CORRECTION - @21:44 I make a statement where I was puzzled why Lotus did not carry thru the S300 gear lever mods to the later Esprits. It seems that is an incorrect statement and that later chassis DID infact have this modification. I have a 1997 GT3 off site which I was certain did not have this modification but I will double check and make a correction video if necessary along with any investigations into any metal fatigue in this area. Apologies for any confusion.
I admire what you've done by creating the cad model and then running simulations on it. It's the sort of content which is extremely valuable and extremely rare at the same time. I wish you all the best and hope you continue on UA-cam, it takes perseverance to get traction here but it's worth it.
Excellent!!! Thank you for taking the time to do this. It is such a treat to see this much quality work and attention being given to a well deserving subject.
@@JonHimself in F1 the bulk head and cutout driver area are extremely thick and reinforced This clearly demonstrates why holes in a monocoque extremely compromise its integrity Its an egg after all
The satisfaction when simulations correlates with reality. In a close enough manner to be trusted for further investigations. 👍 Congratulations to a job well done and very interesting videos. I know fairly well how much work it is to reach such results. Appreciate it!
Yep, I usually do FEA studies to ensure something doesn't fail after it's designed, so it's nice to get some confirmation against something that has damaged. I was pretty shocked and very happy with the result that I tested it a few times to check. I also had a good teacher which helps. Roll cage FEA is incoming, probably sometime in the new year.
I have an '89 Esprit SE with high mileage, and I'm disappointed with it's torsional rigidity compared to several previous (lower mileage) Esprits I owned in the past. Thanks for explaining the problem, and how to address it. All your efforts to produce this great video are much appreciated! I look forward to your future videos concerning chassis modifications and roll cage structure.
Yes it was a bit of an eye opener, I'd love to do a physical test on the chassis as well if I can clamp the wheels down. More to come when I get the time as I am fighting deadlines right now.
Hello John that is a fantastic video. I actually have an Elite but the 2 chassis's seem pretty similar just reversed so to speak. The gear lever hole reinforcement plate seems like a pretty chunky piece of engineering. Would putting a series of holes in it with a hole saw make much difference to its performance. Obviously a series of holes would help in terms of its weight. The other options would seem to be a carbon fiber plate or a welded steel rectangle with a ring in it for the gear level to pass through and diagonals welded from each corner of the rectangle to the ring. The other obvious thing I think would be bracing to the the actual box section itself . Not to overcome the gear lever hole but to improve its rigidity over all. Obviously the plumbing issues would be a problem but I have thought before that a series of welded rectangles with an X welded from corner to corner would be interesting. The idea being that a series of slots would be cut across the box section side to side , the rectangles pushed down into the box section and then welded in across the top and the other 3 sides spot welded through the chassis. The plumbing though would be a slight issue haha last I checked no one has invented bluetooth coolant pipes 🙂 Carbon fibre is stated to be " five-times stronger than steel and twice as stiff" according to Doctor Google so making the gear lever plate from that would seem to be a good idea
Its not as chunky as you'd expect, you're looking at a plate that weighs no more than 600 grams so its benefits way out perform the weight penalty. With design everything is a balance between effectiveness / cost / weight / simplicity. A steel plate cost £10 in materials, and a relatively unskilled person to make. A carbon plate cost many times the cost, and needs skilled people to produce and cure in an autoclave something of similar strength. The saving is weight...but you're only looking at grams. The reason why I did this video was to show this outlook. Lotus solution is clearly thought out, cheap and works very well. Welding internal structures and so on is costly, huge weight detriment for little gains. The back bone suffers from lack of torsional resistance by its sheer design, very little can be done to easily remedy that - you're simply too close to the neutral / torsion axis. The most cost effective way is a roll cage or re-enforcement of the body in some way.
@@JonHimself hi John valid points but Making it from carbon fiber would be easy. Applying vacuum and heat is nice but not necessary. For a simple rectangle you just cut a number of pieces layer them in a simple mould and wet through with a paint brush. The mould could just be made from Styrofoam and a hot glue gun to stick it together and a layer of material the cured piece will not stick to
I am soooo subscribed to this!!! Can't wait to see roll cage simulations. I wonder how close to a europa the torsional rigidity will get??? Thanks for the Vlog.
Sims coming soon, I've done a few but need the time to put them into a video. Which Europa do you refer to ? the old one or the one based on the Elise?
