Das Beast: My E30 track / street build

[dvallis]

Mechanical design is shaping up. Beam bending calculator says the load cell will only deflect 0.005" with 850 lbs applied to it, so we should be Ok with 1/16" travel until it hits the bump stops. (0.0625") I had to make some minor changes due to the reality of bolt length availability. still, looks good.

[dvallis]

I like how the User Interface is coming along. Here's the display with corner weights, total, percentages and cross weights. Pretty cool to have everything on one screen.



We're back to working on suspension setup. Substitute for my 225 lb self in the driver seat.



I didn't get a photo today (duh) but we have the chassis level and this known square frame attached. Strings are mounted level with the ground, about even with the wheel hubs (not as shown). We're using this as the known baseline measurement for ride height.



Adjusted each corner of the suspension until we got even ride height on both sides, obviously with the front lower. You can see the string height. Ended with with a ride height such that the inner control arm ends are 1/4" above the outers, so no need for roll center correction. This should give us decent corner weight as a starting point.

[dvallis]

You're welcome. I could only find 100 kg (220 lb) planar load cells so three wouldn't be enough per plate. Could have made them but it's just one more thing to do. 4 x 220 lb gives me enough capacity. Even then, these won't be "drive on" as two load cells won't take full corner weight. Will have to jack each wheel and slide them under. Not a big deal.

[ForcedFirebird]

Thanks for posting this public!! Hopefully it's uploaded to r3v database and kept.

Why not use 3x 220kg per pad for 660 per corner? Based on simple geometry, three points create a plane, four adds a variance. Pretty sure this is why the tire balance machines have 3x pads. Personally, I was cursing yesterday since the tire balance machine has 3x contacts, and the one leg just had to land on the concrete expansions joint, no matter how many times the stupid thing was moved back-n-forth 6". Grrr

[dvallis]

Finished the scale design. Pretty simple really.



And now we build it. I had all the parts laying around. LCD first, just to get "proof Of Life"



I'l save you the gory details of the MCU code. First power up ..... It lives! Swoosh. Nothing but net.



Going to work on more suspension tomorrow.

[citizen_insane]

I found this one on Amazon. You could check eBay too. Most important thing is load rating. They need to be at least 100 kg (220 lb) rated so four under a plate will have enough capacity. Most you'll find are only rated for 50 kg.

You can also just buy full bridge strain gauges from Omega and laminate them to your own metal load cells. Probably better quality but you need to know how much strain your cell will experience under load.

Awesome, thanks. I haven't put on strain gauges since college, not sure I fully trust myself to do it if there are relatively cheap off the shelf options.

[dvallis]

I found this one on Amazon. You could check eBay too. Most important thing is load rating. They need to be at least 100 kg (220 lb) rated so four under a plate will have enough capacity. Most you'll find are only rated for 50 kg.

You can also just buy full bridge strain gauges from Omega and laminate them to your own metal load cells. Probably better quality but you need to know how much strain your cell will experience under load.

[citizen_insane]

This is VERY relevant to my interests. I've thought about doing the same a few times, but never bothered to actually look up where to get the hardware. Where are you sourcing your load cells?

[dvallis]

This thing is a $9 load cell. It's a piece of steel with a full bridge strain gauge laminated to a location that bends .. slightly. I used similar strain gauges in the Navy to measure deflection of F18 wing beams under a 10,000 lb computer controlled hydraulic press. THAT was fun to write code for. :-) This one happens to be rated for 220 lbs. Put 4 under a metal pate with associated electronics and you've got an 880 lb scale. One of those under each wheel and we're done.



IT'S ALIVE. Volt meter sees 1.2 mV out of the load cell as I lean on it with my thumb. Using a 24 bit ADC we can resolve ~0.6 uV per count over a 5V range. That 1.2 mV would look like 2000 ADC counts. No problem.



Now I know that works, we'll design the scale plate.

[dvallis]

Thanks for the feedback. My rates & height are close to Spec30 so we should be good for now. Getting more into setup.

Working on building a set of 3500 lb digital corner weight scales for $100 next. Proper scales, not bathroom scale ghetto lever hack. Requires some electronics knowledge, coding skill and a bit of soldering.

Stay tuned.

[MrScuba]

I have an e30 track car, with the Spec e30 suspension. It was a huge improvement in responsiveness over the mutt track/street suspension that was on it. The only criticism I am aware of is from a friend who has a problem with the car hitting the bump stops. I think his car is too low.

[dvallis]

Finished our ride height and toe tools today. Top string is on the frame attached to the car. Bottom string is on jack stands, checking the floor with an attached level.



Surprisingly, our floor is completely level, front to back and left to right. Now we know for setup the string attached to the frame will give us accurate ride heights for corner balancing.

[Digitalwave]

I would not worry about spring rates and such until after you have a bit of seat time in the car. Then adjust as needed.

That is a street setup for the most part, but it shouldn't hold you back for a while.

[dvallis]

Revisiting the spring rates while doing alignment research. Back in 2018, Spec30 adopted a Ground Control kit with 535 lb/in front and 700 lb/in rear. We're currently running 400 lb/in front, 650 lb/in rear. Slightly softer but we did a lot of weight reduction. They might be right for this car.

Spec30 fronts are maked with a custom "Ground Control part number. GC150.64.92

My stock Eibachs are marked as "0600.250.0400" ( 6" length, 2.5" ID, 400 lb/in)

Any racers care to comment on spring rates for an M20 powered E30?

[dvallis]

That is some good suspension porn. Didn't realize E30 M3 struts were an option. Hmmmmm .......