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  #21  
Old 10-08-2024, 10:13 AM
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Default Re: 1/16 Scale FrankenDiff

Those parts are looking great! Sounds like the different versions have all lead up to some pretty nice axles. Wheels and diff covers look sweet

It's pretty bad when the model parts need to have a setscrew as a stud, or use a paperclip as drift punch just to align everything
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  #22  
Old 10-08-2024, 11:16 PM
ddmckee54 ddmckee54 is offline
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Default Re: 1/16 Scale FrankenDiff

Last night I worked on the rear wheels, got the design done and started it printing before I went to bed. I think it looks pretty good, but it's got two major boo-boos and one "that just doesn't look right" issue.

Major problem #1 was the depth of the pockets. I pocket the wheel openings and the screw holes at the same time, and must not have been paying that much attention to the actual depth. The wheel openings were a little shallow but still OK, but the screw holes were only 1-2 mm deep.

Major problem #2 was that the 12 mm hex driver didn't fit, it was too small. I have been using Simplify3D for years, but it seems to have an issue with internal pocket and bore dimensions. I scale the model in the slicer to 103%, this gives me a final print that is dimensionally accurate to the 3D model within a few hundredths of a mm, at least externally. Internal pockets and bores were always too small. I've found that if I manually scale the dimensions of the critical bores and pockets to 103% before I send the model to the slicer things work out much better. When I checked the model I had scaled every critical bore and pocket to 103%, except the pocket for the 12 mm driver - you just can't fix stupid sometimes. I'm beginning to wonder if S3D just offsets all the dimensions away from the core of the print when it scales? (Maybe there's an advanced setting that I haven't found yet to cover that?)

My just doesn't look right issue was there's too much gap between the tires. I had it at about 5 mm, which turns out to be too wide. I reduced that to about 2-3 mm, we'll see how that looks on the next print.

Speaking of the next print, I just aborted it. I noticed on the slicer print preview that there were only 2 perimeter walls between the screw hole and the bore for the locknut, there should have been room for 3-4 perimeter walls there. Turns out I had used the clearance diameter of the screw, instead of the minor diameter. At least the print had progressed far enough that I could check the fit of the 12 mm driver - fits like a glove. Oh well, fix model, re-slice, re-print.

Don
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  #23  
Old 10-10-2024, 07:31 PM
Zabco Zabco is offline
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Default Re: 1/16 Scale FrankenDiff

All educational opportunities, best way of learning. Strange though the way your slicer is doing scaling. I use Cura or PrusaSlicer, which is forked from slic3r, depending on which printer I am going to use and have never had that issue. When I size a cavity in one of my designs that's pretty much exactly what I get in the final print.
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  #24  
Old 10-10-2024, 09:45 PM
ddmckee54 ddmckee54 is offline
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Default Re: 1/16 Scale FrankenDiff

OK, progress has been made - but it's been a LOT like doing the Hokey-Pokey. This is my current progress:


From right to left we have the following:
1 - This is the cover for the locknut, The screws that hold this on will simulate the lug-nuts.
2 - This is the first version of the duals as described in Post #22. It didn't fit!
3 - This is the version that attempted to fix the issues from Post #22, it mostly worked. I tweaked the bores in the 3D CAD model by hand and realized this will be a royal PITA on a more complicated model - more on this later.
4 - This is my better idea, it ALMOST worked - more on this later also.
5 - Which you can't see, is bolted onto the other end of the axle and fixes the problem with #4.

This is the later. A couple of days ago I started a thread on another forum about slicer issues - with internal bores and pockets not being dimensionally accurate when scaled, here's the link:https://www.homemodelenginemachinist...-issues.36499/

I use Simplify3D for my slicer and I have always had to oversize the holes if I wanted things to fit together. It sounds like Cura has the same problem. I know from the diff housings that when I use S3D to scale the model to 103%, the external dimensions are within 1/4mm of the 120mm desired width of the housing - which is close enough. All of the internal bores and pockets measured too small though. The really confusing thing was that they were all too small by about same amount. They were all about 97% of the desired size. I got to wondering how the slicer was handling the internal bores and pockets when scaling, and if this was the problem with undersized holes all along. So, like Ford, I had a better idea. I took the task of scaling the part oversize, to allow for shrinkage, away from the slicer and gave it to the CAD program - which I reasoned was better equipped to handle the task. I reset the bores and pockets to their original values and scaled the part to 103% before I exported it to the STL file. #4 is the result, and it almost worked. Remember Major problem #2 from the above post? Yup, I do-ded it again. I didn't allow for any clearance Clarence! The 12mm hex driver would have been a press fit, and that's not good. I fixed the clearance issue and that resulted in #5.

