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PostPosted: December 29, 2010, 4:54 pm 
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For purposes of suspension design, I made a preliminary weight ‘guesstimate’:
• 1500 lbs all-up weight (hopefully a conservative figure)
• 47.5% front weight bias (a WAG)

Using measured weights for tires, wheels, uprights, hubs, brakes, rear axle and A- or trailing arms, and estimates for the WOBLink, and coil-overs, I calculated the following:
• For the front:
o Corner weights 356lbs
o Sprung weight (total) 528 lbs
o Initial spring rate, derived from half corner weight, 293 lbs/in*
o Wheel frequency, per Staniforth, p.137, 154 cpm (2.6 Hz)
• For the rear:
o Corner weights 394 lbs
o Sprung weight (total) 493 lbs
o Initial spring rate, derived from half corner weight, 197 lbs/in*
o Wheel frequency, per Staniforth, p. 137, 168 cpm (2.8 Hz)

* Allowing for coil-over slope and a-arm leverage as required

These calculated wheel frequencies appear to be more competition than road-car like according to Staniforth (and are more than the book figures, which seem to be 275 and 175 lbs/in), but I will continue on that basis. I will likely buy coil-over shocks without springs, until I know, or have a better estimate of actual corner weights.

I calculated weight transfer using the formulae given by Staniforth, 4th ed., Chapter 9, after completing several iterations of front suspension geometry design. Staniforth’s process was straight-forward, apart from the need to be careful of the many typos in the book, especially in the formulae themselves. The sample table below uses 3 and 5 inch roll centres (front and rear) and wheel rates based on half of corner weights. The calculation is limited by assumptions, especially of centres of gravity, which were always assumed to be at half of wheel height. The primary goal of the calculation was the roll angle estimate, to ensure that my suspension design process covered a sufficient roll range. With a roll angle in a 1g turn of less than ¾ degree, performing suspension geometry design in the 0 – 2 degree roll range appears satisfactory. It may also suggest use of softer springs, but I will leave those parametric studies until later. I did calculate variations on roll centre, with roll centres of 2 and 4 inches (front and rear) increasing roll angle from 0.69 to 0.78 degrees relative to the basis 3 and 5 inch case.

I have no appreciation of the effects of tire loadings, but with the outer rear tire carrying the most load I imagine there would be a tendency to oversteer; however, earlier cautions about weight and centre of gravity estimates must be remembered. Any comments from the automotive engineers out there?


Attachments:
Sample Weight Transfer Table.jpg
Sample Weight Transfer Table.jpg [ 408.42 KiB | Viewed 3870 times ]

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Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601


Last edited by Warren Nethercote on December 29, 2010, 6:17 pm, edited 1 time in total.
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PostPosted: December 29, 2010, 5:02 pm 
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My starting point for the front suspension is the Isuzu uprights, plus lower A-arms supplied by COLD. The Front hubs were initially set up with the same track width as the rear axle. (Oct/Nov 2010)

The lower A-arms were marked with the outline of Toyota van ball joints, but after buying some I found their studs much too small in diameter for the Isuzu uprights; consequently, I bought another set of Isuzu lower ball joints. The Isuzu lower ball joints are similar in style to the Toyota ones, but required mounting shims to be made for a good fit. I wonder retrospectively about the Toyota ball joints: they would have needed shimming too. The lower A-arms look suspiciously like a close variant of the ‘book’ design (perhaps CMC A-arms?) and may be replaced at some future date with more robust ones that don’t need shimming of the ball joints.

The intention was to determine what I needed in the way of upper A-arms before seeing if COLD would still make them, or buying them commercially, either as adjustable ones from Speedway Motors, or fixed ones, which are available in ½ inch length increments from HRP. After two iterations of suspension design with the string computer, I ordered a set of tubular upper A-arms from Speedway that had some adjustment capability, using four-bar end bushings rather than Heim joints (Nov 2010). The Chev truck ball joints used by the Speedway A-arms were found to be loose in the Isuzu upright, just like the Toyota ones in the lowers. Once again, I adapted the A-arms to stock Isuzu ball joints, this time by plug welding the existing ball joint mounting holes and re-drilling.

