Jarvis – Drive Train Part II

Now I have my wheels I can refine my design a little. Being able to hold them in my hand gives me a feel for how they attach, and their weight distribution. I refined my wheel hub and added some supports in the middle to keep my pulleys upright and also ordered some components to help me build my axels.

Flipping over the hub you can see where I mounted a stepper motor. Stepper motors do not make good motors for robots but I have a kabillion laying around from all the time spent in 3d printing so why not use them until I can settle on something better.

And so I connected the stepper motor to a driver and step generator and …. it works! tada!!

If you are interested in the components to drive the motor, you can grab them here:

Oak-Pine 3D Printer 42CH Stepper Motor Driver Shield Expansion Board DRV8825/A4988 UNO R3(Black)

DC 5-12V/15-160V Stepper Motor Drive,PWM Adjustable Stepper Motor Controller Signal Generator Speed Regulator

I have everything connected to a meanwell 12v PSU in this instance.

Excuse my lunch making a guest appearance

This is a milestone for me. My belt arrangement worked, my tires move and everything fits!

Jarvis – Getting Wheely Serious

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So starting from where we left off last time, as I said I pretty much designed the chassis around 2.2″ RC wheels with some nice big 120mm tires. That gives me a lot of bounce in just the rubber for absorbing some of the shock of moving around. They also are easily available and not (ridiculously) expensive.

I ordered some wheels from ali express , so we will see how they turn out. In the mean time it would be very nice to see how large these are in real life to get a feel for how big Jarvis is going to be.

This is where 3d printing really comes into its own. Rapid prototyping is its bread and butter. I took a 2.2″ wheel from thingiverse and printed it to get an idea of scale.

Prusa MK3 hard at work

At this point I’d like to Thank Josef Průša and Team for adding filament run out detection to the Prusa line. Half way through this tire my 3d printer ran out and I was able to put some new filament in and finish the job!

I printed the first wheel in full with no infill at all and it came out ok but took a while. I threw some black PETG in and printed the next 3 wheels as half tires so I could understand the scale. I can always put two back to back to make a full wheel if I needed it. The result was quite impressive. I do have some ninjaflex filament somewhere and would loved to have tried that but that will be another days fun.

4 wheels at intended spacing – 150mm apart. Those motors are Nema 17 for scale.

We know the wheels have 17mm hex on the back and a 5mm hole in the middle so I threw together a wheel hub in Fusion 360 so I could plan for the driveshafts

A quick test fit and these actually worked really well. So now I have wheels, and a hub to test not only size but drive when I get to that part. I have a good feeling that I now know the size of the robot and I am comfortable with it. we are going to have plenty of space to work with and it is going to look impressive!