@@JonHimself I'm sorry. The model you referenced in the video was the evora! The magic will be getting the cage and body to exist in harmony I suppose. I remember seeing an X180R and the roll cage was so well integrated but just bolted onto the chassis.
@@jwdiho oh yes the Evora. I doubt I can get close to that. The issue is the compromise between rigidity / strength and weight. The Esprit design doesn't lend itself to this well in my opinion as there are 3 elements to the structure, the chassis, body and cage all with their interfaces and limits and fits. What is important to consider though is the vehicle mass, as it is this that imparts forces on the structure so reducing that will be the same as increasing relative rigidity. If I make a cage super strong, it'll be heavy and high on the centre of gravity, so you see there is likely a sweet spot to be had. The X180R is probably better than you think, bolting isn't the issue, it's the compromise in the design for practicality / servicing. Luckily as a one off I can overlook those consideration on this project and get closer to the race cars.
Thanks for posting this. I was looking at the shift lever on my Esprit and found a crack in the exact same spot. We decided to bolt the body to the front and back of the chassis opening. thought about it a lot, but I couldn't remove the body, so I put steel nut inserts in the front and back of the chassis opening, drilled holes in a 20mm aluminum square bar for the bolts to pass through, and used washers to adjust the gap. Holes were drilled in the upper part of the body tunnel and fastened with three bolts on each side to hold it in place stiffly. (Remove the rubber boot and mounting plate.) As a result, the squeak noise was drastically reduced and the body rigidity was increased. I should have seen this video earlier.
Interesting work around. The test would be to see if the crack propagated further over the miles but you're supporting the collapsing element so it makes sense to me. - stay tuned for updates to this next year when I'm gonna look at bonding a plate on to increase the rigidity.
@@JonHimself Thanks for the reply. I look forward to next year's video. There is a supplement. It seems to be called a rivet nut, not a nut insert, and the size is M6. Since I don't have a rivet nut tool I put a long bolt and a piece of aluminum block over the rivet nut to prevent the rivet nut from turning and I was able to expand the rivet nut inside by turning the nut attached to the bolt while passing a 9mm pipe through it to prevent the bolt from turning. The shift lever mechanism plate, which is normally fixed with rubber bushings, was removed and made rigid and tightened to contribute to the rigidity of the mechanism. (Although the effect is questionable) My Esprit had a crack in the FRP at the joint between the rear of the chassis and the body and was separated, so I connected it to the body with L-fittings. I connected it to the body . This reduced the vibration of the rear part drastically. This area also needs to be checked. This suggests that the body also contributes to rigidity.
@@esprit_hc8885 yep without a doubt the body contributes but the issue is stiffness vs strength. FRP is strong but not necessarily stiff. You know that when you jack the car up and the body bends / shut lines start to close - moving the bare shell around by hand as well, you can feel the flex in it. So whilst it does something, without testing, I don't think it's overly significant especially at the rear which has a huge cut out in it for the engine. Sadly without a full scan of the shell I wouldn't be able to guess.
I stumbled across your project and thought you might want to see one way the hole in an Esprit chassis was addressed. This was an S4s. IIRC, Lotus started adding the plate about 20 cars after mine. Honestly, I never considered the galvanization issue. I sourced the OEM plate from Lotus and handed it to a local fabricator with the requirements "put this on". His solution was delightful overkill IMHO. He didn't like the plate I had dutifully waited months for and cut his own, after fabricating a fitted insert. I'll post a link separately (not sure if YT lets them through).
Thank you that very interesting analysis. I have an S3 that came into my possession with air-ride suspension (slammed or stanced) and a 24V Busso in the back. In looking for replacement suspension, I found that the spring rates increased by more that 100% over the years. Stock front spring rate on an S3 is something like 110-120 lb/in and the rate that GAZ were quoting was over 300. I recall the rule of thumb was that the chassis stiffness did not need to be more that 10 times greater that the roll stiffness of the suspension. Part of the reason for the increase in spring rate was to control the greater unsprung weight of the larger wheels, tryes and brakes fitted to later cars.
Yup 300 lbs is harsh especially when you can control the damping rates. I am going to look into the maths behind the suspension fairly soon, I have not chosen spring rates yet but I might combine it with some of the findings here to produce a similar technical video.