Having wheels on both sides does tell me that I need to go back to the drawing board though. I currently measure about 200mm across the wheels and axle, I need to be at about 185mm. Now the question is where can I lose that 7.5mm on each side?

I added this image, to show that #5 exists and to show the gap between the duals. I think the gap looks about right. But I could shave a couple mm out of the gap, it's about 4mm-ish now. I could easily modify the wheel offsets 5mm and it wouldn't be too noticeable. I've got 100mm between the wheels now and the Bruder frame rails are 80mm outside to outside, so that leaves me a 10mm gap between the tires and the frame rail. If I move the wheels in 5mm that still leaves a 5mm gap, which should be enough for spring shackles and other odds and ends. I'll also have to move the angled transitions on the axle housings in 5mm, to give me a place to mount the springs, but that I'll fix when I re-do the pocket dimensions for the scaling fix.

Last edited by ddmckee54; 10-10-2024 at 11:37 PM. Reason: Added another image
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  #25  
Old 10-21-2024, 12:22 AM
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Default Re: 1/16 Scale FrankenDiff

Progress HAS been made! This is a family photo of the gang - so far.


From back to front on the left side are:
1) The Kong axle with the modified rear wheels. I got my order of tires, so I can actually put tires on everything now.
2) The modified Frankendiff, still haven't shortened the axles though.
3) The prototype of the front axle - it still needs work. It's only got one wheel mounted because I don't have any more 5x9x3mm ball bearings. They are on order, should be here this week?
4) The other front wheel, with hub cover just laying in place.

On the right side are the next donor diff, and the left-overs from the donor front axle.

I've redesigned the rear axle's front and rear halves, making some minor tweaks.
1) I moved all the case mounting screw locations away from the axle bore, They were close enough to the bore that when the screws were threaded in, the inner wall would expand into the axle bore and bind on the axle.
2) I changed the angled transition to allow a convenient spot to bolt the springs to the axle.
3) I took the donor diff apart to see if the binding that I feel was coming from the spider gears - it was/is. There's no clearance in the gears. In fact if the screws that hold the spider gears cover in place are tightened down you can completely lock-up the differential. When I shorten the axles I'll take a little off the back side of the gears. That should make things work a little better.

The front axle needs a little help yet - it's 10mm too narrow. When I initially designed the front axle the plan was to use the steering arms, spindles and king-pins from the donor axle, which measured 205mm outside to outside. I need 175mm-ish, so I had to take 30mm out of the axle. The donor axle had spring perches that are spaced 80mm apart, which is right where I need them, but I need to lose 30mm somewhere. So I played with the design a while. This looked kinda OK on screen, so I printed it out. When I started to install the spindle assembly into the axle the spindle would flop around in the steering arm, they allowed PLENTY of clearance in this one Clarence! So, I am NOT going to use the original steering arms. While designing the new arms I came up with the idea of changing the front wheel offset by 5mm, to tuck the steering knuckle into the back of the wheel - so I did that too. And that my friends is why the front axle is 10mm too narrow. It's a simple fix and the axle only takes about 1/2 hour to print - just forgot about re-printing it.

Unfortunately the "Bag of Misfit Parts" continues to grow.

Don
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  #26  
Old 10-23-2024, 12:31 AM
ddmckee54 ddmckee54 is offline
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Default Re: 1/16 Scale FrankenDiff

My 5mm ball bearing order arrived, so I put both front wheels on the axle. Here's a shot that shows a comparison of the overall widths of the axles.


Well.... The rear axle is pretty close, and there's less than 1mm difference between my red axle and the silver Kong axle. But the front axle - not so much, the front axle didn't work exactly as planned. You know the old joke about cutting something off twice and it's still too short? Well, I printed the axle twice and IT'S still too short! Only this time I don't think that it's all my fault. I noticed that the display on my 8" caliper will periodically jump 5-10mm. All of the outside to outside measurements on the wheels are over 150mm, so I've got to use the 8" caliper. It's a Harbor Freight special, so we'll see how good the lifetime warrantee actually is.

Here's a shot that shows the size of the Lesu tires compared to the Bruder tires.


This will probably be the first conversion victim. This will be one of the simplest, as in addition to forward/reverse and left/right, it will only require the drum to turn.(And maybe lights?)

Don
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  #27  
Old 10-23-2024, 04:55 PM
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Default Re: 1/16 Scale FrankenDiff

I thought the "Bag of Misfit Parts' were to go with the "ghosts of projects future". Todays project doesn't need a 'Dr Seuss differential' with 7 pinions and 3 wheels, but who knows what might later? Or strap the bad parts to some pallets, now it's cargo.

