Pololu Blog (Page 13)
Welcome to the Pololu Blog, where we provide updates about what we and our customers are doing and thinking about. This blog used to be Pololu president Jan Malášek’s Engage Your Brain blog; you can view just those posts here.
Our new programmer, the Pololu USB AVR Programmer v2.1, was supposed to be a minor update to our existing programmer, coming right after the A-Star 328PB Micro that we released last month, with the main point of excitement being the Las Vegas-inspired $7.77 price. But as we were testing the combination of the programmer with the A-Star, we were getting brown-out resets on the programmer when it powered the A-Star. The relevant part of the circuit was just a P-channel MOSFET that connected the programmer’s own logic voltage (which we call VDD) to the VCC pin of the ISP connector:
MOSFET-based target VCC power control used on Pololu USB AVR Programmer v2.
The problem was caused by the MOSFET turning on too well (quickly and with low resistance), causing the logic voltage on the programmer to drop if the VCC of the target device had more than a few µF of discharged capacitance on it. The bigger the capacitance on VCC, the bigger the voltage drop on VDD, until eventually the drop was big enough to trigger the brown-out reset protection on the programmer’s microcontroller. We tried various firmware tricks with our existing hardware, such as turning on the MOSFET for very short pulses to gradually charge up the target device’s VCC capacitance, but none of them worked reliably enough. So in the end, we decided to redo our PCB and put in a dedicated high-side power switch with a controlled slew rate. The new programmer can now power target boards with up to about 33 µF on their logic supplies.
These are the two other improvements we made to the new v2.1 programmer over the older v2 programmer:
- Plugging a v2 programmer into a 3pi robot could cause one of the motors to briefly run at full speed because the programmer’s circuitry for measuring VCC could inadvertently pull up one of the 3pi’s programming pins (which doubles as a motor driver input) before the GND connection was established. The v2.1 programmer has improved circuitry for measuring VCC which limits the duty cycle of this effect to about 0.2%, so the motor won’t move (but it might make a 25 Hz clicking sound).
- The v2 programmer would typically brown-out if a 5 V signal was applied to its RST pin while it was operating at 3.3 V. The v2.1 programmer does not have this problem.
The v2.1 programmer is otherwise identical to the v2 programmer, which means it’s a USB AVR microcontroller programmer that can program targets at 3.3 V and 5 V and offers an extra UART-type TTL serial port (like the popular FTDI USB-to-serial adapters) that can be super handy for debugging, bootloading, or even general connection of your project to a USB port.
Pololu USB AVR Programmer v2.1, labeled top view.
The v2 programmer was already a good deal at under $12, but at $7.77, and with free shipping in the USA, we hope to make AVR development extremely accessible. The manufacturing improvements and other cost reduction initiatives I have been blogging about this year help us make this offer without losing money on it, but I am not expecting to be making money directly off of the programmers, either. My goal is to give you the best value in a basic tool you will use over and over as you build your own projects, with the hope that that will help you keep Pololu in mind the next time you need some electronics or robotics parts.
And, as usual for our new product releases this year, we’re offering an extra introductory discount: the first 100 customers to use coupon code AVRPROGINTRO get that already great $7.77 price dropped to $5.55 (limit 2 per customer). (Click to add the coupon code to your cart.)
As I showed in my last post a few weeks ago, our Tic stepper motor controllers offer six different control interfaces so you can add stepper motors to a variety of projects. Getting started with the Tics is easy. This new video tutorial steps (see what I did there?) you through getting your stepper motor running with our Tic controllers:
As I was making this video, I realized one of the coolest things about the Tic is how quickly you can work out the capabilities of your stepper motor. Even if you’re comfortable using one of our stepper motor drivers along with a microcontroller, using the Tics makes adjusting settings like current limits, step rates, speed, and acceleration as quick as a click of the button, and you can control your motor directly from the software to make sure it’s behaving how you would like. So you might want to keep an extra Tic around for that purpose, just as a stepper motor tester.
Right now you can still purchase our newest Tic at a special introductory price of just $15.53 using the coupon code T500INTRO! (Click to add the coupon code to your cart.) We also cover shipping in the US! Note that this introductory offer applies only to the units without connectors soldered in.
We are now carrying Ion Motion Control’s line of single-channel RoboClaws, the Solo 30A and Solo 60A. These versatile, high-power motor controllers have nearly all the same features and performance capabilities as their dual-channel 2×30A and 2×60A counterparts, just with one fewer motor channel. Just like the rest of the RoboClaw family, the Solos support a variety of interfaces, including USB serial, TTL serial, RC hobby servo pulses, and analog voltages, and integrated quadrature decoders enable closed-loop position or velocity control.
