Please, please stop asking, I’ll give you anything!

Me: My order was returned without ever having got to me.
Amazon: I can see that it got sent to the wrong distributor who must have realise this and just returned it.
Me: I see, this has happened twice in the last few weeks, is it going to happen again?
Amazon: I’m sorry to hear that, I’ve extended your Prime by a month free of charge.
Me: Thanks for that, but it seems odd that this never happened before, but has happened twice in a few weeks now. Is this likely to happen again?
Amazon: I’ve upgraded the delivery on your new order to Express, you’ll receive it tomorrow before 1:00PM.
Me: …

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I got my pan tilt servos working

I’m making a simple camera gimbal and tonight I wired up the right analog stick on my xbox controller to control the pan/tilt servos:

Tomorrow I will print out a prototype gimbal structure.

Testing Github commit hook one liners

A couple of ruby one-liners for dumping out the content of a github commit hook payload:

For hooks that use type application/json:

$ ruby -rpp -rjson -rsinatra -e 'set :port, 8000; post "/*" do; pp JSON(request.body.read); end'

For hooks that use type application/x-www-form-urlencoded:

$ ruby -rpp -rjson -rsinatra -e 'set :port, 8000; post "/*" do; pp JSON(params[:payload]); end'
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AWS IAM Policy for allowing s3cmd to sync to an S3 bucket

It’s a good idea to set an IAM access policy for anything that accesses AWS using your account details, I wanted to do this for s3cmd syncing a local directory to an s3 bucket. There are a number of posts on setting up the IAM policy for s3cmd already but none of the examples worked, I got a 403 permission denied error when running the s3cmd sync command.

After some digging it turns out that s3cmd now tries to set an ACL on the files it uploads, and this needs to be specifically allowed in the ACL. I’m guessing that it didn’t in the past, hence the now incorrect IAM advice. So here is the new working IAM policy, complete with the s3:PutObjectAcl permission added:

ping-pong press!

My robot was written about recently on the Raspberry Pi foundation blog, and now on the Pololu blog too, the place I originally got my tracks from!

Robot at RubyConf

I took my robot to RubyConf. It’s not really Ruby related, but I figured it would go down like a robot at a programmers conference… So I took the robot apart, packed it away and headed to Miami:

Miami

First job, putting the robot back together again. I was happy it made it through security. It was the first time I’d flown with a small toolkit.

The robot laid bare

I was carrying the robot around most of the first day, people constantly asking to try it out:

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It worked well on the shiny floor of the lobby. You can just about see the new 3d printed lifter arm:

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Totally coincidentally Ron Evans also did a great talk on Artoo and the newly announced Gobotio.

Programmers love robots!

Prototype lifter arm

I added a prototype lifter arm to my robot yesterday. It needs re-doing (it’s unreliable and heavy) but it works for now.

I’m using a new motor driver circuit for it as I burned out the SN754410 motor driver I was using, the lifter motor seems to peak briefly at about 1.5 amps when starting to lift the arm, and that’s out of the chips range. I stayed up late making a new motor control circuit with a L298N that can provide a lot more power.

Here is the robot picking up 12 ping-pong balls. I was driving, Morwenna was filming:

Here is the same run seen through the on-board camera. Almost all of the run was done watching the live feed rather than watching the robot itself:

Here is the paper strip-board design for the L298N circuit.

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Testing the circuit out on breadboard:

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The finished circuit. You can see it bolted to the back of the robot in the video.

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First robot remote driving test

I programmed some remote control software using a Golang receiving program on the robot and a ruby control client using my gamepad ruby gem and an xbox1 controller. It worked OK. It was a bit jerky, there’s no PWM so no acceleration, it’s either go or stop; anything not totally rigid on the robot wobbles. Also the position of the camera doesn’t show enough of the robot so it’s hard to get a real idea of where the robot is.

I was filming, the robot was being controlled my my wife, Morwenna, from upstairs.

The robot is also prone to shed a track if the “half turn” is used too much, that is one track forwards or backwards, the other one stationary. I can fix this in software if I can work out a way to do PWM on the robot that doesn’t run the Raspberry Pi CPU.

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Rejects and prototypes

Prototypes and rejects from the 3d printer. All part of the design process for my robot:

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New robot base design and completed prototype arm assembly

I spent all day at hacman Tuesday and Wednesday printing and tweaking robot parts. I put it all together when I got home. This is the front, the lifter arm has holes to allow me to screw in different attachments, I’ve still not designed that part of the robot yet:

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Here is the back view, you can see the lifter arm gear housing (the curved structure) and the motor that drives it, also the battery (underneath the ball hopper)

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The lifter arm gear system looking through where the hopper would be:

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I need to design an attachment for the end of the lifter arm. Here I’ve created a simple one using meccano. It’s too heavy, the bolts catch on the floor and it dumps the ping-pong balls short of the hopper. Other than that it’s perfect. You can see the camera with capped lens that I’ve just wedged into the structure temporarily:

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Next-up: better lifter attachment design, a couple of re-prints with tweaks and some software.

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