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Learning how to build Lotus Seven replicas...together!
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PostPosted: March 21, 2019, 5:53 am 
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Yea, I thought there was something like that. Problem is there's no good place to fit a small concentric bearing. There are 4 big bolts in the diff that take up space. There's no room on the diff journal, unless I was to mount that bearing out away from the diff.

I'm thinking maybe I don't need bearings, maybe just a bushing of sorts might work for the coaxial intermittent motion.

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PostPosted: March 21, 2019, 3:27 pm 
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Here is a crude pic of what I was attempting to describe before. No bush or bearing, just greased but you could fit a plastic ring there if you ever wore it out. This design allows you to move the chain over a bit for improved symmetry. This also allows tuneable cush and you could augment compliant bushes acting as bump stops with external tension springs for the cush.


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JOHNSINSKI DIFF.JPG
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PostPosted: March 21, 2019, 5:54 pm 
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That's sort of what I was originally thinking. But to get any significant rotary shock absorption it would need large and/or soft bushings and that would inherently allow the sprocket to move off axis also (chain would loosen). That's why I've been obsessing over something with bearings to keep the sprocket and diff coaxial.

Here's what I came up with: It's very similar to a motorcycle cush drive, but it's "bearing" is the little yellow things, likely UHMW bits. With a few strategic o-rings I think it should hold some grease also. The grease should fling to the outer surface that the yellow bushes ride on. The round bit is just to hold the bush in place. The transparency doesn't show the sprocket hub too well, but hopefully it makes sense. It'll need another thin plate on the underside, to hold it together. Good place for an o-ring.

Maybe I should just design a sealed aluminum diff housing to fit all the torsen gears and with all the associated flanges built in, and have somebody in China make it for me.


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cush_drive_01.jpg
cush_drive_01.jpg [ 50.71 KiB | Viewed 679 times ]
cush_drive_02.jpg
cush_drive_02.jpg [ 42.61 KiB | Viewed 679 times ]

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PostPosted: March 21, 2019, 7:02 pm 
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In my drawing, the allowable axial runout is controlled by the pink washer, purple spacer, hub, and sprocket thickness. When I say washer, it could be a ring that picks up all the bolts to allow for as much range of motion as you might want while keep the socket secure to the hub. Radial runout would be controlled by the fit to the hub and since the relative motion is so little, even a bushing would be overkill imho. I drew a fat gap at the washer but like I said, crude.

Might as well move forward without cush for now. You can always built it in to work with your current diff.

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PostPosted: March 22, 2019, 2:20 am 
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Oh, I see now, the inside hole of the sprocket rides on the hub, yea, that should hold the radial motion.

All good ideas to simmer. It's not a rush. I was just looking at the wiring harness and holy crap, I got some work to do. There an intake solenoid, an exhaust servo, a HGEC blah something and maybe a jeffries tube in there too somewhere, jeez!

A bunch of metal should be arriving any day now, so I can continue the build.

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PostPosted: March 29, 2019, 5:02 am 
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Got another batch of metal in. I should have aluminum for rockers and the diff plates/bearing housings. And steel for the steering column, rack extenders and axle extenders. That small block is to make another upright that the machinist screwed up.

For the axle extension, I've got a 1.375x.188 tube and I turned the two ends of the cut axle to fit it (about .995"). I guess the axle is still pretty hard, while the carbide lathe tool works, I did have to sharpen it a few times.

When I get to the welding, I'll weld around the obvious joint, then (or beforehand) drill 1/4" holes in it near the ends to weld some spots on. There's about 2" of overlap.


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plates.png
plates.png [ 1.16 MiB | Viewed 520 times ]
axle_extention.png
axle_extention.png [ 473.39 KiB | Viewed 520 times ]

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PostPosted: April 2, 2019, 5:25 am 
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Got at the diff bearing carriers tonight. I roughed them out on the CNC, and I plan on finishing them on the mini lathe.

Broke the wire my servo operated squirter! Maybe string would work better.

Just 2 more plates and I should be able to mount the diff to the engine.


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roughing.png
roughing.png [ 1.76 MiB | Viewed 432 times ]
squirt_link.png
squirt_link.png [ 899.78 KiB | Viewed 432 times ]
diff_bearing_cupa01.png
diff_bearing_cupa01.png [ 1.25 MiB | Viewed 432 times ]

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PostPosted: April 3, 2019, 4:39 am 
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I think this one is finished. Each bearing has a tight fit, probably not much, I can push them in halfway by hand, but I don't feel like trying to get them out so I haven't pushed them in all the way yet. I think it'll go well. I'm contemplating putting some locktite on the bearing surfaces so to minimize the possibility of the bearing spinning in the housing.

I had to make some jig plates to hold them in my Mini lathe, basically just rings, the ID fit the lathe jaw outside and in OD fit the rough bearing hole. I slit the ring to allow it to move (clamp) a bit. Seemed to work good.


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PostPosted: April 5, 2019, 3:19 am 
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If it looks like I don't know what I'm doing, well...

But I am almost done with major aluminum work for the moment. Back to fabbing and welding!


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diff_cage_01.jpg
diff_cage_01.jpg [ 276.07 KiB | Viewed 336 times ]

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PostPosted: April 19, 2019, 5:24 am 
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I'm putting the diff mount cage on the back burner. I decided to work on the rocker plates, it was a moderate success. although I went a bit deep and cut through the plastic protecting the machine, oh well, it got a bit wet.


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rocker_plate_before.jpg
rocker_plate_before.jpg [ 235.52 KiB | Viewed 92 times ]
rocker_plates_after.jpg
rocker_plates_after.jpg [ 225.45 KiB | Viewed 92 times ]
rocker_shocker.jpg
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PostPosted: April 19, 2019, 9:00 am 
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Nice. I guess you are going to bolt the halves together with those extra holes? Margins around the pivot look pretty thin but I see why you did it, for coilover mount adjustment while trying to get the right bellcrank operating angles. Might provide bump stops at the lca so you can't bottom out coilovers and overload the rockers. Interesting built-in spacers for the sphericals.

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PostPosted: April 19, 2019, 11:01 am 
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Yes, the two 5/16 plates will bolt together, but with a 1/2" spacer plate. That puts the outside thickness just fitting inside the shock end (.018" clearance).

I needed the built-in-spacers to allow some angle movement coming from the pushrod.

I haven't really thought about or had a good idea for down stops. I was maybe thinking about a bump stop on the rocker somewhere. Something with a screw adjuster would be nice.

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PostPosted: April 21, 2019, 3:19 am 
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More ray gun parts. Ya got your front coil pack space with the ZPE (zero point energy) device behind it...ah, it's late.

Now I realize I didn't plan for any kind of bearing at the shock mount, hmmm...might just have to be grease for now.


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rocker_core.png
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