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Learning how to build Lotus Seven replicas...together!
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PostPosted: March 31, 2020, 1:33 am 
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Yea, fixed calipers. I thought maybe with more rear weight and less rear pad area I could get the same size M/C. Probably a toss up, I'll probably get the slightly bigger one.

I put a spring on the brake pedal, but the springs in the M/C seem plenty heavy. Even just one M/C installed is quite stiff. The Wilwood kit comes with a remote mount, I'll probably do that.

Got a Simpson 6-point harness, seems like something you should buy... :oops: From reading the instructions I guess the ends shouldn't be bolted tight, so I'll probably make some crush spacers.

The horrible freight tig welder was acting funny, eventually the torch button wouldn't work. After some surgery this area of the switch wires pulled apart fairly easily. This location was about where I sling it around my neck. I replaced it with some hobby type wire (16-18 gauge, silicone covering). I tried to stuff "extra" wire inside the bundle so the switch wires hopefully won't be in any tension. Works so far...


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Last edited by Johnsinski on March 31, 2020, 9:37 pm, edited 1 time in total.
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PostPosted: March 31, 2020, 1:52 am 
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And Monday night's project was to start cutting foam blocks for the seat mold, ugh...

Less than an hour each though, not too bad.

The blocks are 2"x2 glued up for the CNC work.

There are some undercut areas around where I've put hard points for bolts/nuts. I'll probably sand those areas by hand and that will make the mold undercut, but I'm hoping I can still flex the part off. I'll use lots of carnuba wax and PVA. I'm thinking about 1/8" total thickness of carbon.

Once cut, I'll glue them all together, smooth/sand to my liking. Then seal with a coat of Smooth-On Epsilon epoxy (that specifically will not harm the foam) and then probably spray some gelcoat to finish it.

I'm guessing this will be the method I use to make body panels.


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PostPosted: March 31, 2020, 7:36 am 
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1/8 inch of carbon won't flex off the mould: it will be like a piece of steel. :D If you are using CF for the seat, 3 laminations of 10 or 12 ounce cloth will probably be more than enough, with extra layers where fasteners are required. That will give a finished thickness under 1/16th. I recently made some spike protectors for my iceboat runner plank using two layers of 9 ounce carbon biaxial CF cloth. Thoughts of 'popping' the moulding on and off the runner plank were soon dashed. It was possible, but a struggle with prys and pinched fingers.

But I am jealous of direct production of tooling by NC milling!

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PostPosted: March 31, 2020, 3:18 pm 
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Thanks for the tip Warren. I guess, yea, I can see 1/8" curved carbon not flexing. I could also cut into the back of the mold so it could flex, meh who knows?

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PostPosted: April 1, 2020, 9:24 am 
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Johnsinski wrote:
I still got brakes on my mind. The weight balance of the car is about 45/55. I'm planning on putting 235 tires on the front and 255 on the back. My front calipers are 2.4 in^2 each and the rears are 2.0 in^2. I bought one master cylinder so I could finish my pedal box, It's a 3/4" bore, so about .44 in^2.

I'm thinking when I get the other master cylinder that it would be about right to get another 3/4" bore and the bias bar should be enough to fine tune it.

Thoughts?


I have been working on a spreadsheet to help me calculate this exact question. I'm closer to a 40/60 split with a pretty long wheelbase. From my calculations, you want a lot more rear brake until you get enough weight transfer to the front. I'm looking at a static bias to the rear and then using a proportioning valve to reduce rear brake pressure at higher deceleration rates. My sheet isn't done yet, but it's far enough along to give me a good idea of what I should try. If you like, I can run your numbers through it. You can shoot me an email at boracing@comcast.net if you're interested.

Ken


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PostPosted: April 4, 2020, 2:29 am 
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The spreadsheet sounds interesting. I already have the master cylinders in hand though. I ordered a 7/8" and a 5/8". So now I have 3, a 5/8", 3/4" and 7/8". I'll probably use the 5/8" for the clutch.

It would be interesting to have a dynamic bias based on deceleration or traction. Maybe a harder or progressive spring at the bias bar so the further the pedal is pushed the more that spring engages one side of the bar.

I think I'm close to having enough stuff to make a roller, I may try a test assembly outside soon. I guess it depends on the definition of "roller". If I can get it to "go kart" status by mid summer, I'll be happy.

I'll need to figure out a better technique for the body panels. Where I glued the original blocks together to make 4" (pre CNC) there is quite a line from the glue being harder than the foam. Gluing the cut blocks together worked pretty good since I could control where the glue would be (keep it away from the edges).

So my current process is grind the glue out, paint the whole thing with a latex paint, and then fill the grooves with bondo. Then the whole surface can be sanded consistently. The latex and bondo sand about the same. On another thread here somebody mentioned using plaster, I might try that too (to top coat the foam).

Maybe it won't be so laborious for body panels if I can get 4" foam and try to place them to minimize glue seams. I would already do the seat differently and place blocks in 4 different planes, the bottom of the seat plane, the back of the seat plane and the 2 side planes.

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PostPosted: April 4, 2020, 8:30 am 
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Have you guys looked at the brake spreadsheet already posted here a long time ago?

viewtopic.php?f=5&t=14424&p=153058

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PostPosted: April 4, 2020, 10:44 am 
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rx7locost wrote:
Have you guys looked at the brake spreadsheet already posted here a long time ago?

http://locostusa.com/forums/viewtopic.p ... 4&p=153058


I was not. My sheet pretty much does the same thing, but isn't prettied up yep. That is a very useful sheet.


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PostPosted: April 6, 2020, 1:52 am 
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Not quite a roller. Nice day out to do another test assembly. I can still lift the frame by myself, but it's getting heavy. Probably 75% of the welding is done, I'm itching to get the frame primed so I don't have to worry about it rusting. But I know I will need more bracketry.