A disadvantage of my original tall 205/65R15 tires became apparent when developing suspension geometry: achieving low roll centres would be challenging. As a result, I set a 3 inch roll centre as my front-end target, rather than the oft-suggested 2 inches. The 3 inch front roll centre target simplified my rear suspension design issues by suggesting a rear roll centre of 5 inches, which would be achievable without necessarily going to a Mumford Link.

I used a Staniforth ‘string computer’ for my design process, with 1 inch of bump and 2 degrees of roll as a test case. My first attempts were discouraging: the geometry worked well for the test case, but less so at 2 degrees of roll alone. The first attempt at improved geometry involved increasing the inclination of only the upper A-arm which both shortened the instant arm length and raised the roll centre significantly. Next steps examined variations of the lower A-arm mounts.

After two cycles of experiments with the string computer, a roll centre of 3 inches was obtained, together with good camber performance at 1 inch bump and 2 degrees roll. Roll-only performance was still problematic, so I investigated the effects of caster and kingpin inclination-induced camber (see

viewtopic.php?f=5&t=11512 )

Forum advice suggested that further improvement would be beneficial:

viewtopic.php?f=5&t=11520

so I tried further variations, starting by shortening the upper A-arm. I also increased track to reduce an interference issue for the top A-arm. I made the happy discovery that my required rack length would only be ¾ inch longer than that of the MGB, so that a custom-length rack might not be required if I selected a track intermediate to my two earlier choices.

At about this point in the design process I discovered a serious dyslexic moment: I had set up my build table and string computer using 24.5 inches as the rolling diameter of my 205/65R15s, rather than the correct 25.4 inches. All my results to date, especially for roll centre, were toast, albeit of some use as indicators of trends. I phoned Tire Rack and ordered a set of 205/50R15 Dunlop Direzza DZ10s, and faced up to the need to do it all over again. One positive outcome was that my roll centre problem was reduced, at the expense of loss of some of ground clearance on my gravel road. It is literally my gravel road, so no end of lobbying local government will get it paved (and the road’s total width is too narrow, so they wouldn’t even consider expropriating it). Fortunately, the neighbor owns the ultimate boy-toy, a Kubota tractor with a scraper and enjoys playing with it to keep the worst of the potholes at bay.

After my post-Christmas chores are done I will get back to bringing the front suspension design to conclusion.


Attachments:
File comment: Front hub, rotor, spindle, and A-arms on the build table. The steering
arm is supported to maintain a 7 degree caster angle. The upper A-arms will be shortened to allow use of lock-nuts on the adjustable ends. (December 2010)

Hub and A-arms wo brkts.jpg
Hub and A-arms wo brkts.jpg [ 50.73 KiB | Viewed 3881 times ]

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Build Log: viewtopic.php?f=35&t=11601
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PostPosted: April 3, 2011, 7:27 pm 
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Back from the wilderness of Page 2 (or, time to stop living vicariously through LocostUSA and actually DO something!)

I’ve made little direct progress since my last post, but contributed to the end goal by taking a welding course (see viewtopic.php?f=15&t=12010 ). The automotive engineer used by Nova Scotia was actually the instigator of this, once we determined that my interpretation of his welding requirements was overly stringent. Since doing the course I built a welding cart and a welding table using flux core, and more recently got myself a 110cf cylinder of argon/CO2 mix. My MIG welds are much prettier than my flux core efforts (no surprise here) but my biggest challenge still appears to be seeing well, and keeping the bead where it’s supposed to be. Stuff doesn’t stick together very well if you miss the joint!

I’ve had diversions, from ‘honey-do’s’ to enjoyment of the ice-boating season, which is actually waaaay better than soft-water sailing. That brought its own work when my first collision in 25+ years of iceboating required me to do some unplanned repairs.

I took advantage of one of my friend’s orders for parts from Birkin to order two seats, seat rails, and three-point seat belts. I ended up with the shipping crates for our shared order, a corrugated box within a steel exo-skeleton that yielded a good supply of short lengths of 1x2 inch 18 gauge rectangular tube, 1x1 inch angle, 1x3/16 flat bar, and expanded mesh, all of which could contribute to construction of small parts, or more importantly, to learning how to weld. Thus, my welding cart is a dog’s breakfast of 1x2, 1x1, flat bar, angle iron, expanded mesh and 16 ga. sheet steel.