Bravo, well done Jon! I have too many thoughts after seeing your demonstration. It sold me on a shifter reinforcement plate. I have spent a lot of time questioning just how well this frame design holds up and now I know. I am interested quite a bit when you have the body attached as a system how well it performs. From observation one can tell they tried to reinforce certain points of the body, but I am curious how successful it really is. I thank you so much for doing all this work and sharing it with the commuting. Keep it coming as it is such valuable information none of us have.
I think the gear lever plate is a must for the old cars. The issue with the body and with composites in general is the tolerance, to get it to work you need to bolt things together tightly and you just dont see that in the Esprit body due to the fit. It definitely adds something to the chassis but as I say without a decent model or ideas of the layups I cant really tell right now, maybe 1,500Nm / degree. What I would like to do is back this up with a physical test to get predicted, simulated and actual results all in a row - but I lack the equipment here to do that here. This isn't meant to be a definitive answer but where ever the rumored value of 5800Nm ish came from.... I got shockingly close to it.
Very interesting video. Essential reading is the Lotus 25 book by John Tipler (no affiliation)...who describes how Colin Chapman / Cheshunt stumbled on the torsion box while developing the Elan. What remains an eternal mystery is why Eric Broadley copied the torsion box idea for the Ford GT (with one on each side of the cockpità...but Colin did not for the 30, the 40, the 46...Esprit. I am building an Elan GTS and there are a few similar subjects. The Elan chassis has some welded in flanged parts within the torsion box which I believe could be interesting to put into your project. However, the Elan also has pressed holes in what seem to be poor locations...probably to help production.
Great comment, I was thinking the same thing when I did this study - how it could have been done differently and the only thing that came to mind was splitting the chassis in two and putting it either side. The body of the esprit itself is sort of designed this way but I was thinking more about something similar to the Elise (tub chassis). The issue with anything inside the Esprit tunnel / backbone, is all the coolant pipes, and a lot of work. A modification to the gear lever aperture, safety cage and significant weight loss should provide me with enough rigidity.
@@JonHimself It might be worth you looking at the Miura and the Stratos designs. Many other mid-engine cars simply continued with bird cages. Part of the answers are in the relative weights of the chassis. My 26R chassis weighs 38kg (the cage alone will add 32kg and the body a whopping 45kg (without the doors, roof panels).
@@Andrew-vx2ls when you look at the ultimate Esprit (V8 GT1 that raced with the McLaren F1s) the chassis is almost a space frame, almost indistinguishable from the original chassis. Another chassis that interests me was the Noble M12. Cant wait to get into this part of the project, its going to be really interesting. Those weights for the Elan are crazy, amazing car - I tried getting my hands on one in the past but the right one didnt come along.
Shell using 'sheet metal' and weldments. I had probs with 3 component stacks (chassis / bolt plate / capping plate) so I was tempted to go solid but it runs a lot quicker and more stable this way.
@@TheOnlyMosesMalone thanks, I was really happy with the results as it proves the software and method, but I also have other collaborating data, such as the damage and the 'rumored' torsion values. The fact they all correlate is really satisfying and can lead to improvements later.
Did you try running the simulation with the reinforcing plate on a chassis with cracks/stress risers? Wondering if that might guide you/others whether to undertake sheet metal repairs or just reinforce with the plate…
thank you very much! I (only) have a '85 s3 but am planning to close the gear hole as well, I copied the stiffening plate between the T and backbone as well, wonder what that does, had an broken weld in this area on a friends chassis so when I had to work on my chassis I just welded it in. if it is good for the later esprit it is good for my s3 as well...
I'm no S3 expert but I think your chassis is not galvanised, but if you can hold out I am going to do a study on the modification to that gear lever aperture where I will compare welding to bonding. Bonding has significant advantages where toy wont put heat into the original metal and affect its performance. From a brief observation the underside stiffening plate helps shore up the sheer between the front cross member and the tunnel which want to always move in opposite directions (if if you took all the welds off the tunnel would fall to the ground. It also likely provides stress relief at the butt welded interface between the tunnel and cross member for things like when a single wheel hits a pot hole or bouncing up a kerb. Remember Lotus would have only had their expertise, experience and physical testing to sort these issues, not the tools we have today - and they didn't have the biggest budgets to work on by a long shot. This makes me appreciate the chassis design even more, its a masterful piece of design.
