Pololu Blog (Page 4)
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.
Artist David Gardener contacted us recently to share his work, Empty Vessels (seen in the above video), an immersive audio visual installation that explores the connection between machines, data, and their environment. The piece features three cellos played by custom built robotic structures that perform music composed in real time. It premiered in November 2019 at the Society for Arts and Technology in Montreal, where it performed for sold out audiences for two weeks! David was kind enough to answer our questions about the piece and allow us to share his answers along with some more footage and pictures with you below:
How long did you work on the piece?
The project started as an idea by myself (David Gardener) and Greg Debicki about a year ago. It remained an idea for most of the year until we were approached by the Society for Arts and Technology in Montreal (SAT) for help funding the project, where we could work on the project as artists in residence. At the end of the residency (in November) we would also premiere the show. This gave the project a very fast timeline taking just two and a half months from concept to presentation for two weeks of shows. I think it is probably the quickest timeline I have ever worked to, having to design, engineer & build the whole project.
Can you tell us which products of ours you used and how they were used in your project?
For the project I used the following components from Pololu:
- 12 x 9.7:1 Metal Gearmotor 25Dx63L mm HP 12V with 48 CPR Encoder (one for each string on each cello)
- 6 x RoboClaw 2x7A Motor Controller (two per cello to drive those motors)
These were used to drive linear slides that moved the note sliders up and down the fingerboard. The reason for using this method was because I am a cellist myself, and the ability to slide between notes is really important in the sound of the cello. Unlike a guitar, there are no frets on a cello’s fingerboard, so the note sliders have to move to very accurate positions on the fingerboard to make sure that the notes are nicely in tune. On startup the motors would all drive the sliders to a home position using a limit switch. From there they would move to the different notes just by driving the motors to pre-defined positions. I decided to use a slider per string on each cello to maximise the amount of notes that could be played simultaneously, meaning they could play 12 note chords, or fast melody lines by splitting the melody across the 3 cellos.
Did you design the slider systems for the fingerboards? It looks like some of the parts might be 3D printed; are the design files available anywhere?
Yes, I designed the whole robotic system from scratch. The cello is such a beautiful instrument in both design and sound. However it is designed specifically for a human body, none of the strings are parallel or in the same plane even, they all diverge towards the bridge. I didn’t want to change the actual instrument in any way for this project. This complicated the build a lot! On top of that, no two instruments are the same, so I had to make sure that the parts could be adjusted in the different planes depending on the instrument they were attached to. Another difficulty is at the top end of the finger board the strings are very close together meaning the sliders all had to be very thin so as not to collide with each other. In the end all these considerations led me to the decision that I would 3D print all the parts. With such a short build timeline, this meant I could design and print revisions of all the parts much quicker than if I was making all the parts by hand in the workshop.
The designs for the parts are not available at the moment as they are very much working prototypes! I plan to upload them for anyone that wants to see them at a stage in the future that I am happy with them.
Can you tell us what your motor control setup is? (What motor drivers are you using, how are you processing the encoders, how are you coordinating all the movement, etc.?)
So I think I answered this in question 2. But a more general overview of the working of the cellos is – The main brain of the three cellos is the software MAX MSP (running on a PC). This would send position data over serial to an Arduino which then told the RoboClaws the next position to send the motors to. The RoboClaws were running in closed loop mode so they were dealing with the encoders directly.
We noticed you have some fans pointed at the upper bank of motors on each cello. Are the motors or controllers overheating, or is that to protect the cellos from getting too warm?
That is funny. Yes, originally I was using your 4.4:1 gear ratio 12 V motors as I really wanted the note sliders to be whizzing up and down the fingerboards like a cello maestro. But after burning out some of the motors by driving them too hard, I decided to switch to the next gear ratio down (and actually even they were getting hot). But by this point I had already locked off the design and ordered all the motors as the opening night for the piece was in three weeks. So to make sure I didn’t lose any more motors, I added some forced air cooling (just a silent fan sat on a bar stool pointed at the motors of each cello)… it added a slight bit of rock ‘n’ roll to the show.
Can you give us some details about how the music is generated?
So the project is headed towards having a fully artificially intelligent score where the music is generated on the spot and then played. The project is designed to also play in a museum environment where it will sit and play for its audience forever evolving music, with the intensity of the compositions controlled by the number of people it is playing to. However, it is currently in a more generative state where it will play music based on a set of musical rules from which it generates the music. This is where my collaborator Greg came into the project, developing patches in MAX MSP that generate the compositions and then work out which string on which cello to send each note to.
Is the piece on exhibit anywhere currently, or are there any planned exhibits coming up?
The piece was shown for a week at the SAT at the end of last year, but it was almost totally sold out so an extra week was added straight after that. The cellos are now back in my studio, where they will be upgraded. They are scheduled for another two weeks of shows at the SAT from March 24th 2020. There are some other shows in Montreal where it will be shown as part of some electronic music and tech festivals (unannounced as of right now). It is then planned for a European tour late summer 2020. It is best to keep track of the dates from my Instagram, @montreal_life_support.
Do you have a website or any social media channels where people can follow your work?
Instagram is probably the best. These are the handles:
Other than that I will be releasing a making-of style video documenting the build in the coming weeks on the YouTube channel.
Thanks so much to David for sharing your work with us and answering all our questions. For readers in the Montreal area near the end of March/beginning of April, visit the Society for Arts and Technology’s website for showtime and ticket information.
