Belt drive idler pulley

The black pulley in the photo is a urethane casting from a silicone mold pulled from a 3D SLA printed part, but the mold core for the bearing bore shifted off center during cure.

So I decided I could just weld up an acrylic version instead, and decided to go with clear just for giggles… almost went with fluoro orange :smile:

This is 85mm OD for scale reference.


Very cool! :sunglasses:
(I’m just curious…are the properties of acrylic the same as those of urethane? Will it hold up under whatever it’s being used for?)


This particular urethane is a pretty tough formulation and does exceed load capacities of the acrylic, however the only loads on the acrylic are a compressive load (which acrylic is adequate) where a drive belt contacts it, and the centrifugal force of the acrylic itself.

If it fails, it will be spectacular! :smiley:


Spoken like a True Maker.

Wake up the kids, they are going to remember this one…


Neat project! When are we gonna see the finished car?


Interesting iteration! Happy Birthday Mike :tada:
Yes, how is your build going?


What? I have to finish it?? :slight_smile:

It’s just about ready for safety inspection and registration. Really just need to arrange the appointment with the DOT officer and get a buddy to help me trailer it down there.

Also already made another design change on the pulley. The raised shoulders are removed, and went with the fluoro orange. Man it spins so smoothly. Here it is running at 90mph.


We are all looking forward to seeing this beast rolling.
Oh, and happy birthday!


Nice job on that. The whole thing is amazing!
Have you weighed it yet? About a quarter of the Tesla weight is the battery. I wonder has your choice of battery chemistry changed since you started building?

Riding the instant torque of an electric motor is a fantastic experience!
When did you pull the trigger on commiting to that build?
How long has it taken one man to manifest such a massive project when there is the constant obstruction of life on your back?
I imagine not having to answer to a spouse has made the journey smoother!

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I havent gotten it onto a scale, but since I have installed an adjustable air suspension with fairly precise pressure control, I can estimate the weight by filling the springs and noting at what pressures the chassis will lift up off the ground ~800lbs right now. My battery chemistry choice is forced into change if I ever need to service or update because the sole US importer of my current cells is an enormous PITA to deal with. My supplier flat out stopped carrying them as a direct result of issues that we had with the company on my last order. There are other cells of the same chemistry but not in a size format that works for this car. Luckily, Tesla modules are easily available and will fit fantastic, as will LG Chem modules from the Chevy Volt.

This coming November will be 8 years into the build. If I ever had a spouse, I wouldn’t still have one. :smiley:


I can hardly imagine the technical hurdles in a project like that. How did you handle the BMS? Is that adaptable or will a battery change require an updated system?

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I’m using an OrionBMS which is widely available and works with home-built packs with up to 180 cells in series. If I had to swap to Tesla modules, there are companies that are developing turnkey swap kits and making their own BMS boards that replace the OEM ones in the modules for easier interfacing (ie circumventing Tesla’s computers).


Self Fulfilling prophecy! OK, nothing actually broke… but apparently the recommended max torque for a 1/2" dia. stainless bolt is not enough clamping force to keep the adjustable idler mount from turning.


Back to the drawing board? :grimacing:

I’ll try a couple higher grades bolts first that I can torque higher, but I have a full design revision ready for production if needed. I even already ordered some fluorescent blue acrylic to make new roller revisions. :slight_smile:

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Where you getting the bolts? McMaster Carr?

Noooooo… I don’t pay retail for fasteners! :smiley:


Oh yeah…you’ve probably got connections huh? (I have to buy the damned things, no one ever has any of the sizes I need when I hit the local stores. Well, not quite true, but I’ll need a dozen and they’ll have 3 left. No one restocks worth a damn.)


Most retail hardware stores source their fasteners through Midwest Fastener or Hillman, and let their Vendor’s rep come in to inventory/place orders, which is typically a two week cycle. We use Midwest and have taken over ordering ourselves on a weekly basis because we move a lot of inventory.

I do order from McMaster for harder to find items or Fastenal.

Here we go… found a suitable bolt laying around and torqued 'er right up. No more ka-blooey. That torque rotating the swingarm towards the ground though!!


Oh silly me, I didnt even have the throttle mapping on the motor controls set up to give 100% throttle input… so once I fixed that… she went ka-blooey again.

So… new design it is! Look close and you can see I used the laser to actually label the parts with their revision numbers… because this one took some iteration to fine tune the tension on the belt.