I diverted from the focus on getting a rolling chassis to do some ‘less risky’ welding on the Locost. I decided to duplicate the Birkin seat support structure as my first effort, based on measurement of my friend’s kit. The Birkin seat support is quite simple really: some ¾ x ¾ rails linked by flat bars, sloping up to rest on a 1x1 cross member. The adjusters for the driver’s seat attach to the cross pieces between the rails, and the fixed passenger seat attaches to the rails themselves. Of course, I don’t have a cross rail in the right spot, so I’ve had to add one, which I will weld in.

The Birkin fastens the rails to the car mechanically, but I’m tempted to weld mine in for simplicity, but for the concerns around how I would provide corrosion protection to the underside of the rail structure. I could paint it before installation, but the paint could contaminate the welding – and the welding would burn off the paint. Any opinions on the pros and cons of welding this non-critical pre-painted structure ? (I know that my welding instructor would say ‘No way!’) I suppose I could flood the heat affected zone with paint or RustChek after the welding. Arguably, seat rails are ‘critical structure,’ but in extremis it’s the seat belts that carry the load.


Attachments:
File comment: My first project, a welding cart, built of odds and ends. One day I'll build another which looks like I knew what i was doing!
WN_Welding_Cart (Medium).jpg
WN_Welding_Cart (Medium).jpg [ 46.6 KiB | Viewed 3781 times ]
File comment: My second project: a welding table per the Lincoln Electric site. Neither close-ups nor application of squares allowed! It seems that fabrication is a bigger challenge than welding at times.
WN_Welding_table (Medium).jpg
WN_Welding_table (Medium).jpg [ 37.74 KiB | Viewed 3781 times ]
File comment: Birkin style seat supports. The 1x1 cross-rail will be welded in. The Birkin attaches the longitudinal rails mechanically at the ends, as circled. I am contemplating welding, but struggling with paint/corrosion protection decisions.
Birkinseatrails_Paint.JPG
Birkinseatrails_Paint.JPG [ 69.06 KiB | Viewed 3781 times ]

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Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601
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PostPosted: April 5, 2011, 12:07 am 
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Any reason not to make them bolt in like the Birkins? A couple of 1/4" bolts would probably do the trick.

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PostPosted: April 5, 2011, 8:11 am 
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Andrew,

No real reason to avoid mechanical fasteners here, aside from 'weld more, weld better', and reduction of piece parts. The Birkin just uses two bolts through tabs at the aft end, and two more at the front end (i.e., one at each end of each longitudinal). As I recall they looked like 5mm or so, so even smaller than a quarter inch.

Corrosion protection should be a design criterion, so rationally, my best approach should be to weld the new cross-member in and then mecahnically fasten the rails, allowing me to pre-paint.

(Yesterday I dropped a seat onto the loose rails and dug the Isuzu steering column and wheel out of my workshop attic. My next question is, do I go through the effort of shortening the Isuzu (fixed) column or go find myself a used or aftermarket GM-based tilt column. I will need to mock up the column position to see how easy/difficult entry/egress is with the fixed column. It may well be that the Isuzu wheel is just too big.)

Thank you for challenging my thought process.

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Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601


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PostPosted: April 5, 2011, 10:23 am 
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Warren Nethercote wrote:
Thank you for challenging my thought process.


No problem. All too many times I have done something similar, asked for an opinion, liked what I heard, and continued on instead of scratching my head pondering for a few more hours.

Will you be using a quick release for the steering wheel?

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PostPosted: April 5, 2011, 12:18 pm 
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Andrew,

Quote:
Will you be using a quick release for the steering wheel?



It's probably unlikely if I'm able to use the Isuzu wheel and column and still get in and out of the cockpit. If the Isuzu wheel doesn't work (for entry-egress), or shortening the column looks too ugly, I may be just get a different GM-based column with tilt, which would not require quick release, and would also open up the wheel choice. To further confuse me, I just had a peek at your build log where your 'build it from racing components' approach looks quite elegant and cost-effective, not to mention reducing interference issues with pendant pedal boxes.