@@JonHimself thanks Jon for the quick reply, the S3 was the first esprit to be galvanised. my '85 S3 has nearly the same front and rear as the later ones. (trunniunless front with vented brake discs) after I found that broken weld I saw what lotus had done on the later esprit chassis to make that part stronger. I had heard about the weakness in the gear lever but was surprised how bad it was.
Bravo! Fascinating. I am very curious to see if a minimal roll cage structure will raise the torsional stiffness to say 20000 Nm/degree. I was all excited until you showed the comparison to a modern car.... )-: It would be fascinating to know what level the factory went to when figuring out the benefits of the gear lever plate and the engine bay brace. Do you suppose they fabricated and installed the parts and then loaded the chassis to failure? I dont think there was any way to calculate it on such a complex structure back then. As always - thanks so much for doing this stuff! I know its going to pay off for you in the end. Some day soon you will be playing with Ferraris and Porsche GT3 RS - leaving us pedestrian Esprit lovers in the gutter!
Hi Erik - It depends how full on you wanna go with the cage. I want a race car for the road so I'm not even going to have a passenger seat therefore I can also have a petty bar. That is going to REALLY increase the rigidity. Also have a look at the Esprit GT1 vs the GT2 roll cage (pictures are about somewhere) they are two different designs. They probably did physical tests, anchoring the rear down and then jacking the front and looking at a load cell or hydraulic pressure (thats how I'd do it) and measuring the deflections. Plus accelerated ageing tests like driving it over cobbles etc (see the Elise Story video) to shake it down. You buy a Lotus for the handling imo and the Esprit does that very well, even with circa 6,000Nm / deg. We all get obsessed with numbers at some point but for me it is just fact finding, not top trumps. The Evora is really next level, I've never driven anything like it since, it's like it has active suspension, its a stunning car to drive. After the work I have in the GT2 I doubt I'll ever get rid of it - it is part of me now which is why I am putting so much effort into it.
@@JonHimself Yeah, I bet they loaded the chassis and saw the buckling around the gear lever opening like your model showed. Immediately went there and reinforced. That has me thinking - Assuming they did physical tests as you describe, I wonder if they had failure in the rear related to the parts you had to remove from the model (tie in pieces) for simplicity? Then when they added the rear brace the failure in this area was reduced or delayed?. After watching your demo I dont see how the rear engine brace was worth the headache and cost. maybe that is why they never moved forward on the S4s with the brace?
@@eriklombard322 tbh we're just guessing but as I say in the video I am not sure why they didnt fit the gear lever plate on ALL Esprits. That said car manufacturers are not in the business of making cars last a life time - 100,000 miles in and the last time I drove the GT2 in its SE guise it was fine, very spritely - so job done. I dont think there is a weakness in the rear - again guessing but I think they might have put the rear brace in there for a lot of marketing - yes it works but it's not a huge gain vs the cost and weight / CG. I think you're right which is why you dont see it on the V8 or the S350.
good question - I mentioning this at 18:08 The simulation assumed an infinitely rigid beam between the two suspension points as shown by the thin purple line and the 'pin' in the centre. This is the 'jig' if you like which applies the torque to the suspension mounts, the 'pin' being the centre of rotation where the torque is applied. I was running out of time to simulate this to an nth degree as explained. The rear cross member has shown zero stress on the real part and when briefly studied it is extremely strong in compression as one might expect. So it is taken into account, even if it is assumed to be infinitely rigid - it is just assumed to have no significant impact. Simulations are fun but there becomes a point of real diminishing returns.
@@themikegriese np, I take it you mean the S300 rear engine brace? I personally don't need one as I am going full roll cage but I know a few people who are interested in the design and possibly replicating it.
Well, YT wouldn't let me post. If you see this and you're interested, share another way to connect and I'll send the page. Alternately, a guy named Zig on LotusTalk owns the car and would be easy to track down but I'm not sure he has the original pics.
CORRECTION - @21:44 I make a statement where I was puzzled why Lotus did not carry thru the S300 gear lever mods to the later Esprits. It seems that is an incorrect statement and that later chassis DID infact have this modification. I have a 1997 GT3 off site which I was certain did not have this modification but I will double check and make a correction video if necessary along with any investigations into any metal fatigue in this area. Apologies for any confusion.
Brought here by a commenter on Soup Classic Motoring.
Same here.
I admire what you've done by creating the cad model and then running simulations on it. It's the sort of content which is extremely valuable and extremely rare at the same time. I wish you all the best and hope you continue on UA-cam, it takes perseverance to get traction here but it's worth it.
