JJLudemann's Design Thread

[glenn cooper]

import an engine in a box labeled "New Suzuki GSXR1000 Engine"?

What are they gonna do, Cane ya or someting?

Wrong country?

[JJLudemann]

keep it up.. your are an inspiration to the entire community.

who did you aero dynamic work on your car ?
are you supportiong your entire rear wing structure from your lower diffuser assembly

Wow, thanks! My inspiration is Jerry Freeman. Go, Jerry!

I did all the aerodynamic work myself. It took many months and I had to figure it all out for myself, as just about everything on the Internet is wrong. The people who really understand how it works aren't talking, but eventually I put together a few clues I found and now have a good intuitive understanding. I think.

My current plan is indeed to support the entire rear wing structure with the diffuser structure, but I admit I haven't done the detailed design or structural analysis of this section. Am I too optimistic to think it can be done this way? On my car the diffuser will have good strong structural attachment to frame, but then I can't use carbon fiber like an F1 car, either.

Thanks.

-Jim

[Wright D]

Most cars are built the opposite. I am not saying that your idea is wrong, just that all the cars I have seen use the rear wing to hold the diffuser up. I think this is most likely due to the "that's the way we've always done it" type thinking. However, the lower rear wing element typically has a fair amount of thickness, and thus a pretty high bending stiffness. Making it an ideal structure to hang a diffuser mount from. Like wise; most diffusers are relatively thin diaphragms, and don't offer much in the way of bending or twisting stiffness. If you could add thickness/stiffness to your diffuser, and endplates too for that matter, then I think it is perfectly fine to flip flop from the norm.

[Wren]

a diffuser with a "good strong structural attachment to frame" is a pretty terrible idea whether you are going to use it to support the rear wing or not

[Wright D]

a diffuser with a "good strong structural attachment to frame" is a pretty terrible idea whether you are going to use it to support the rear wing or not

Can you explain why you think it is a bad idea?

[provamo]

it seems to me that diffusers utilized on amatuer driven race cars are likely to get whacked so maybe it is not a great idea to integrate the wing (s)......i dunno.........

[jerry freeman]

[quote=JJLudemann;344420]Wow, thanks! My inspiration is Jerry Freeman. Go, Jerry!

I've been called alot of things but an "inspiration" is a first. Hopefully in the near future I'll have something more to look at on the new car to keep the drive alive.

[JJLudemann]

a diffuser with a "good strong structural attachment to frame" is a pretty terrible idea whether you are going to use it to support the rear wing or not

More specifically, the top of the diffuser can/will be attached firmly to the chassis. The vertical strakes that go down from there will still be a consumable item when the car is used for reverse rototilling.

-Jim

[JJLudemann]

[quote=jerry freeman;344577]

Wow, thanks! My inspiration is Jerry Freeman. Go, Jerry!

I've been called alot of things but an "inspiration" is a first. Hopefully in the near future I'll have something more to look at on the new car to keep the drive alive.

Well, Jerry, you're stuck with it. You're the guy who's actually DONE IT. I'll consider myself in your class when my car has run a race-length test. Without falling apart. Don't worry, that's a long way away.

-Jim

[JJLudemann]

My computer exploded (figuratively), so while it's being repaired I have some time to update my blog. Two new posts, one on building a really simple hydraulic press, and the newest one on building the lower control arms. I've also been redesigning the suspension uprights for the third time. The current design will use a 3D printer to make a master model, which will be used to make plaster casts, which will be used to cast the uprights from aluminum. It turned out to be a bigger project than I expected, but I felt that on my previous fabricated aluminum design I couldn't predict the impact of the heat-affected zones. No blog on that yet.

Fabricating the Lower A-arms

Enjoy!

-Jim

[S Lathrop]

When you made your suspension, did you condsider using oval tubing vs. round?

The DB1 Swift made all their suspension from tubing that was flattened in a press. I call this Bruns foil. The trick is to place a piece of flat stock inside the round tubing and press the tube against the flat stock inside. I used a 10 ton shop press for the job.

The oval tubing makes coping the outer ends of the a-arm much easier.

[nulrich]

It looks like the crossbars connected the two legs of the wishbone are solidly welded. That will put a hard constraint on the position of the inner rod ends. Is that your intent?

Nothing wrong with that if you have some other way to adjust caster or square up your suspension geometry (shims under your inner clevises? slotted mounts?). But you need some way of allowing for deviation from the exact design position of your mounting points and wishbones.

