FSAE BPSD Design

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NormanAlphaspeed
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FSAE BPSD Design

Post by NormanAlphaspeed »

Hey guys, I'm sponsoring a few FSAE teams and I'm thinking about helping them with the BPSD (Brake System Plausibility Device), a device with NO PROGRAMMABLE CIRCUITS that can detect some rules which I will state up next. Since that could be an actual safety product to be sold to more teams with proper documentation.

First off, there's something called a BSE, Brake System Encoder, which is a fancy acronym for a brake pressure or brake pedal position sensor. This must be fed to the control unit that controls throttle (through Analog or CAN, in our case it'll be CAN since the 4chan is already out of analog inputs), but it must also go the BPSD

The rules are as follows:
The BSPD must monitor for the following conditions:
a. Both of the following for more than one second:
• Hard braking (for example >0.8 g deceleration but without locking the wheels)
• Throttle greater than 10% open
b. Loss of signal from the braking sensor(s) for more than 100 msec
c. Loss of signal from the throttle sensor(s) for more than 100 msec
d. Removal of power from the BSPD circuit
IC.4.8.4 When any of the above conditions exist, the BSPD must Open the Shutdown Circuit IC.9.2.2
IC.4.8.5 The BSPD must only be reset by cycling the Primary Master Switch IC.9.3 OFF and ON

A, B, and C are somewhat easy. I already have a basic design which I'm pretty sure will work, using a few comparators (for "hard braking" and TPS), an AND and two OR's, which should take care for A, B and C.

To tackle D, the device needs to boot up the output when it turns on (and all conditions are OK), and power it off when unpowered, which I'm not too sure on how to do (not an electrical engineer here)

IC 4.8.4 is handled by the main output so that's fine

My big conundrum is with IC4.8.5, having the output NOT change when conditions are back to normal, only on power down. I assume that would need a flip flop on the output, but I have basically forgotten everything I ever learned about flip flops lol, so

What do? I have attached a base design which I'm basing myself off (this design is for an Electric FSAE, which can reset on it's own and the timing is different on the shutdowns [500msec instead of 100msec, but that's just recalculating the RC circuit which I already did]), but I have no idea how to latch the output to stay off until power down while ignoring any change in state of the inputs. Halp pls
FSAE Electric BPSD
FSAE Electric BPSD
image.png (16.72 KiB) Viewed 696 times
My BPSD for IC
My BPSD for IC
image.png (90.83 KiB) Viewed 696 times
User avatar
NormanAlphaspeed
Posts: 30
Joined: Fri Jan 13, 2017 7:15 am
Location: Puerto Rico
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Re: FSAE BPSD Design

Post by NormanAlphaspeed »

https://www.fsaeonline.com/cdsweb/rqa/ViewFAQ.aspx?faqnum=106

Here's a question that might/might not have to do witha quesiton asked previous about using FPGA's

Also,
GR.2.5 Violations on Intent
The violation of the intent of a rule will be considered a violation of the rule itself.

I think this one covers using an FPGA or anything that isn't a simple electrical circuit.

I just wonder if using pots passes as "programmable"
rubmack
Posts: 6
Joined: Thu Jun 04, 2020 5:55 pm

Re: FSAE BPSD Design

Post by rubmack »

Hi Norman,
this is an interesting idea. Attached you will find a design, that i did for FSAE 2017. It passed inspection and worked pretty well, i think. Maybe it can provide some ideas for your design.

image.png
image.png (43.81 KiB) Viewed 298 times
image.png
image.png (29.27 KiB) Viewed 298 times

Regarding the pots. This device used potentiometers as well and it was no problem during inspection. But that does not prove the compliance.

I think i had to modifiy the inputs of the RS-Flip Flop a little bit, but i dont remember the modification.

The idea behind the counter as the timing device (and not a RC curcuit) was, that i wanted the device to fully reset immediately after the error disappears.

Best regards
Marcel
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NormanAlphaspeed
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Re: FSAE BPSD Design

Post by NormanAlphaspeed »

Thanks a ton for your input!

My only question about what you said about using a counter, is that I think the BPSD has to stay latched if an error occurs,
image.png
image.png (12.04 KiB) Viewed 235 times
as IC4.8.5 states. Besides that everything else is a great help!
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