My first step is to look at the Isuzu column to see how big a job it is to shorten (I would need to shorten not only the shaft, but also the external tube, which looks to be casting, rather like rack and pinions).

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Build Log: viewtopic.php?f=35&t=11601


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PostPosted: April 5, 2011, 8:39 pm 
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Andrew,

You're bad! :D Every time you ask a question I run off into options analysis and end up having to do something rather than snoozing on the couch with the cat.

This afternoon I couldn't ignore my own steering column thoughts and went out to the shop. I stripped the Isuzu column of its many layers of pallet wrap (the wrap was not for the column's own protection, but to protect my shop attic from the greasy column) and made the happy dicovery that the column tube was a fabrication, not a casting. See photo1 (it's not really a 'before' picture, but it's all the bits.).

I extracted the shaft from the tube to discover that Isuzu had made the column collapsable by using a slip joint in the tube and a double D shaft for the upper column. Out with the hacksaw, and pretty soon I had a 14 1/2 inch long shorty column(Photo2, a detail) with a double D lower end, that only needs the addition of a lower bearing. I will be seeing if an old colleaguewill take that on (Toolie, who is also a forum member).

I did plop myself in the seat to mock up a steering wheel (sorry, no vroom vroom picture), but the 15 inch Isuzu wheel which looked so small in the truck is simply too tractor-like in the Locost. I will need to look for a new, smaller wheel, which might yet involve a removable hub, although I was able to get in and out, even with the fixed 15 inch wheel.


Attachments:
File comment: The complete Isuzu column, after cutting and reassembly of the upper portion
Isuzu steering column (Large).jpg
Isuzu steering column (Large).jpg [ 107.02 KiB | Viewed 3672 times ]
File comment: The shortened Isuzu column, now only needing final adjustment of tube length and addition of a lower bearing
Shortened Isuzu column (Large).jpg
Shortened Isuzu column (Large).jpg [ 134.79 KiB | Viewed 3672 times ]

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Build Log: viewtopic.php?f=35&t=11601
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PostPosted: May 11, 2011, 7:46 pm 
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I've made little progress of late: when the weather's good spring gardening is the priority, and when it's bad I've been in my workshop, but concentrating on getting my boat ready for launching. You'd think that I wouldn't wait until Spring if I had it indoors all winter .....

I did get a Grant adaptor for my Isuzu column and am looking at Grant wheels; they are not really locost, but a hundred bucks or less (or more) will get one.

Today I picked up my shorty steering column from Toolie, an old colleague, also retired and also looking at a locost build. As shown in the photo, he squared up my hacksawed outer tube, turned a Delrin bearing for the bottom end of the column, and fitted a set-screw to capture the bearing. We had an interesting talk about the not-so-nice bits of production parts. The mounting bracket welds made the tube go out of round for starters, and while the welding penetration was good for the bracket, it meant that the inside of the tube had to be cleaned up to allow the bearing to fit. What's more, the double-d shaft was a forging, so the shaft swelled where the taper ended, affecting bearing clearance choice. We won't mention the slight bend in the steering shaft, but if I never noticed it on the truck, why worrry now?

While I was there, Toolie showed me a Suzuki column which had the same taper and spline as mine, and was made in much the same way, except that the main part of the column was only about 20 inches long, with a universal betwen the upper part and a short lower section. It's probably usable as is, although Toolie was inclined to convert it to a shortie like mine.

Next I need to get on with a mount, but not too soon. There's the garden, the boat, and then 10 days in San Diego in early June where I will be judging at the Etchell's World Championship regatta. I don't know if I'll have free time, but are there any locosters in that area?

When I get to the mount I hope to integrate it with the windshield frame which I will make out of 1 1/2 inch DOM, tied back to the roll bar. The legs of the windshield frame will carry on down to the bottom of the chassis. A couple of sketches are shown below.


