Progress Update

He’s not naked. He just needs a respray.

The chaps at PiWars HQ want an update… So, here it is in a blog post.

PJD Mk1 has been built with some temporary electronics (which allow it to be driven by RC). We’ve been driving it around; and basically it works fine. Even the slightly risky 3D printed crown gears seem to be holding up.

But all is not well. It’s too slow. Which should have been obvious since the track units include a 4:1 reduction ratio.

Therefore Mk2 is on the drawing board / CAD system. It will use four independent motors (thereby allowing the use of mecanum wheels), with a direct drive onto the tracks, so it will drive at the same speed as P21. This will be fast enough.

There is one further problem: some of the components we planned to use for the electronics have a five month lead! Team PiDrogen is a victim of the global chip shortage. :0( Looks like we will have to come up with a different design.

Now, where’s the tin of red paint?

Apple Picker MkII


The apple picker I blogged about a couple of days ago is nice and it works. But I’m not going to use it.

MkII is better because it has no moving parts; the robot will just drive up to the tree and the top prongy-thingy will knock the apple off the tree and into the chute. At least that is the plan.

MkI was a case of reaching for the the CAD package before actually engaging brain.

PiWars 2022 at Home; We’re In!

Hmm, possibly a bit behind the curve for this post but…  We’ve been accepted into PiWars 2022 at Home!  Wahoo, here we go again! :0)

And here’s the robot we plan to build for the competition:

For context, the theme of this year’s competition is “Old McDoofus had a farm” (Doofus is the name of the little red robot logo for the competition).

We call our new robot, “PiDrojon Deer” (or “PJD”) and you can find out more here.

Here’s a synopsis of the conversation that took place at PiDrogen HQ that lead to the design…

Dad: “Let’s enter PiWars, entries are open!  We could use last year’s robot to keep things simple.”

Eldest son: “Well, we could… But… A tracked robot would be way better than last year’s robot. And last year’s robot isn’t cool enough. We need a new robot. It should have tracks and look cool. Cooler than last year’s anyway. Tracks would be better over obstacles, wouldn’t they?…”

So, this year, eldest son will have it his way. Our new design has tracks, is hopefully cool enough for his nibs, and is bang on theme!

To be honest, I think this design is risky.  To do well this year we are going to need a robot that can whizz about the arena autonomously and accurately.  I have the feeling that a tracked machine will neither whizz, nor be accurate with its movements.  Furthermore, a tracked machine will not offer a smooth ride; I’m expecting a blurred video feed. So, the pressure will be on to upgrade the control system!  (But in case that doesn’t work, this design has a trick up its sleeve. But that’ll be the subject of another post).

Take a look at PJD’s page if you want to find out more.

Is this the cause of P21’s dodgy wheel?

Up close to P21’s back right wheel encoder

P21 has had a dicky back wheel since it fell off the roof during filming of the Obstacle Course for PiWars at Home. The motor runs, but the speed is not well controlled, so I assume the problem is related to the encoder.

After the competiton I dismantled the back axle, reseated the connectors, and all seemed to be fine again… for a while.

But recently I’ve been testing a new game for the Sidmouth Science Festival and was frustrated to see that the robot was quite unreliable when aligning on the game pieces. I set to re-tuning the vision system, because that’s always the source of any problems, isn’t it? But this time that didn’t really help.

Finally I realised the robot was sometimes dragging it’s back wheel. I dismantled the back axle again (which is too fiddly and frustrating) and removed the motor.

I see that one of the encoder Hall sensors is leaning out from the magnetic wheel on the motor; see above. Hopefully this is the real source of the problem. I suppose this is due to the fall, but it’s hard to see how.

My plan is to re-print the lower half of the back axle (since it is damaged), re-align the Hall sensor, then put the whole thing back together… But I think I will swap the offending motor with one of the front ones; I really dislike rebuilding the back axle!

Sidmouth Science Festival

Each year, Sidmouth (in the southwest of England) has a science festival.  This, year it takes place between the 8th and the 17th October 2021.

We like to go to the festival for the rocket car contest. If you’re an avid follower of our blog, you may recall that our entries won the rocket car contests in 2017 and 2018; see this blog post.

This year, on the 16th of October, there is to be a robot workshop where families can build, drive and code robots.  We have agreed to demonstrate P21, probably doing a derivative of the Tidy Up the Toys challenge.  However, we decided to make some changes to the robot (and a new arena) first:

  • The TUtT gameplay will change.  The arena (which I hope will be on a tabletop) will have a robot parking bay at one end and a “stack zone” at the other.  People will be able to place the blocks in the arena, then press a go button (either P21’s existing start button, or perhaps one on the arena).  The robot will collect the boxes and re-stack them in the stack zone.  Possibly there will be a P21 camera view displayed on a monitor somewhere.
  • The end zones on the arena will be coloured so that the robot can use them to localise.  We will use walls to stop the robot from falling from the table; the walls will also be coloured so that the robot should be able to avoid them visually too.
  • We may use barrels instead of boxes since they have the same width from any direction; this means the robot can approach them from any direction to lift them too.
  • We might take a look at P21’s headlights.  We don’t know what the lighting is like in the demonstration venue; it would be a good idea if P21 could provide it’s own illumination of the game arena if required.
  • Finally, we’ll update the start-up and shut-down procedures for the robot; SSH-ing into the Pi to do a demonstration is going to be too slow!

So, if you find yourself near Sidmouth on October 16th, come and say hello!