Excellent!!! Thank you for taking the time to do this. It is such a treat to see this much quality work and attention being given to a well deserving subject.
Too kind :)
Glad you enjoyed it - more to come.
@@JonHimself in F1 the bulk head and cutout driver area are extremely thick and reinforced
This clearly demonstrates why holes in a monocoque extremely compromise its integrity
Its an egg after all
The satisfaction when simulations correlates with reality. In a close enough manner to be trusted for further investigations. 👍
Congratulations to a job well done and very interesting videos.
I know fairly well how much work it is to reach such results. Appreciate it!
Yep, I usually do FEA studies to ensure something doesn't fail after it's designed, so it's nice to get some confirmation against something that has damaged. I was pretty shocked and very happy with the result that I tested it a few times to check. I also had a good teacher which helps. Roll cage FEA is incoming, probably sometime in the new year.
I have an '89 Esprit SE with high mileage, and I'm disappointed with it's torsional rigidity compared to several previous (lower mileage) Esprits I owned in the past. Thanks for explaining the problem, and how to address it. All your efforts to produce this great video are much appreciated! I look forward to your future videos concerning chassis modifications and roll cage structure.
Yes it was a bit of an eye opener, I'd love to do a physical test on the chassis as well if I can clamp the wheels down. More to come when I get the time as I am fighting deadlines right now.
Hello John that is a fantastic video. I actually have an Elite but the 2 chassis's seem pretty similar just reversed so to speak. The gear lever hole reinforcement plate seems like a pretty chunky piece of engineering. Would putting a series of holes in it with a hole saw make much difference to its performance. Obviously a series of holes would help in terms of its weight. The other options would seem to be a carbon fiber plate or a welded steel rectangle with a ring in it for the gear level to pass through and diagonals welded from each corner of the rectangle to the ring.
The other obvious thing I think would be bracing to the the actual box section itself . Not to overcome the gear lever hole but to improve its rigidity over all. Obviously the plumbing issues would be a problem but I have thought before that a series of welded rectangles with an X welded from corner to corner would be interesting. The idea being that a series of slots would be cut across the box section side to side , the rectangles pushed down into the box section and then welded in across the top and the other 3 sides spot welded through the chassis. The plumbing though would be a slight issue haha last I checked no one has invented bluetooth coolant pipes 🙂
Carbon fibre is stated to be " five-times stronger than steel and twice as stiff" according to Doctor Google so making the gear lever plate from that would seem to be a good idea
Its not as chunky as you'd expect, you're looking at a plate that weighs no more than 600 grams so its benefits way out perform the weight penalty.
With design everything is a balance between effectiveness / cost / weight / simplicity.
A steel plate cost £10 in materials, and a relatively unskilled person to make. A carbon plate cost many times the cost, and needs skilled people to produce and cure in an autoclave something of similar strength. The saving is weight...but you're only looking at grams.
The reason why I did this video was to show this outlook. Lotus solution is clearly thought out, cheap and works very well. Welding internal structures and so on is costly, huge weight detriment for little gains. The back bone suffers from lack of torsional resistance by its sheer design, very little can be done to easily remedy that - you're simply too close to the neutral / torsion axis. The most cost effective way is a roll cage or re-enforcement of the body in some way.
@@JonHimself hi John valid points but Making it from carbon fiber would be easy. Applying vacuum and heat is nice but not necessary. For a simple rectangle you just cut a number of pieces layer them in a simple mould and wet through with a paint brush. The mould could just be made from Styrofoam and a hot glue gun to stick it together and a layer of material the cured piece will not stick to
I am soooo subscribed to this!!! Can't wait to see roll cage simulations. I wonder how close to a europa the torsional rigidity will get??? Thanks for the Vlog.
Sims coming soon, I've done a few but need the time to put them into a video. Which Europa do you refer to ? the old one or the one based on the Elise?
@@JonHimself I'm sorry. The model you referenced in the video was the evora! The magic will be getting the cage and body to exist in harmony I suppose. I remember seeing an X180R and the roll cage was so well integrated but just bolted onto the chassis.
@@jwdiho oh yes the Evora. I doubt I can get close to that. The issue is the compromise between rigidity / strength and weight. The Esprit design doesn't lend itself to this well in my opinion as there are 3 elements to the structure, the chassis, body and cage all with their interfaces and limits and fits.