Unlike our selection of dual-channel RoboClaws, the Solos also feature a rugged, all-metal case that protects the driver while simultaneously serving as a heat sink, and they have four 12 AWG unterminated leads for supplying power and connecting a motor.
The following table shows our full updated offering of RoboClaw motor controllers:
|Operating voltage:||6 V to 34 V||6 V to 34 V|
|Continuous output current:||30 A||60 A||7.5 A||15 A||30 A||45 A||60 A|
|Peak output current:||60 A||120 A||15 A||30 A||60 A||60 A||120 A|
|5V BEC max current:||1.2 A||1.2 A (V5B or later)||3 A|
|Size||60 × 32.5 × 23.5 mm||48 × 42 × 17 mm||74 × 52 × 17 mm||100 × 86 × 25 mm|
|Weight:||130 g||18 g||60 g||295 g|
Erik Pettersson’s interactive sculpture, Roball, is a gripping take on the classic rolling marble kinetic sculpture. Roball uses a robotic arm to pick up a small ball and randomly place it on one of five tracks, where it twists and turns as it rolls down the track, eventually coming to rest at a holding station. The input to the system is a single pushbutton, and when the user presses the button, the arm picks the ball up wherever it stopped. Then, the device randomly selects another path, moves the marble to the start of that track, and releases it. A 12-channel Maestro controls the whole system and analog sensors (which might be our QTR-1A) at each holding station at the end of each track help not only detect the ball, but help the Maestro randomize its next move. Because of the ball’s non-uniform surface, the analog sensor will read different values depending on how the ball is positioned. That reading is then used in a calculation to determine what track to roll the ball on next.
You can learn more about this project on its Thingiverse page.
Our Tic stepper motor controllers are pretty awesome, and the new Tic T500 we released today should make stepper motors even more accessible for your next project. This latest version features a broad 4.5 V to 35 V operating range that covers everything from small 2-cell lithium battery packs up to 24 V batteries or power supplies while costing just $20 in single-piece quantities. This video gives you a quick overview of what the Tic stepper motor controllers offer:
The Tics make basic speed or position control of a stepper motor easy, with support for six high-level control interfaces:
- USB for direct connection to a computer
- TTL serial operating at 5 V for use with a microcontroller
- I²C for use with a microcontroller
- RC hobby servo pulses for use in an RC system
- Analog voltage for use with a potentiometer or analog joystick
- Quadrature encoder input for use with a rotary encoder dial, allowing full rotation without limits (not for position feedback)
|Operating voltage range:||4.5 V to 35 V(1)||2.5 V to 10.8 V||8.5 V to 45 V(1)|
|Max current per phase
(no additional cooling):
|1.5 A||1.5 A||1.5 A|
|Automatic decay selection:|
|Price (connectors not soldered):||$19.95||$29.95||$29.95|
|Price (connectors soldered):||$21.95||$31.95||$31.95|
1 See product pages and user’s guide for operating voltage limitations.
Basically, the new T500 does not offer the finer microstep resolutions of the T834 and T825, and the T834 supports very low operating voltages while the T825 supports higher operating voltages.
For those of you interested in more of the details of the stepper motor driver, the Tic T500 uses the new MP6500 from MPS, which we also offer on some low-cost MP6500 breakout boards with analog (small trimmer potentiometer) and digital (via PWM) current limit setting options.
In keeping with the tradition we started this year, we are offering an extra discount for the first customers, to help share in our celebration of releasing a new product. The first hundred customers to use coupon code T500INTRO can get up to two units for just $15.53! (Click to add the coupon code to your cart.) And we’ll even cover the shipping in the US! Note that this introductory offer applies only to the units without connectors soldered in.
Pi Day is nearly upon us, and to celebrate, we are discounting a variety of exciting products that can be loosely associated with “Pi”. The sale starts tonight at 8:36 PM PDT and runs through the end of the 15th. And in case you are wondering about the strange start time, that makes the sale 3.14159 days long in yet another tribute to this wonderful irrational number (if it bothers you that 3.14159 is not irrational, you can pretend that the sale lasts exactly π days).
MIRR, which stands for Mobile Interactive Responsive Reflector, is an interactive installation that responds to people’s movement by independently rotating elements in its array of 98 mirrored panels. A FEETECH Mini Servo FT1117M actuates each panel and a total of five Mini Maestros control the servos. People can also use a custom box of arcade buttons to independently move each panel. You can read more about how MIRR works in this post on our forum.
