Jarvis – Getting Wheely Serious


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!

Jarvis – Revisited

There’s something about this COVD crisis that makes me want to dust off old projects, old hobbies and pick up where I left off. I wonder how we will look back on this in years to come. Will we think that the stay at home measures were excessive? or will we think that our actions saved society from unfathomable suffering. Will we have learned that for weeks we did not need the things that we thought our life was impossible without, will we care more for the people we were separated from, and the places we could not visit. I hope so, I hope something positive and permanent comes from something so devastating.

I think my desire to pull some old projects from cold storage comes from the reminder that not all that is gone is lost. Not all that you’ve moved on from has passed by. When I first put together my robot Jarvis, times were simpler, life was easier. There is a nostalgia from the time before I put in the box that I hope to release by opening it. Right now these little projects are helping to lift my mood, keep me challenged and help me feel like I have forward motion. Time to open the box. Deep breath…

Where to begin?

In the time since I built Jarvis I have learned so much. I have built things I am truly proud of. I hope some of them make blog posts one day in the future. I am not an engineer by trade, but I enjoy creating things from my own designs. I am often wrong, but I also often surprise myself with where I end up. My aim is never to make something that’s perfect, its to make something that’s a challenge for me.

So where should we begin? If I were a little robot that’s lived in dusty box for almost ten years, what would I want? I think I’d want to stretch my legs for starters..

Some design decisions then, to give Jarvis a good start:

  • Wheels – Tracks are great, but they are noisy, expensive and complex. Jarvis needs to be fast on his feet, and agile. He has to shake the dust off. Legs are too expensive (Jarvis MK4?)
  • Suspension – Jarvis needs to react to his terrain, he has to get up from a small knock or fall, no cracked plastic
  • Higher ground clearance – no more beaching on small objects, lets give him some space underneath
  • Modern Electronics – Arduino have changed the world in the last decade. It is now impossible to think about a microprocessor or motion control project without them. Jarvis development will be rapid using modern tools
  • Strength – Jarvis needs some power and some strength. He needs a strong drive, and a strong back. I need a rigid chassis but with the capability to move.

I feel that’s a good set of objectives. Time to open Fusion 360.

A new design

Excited to get started, I roughed out a new design. I took inspiration from around the internet. 8 wheels, pivoting in pairs, and a body that can move. No suspension yet, but its an early start. With this body Jarvis can have ground clearance, can tackle many obstacles and should be able to carry some weight!

I think this is a great place to start. 4 motors to power the 8 wheels.

This is a great platform because If I can spare enough power I can even use stepper motors with trinamic drivers and measure how much current is needed to move the wheels and make an electronic traction control of sorts. I can also position angle sensors that allow me to understand the positioning of the drive sections (that power 2 wheels) and the main body. I am not sure at this point if I like the swivel in the middle, I wanted flexibility but this gives me many other design headaches around placing electronics, batteries, and even picking the darn thing up.

The whole scale is designed around standard (I learned from my research) 2.2″ RC Wheels. The tires are around 120mm wide so nice and large for getting around.

Things are starting to come together. anyway, that’s enough for tonight, next stop I need to order some wheels.