must prevent the passage of a 12 mm (1/2 inch) diameter object through the guard." I realize the other language at section T8.4.6 regards 'parts that spin while the car is stationary,' but after discussing we request that you use the perforation details stated there, as a minimum specification."

Oh boy. Well, at least it will be less heavy than the extra case. Thanks a lot for the info.
I wonder what 'exposed' in this context exactly means but I guess every motor must be considered exposed no matter how thick the case is. (Looking forward to tell the mech-people: Good news folks, probably no extra case from the EV-Rules. *party* But you missed one of your own rules - so basically "Swiss-cheese case" it is! - And for the x-time: Read the **** rules again! I am going to have a field day. :D )

Again, thanks a lot for your valuable help!!

Kind regards,
Tobias R
Combined University Racing Berlin (CURB) - Germany

[uG]

Hi all,

For the benefit of everyone... here are the official answers to my previous questions:

EV4.8.1 (HVD): "Hugues, using a handle that operates the actual HVD is allowed, if it is built in a reliable way. Behind the vehicle means behind and on the centerline of the vehicle, not slightly on the side. "

EV8.3.5 (Charging): "Dear Hugues, turning off the charger means electrically turning off the charger. Thus you will need a contactor disconnecting the charger from mains power supply."

Electric Design Event: "Hugues-

The topic of points distribution (including Formula SAE Electric) has been discussed amongst the Competition and Design Event Organizers and Chief Design Judges at fair length.

While it may appear that only 25 of the 150 points is attributable to EV aspects, it should be noted that EV influences overflow into several other areas. These include: vehicle dynamics/suspension (ex. via torque vectoring), frame (battery and motor mounting), Controls (power delivery and driver information), System Management/Integration (power management), Manufacturability/Serviceability, and Creativity.

As we discussed the point allocations, we determined that EV aspects flow into (or at least 'should' flow into) nearly all categories of your design. Secondly, even though the EV project is admittedly very involved (in particular due to safety rules/requirements), this in no way diminishes the importance of attributes such as suspension geometry or aero design on overall vehicle performance.

Please rest assured that the rules committee and event organizers have discussed (and shall continually revisit) the topics of points distribution between and within events. There is a healthy tension that exists within the organizers that drives frequent discussion about topics such as this. Also know that the educational value for and safety of the participants remain our highest priorities.

From a functional standpoint, the 2013 FSAE Electric event was run concurrently (but separate) with the IC engine event in order to streamline the activity. The FSAE-E cars were only judged against / compared with other FSAE-E cars. With only 5 of the 20 registered team showing up for the Design Event, this remains the most efficient way to run the event. Naturally, as the number of active participants grows, so shall the event's independence from the IC engine event.

Much like the Design Event, discussions about how best to approach the cost event for FSAE-E have taken place as well. Over the years, several changes have been made to the cost event to improve its fairness, relevance, and educational value. We shall regularly revisit our approach to make the event the best it can be.

We thank you for your inquiry and wish you the best of luck in future competitions. "

Good luck to all of you!

[SomeOldGuy]

I wonder what 'exposed' in this context exactly means but I guess every motor must be considered exposed no matter how thick the case is.

Hello to everyone that has been wondering about this rules question about motor cases and the allowance of a mesh cover over the "exposed" high speed final drive.

This was a question that my team asked last year.
We use the EMRAX motor which spins the entire motor case which is why we asked the question and is what is meant by "exposed".
Our theory on why they wanted it covered in the way that typically applies to CVTs and the like, was that there was a concern that if we were running it with the Wheels off the ground, in the pits lets say there, would be a safety concern. (eg. a tool gets dropped on the motor when it is spinning at 2000 rpm)

In any case this question was asked prior to the new rule about having to have a 3mm structural case around the motor so any questions about this will need to be asked again. For instance our motor does use air cooling to a small degree through the entire outer perimeter of the case having small holes in it. Our interpretation of this new rule, with the specifics of our motor makes us think that we need to put the 3mm case around the entire motor...We will be getting an official answer through the Rules committee but any insight from the forum would be appreciated.

[Ceboe]

Hello to everyone that has been wondering about this rules question about motor cases and the allowance of a mesh cover over the "exposed" high speed final drive.

This was a question that my team asked last year.
We use the EMRAX motor which spins the entire motor case which is why we asked the question and is what is meant by "exposed".
Our theory on why they wanted it covered in the way that typically applies to CVTs and the like, was that there was a concern that if we were running it with the Wheels off the ground, in the pits lets say there, would be a safety concern. (eg. a tool gets dropped on the motor when it is spinning at 2000 rpm)

In any case this question was asked prior to the new rule about having to have a 3mm structural case around the motor so any questions about this will need to be asked again. For instance our motor does use air cooling to a small degree through the entire outer perimeter of the case having small holes in it. Our interpretation of this new rule, with the specifics of our motor makes us think that we need to put the 3mm case around the entire motor...We will be getting an official answer through the Rules committee but any insight from the forum would be appreciated.

Hi, SomeOldGuy,

Did you already got an answer on your question?
We are dealing with the same problem..