Greenpower Car using LowRiderv2

My son has been building an electric car for the Greenpower Formula 24+ series (Standard motor and batteries - rest is custom, within regulations).

The LowriderV2 has been an absolute star : cutting the plywood chassis, and then slabs of insulation foam for the body plug.

The only slight issue was one of the Z steppers getting out of sorts and diving into the foam. Those do the hardest work - don’t skimp on the spec, and keep the threaded rods clean.

CAD/CAM was all Fusion 360.

 

 

 

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This is awesome! You cut the foam a couple sheets at a time and glued them up then sanded?

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Yup, we cut 27 layers of 100mm EP70 foam. Most layers were 3 or 4 simple contours, depending on gradient(so it does like separate layers). The nose and tail had additional parallel passes to get the right curves. Main trick was to have an initial contour pass that cut away as much waste as possible.

Gentle sanding to shape, a coat of household acrylic primer, then lightweight filler. Finished with a layer of glass (using epoxy resin to avoid melting foam) , followed by more filling and sanding (mostly wet).

Finally laid up and vacuum bagged.

Mostly went OK, biggest snafu was not keeping underside open to let air in when we did bagged main body - so had creases in styrofoam (resulting in rather more filling and sanding than we anticipated).

 

 

 

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OMG!!! I love it!

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That is really neat! Great project. I hope to do things like this with my kids someday.

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So cool… what a great experience to have with your kid.

 

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That looks absolutely incredible!!
I just posted a question about doing something similar (though much less involved). Do you happen to have a build log somewhere I can read? I bet I could learn a TON.

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Thanks!

Unfortunately, we don’t have a build log - it was all a bit of a mad rush to get the car on the grid after the first stab at the bodywork failed - Happy to answer questions tho’.

Various observations from the top of my head:

Overall shape, slices, and toolpaths were all developed using Fusion360 - and included locating holes for internal dowels.

EPS70 foam was cheap and OKish, but for a better finish I’d probably go with styrofoam (blue/pink/gray).

Be prepared for a lot of dust - will need a hoover stooge.

Helped to use a good quality long reach ballnose cutter - eg: 8m dia, 150m long carbide cutter. Cheap things off ebay had a bad habit of shaking/bending.

Did lots of dry runs of the worst case toolpaths to check acceleration settings - we had to really dial it down to cope with the steep parallel passes

We did (IIRC) four passes with spackle and abrasives to get a good finish before skinning the plug - much easier than trying to shape that after epoxy+glass skin (even so - had a few rounds of bondo afterwards).

We were not too bothered about surface finish (and were in a hurry), so laid up the final body shell directly onto the plug, rather than making a mould such that the good surface is outside. If we need another, we may make the effort to go with a mould.

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Wow. This is truly awe inspiring. Congrats to ya’ll for finishing such a cool project.

Thanks for taking the time to reply. That’s a really long mill. I’ll make sure to look for a good one, since it makes sense to buy one good one vs my usual strategy of several bad ones then a good one, lol. I hate the idea of breaking a good tool right off the bat, but that probably isn’t much of a risk with foam.
I also thought I might get away with the thinner construction foam at the home depot. Stacking them up means that for a lot of them, the top surface won’t need to be machined at all, but I have a lot of practice to do first.
I had also thought about laying up on the foam, then dissolving or breaking /sanding the foam out. Hadn’t really thought about the surface quality, because my first goal is car interior, which will be covered. I would like to make smaller exterior parts and eventually a ground - up car build, so maybe full-on body panels for that. Sounds like it might be a better idea to plug then mold like you suggest and trade a few dollars of fiberglass for many hours of finishing.
I appreciate the pointers!

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Great job! My son is two now so have to wait for a fun project like this. BTW is it full sheet lr2?

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Thanks! Although he did it for the challenge - It has been extremely good for interviews and college applications.

It is not a full sheet sadly - only 6’ by 3’. That was enough for the car, and also was the size of the remarkably solid table that the school was throwing out. I have enough spare tube to convert to full size if needs be - one of the features that really sold me on the LR design.

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Very cool! What is your Z axis usable height? I am going to build a LR2 for building horn loudspeakers from foam and later from plywood and hardwood.

Thanks!

We used 300mm Z leadscrews - giving room for ~120mm tool stickout and 100mm of workpiece.

It worked well - with supervision. Notable points:

  • A good router with low runout - we switched from Makita clone to real Makita - RT0700CX4. The clone was fine for the plywood work, but was NOT good with a long tool.

  • Good bits - particularly for long stickout. There are cheap long router bits around that fail in scary and dangerous ways. We used a 150mm long 8mm ball nose general purpose carbide bit.

  • I have since put thrust washers on the Z axis ( between shaft couplers and motor) to take end loads off the steppers. We had a stepper fail - an internal plastic spacer disintegrated.

Overall - 100mm styrofoam stock worked out well - I’d not want to go much thicker than that on this setup.

Good luck!

Thanks! If I understand it correctly, a thrust washer is just a washer placed between the coupler and frame? So that the load is taken by the motor frame and not motor bearings? I came from the electrical side to this project, so my questions about mechanical stuff may sound a bit dumb:)

Being able to carve things out of 100 mm styrofoam would be perfect, noting down the lead screw length.

Yes, hmm, actually, thinking about it, i started with ptfe thrust washers, then switched to ball thrust bearings - the three part thingys. Important thing (IMO) is to take end load of steppers, which are supporting the weight of the router.