What is important to consider though is the vehicle mass, as it is this that imparts forces on the structure so reducing that will be the same as increasing relative rigidity. If I make a cage super strong, it'll be heavy and high on the centre of gravity, so you see there is likely a sweet spot to be had.
The X180R is probably better than you think, bolting isn't the issue, it's the compromise in the design for practicality / servicing. Luckily as a one off I can overlook those consideration on this project and get closer to the race cars.
Thanks for posting this. I was looking at the shift lever on my Esprit and found a crack in the exact same spot. We decided to bolt the body to the front and back of the chassis opening. thought about it a lot, but I couldn't remove the body, so I put steel nut inserts in the front and back of the chassis opening, drilled holes in a 20mm aluminum square bar for the bolts to pass through, and used washers to adjust the gap. Holes were drilled in the upper part of the body tunnel and fastened with three bolts on each side to hold it in place stiffly. (Remove the rubber boot and mounting plate.) As a result, the squeak noise was drastically reduced and the body rigidity was increased. I should have seen this video earlier.
Interesting work around. The test would be to see if the crack propagated further over the miles but you're supporting the collapsing element so it makes sense to me. - stay tuned for updates to this next year when I'm gonna look at bonding a plate on to increase the rigidity.
@@JonHimself Thanks for the reply. I look forward to next year's video.
There is a supplement. It seems to be called a rivet nut, not a nut insert, and the size is M6. Since I don't have a rivet nut tool I put a long bolt and a piece of aluminum block over the rivet nut to prevent the rivet nut from turning and I was able to expand the rivet nut inside by turning the nut attached to the bolt while passing a 9mm pipe through it to prevent the bolt from turning.
The shift lever mechanism plate, which is normally fixed with rubber bushings, was removed and made rigid and tightened to contribute to the rigidity of the mechanism. (Although the effect is questionable)
My Esprit had a crack in the FRP at the joint between the rear of the chassis and the body and was separated, so I connected it to the body with L-fittings. I connected it to the body . This reduced the vibration of the rear part drastically. This area also needs to be checked.
This suggests that the body also contributes to rigidity.
@@esprit_hc8885 yep without a doubt the body contributes but the issue is stiffness vs strength. FRP is strong but not necessarily stiff. You know that when you jack the car up and the body bends / shut lines start to close - moving the bare shell around by hand as well, you can feel the flex in it. So whilst it does something, without testing, I don't think it's overly significant especially at the rear which has a huge cut out in it for the engine. Sadly without a full scan of the shell I wouldn't be able to guess.
I stumbled across your project and thought you might want to see one way the hole in an Esprit chassis was addressed. This was an S4s. IIRC, Lotus started adding the plate about 20 cars after mine. Honestly, I never considered the galvanization issue. I sourced the OEM plate from Lotus and handed it to a local fabricator with the requirements "put this on". His solution was delightful overkill IMHO. He didn't like the plate I had dutifully waited months for and cut his own, after fabricating a fitted insert. I'll post a link separately (not sure if YT lets them through).
Great bit of work Jon, fantastic effort and attention to detail 👏 👍
Thanks for your help 💯
Thank you that very interesting analysis.
I have an S3 that came into my possession with air-ride suspension (slammed or stanced) and a 24V Busso in the back. In looking for replacement suspension, I found that the spring rates increased by more that 100% over the years. Stock front spring rate on an S3 is something like 110-120 lb/in and the rate that GAZ were quoting was over 300. I recall the rule of thumb was that the chassis stiffness did not need to be more that 10 times greater that the roll stiffness of the suspension. Part of the reason for the increase in spring rate was to control the greater unsprung weight of the larger wheels, tryes and brakes fitted to later cars.
Yup 300 lbs is harsh especially when you can control the damping rates.
I am going to look into the maths behind the suspension fairly soon, I have not chosen spring rates yet but I might combine it with some of the findings here to produce a similar technical video.
Really interesting analysis. A return on the gearshift reinforcing plate looks like a good idea to me.
Yep, nice thing is you can try different designs on a bolt on part, or replace it if it deforms.
Wow... FEA has come a long way since I was at uni in the early 90's where we left the computer models running over the weekend for one simulation!!!
