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Learning how to build Lotus Seven replicas...together!
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PostPosted: June 12, 2021, 3:10 am 
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Close up details of gear selector mechanism. Will 3D print these first and use the parts for testing in the seating buck.
Attachment:
1st gear.jpg
1st gear.jpg [ 83.54 KiB | Viewed 2015 times ]

Attachment:
rev gear.jpg
rev gear.jpg [ 83.02 KiB | Viewed 2015 times ]


In light of the "inadequate" exit air vent sizing of the original design (as discussed during the GMA T50 reveal) have decided to locate a large vent by the rear cabin window. The fan drawing air out of the cabin will be plumbed to exhaust air into the heatshield airgap to help prevent cooking the passengers kidneys.
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Interior exit air.jpg
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PostPosted: June 12, 2021, 5:52 am 
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Interesting shifter design! I can appreciate your trying to keep the shift rod low yet close to the bottom of the shifter. Looks like you will need a spherical joint on the shift lever, but this will make the knob able to rotate back and forth (slop) in the overhead view based on clearance to the gate throw rod that floats in the upper shift lever.
I recommend using the spherical on the shift lever but replace the bottom with a ball instead of a fork, with the shift rod moved to the lower position and pin a cup to sit above the shift rod centerline to accept the ball. If not clear, I can draw a crude mspaint pic.

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PostPosted: June 12, 2021, 6:15 am 
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Shifter angles.jpg
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Spherical does not allow the relative motion between the 2 offset centers, the shifter arrangement is designed this way for 2 main reasons;
1) reducing the angle of throw of the gearstick compared to that required by the transaxle selector shaft
2) reversing the direction of action

First gear is up and to the left on the stick , however the trans is engaged into first when the shaft is pushed in.

With this arrangement the gearstick only has to move 9 degrees to give full 16 degrees (highlighted) required by the box selector shaft, but as they are different radius arcs there has to be a solid connection that is constrained to the plane of the gearlever but allows movement within that plane as the mechanism moves between the gates.

Once I build the test rig it will be easy to adjust the feel and accuracy of the shifter by changing the center distance. The first cabin mockup showed that the right passenger leg can interfere with the shifting if the stick goes past the chassis spar, hence keeping the throw really tight.


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PostPosted: June 12, 2021, 7:19 am 
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I see it now. I thought the shift lever pivot was fixed from side to side rather than rotate with the lower rod. Clever!

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PostPosted: June 16, 2021, 6:16 am 
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Back on page 3 of this thread I roughed out the UCA mounting plate, but have now developed the idea a bit further. The UCA mount plate is a bolt on part that allows quick and easy swap out to allow experimentation on the test mule settings for caster, camber and antidive angles on the front suspension. The shock loads transfer directly into a backing plate that is welded to the chassis tubing. The mount plate also stiffens the control arm chassis tube by acting like a huge gusset. It is also another part that has been designed to be 3D printed and cast.

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UCA mounting plate.jpg
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PostPosted: June 17, 2021, 5:46 pm 
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CAD model said weight would be 933 grams, casting has come out at 948. Now that the part is actually in my hands it makes me realise that every gram counts and this is overkill compared to the Tilton forged aluminium pedal. I have realised that "just because you can doesn't mean you should", the 3D printed pattern was so light that I sucked myself in a bit. Really happy with the result, but in reality it won't be going on the test mule as the off the shelf solution will be easier to get through compliance and is lighter.

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brake pedal casting.jpg
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PostPosted: June 19, 2021, 6:40 am 
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Plenty of places to draw air from besides a hole in the firewall next to the passenger and less noise from the drivetrain, tires, and fan. The pontiac fiero fan is located in the completely isolated rear trunk and has aluminum tubes to direct the flow. You might also consider oem type rubber seals/check valves near the door jambs so a rapid door closing does not cause a pressure change in the ears of the occupants. Similar check valves are used on radiator shrouds where a significant amount of the core is blocked by the shroud. The valves allow air flow through the shroud without forcing it through the fan for better cooling. At low speed the low pressure from the fan inside the shroud keeps the valves closed, sucking air through the core.

You could reduce weight with hanging pedals opposite the masters for a shorter distance to the reservoirs and the pushrod on the same end of the fulcrum as the pedal pad and potentially shorter hard lines to the calipers.

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PostPosted: June 21, 2021, 12:03 am 
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Miatav8,MstrASE,A&P,F wrote:
The pontiac fiero fan is located in the completely isolated rear trunk and has aluminum tubes to direct the flow. You might also consider oem type rubber seals/check valves near the door jambs so a rapid door closing does not cause a pressure change in the ears of the occupants. Similar check valves are used on radiator shrouds where a significant amount of the core is blocked by the shroud. The valves allow air flow through the shroud without forcing it through the fan for better cooling. At low speed the low pressure from the fan inside the shroud keeps the valves closed, sucking air through the core.


Good design info, I was not aware of the Fiero details - they are not a common car in NZ. I have a lot of space in the rear flanks that is unused, so a good option to look into - Thanks!