Nathan

[Christopher Crowe]

Steve,

Is this done with a strip sheet/plate stock placed inside the tube (horizontally), and then pressed?

If so, what thickness sheet/plate would be a good starting point? This is a neat technique if I can get it to work!

Thanks,

Chris Crowe

[R. Pare]

You can use 1/2 x 1/2 square stock on the inside to crush against for squashing 1" tube (if I remember correctly), but will need something wider and thicker on the outside (you need the bending stiffness there). Be aware that this technique will often leave the upper and lower surfaces slightly concave, so don't panic if you see that in your first tries.

[JJLudemann]

Does anyone know the correct diameter for OZ Racing/Van Diemen wheel drive pins? I found a reference to 1/2" diameter drive pins on the web, but a 1/2" gauge pin feels sloppy and a 17/32" drive pin fits in the holes perfectly well. Is it designed to have a little slop in it or something?

Thanks,

-Jim

[Wren]

I have always heard pin diameters of .50" for VD and .49" for Swift.

The drive pins should not be a slip fit, they should be looser than that. The clamping between the wheel and the brake hat is what does the real work.

[S Lathrop]

Swift uses a 1/2 inch holes for the pins and VD uses a 1/2 inch diameter pins. The actual hole size will depend on you choice for tolerances.

[RobLav]

Swift/Citation use .5" pins. Van Diemen's are larger at roughly .532 to .534".

[Mike B]

Jim,
If I remember, I'll send a dimensioned drawing of the VD drive pins tonight.

Mike

[JJLudemann]

Swift/Citation use .5" pins. Van Diemen's are larger at roughly .532 to .534".

That must be what I have. As I mentioned above, a 17/32" gauge pin fits easily, and 17/32" is 0.5312". Thanks for the information.

-Jim

[ghickman]

Correct drive pin size for the VD OZ wheels are .528 plus or minus .0005". We've turned several thousand of these over the past 20 years and this is what we came up with.

The OZ wheels are drilled 13.5MM.

[JJLudemann]

Jim,
If I remember, I'll send a dimensioned drawing of the VD drive pins tonight.

Mike

That I would love to see! I doubt there's a Van Diemen within 1000 miles of me, so that information is hard to get.

-Jim

[starkejt]

Swift/Citation use .5" pins.

I don't think all Citation peeps use the same size. I have a pile of each size in my accumulation of Citation parts from the various Citation OEMs.

[RobLav]

Yes Josh... perhaps I was being too general... I'm one who has VD pin sizes. The number I gave is also based on the 17/32" drill size for the wheels.

[starkejt]

Well, I don't remember which size we use, nor did I know for sure if anyone actually uses the other size, just that I have 2 little red bins each with different size pins in them.

[R. Pare]

I don't think all Citation peeps use the same size. I have a pile of each size in my accumulation of Citation parts from the various Citation OEMs.

All Citations were .490" for the last 25+ years, though I cannot vouch for the last couple of years - Steve may have changed things that I do no know about. If you have something else on an older car, they were not Citation made pins.

[starkejt]

All Citations were .490" for the last 25+ years, though I cannot vouch for the last couple of years - Steve may have changed things that I do no know about. If you have something else on an older car, they were not Citation made pins.

I only have late model Citations and parts for same. I am pretty sure both size pins were made by Brandon or Wren. They are just SS socket head cap screws with the heads turned.

[JJLudemann]

I only have late model Citations and parts for same. I am pretty sure both size pins were made by Brandon or Wren. They are just SS socket head cap screws with the heads turned.

That's a clever idea. I'm disappointed to find it won't work for my design.

-Jim

[CSHAW]

Most cars are built the opposite. I am not saying that your idea is wrong, just that all the cars I have seen use the rear wing to hold the diffuser up. I think this is most likely due to the "that's the way we've always done it" type thinking. However, the lower rear wing element typically has a fair amount of thickness, and thus a pretty high bending stiffness. Making it an ideal structure to hang a diffuser mount from. Like wise; most diffusers are relatively thin diaphragms, and don't offer much in the way of bending or twisting stiffness. If you could add thickness/stiffness to your diffuser, and endplates too for that matter, then I think it is perfectly fine to flip flop from the norm.

Dustin, You are right, There is a reason cars have evolved to both hanging the diffuser from the wing mount boom and supporting the aft bodywork also from the same structure. That is what has proved to work the best over time for both formula cars and sport prototypes as well. The bodywork, both upper and the diffuser must be considered as consumable items and thus are expected to be compromised through normal operation. In contrast the wing boom is to be considered the least consumable structural member at the rear of the car and it make sense to mount the other elements to this structure.

