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:
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.
I was carrying the robot around most of the first day, people constantly asking to try it out:
It worked well on the shiny floor of the lobby. You can just about see the new 3d printed lifter arm:
Programmers love robots!
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.
Testing the circuit out on breadboard:
The finished circuit. You can see it bolted to the back of the robot in the video.
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.
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:
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)
The lifter arm gear system looking through where the hopper would be:
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:
Next-up: better lifter attachment design, a couple of re-prints with tweaks and some software.
First test of the Raspberry Pi running off battery power with no external supply at all. In the picture the 5000mAh battery is the object at the back with “5000” written on it. My multimeter is measuring the voltage output. One of the Raspberry Pi (the thing with the red light on it) output pins is connected through the MotorPiTX board (the yellow circuit board on-top of the Raspberry Pi) to the breadboard.
The breadboard contains two circuits, the top-right cluster of components is the circuit that turns the output of the Raspberry Pi into something relevant to the motor driver in the bottom left, the bottom left cluster of components is the motor driver itself.
The Pi is pulsing the output causing the motor driver to spin the motor. The micro-switch just on the very bottom of the picture is one of the limit switches for the ball lifter arm.
Today I printed out and glued together the first iteration of the ping-pong ball hopper that takes up most of the space of the robot.
The assembled hopper:
Full of ping-pong balls, I can get 12-14 in without packing them manually. That seems like enough for now, but a larger hopper would be good.
Mounted on the robot. You can see the completed camera mount and Raspberry Pi mounted on the side in the foreground:
The reverse angle:
I needed to re-design the motor mounts on the robot base, they didn’t hold the motors securely enough and tended to shift around.
The new mounts are better fitting and include a small wedge that fits between one of the gearbox plates where there are no cogs.
One of the great things about 3d printing is being able to pull out part of a design and iterate over in isolation, then when you’re done incorporate it back into your main design.