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PostPosted: July 16, 2021, 7:41 pm 
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Mocking up assemblies is always a good idea before committing to metal. The gear shifter mechanism works as intended however was impossible to assemble. A little extra "clearance" provided by an air grinder and all is well, so next step is making the final parts (some are castings, most are machined from stock).
Attachment:
Gear shifter.jpg
Gear shifter.jpg [ 196.64 KiB | Viewed 1637 times ]


Sometimes there are unexpected alternative uses for the parts, turns out the gear shifter will also be handy as a blaster for a kids Star Wars costume.

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PostPosted: July 17, 2021, 11:53 am 
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Your mockups are very nice, and very smart, I'd say.

Even those of us without CNC machining centers, or 3D printers can benefit from mocking up parts using 2D drawings glued to cardboard or Foamcore board. Just that ability has saved me a lot of wasted material.

Cheers,

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Damn! That front slip angle is way too large and the Ackerman is just a muddle.

Build Log: viewtopic.php?f=35&t=5886


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PostPosted: July 26, 2021, 5:11 am 
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Thanks Lonnie! Delayed response because the build approval paperwork is finally done and submitted. I noticed the first entry in my design journal for the project was July 1st 2011 - feels like 10 years has gone by in a blink. Currently designing the build table while awaiting feedback from the next TAC meeting on August 3rd. In the last 18 months there have been no requests for technical variations from the rule book, this project requires 5 - so will have to see how that pans out!

Also reverse engineering the nose mount for the engines, put the part up on the CMM tonight as the timing belt covers have to fit perfectly around the flanged edge. The block out model is a bit too simple currently and needs fleshing out.
Attachment:
nose mount.jpg
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Attachment:
nose mount in situ.jpg
nose mount in situ.jpg [ 166.59 KiB | Viewed 1530 times ]

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nose mount position.jpg
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PostPosted: August 12, 2021, 3:40 am 
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LVVTA paperwork is back and approved, with a strong recommendation to use certified glazing. That is going to be a difficult task given nothing to date is even close in size or shape, however that hurdle is a long way in the future with plenty of short term challenges to work through beforehand.

Next major milestone is constructing the fuel tank and test engine rig so that the Speeduino ECU can be setup. The J35Z2 has a unique code pattern for the cam signal (back on page 5 - a year ago!) so getting the engine to run on sequential fuel will require more brainpower than I currently have. Initially it should run just fine on batch fire as that only requires synchronisation with the crank signal, which is a high resolution 60-2 tooth pattern.

Next minor milestone is to complete a proper interior buck so that the door hinge system can be tested. Due to the fact that I never want to be trapped in an inverted vehicle with dihedral doors I have been given a concession on the hinge design rules to allow removeable hinge pins, released by a lever inside the cabin (positioned such that it cannot be inadvertently operated by a passenger).

Picked up the steel for the build table, start cutting that this weekend. Need lots of little welding jobs to practice on before starting on the spaceframe though. The certification process requires tack welding all the tubing in place so that the certifier can inspect all the fitting gaps BEFORE full welding is done - it's a good test of workmanship.

Plenty of tasks to knock off on the road to the test mule, which the TAC agreed was a good way to test the very complex design before building the road car from it.

Part of the approval process was specifying the wheel and tire combo, shown are the standard Corvette C7 Z51 rims I have settled on - tires will be some form of Michelin.

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test mule.jpg
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PostPosted: August 26, 2021, 7:43 pm 
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Printed out a 60-2 tooth chart and glued it to the civic flywheel using a precision whittled piece of PVC electrical conduit the same diameter as the pilot bearing and hammered it into place with a precision 4" x 2". While the glue was curing I rotated the engine to the 2 tooth gap position and then measured the crank sensor signal until it went low (from 3.3V when no tooth is present to 0v when it detects the leading edge of the first tooth) and aligned the printed pattern with the precision bent piece of welding filler wire. The ECU needs to be programmed with the precise angle of the first tooth after the gap is detected to the crank No1 TDC, i.e the falling edge of the CKP signal. To run sequential fuel injection the cam pattern has to be determined (todays job!) so that the ECU can at any time during synchronized counting of the cam pulse train determine if it is coming up on TDC cylinder 1 or Cylinder 5 after the tooth gap (since firing order is 142536 - refer cam pulley on page 5 of this thread)

Crankshaft Pulse train with photo trying to account for parallax error on wire;
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ckp pulse train.jpg
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PostPosted: August 27, 2021, 10:37 pm 
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Day zero of the build - have spent the last couple of days clearing out the workshop and it is now ready for the build table to go in this afternoon. Second job was mounting a fire extinguisher on the wall.

First fixtures on the table will be front and rear temporary fabrications that position the suspension knees (sitting against the right wall) in 3D space so that the true geometry, alignment and bump steer can be confirmed - any modifications will then be transferred back into the master CAD model before work proper begins on the frame.

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PostPosted: August 28, 2021, 12:58 am 
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That work space is just too clean, like I would need sun glasses to work with you..
In my shop its sooo dingy and dirty you need a headlamp on your forehead :rofl: :rofl: while holding the trouble light.
At least pour a spot of oil on the floor please.

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Perry

'If man built it, man can fix it'
"No one ever told me I couldn't do it."
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Perry's Locost Super Che7enette Build
Perry's TBird Based 5.0L Super 7 L.S.O.
Perry's S10 Super 7 The 3rd
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Perry's 5th Build, the Super Slant Six 7


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