Is one of those Flambeau 5 gallon plastic tanks ok for this?


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PostPosted: April 6, 2020, 7:32 am 
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Johnsinski wrote:
Is one of those Flambeau 5 gallon plastic tanks ok for this?


Don't forget an appropriate length neck vapor tube insert for a fill capacity 10% or so less than 5 gallons.
I'd fit a nylon pickup straw through the top surface to pull fuel to a prefilter and inline pump within a foot of the tank, then post filter. Maybe a swirl sump 4 line pot to house a wet pump inline for hard cornering. They came on fords in the 80s without any tank baffles and return systems.

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PostPosted: April 8, 2020, 12:59 am 
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In my best Carson impression, "I did not know that!". About the swirl sump. I guess it's a bit like a dry sump oil system.

I do recall in RC airplanes a feeder tank, I've not done much nitro though.

Would I still put foam in the main tank? No foam in the swirl tank?

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PostPosted: April 8, 2020, 6:25 am 
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Avoid foam. What psi do you require? Do you have a return line system?

Run the 5 gal tank and vent loop with a rollover valve, fit your pickup tube and return dump fittings with an aluminum top plate with a split (so you can get it in the tank opening) aluminum nut plate/clamp ring inside that you can hold in position through the filler neck to start a few screws, an external cheap carb lo-psi box pump as xfer pump, ford single tank reservoir with internal filter, ford external high pressure pump and after pump filter, return to the res hose, res to tank return hose. No baffles or foam to crumble and cause problems.

Or, instead of making the cup, fit an oem pump/res assembly they started using around 95 or so. They are spring loaded to push against the bottom of tank but you could design the mount to place it there instead of using compression springs. The corrugated clear in-tank fuel hose will require some adaptation.

Or, make an aluminum top plate that fits a return dump and a high psi pump inside and make a foot that forms a deep cup around the pump with inward hinged trap doors to allow fuel to slosh into but not out of the cup. Much cleaner setup, fewer lines, no swirl, no extra pump but a little less range/ fuel capacity.

If you want a level indication too, use an appropriate length (tank height) marine stainless fuel level sender with matching ohm gauge (looks like a stick with a donut float versus an arm float). You may need to find a tank with more flat space on top to fit both.

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PostPosted: April 11, 2020, 10:46 pm 
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It says 50 PSI in the Honda manual. I don't think it's recirculating, I believe there is only 1 line from the tank.

I keep jumping around a bit, I decided to think about the shifting. I had early thoughts of trying to do some kind of servo shift by wire. But I don't feel like trying to develop that right now.

I don't have the shifter arm with a spline to fit the gear change shaft on the engine. I'm also thinking it would be nice to have that shaft extended a few inches, then I can more easily get linkage hooked up. I made an adapter tube that fits over the gear change shaft snuggly. And I was thinking of holding it with set screws (maybe 2 at 90 degrees) at the point on the gear change shaft where the stock clamp bolt notch is. I would grind 2 flats on the shaft for the set screws. Does that seem reasonably? I know there will a bit more of a bending moment on that shaft since it will be extended.

First pic is my shifter (left hand shift), approximate size. Pull to upshift, push to downshift.

Second shows roughly the angle of the shift linkage coming back and the offset (extension) from the splined shaft.


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PostPosted: April 12, 2020, 7:32 am 
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You’d be much better off in several ways by modifying a stock shift lever and a bolt on brkt to mount a push-pull cable. This is the standard method for most bec shifters for good reason. Forces are limited if you add adjustable travel stops at the shifter. I’d make a brkt from .050” steel to mount the cable and ¼-20 rod ends. Such thin material would allow you to reuse the original engine hardware to mount the brkt without sourcing longer bolts. You can buy very high quality marine steering cable as short as four feet for under $50 with threaded ends and Teflon liner but you may want longer to reach your right hand and have as large a bend radius as practical for minimal friction. I’m thinking the lever would be straight down, with a 6-8 foot cable that follows the outer rail, makes a 180 around the back of everything near the taillights, then comes up the right. You could make a bellcrank for only a 90 deg bend to the cable but the tolerances in the bellcrank bush and extra rod ends would add slop to the feel.

For an adjustable ratio shift lever on the trans, weld a 1x3x1/8 strip and drill for two ¼ fasteners, then lap that with another strip that contains the ¼ hole for the actual arm. It doesn't need to be welded over the center to put the rod end at the end if the lever, just look at the ends to determine the effective angle for setting up the linkage. You can slot the strip or drill multiple holes to get the ratio right. The same goes for the cable housing clamp. There are several different designs to choose from with marine cables.

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PostPosted: April 14, 2020, 2:56 am 
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Well, don't be offended, it was mostly done already but ran out of argon. So I finished it up today after I got a refill. The upside is I had everything laying around so it didn't cost much. The extension on the shift shaft isn't too bad.

I have one "see-saw" arm in the middle. Both my shifter and that see-saw arm have Delrin bushings in them that I made and they ride on 1/2" steel shafts welded to the frame and a threaded hole in the end to bolt a cap on.

I did put several hole positions into the arms. The rear pushrod clears the alt cover by about 1/2". The rear pushrod will go through the firewall, however.

I tried my best to make it operate smoothly, since you warned of possible problems. I hope it doesn't vibrate from the engine too bad. And I'll try to make some stops at the shifter.

I gotta say it feels pretty good, very little slop or friction. It's got about +-1.25" travel at my fingers. It snaps back to center very nice and it's no problem to get to neutral.

I am still in the process of sanding and smoothing my seat. Uh, the seat mold that is.


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