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And then for the fist time in over 30 years in a leafy Surrey village under the baking July sun a man thought " I'm going to make that chassis out of Kydex "

Just a little tip for anybody using Kydex , pre cook it before cutting or drilling , the sheet I had I cut and drilled before heating and bending up the bumper , all the drill holes lined up until I heated it , I think at that point it shrank , not a lot but enough to be really annoying !

I started modelling the gears and gearbox today , Fusion 360 has a gear modelling feature that makes it quite easy , of course that didn't stop me getting the measurements wrong ! The gearbox is maybe 85% modelled and the gears are printing but I've been at it most of the day and I've lost the ability to do simple arithmetic , my brain is totally fried both sides and then some !

haha yeah gears are a pita! I found it easier to hop on SDP-SI and find the gears that are the correct pitch and pressure angle. Then I use that as the profile to make my own

Fusion has a gear maker , you just fill in the boxes with pitch, number of teeth , pressure angle ,lash ,width and centre hole die etc and it generates the gear , my problem was just measuring and copying the originals correctly , just dumb errors , I got the actual gear type spot on .
The gears finished printing and it all looks good for mesh and fit ,the gears are only in PLA and just a quick draft print so not strong or high quality , I'll post some pictures in the morning .

I have a quick draft print of the gearbox printing , should be finished at 6pm ish , frankly I'll be stunned if I have it all correct !
I thought I'd lost 2 hours work earlier as we had a power cut , I lost the first test gearbox I'd already started and I'd been refining the design models , fortunately Fusion 360 had auto saved only about 10 min before the power went out so I lost very little , it gave me a chance to start printing again with a far more refined design so its not all bad .

New gears in a genuine box , i thought the 20 tooth idler gear was oversize and tight but on closer inspection it had a bit of elephants foot , elephant foot is where the print swells out a little on the first 2 or 3 layers on the bottom , i just flipped the gear the other way up so the wider bit was no longer in contact and it all runs smoothly .


Again these gears are draft quality made in PLA just to check the fit , ill print higher quality ones later on probably in nylon .I dont have all the components for the diff yet so the gear is not shown .
The diff is going to be an area where I'm going to modify the design slightly , the original gearbox has a round 1mm deep protrusion for the diff bearing on the left side , thats easy for an injection molded part but with a 3d printed part it would mean the rest of the left of the gearbox would be printed on support material and have a rough surface texture , the reason Yokomo designed it that way was for the diff to line up perfectly with the rest of the gears putting no axial twist on the gears , I'm going to have the diff 1mm out of alignment , it will still have full width gear engagement , its a price I'm willing to pay .The picture below shows the bearing protrusion around the out drive.

The gearbox came out better than i had hoped , it all fits and the gears run free ! my only three little finish touches will be 1 i forgot the holes for the top deck/chain guide to mount, 2 i need to extend some screw holes inside the box and 3 the hexagonal holes to capture the nuts are too small . I'm chuffed to bits that its going so well !

OK I think I've made all the revisions to the design and a second prototype is starting to print now , 8.5 hours print time ,hope it works !

Second version gearbox came out well with just one further modification needed ,the hex holes for the captive nuts are still a little tight , I had to press them in with a vice so I'll make them larger still . The only other thing is to add the mono shock bell crank mounts , I have no plan to use them but it completes the design .
I'm waiting on bearings, 5mm steel rod to make gear axles and the diff bearings and thrust washers , there's nothing more to do till they all arrive .

Now have chain sprockets printing ! unfortunately I'll have to wait till next month to get nylon filament , its my 20th wedding anniversary on the 17th so funds are tight .

GoMachV wrote: ↑Sun Jul 07, 2019 2:17 pm haha yeah gears are a pita! I found it easier to hop on SDP-SI and find the gears that are the correct pitch and pressure angle. Then I use that as the profile to make my own

Turns out you were right , I've had to play about with the gears to get them working right , they ended up being a bit tight once I had them on decent 5mm axles , I was using M5 threaded rod before and its got a bit more wiggle in the bearings that allowed them to run smooth ,I've re printed them with 0.2 mm lash and they seem better .
I've also been modeling some sprockets for the chain , I kind of just tried to copy the original ones as best as I could , very trial and error but I think after about five attempts that I have a nice sprocket that is positive and smooth , another few days and I'll have all the parts to finish the whole box , its probably time to print a better quality gearbox as well .

Just wondering if you have the little brass spacer on the right out drive, I might have missed it as I've not read every word of your thread but I congratulate you this a really cool undertaking.





just realized this is left side outdrive but just asking ?

In that picture I'm not sure where the spacer is , I even took it out at one point , the gearbox I've made will be 1mm narrower at the diff so the spacer will need to be 1mm narrower as well , the stock gearbox has a protrusion around the left outdrive so the bearing can be further over and allow the diff gear to be aligned on the same plane as the gear on the other side of the 20 tooth idler , this puts less strain on the 20 tooth idler , mine will be 1 mm out of alignment in order to avoid having the protrusion on the left side of the gearbox , otherwise only the protrusion will touch the build plate and have a smooth finish and the rest of the side of the gearbox will be built on support material and look crap , its a compromise but acceptable in my opinion , all the stock gears will still fit in my gearbox but the diff spacer will need to be 1mm thinner .

I think I've finished the outer gearbox design so below are the last pictures of the development box , i had a motor fitted earlier and had it spinning albeit without the diff and it was very free , I think the gears are all in good shape too with the exception of the untested diff gear , the new gearbox is printing now but its going to be over 12 hours as I'm doing it slower and at higher resolution .