My posts last month (here, here, and especially here) about the new electronics manufacturing equipment we installed focused on our new pick and place machine and stencil printer. This post is about the other major new machine we got at the same time, an automated optical inspection (AOI) machine from Mirtec.
AOI machines have cameras that move around over an assembled board to take a bunch of pictures that then get processed to determine whether or not the board is assembled correctly. The machines often have several cameras that enable taking pictures from various angles, along with fancy lighting to variously illuminate the boards and components being inspected. Our AOI machines have rings of LEDs of different colors at different angles, so that, for example, red light highlights a different portion of a solder fillet than blue light. This picture shows a panel of our Dual G2 High-Power Motor Drivers in one of our older AOI machines:
A panel of Dual G2 High-Power Motor Drivers illuminated by blue LEDs during automated optical inspection (AOI).
The tricks with lighting are basically attempts to generate more three-dimensional information than you can get with just 2D pictures out of a camera. What is exciting about our new machine is that in addition to the traditional lighting and cameras, it also has a sophisticated sensor for doing precise height measurements everywhere along a component. Machines with this kind of sensor are called 3D AOI machines.
5-pin SOT-23 component getting set up for 3D automated optical inspection (AOI).
The machine we got is Mirtec’s latest AOI machine, the MV-3 OMNI, which is a desktop or batch version of their inline inspection machine that has the same technology. I ordered the machine with the optional stand, which turned out to be a good thing because for a desktop machine, this thing is huge. The crate was much larger than I expected, and while not requiring a 10,000 pound forklift rental like the pick and place machine, we did have to use our fork extensions.
Out of the crate, the machine and stand are quite a bit smaller. Something to keep in mind for anyone considering such a machine is that this one is too big to fit through a single three-foot door.
We had an especially busy week, with the installation and training for the AOI machine happening at the same time we were doing the Europlacer pick and place machine and stencil printer installation that I wrote about earlier.
Mirtec MV-3 OMNI 3D AOI machine training.
Our Yestech AOI machines are visible in the background of that last training photo. (They are also featured in our The Manufacturing of A-Star 32U4 Micro video.) We already performed 100% AOI on every board we made before we got this latest machine. We are happy with those machines, and since we had two, capacity and redundancy were not primary motivations for getting this new one. With any piece of equipment like this, the challenge is to find every possible defect without generating a lot of false positives. If the settings are too lax, or the machine is not capable enough, defects will make it through, but it’s not enough to just flag every mismatched pixel since the ultimate authority is still the human operator that inspects every spot the machine identifies as suspect. If the machine inundates the operator with a thousand possible defects for every actual defect, the operator is likely to miss the one actual problem. It’s difficult to characterize this since there are many different components and every design is different, plus how we set up or train the machines also matters a lot.
3D automated optical inspection (AOI) setup for Pololu DRV8825 stepper motor driver carrier.
So, the main motivation for getting this new machine was the hope that it will give us more capabilities going forward to have the highest possible confidence in the quality of our products. The new machine is almost twice the cost of the older ones, and especially with the 3D capability, it should be able to deliver that. Our first impressions have been very positive, but to really know, it will take some time to get familiar with the machine’s strengths and weaknesses and to integrate it well into our manufacturing processes.
3D automated optical inspection (AOI) setup for Pololu Dual VNH5019 Motor Driver Shield for Arduino.
A Maestro commands this Luftwaffe pilot to direct his steely-eyed gaze out into the wild blue yonder.
Klaus Herold, who makes RC models of World War II aircraft, used one of our Maestro servo controllers to elevate one of his German Luftwaffe models to new heights. A 6-channel Micro Maestro adds a touch of reality to his model by animating the movement of the head of the pilot. The movement has two degrees of freedom: the head rotates side to side and tilts up and down. Additionally, the cockpit canopy extends and retracts. You can see the pilot in action in the video below:
Making this video was actually the first time I’ve had a chance to play around with the Tics, and I was pleasantly surprised at how quickly I was able to set up the Tic with each interface option. Once I had everything connected, it only took a few minutes using the control software to get things moving for each setup.
This video also gives a sneak peek of our new Tic T500 (the red Tics in the opening shot). Like our new stepper motor drivers, the T500s are based on the MPS MP6500 bipolar stepper motor driver. Keep an eye on this blog for their release in the coming weeks.