Those axles & wheels are looking nice! Those seem to be a great fit on the bruder

That sucks about the measurements! The dial-calipers from Harbor are pretty solid. I've never messed with their digital calipers, because i don't really even care for digitals from good brands that are in a calibration program.
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  #28  
Old 10-23-2024, 10:20 PM
ddmckee54 ddmckee54 is offline
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Default Re: 1/16 Scale FrankenDiff

I don't use the calipers for any critical measurements. Harbor Freight WOULD have replaced them, but nobody within 100 miles had any 8" calipers to replace them.

I tried using a spline in Alibre to get the curve I wanted on the front axle ends. I found out that they can behave unpredictably when you modify parameters, at least the way I used it they can. It would be nice if somebody would actually WRITE a user's manual.
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  #29  
Old 10-24-2024, 12:38 PM
Zabco Zabco is offline
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Default Re: 1/16 Scale FrankenDiff

It doesn't always pay to buy cheap. I bought a Starret digital caliper for about $100 thirty odd years ago. Big money at the time. Other than having to replace the battery a couple of times it has worked great and is my go to for precise measurements. I have other measuring tools including analog and digital micrometers but the Starret is what I keep using. Was money well spent.
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  #30  
Old 10-24-2024, 04:18 PM
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Default Re: 1/16 Scale FrankenDiff

I love the little 4" caliper that I got at HF years ago, but I think I just got lucky with it. I need a caliper that I can trust for a reliable measurement over 4", so I bought an 8" Mitutoyo last night.
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  #31  
Old 10-25-2024, 07:18 PM
Zabco Zabco is offline
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Default Re: 1/16 Scale FrankenDiff

Yea, Mitutoyo makes very good measuring tools. I've got one of their digital micrometers. Dang thing will read down to like 0.00001 inch. Does like it's batteries though, always try to remember to remove battery if I'm not going to be using it for awhile.
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  #32  
Old 10-27-2024, 10:55 PM
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Default Re: 1/16 Scale FrankenDiff

My digital angle gage is hard on batteries too, and it goes through three 2032's at one time.

I'm waiting on more parts to arrive, I was looking for a replacement pinion so I could build my center axle. Turns out the only way I could find the pinion was either as part of the replacement differential assembly, or as a complete rear axle. This diff assembly was only a couple of bucks less than the entire rear axle, and didn't even include any bearings. So I ordered enough rear axles to be able to do the next truck too. I've got some square aluminum tubing coming that I'll split and use for the frame rails, also got enough of it for the next truck.

While I'm waiting, I'll start on the rear suspension. I plan on making something like a Hendrickson Walking Beam suspension. I downloaded their tech manual last night and it's got enough illustrations that I've got a pretty good handle on how things are supposed to go together.

I do know that I'll need to make a couple of minor modifications to my axle housings, to give me locations to mount the axle brackets for the equalizer beam mounts, and the torque rod mount.

Don
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  #33  
Old 10-28-2024, 07:13 PM
Zabco Zabco is offline
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Default Re: 1/16 Scale FrankenDiff

Don - sent you a private message.
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  #34  
Old 10-31-2024, 11:29 PM
ddmckee54 ddmckee54 is offline
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Default Re: 1/16 Scale FrankenDiff

For the last couple of days I've been playing with assemblies in Alibre. So far I'm batting 1000, I've managed to break every one of them that I've tried - but I'm learning from my mistakes. That doesn't mean I'm making less mistakes, it just means that when they happen now they are WAY more impressive. This is my latest test assembly, I'm still trying to figure out how to save the current view.

I hope I didn't screw up the previous posts, when I previewed my post I noticed that I hadn't scaled the image for posting. Somehow instead of deleting just the unscaled image, I managed to delete the entire Frankendiff album. I put it back, reloaded the photos, and shared it again - hopefully all is well. Where's the EASY button when you really need it?

Now all I've got to do is figure out how to get my spring hangers, springs, and equalizer beam center pivot to fit into a 32x65x10mm volume.

Don
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  #35  
Old 11-01-2024, 07:46 PM
Zabco Zabco is offline
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Default Re: 1/16 Scale FrankenDiff

Assemblies in Alibre can be one of the more frustrating things to do in that program. If two parts are off by only the smallest fraction of an angle, they won't go together. If two holes are out of alignment by as much as half the thickness of the hair on fly's ***, they cant be made concentric. Absolutely no more than three constraints on any component. Always anchor one of the first components you add, otherwise you chase components all over the screen. You can add constraints between components and planes or axis lines as well as other components. With constructions that have a lot of components make small sub-assemblies and then assemble the sub-assemblies. Sometimes you just have to try a number of different constraint configurations to find one that works.