Attachments:
Steering Column 001.jpg
Steering Column 001.jpg [ 29.21 KiB | Viewed 3576 times ]
File comment: First thoughts on braces back to the roll bar - too complicated! Note: this is not a roll cage; I just don't want the windshield to fold back if we go upside down.
WN Windshield and RBar (Large).jpg
WN Windshield and RBar (Large).jpg [ 54.56 KiB | Viewed 3576 times ]
File comment: Second cut: simpler to build, with similar ease of entry/egress (that's why the braces are at an angle).
Warren_Windshld_RBar_2 (Large).jpg
Warren_Windshld_RBar_2 (Large).jpg [ 62.42 KiB | Viewed 3576 times ]

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Build Log: viewtopic.php?f=35&t=11601
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PostPosted: May 11, 2011, 11:40 pm 
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Nice compact column Warren. Until I read your post, I couldn't tell it had been modified - very clean work.

I would agree to there being some merit to a more structural windshield frame. Having the windshield bolt to the scuttle didn't sit well with me either. I read about a few 7 owners that had passengers use the windshield frame as an assist handle and it damaged the scuttle. I'd hate to see what a piece road could do.

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PostPosted: June 23, 2011, 12:36 pm 
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Back from Page 2 ....

My nephew is visiting and I lured him into car building with the promise that it's better than spending time with his aunt and his mother. We've installed the seat rails. After that we made the happy discovery that the steering column mounts end up just above tube P, which is very convenient for building mounting brackets. We're working on bending up the tubular windshield frame next.

The first photo is me, in Vroom-vroom mode, together with David. The second photo is David in the car. The only way his 6'1" will fit in a book length cockpit is without pedals. Soapbox Derby anyone?


Attachments:
Vroom_vroom.jpg
Vroom_vroom.jpg [ 55.06 KiB | Viewed 3482 times ]
David in Locost.jpg
David in Locost.jpg [ 68.86 KiB | Viewed 3482 times ]

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Isuzu Pickup/SR20DE, +401 COLD frame
Build Log: viewtopic.php?f=35&t=11601
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PostPosted: June 23, 2011, 9:58 pm 
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Yo, Warren-
Looks like progress! That's a good thing. If you actually made "Vroom Vroom" noises, we really should get to see it on video, with sound...

Take Care-
JD

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PostPosted: June 24, 2011, 2:01 pm 
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JD,

Nah, too embarrassed for noises ....

David's visit is coming to an end and we couldn't quite keep the ladies' agendas at bay, to the detriment of progress.

We did get a mock-up of the proposed windshield bent up. I will tell more in a day or so, but here's a few pictures. It is inclined at 30 degrees, and just works with the COLD scuttle, after minor surgery.


Attachments:
Windshield mockup 2.jpg
Windshield mockup 2.jpg [ 63.83 KiB | Viewed 3417 times ]
Winshield Mockup 1.jpg
Winshield Mockup 1.jpg [ 64.93 KiB | Viewed 3417 times ]

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Build Log: viewtopic.php?f=35&t=11601
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PostPosted: June 25, 2011, 4:34 pm 
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The integrated hoop windshield hoop looks slick. I take it you will be attaching the glass to the hoop?

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PostPosted: June 25, 2011, 8:29 pm 
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Andrew,

Yes - my current intention is to run a 1 1/2" tube transversely between the windshield frame uprights at cowl level (which will require a little more cowl surgery) so that a pook/b-t style gasket can be used all around the glass ( http://www.appletreeauto.com/WINDSHIELD ... NG-RUBBER/ ) so that the cowl can be removable. To do that I should find someone locally with rollers to bend the tube appropriately - although I may first try approximating the curve of the scuttle top with a sequence of very small bends using the tubing bender.

An alternative approch would be to cut the forward bulkhead out of the cowl (for access to the forward side of the instrument panel) and end up with a Haynes style 'open-ended' cowl. In that case, the base of the glass would rest on a gasket on the cowl itself, and the cowl would not be removable without pulling the glass. This approach would look cleaner, and make defrost vents easier to install, but make servicing anything located in the cowl more difficult.

I believe my engineer inspector will require full wipers and defrost, so the inside of the scuttle is likely to be a busy place.

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Build Log: viewtopic.php?f=35&t=11601


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