Bravo, well done Jon! I have too many thoughts after seeing your demonstration. It sold me on a shifter reinforcement plate. I have spent a lot of time questioning just how well this frame design holds up and now I know. I am interested quite a bit when you have the body attached as a system how well it performs. From observation one can tell they tried to reinforce certain points of the body, but I am curious how successful it really is.
I thank you so much for doing all this work and sharing it with the commuting. Keep it coming as it is such valuable information none of us have.
I think the gear lever plate is a must for the old cars. The issue with the body and with composites in general is the tolerance, to get it to work you need to bolt things together tightly and you just dont see that in the Esprit body due to the fit. It definitely adds something to the chassis but as I say without a decent model or ideas of the layups I cant really tell right now, maybe 1,500Nm / degree.
What I would like to do is back this up with a physical test to get predicted, simulated and actual results all in a row - but I lack the equipment here to do that here.
This isn't meant to be a definitive answer but where ever the rumored value of 5800Nm ish came from.... I got shockingly close to it.
Very well done and informative video mate
Glad you enjoyed it.
Very interesting video. Essential reading is the Lotus 25 book by John Tipler (no affiliation)...who describes how Colin Chapman / Cheshunt stumbled on the torsion box while developing the Elan. What remains an eternal mystery is why Eric Broadley copied the torsion box idea for the Ford GT (with one on each side of the cockpità...but Colin did not for the 30, the 40, the 46...Esprit.
I am building an Elan GTS and there are a few similar subjects. The Elan chassis has some welded in flanged parts within the torsion box which I believe could be interesting to put into your project. However, the Elan also has pressed holes in what seem to be poor locations...probably to help production.
Great comment, I was thinking the same thing when I did this study - how it could have been done differently and the only thing that came to mind was splitting the chassis in two and putting it either side. The body of the esprit itself is sort of designed this way but I was thinking more about something similar to the Elise (tub chassis).
The issue with anything inside the Esprit tunnel / backbone, is all the coolant pipes, and a lot of work. A modification to the gear lever aperture, safety cage and significant weight loss should provide me with enough rigidity.
@@JonHimself It might be worth you looking at the Miura and the Stratos designs. Many other mid-engine cars simply continued with bird cages. Part of the answers are in the relative weights of the chassis. My 26R chassis weighs 38kg (the cage alone will add 32kg and the body a whopping 45kg (without the doors, roof panels).
@@Andrew-vx2ls when you look at the ultimate Esprit (V8 GT1 that raced with the McLaren F1s) the chassis is almost a space frame, almost indistinguishable from the original chassis. Another chassis that interests me was the Noble M12. Cant wait to get into this part of the project, its going to be really interesting.
Those weights for the Elan are crazy, amazing car - I tried getting my hands on one in the past but the right one didnt come along.
Very interesting, thanks!
Thanks much!
Good effort
question: if you see the stress on the hole of the gearlever plate why not dimple the hole?
Really interesting video Jon and some good results. Was that a shell or solid mesh you used for the beam?
Shell using 'sheet metal' and weldments. I had probs with 3 component stacks (chassis / bolt plate / capping plate) so I was tempted to go solid but it runs a lot quicker and more stable this way.
@@JonHimself I'd say that's a fair assumption and the results look great!
@@TheOnlyMosesMalone thanks, I was really happy with the results as it proves the software and method, but I also have other collaborating data, such as the damage and the 'rumored' torsion values. The fact they all correlate is really satisfying and can lead to improvements later.
Did you try running the simulation with the reinforcing plate on a chassis with cracks/stress risers? Wondering if that might guide you/others whether to undertake sheet metal repairs or just reinforce with the plate…
thank you very much! I (only) have a '85 s3 but am planning to close the gear hole as well, I copied the stiffening plate between the T and backbone as well, wonder what that does, had an broken weld in this area on a friends chassis so when I had to work on my chassis I just welded it in. if it is good for the later esprit it is good for my s3 as well...
I'm no S3 expert but I think your chassis is not galvanised, but if you can hold out I am going to do a study on the modification to that gear lever aperture where I will compare welding to bonding. Bonding has significant advantages where toy wont put heat into the original metal and affect its performance.
From a brief observation the underside stiffening plate helps shore up the sheer between the front cross member and the tunnel which want to always move in opposite directions (if if you took all the welds off the tunnel would fall to the ground. It also likely provides stress relief at the butt welded interface between the tunnel and cross member for things like when a single wheel hits a pot hole or bouncing up a kerb.