The real nice feature of assemblies is that you can edit individual parts, or create new parts, from within the assembly. For example in the assembly you posted, if you want to add a cross member to your frame you can create the cross member, put it in position where you want it and then edit the frame rail to put the mounting holes to match the location of the holes in the new cross member. When you save the assembly the cross member will be saved as a new part file and the frame file will be updated with the new holes. FM

Have fun.
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  #36  
Old 11-02-2024, 04:49 PM
ddmckee54 ddmckee54 is offline
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Default Re: 1/16 Scale FrankenDiff

Zabco:

I found about the sub-assemblies after about the 2nd or 3rd time my suspension assembly tried self-destructing the axle on me. I tried to pivot the axle around the equalizer beam pivot, and just about every part of the rear axle moved separately - and I couldn't undo it. The rear axle, the center axle, the equalizer beams, and the torque rods are all separate sub-assemblies now. I did discover that when you insert sub-assemblies they are rigid until you tell them to be flexible. It took me a while to find out why the axle beam mount brackets would pivot in the equalizer beam assembly, but when that sub-assembly was inserted into another assembly they wouldn't pivot.

This frame is just a test jig so I haven't made it a sub-assembly. It will be a sub-assembly when I start working on the actual frame though. The frame rails shown are sized to the 1-1/4" square aluminum tubing with 0.063 walls that I got. The rails and the cross-member are the only parts that are currently anchored.

I've been poking and prodding at my current suspension assembly so much that I've gotten it completely confused. I think I am going to throw this version away and start fresh - and LEARN from my mistakes, instead of repeating them. That's tonight's task, now I've got to finish the yard work.

Don
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  #37  
Old 11-02-2024, 07:12 PM
Zabco Zabco is offline
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Default Re: 1/16 Scale FrankenDiff

All educational opportunities. What I love about all this. Keeps my brain functioning.
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  #38  
Old 11-03-2024, 05:20 PM
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Default Re: 1/16 Scale FrankenDiff

I've given up on making a functional suspension assembly - at least for now. It seems like every time I add another part to the assembly, and try to constrain that part, it breaks a half a dozen other constraints. For now I'm just going to use the assembly to provide feedback for the design of the beam pivots, springs, and spring hangers. I already found out that I'll need to make spacers for my torque rods, to get them to the correct length. My torque rods are a pair of M3 ball links that are screwed together with M3 threaded rod, and a 1/16" spacer between them.

I know that when the axles articulate, things are going to want to twist around. That's why they use the rubber bushings on the real deal. I've been wondering how I could easily duplicate that. I first thought of using silicon fuel tubing, but quickly scratched that idea - the tubing was too thick. My current plan is to use O-rings with a 1mm cross section, on both sides of the equalizer beam. I'll use a piece of brass tubing as a bushing. The bushing will also keep the threads of the mounting bolts from cutting into the plastic parts or the O-rings. If I oversize the 3 bores in the equalizer beam, that'll give it a little room to wiggle around when the axle articulates - I think.

I guess the proof will be in the building.

Don
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  #39  
Old 11-04-2024, 01:11 PM
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Default Re: 1/16 Scale FrankenDiff

If the Oring idea doesn't work out, you might be able to build up something like a bushing with Heatshrink tubing.
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  #40  
Old 11-05-2024, 02:29 AM
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Default Re: 1/16 Scale FrankenDiff

Progress is being made, even if I don't have any pretty pictures to prove it. (I forgot to get a snapshot of the suspension assembly before I called it a day.) I will try to update the assembly drawing tomorrow, there's a bunch of stuff that's been added. I've added the cross-member that supports the frame end of the torque rods. I even edited the cross-member to put the holes for the torque rod bracket mounting bolts in the right spots. I've added the torque rods, the torque rod brackets on both the axles and the cross-member. I've added the spring hangers, springs, and spring perches - though they've only been added to one side so far.

I've kinda figured out how I'm going to make the leaf springs. The current plan is to sacrifice the tines from an old lawn broom to make the spring leaves. The tines are about 5mm wide and 0.5mm thick. The SEEM pretty flexible, but they still may be entirely too stiff.

I'm debating whether I want to try making U-bolts for the springs or not. I've got a bunch of bike spokes left over from re-lacing a couple of 20" bike wheels for another project. That would give me plenty of raw stock for making the U-bolts. For a limited production run like this, 3D printed forming dies will be up to the task.

Don
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