If you put a lot of effort into making the diffuser your structural foundation at the aft of the car, then my gut tells me that you are asking for parts flying every which way when it suffers impact damage. Also the diffuser and its strakes continuously make contact with the ground and objects while in operation. Each of these impacts produces shock kinetic loads to be transmitted to all the other components attached to it. For this reason, most designers develop the diffuser in the context of "consumable and collapsible" and thus use the destruction of the diffuser as a means of dissipating impact energy thus protecting the more important structural components of the car. If it works then great, but I prefer to design the rear diffuser to be an expected crash part.

As to the author of the thread, I know how much work there is in all the cad work and applaud your efforts here and the stunning renderings. I would caution you to avoid getting trapped in the virtual world and out of the shop. Billy is very correct concerning the pitfalls of FEA on welded structures. It is impossible to exactly model what will actually be the producible end product. Build it, break it, then go back and compare your results to what you predicted and apply what you learn to future analysis, but don't get too distracted from actually building parts by spending too much time sitting in front of the tube as it can be an addicting distraction from actually making parts. (unless you are using it as an exercise to build a CAD skills portfolio.) Beautiful work by the way.

Corey
SCT Sports Cars

[JJLudemann]

It looks like the crossbars connected the two legs of the wishbone are solidly welded. That will put a hard constraint on the position of the inner rod ends. Is that your intent?

Nothing wrong with that if you have some other way to adjust caster or square up your suspension geometry (shims under your inner clevises? slotted mounts?). But you need some way of allowing for deviation from the exact design position of your mounting points and wishbones.

Nathan

You're correct that the crossbars are welded in. There are spacers under the inner clevises that could be adjusted, but my hope is that the lower outer spherical joint will be the fixed point about which everything else will be adjusted. If that fails, I can always cut and reweld the crossbar or install some sort of adjuster. Since it's only use is in a crash, I wanted the crossbar to be hella strong.

-Jim

[JJLudemann]

You can use 1/2 x 1/2 square stock on the inside to crush against for squashing 1" tube (if I remember correctly), but will need something wider and thicker on the outside (you need the bending stiffness there). Be aware that this technique will often leave the upper and lower surfaces slightly concave, so don't panic if you see that in your first tries.

I'm just not comfortable with attempting that. I plan on forming airfoils from thin sheet steel and welding them onto the A-arms for stiffening purposes. I think this brings up an inconsistency in the FB rules, which specifically allow A-arms in the shape of a symmetrical airfoil but don't allow movable aerodynamic devices. If that means faired A-arms can only be fabricated from airfoil-shaped tubing, that's not in keeping with trying to keep FB cars inexpensive. Real airfoil-shaped tubing is seriously expensive. It seems to me that fiberglass or plastic fairings on the A-arms should be allowed.

-Jim

[JJLudemann]

Thanks to Wren, S Lathrop, RobLav, Mike B, G Hickman, starkejt, and R Pare for all the help on the OZ/Van Diemen drive pins.

ApexSpeed is great!

-Jim

[JJLudemann]

Dustin, You are right, There is a reason cars have evolved to both hanging the diffuser from the wing mount boom and supporting the aft bodywork also from the same structure. That is what has proved to work the best over time for both formula cars and sport prototypes as well. The bodywork, both upper and the diffuser must be considered as consumable items and thus are expected to be compromised through normal operation. In contrast the wing boom is to be considered the least consumable structural member at the rear of the car and it make sense to mount the other elements to this structure.

If you put a lot of effort into making the diffuser your structural foundation at the aft of the car, then my gut tells me that you are asking for parts flying every which way when it suffers impact damage. Also the diffuser and its strakes continuously make contact with the ground and objects while in operation. Each of these impacts produces shock kinetic loads to be transmitted to all the other components attached to it. For this reason, most designers develop the diffuser in the context of "consumable and collapsible" and thus use the destruction of the diffuser as a means of dissipating impact energy thus protecting the more important structural components of the car. If it works then great, but I prefer to design the rear diffuser to be an expected crash part.

As to the author of the thread, I know how much work there is in all the cad work and applaud your efforts here and the stunning renderings. I would caution you to avoid getting trapped in the virtual world and out of the shop. Billy is very correct concerning the pitfalls of FEA on welded structures. It is impossible to exactly model what will actually be the producible end product. Build it, break it, then go back and compare your results to what you predicted and apply what you learn to future analysis, but don't get too distracted from actually building parts by spending too much time sitting in front of the tube as it can be an addicting distraction from actually making parts. (unless you are using it as an exercise to build a CAD skills portfolio.) Beautiful work by the way.