Remember Lotus would have only had their expertise, experience and physical testing to sort these issues, not the tools we have today - and they didn't have the biggest budgets to work on by a long shot. This makes me appreciate the chassis design even more, its a masterful piece of design.
@@JonHimself thanks Jon for the quick reply, the S3 was the first esprit to be galvanised. my '85 S3 has nearly the same front and rear as the later ones. (trunniunless front with vented brake discs) after I found that broken weld I saw what lotus had done on the later esprit chassis to make that part stronger. I had heard about the weakness in the gear lever but was surprised how bad it was.
Bravo! Fascinating. I am very curious to see if a minimal roll cage structure will raise the torsional stiffness to say 20000 Nm/degree. I was all excited until you showed the comparison to a modern car.... )-: It would be fascinating to know what level the factory went to when figuring out the benefits of the gear lever plate and the engine bay brace. Do you suppose they fabricated and installed the parts and then loaded the chassis to failure? I dont think there was any way to calculate it on such a complex structure back then.
As always - thanks so much for doing this stuff! I know its going to pay off for you in the end.
Some day soon you will be playing with Ferraris and Porsche GT3 RS - leaving us pedestrian Esprit lovers in the gutter!
Hi Erik - It depends how full on you wanna go with the cage. I want a race car for the road so I'm not even going to have a passenger seat therefore I can also have a petty bar. That is going to REALLY increase the rigidity. Also have a look at the Esprit GT1 vs the GT2 roll cage (pictures are about somewhere) they are two different designs.
They probably did physical tests, anchoring the rear down and then jacking the front and looking at a load cell or hydraulic pressure (thats how I'd do it) and measuring the deflections. Plus accelerated ageing tests like driving it over cobbles etc (see the Elise Story video) to shake it down.
You buy a Lotus for the handling imo and the Esprit does that very well, even with circa 6,000Nm / deg. We all get obsessed with numbers at some point but for me it is just fact finding, not top trumps.
The Evora is really next level, I've never driven anything like it since, it's like it has active suspension, its a stunning car to drive.
After the work I have in the GT2 I doubt I'll ever get rid of it - it is part of me now which is why I am putting so much effort into it.
@@JonHimself Yeah, I bet they loaded the chassis and saw the buckling around the gear lever opening like your model showed. Immediately went there and reinforced. That has me thinking - Assuming they did physical tests as you describe, I wonder if they had failure in the rear related to the parts you had to remove from the model (tie in pieces) for simplicity? Then when they added the rear brace the failure in this area was reduced or delayed?.
After watching your demo I dont see how the rear engine brace was worth the headache and cost. maybe that is why they never moved forward on the S4s with the brace?
@@eriklombard322 tbh we're just guessing but as I say in the video I am not sure why they didnt fit the gear lever plate on ALL Esprits. That said car manufacturers are not in the business of making cars last a life time - 100,000 miles in and the last time I drove the GT2 in its SE guise it was fine, very spritely - so job done.
I dont think there is a weakness in the rear - again guessing but I think they might have put the rear brace in there for a lot of marketing - yes it works but it's not a huge gain vs the cost and weight / CG. I think you're right which is why you dont see it on the V8 or the S350.
Did you include the rear cross brace when running your simulations? I’t doesn’t appear in your diagrams.
good question - I mentioning this at 18:08
The simulation assumed an infinitely rigid beam between the two suspension points as shown by the thin purple line and the 'pin' in the centre. This is the 'jig' if you like which applies the torque to the suspension mounts, the 'pin' being the centre of rotation where the torque is applied. I was running out of time to simulate this to an nth degree as explained. The rear cross member has shown zero stress on the real part and when briefly studied it is extremely strong in compression as one might expect. So it is taken into account, even if it is assumed to be infinitely rigid - it is just assumed to have no significant impact.
Simulations are fun but there becomes a point of real diminishing returns.
@@JonHimself Thanks - I must've missed that first time around. By the way, I have one of the cradles if you would like some measurements.
@@themikegriese np, I take it you mean the S300 rear engine brace? I personally don't need one as I am going full roll cage but I know a few people who are interested in the design and possibly replicating it.
Well, YT wouldn't let me post. If you see this and you're interested, share another way to connect and I'll send the page. Alternately, a guy named Zig on LotusTalk owns the car and would be easy to track down but I'm not sure he has the original pics.
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