Corey
SCT Sports Cars

Thanks, I'll keep all that in mind when I design the details of the rear wing/impact attenuator/diffuser, which hasn't been done yet.

Sorry if it seems like I spend too much time designing and too little time building. I come from an industry where we could spend two years designing a product that would take an afternoon to build (not counting chip fab time, but that was done by robots in a big factory elsewhere). Don't worry, it's coming.

-Jim

[JJLudemann]

Here's an update to my blog detailing the process I went through to design the suspension uprights, resulting in this nifty 3D-printed master pattern for an aluminum casting:

http://ludemannengineering.com/2012/...ght-3-d-print/

Enjoy!

-Jim

[provamo]

just a comment....that "cylinder protruding from the 3-D print" is called a sprue not a gate

[Fatoldman7]

Funny this post came up, I was thinking about the possibility of casting a few parts that I have in mind for my car. My lack of casting high performance parts shut down my foundry dreams. I have done foundry work casting sculpture, and jewelry, but casting an upright for a race car is another matter. What would be the recommended alloy(365?), and post heat treatment be for an upright, and what design changes would be made to a part that was going to be cast, versus machined from billet. In the end I would rather watch my cutter wiz around my CNC machine, than to go to the bother of casting a part, only to see thousands of tiny porosity bubbles when I cut off the sprue!

[R. Pare]

I'm just not comfortable with attempting that. I plan on forming airfoils from thin sheet steel and welding them onto the A-arms for stiffening purposes. I think this brings up an inconsistency in the FB rules, which specifically allow A-arms in the shape of a symmetrical airfoil but don't allow movable aerodynamic devices. If that means faired A-arms can only be fabricated from airfoil-shaped tubing, that's not in keeping with trying to keep FB cars inexpensive. Real airfoil-shaped tubing is seriously expensive. It seems to me that fiberglass or plastic fairings on the A-arms should be allowed.

-Jim

Flattened and oval drawn tubing is allowed as well as the drawn airfoil tubing, so it is up to the manufacturer just how much money he wants to spend. Each type has had extensive use over the years by different manufacturers

Add-on 'glass fairings are not considered suspension - a prerequisite is that it has to help support the chassis, meaning essentially that if you remove it, the chassis falls to the ground.

Since it is not suspension, it can only be considered to be bodywork, and therefore would be subject to the rules governing such.

As for aerodynamic devices, I'd have to go back to the Glossary, but I think that it defines them as creating downforce, which symmetrical aero tubing does not do when set symmetrical to the direction of the airflow.

[R. Pare]

Funny this post came up, I was thinking about the possibility of casting a few parts that I have in mind for my car. My lack of casting high performance parts shut down my foundry dreams. I have done foundry work casting sculpture, and jewelry, but casting an upright for a race car is another matter. What would be the recommended alloy(365?), and post heat treatment be for an upright, and what design changes would be made to a part that was going to be cast, versus machined from billet. In the end I would rather watch my cutter wiz around my CNC machine, than to go to the bother of casting a part, only to see thousands of tiny porosity bubbles when I cut off the sprue!

A356 would be the minimum alloy I would want to use - it is equivalent to 6061-T6 when heat treated to the T6 condition - but would prefer A206 if I could get my hands on it (equivalent to 7075-T6 when heat treated to the T6 condition). I use A206 for my large quickchange differential bodies, cast at Ward Aluminium up in Ft. Wayne, IN. They use the in-gate and riser cutoffs from the Corvette a-arm castings, which helps get the material cost down quite a bit.

For doing one-offs of only small production runs, using either 6061-T6 or 7075-T6 (or T651) will be far easier, faster, and cheaper. Naturally, the design needs to be compatible for the alloy you use.

If you go with 7075, it will definitely need some sort of corrosion protection, but do not anodize it - anodizing will drop the fatigue limit by 50%. Instead, have it iridited. Iriditing can be done on a variety of alu alloys ( it's a chemical chromate conversion process).

[Christopher Crowe]

I got some 7075, and then, without marking it, tossed it into my small shop repository that contained all else -- 2024, 6061 etc.

Is it now forever lost... or is there some way of knowing which pieces are the super alloy without having a microscope and a lab full of metalurgists to look at it?

Thanks,

Chirs

[starkejt]

Cut it in half and weld the 2 pieces back together. If it fails when subjected to the slightest of loads, there's a good chance it is 7075.