We are thrilled to announce the release of our wheels for micro and standard sized servos. These wheels are similar to our wheels for 3mm D shafts and consist of a durable ABS hub with a silicone tire. They are currently available in 40, 60, 70, and 90 mm diameter options. All but the 40 mm size feature mounting holes that are compatible with various versions of our universal mounting hubs and slots in the spokes that allow additional accessories to be mounted to the wheel such as decorations or parts of an encoder system.
Black Pololu Wheels for Standard and Micro Servos – 90, 70, 60, and 40 mm diameters.
The 40 mm and 60 mm sizes are compatible with micro servo splines with 20 teeth and a 4.8 mm diameter and can be used with the following continuous rotation servos that we carry:
- FEETECH FS90R Micro Continuous Rotation Servo
- FEETECH FT90R Digital Micro Continuous Rotation Servo.
The 70 mm and 90 mm sizes are compatible with standard servo splines with 25 teeth and a 5.8 mm diameter and can be used with the following continuous rotation servos that we carry:
- FEETECH Continuous Rotation Servo FS5106R
- Power HD Continuous Rotation Servo AR-3606HB
- SpringRC SM-S4303R Continuous Rotation Servo
- Parallax Feedback 360° High-Speed Servo
If you plan on using the wheels with a servo not listed above, be sure to check your servo’s specifications for compatibility as servo splines are not standardized for particular sized servos.
These wheels, like many of our plastic parts, are designed by us at our Las Vegas facility and then injection molded in China. Usually, we ship bulkier parts made overseas by boat, which can take several months to get here. We were so excited about these, though, that we couldn’t wait that long! So, we had a small amount shipped by air to make them available as soon as possible. This means the initial stock of these is limited, and while we’ll have more coming by boat, the upcoming Chinese New Year will delay that even more than usual. So if you don’t want to miss out on these initial units, order yours soon!
As usual, we are offering an extra introductory special discount on these wheels, to help share in our celebration of releasing new products. The first hundred customers to use coupon code SERVOWHEELS can get 22% off up to 3 pairs of each size!
We are excited to share that we have expanded our line of 37D Metal Gearmotors to include 24 V options. These brushed DC gearmotors are the largest and most powerful we carry, measuring 37 mm (1.46″) in diameter. They are available in gear ratios ranging from 6.3:1 to 150:1 and with or without integrated 64 CPR quadrature encoders on the motor shafts. The 12 V and 24 V motors offer approximately the same performance at their respective nominal voltages, with the 24 V motor drawing half the current of the 12 V motor. The table below summarizes all of the options we now have available. Please see our newest revision of the 37D metal gearmotor datasheet (2MB pdf) for the full specifications and performance graphs for all the options.
|Gear Ratio||No-Load Speed
|(kg ⋅ cm)||(oz ⋅ in)|
|12 V||5.5 A||0.2 A||1:1 (no gearbox)||10,000||0.5||7||–||–||item #4750|
|6.3:1||1600||3.0||42||12||item #4747||item #4757|
|10:1||1000||4.9||68||12||item #4748||item #4758|
|19:1||530||8.5||120||12||item #4741||item #4751|
|30:1||330||14||190||12||item #4742||item #4752|
|50:1||200||21||290||10||item #4743||item #4753|
|70:1||150||27||380||10*||item #4744||item #4754|
|100:1||100||34||470||8*||item #4745||item #4755|
|131:1||76||45||630||6*||item #4746||item #4756|
|150:1||67||49||680||6*||item #2829||item #2828|
|24 V||3 A||0.1 A||1:1 (no gearbox)||10,000||0.55||8||–||–||item #4690|
|6.3:1||1600||3.5||49||14||item #4688||item #4698|
|10:1||1000||5.5||76||14||item #4689||item #4699|
|19:1||530||9.5||130||13||item #4681||item #4691|
|30:1||330||15||210||13||item #4682||item #4692|
|50:1||200||23||320||12||item #4683||item #4693|
|70:1||140||31||430||10*||item #4684||item #4694|
|100:1||100||39||540||8*||item #4685||item #4695|
|131:1||79||47||650||6*||item #4686||item #4696|
|150:1||68||56||780||6*||item #4687||item #4697|
|* Output power for these units is constrained by gearbox load limits; spec provided is output power at max recommended load of 10 kg⋅cm.|
Note: The listed stall torques and currents are theoretical extrapolations; units will typically stall well before these points as the motors heat up. Stalling or overloading gearmotors can greatly decrease their lifetimes and even result in immediate damage. The recommended upper limit for continuously applied loads is 10 kg-cm (150 oz-in), and the recommended upper limit for instantaneous torque is 25 kg-cm (350 oz-in). Stalls can also result in rapid (potentially on the order of seconds) thermal damage to the motor windings and brushes; a general recommendation for brushed DC motor operation is 25% or less of the stall current.
We have a new set of regulators to announce: the D36V50Fx family of step-down voltage regulators. Measuring a compact 1″ × 1″, these regulators support input voltages up to 50 V and can typically deliver around 5 A of current, although some versions can output much more under certain conditions.
Step-Down Voltage Regulator D36V50Fx, bottom view with dimensions.
The family consists of six fixed output voltage versions between 3.3 V and 12 V:
- D36V50F3: Fixed 3.3V output
- D36V50F5: Fixed 5V output
- D36V50F6: Fixed 6V output
- D36V50F7: Fixed 7.5V output
- D36V50F9: Fixed 9V output
- D36V50F12: Fixed 12V output
We can also manufacture a customized version for you here in our Las Vegas facility. For example, we could make regulators with a different output voltage that your project needs, or we could replace the 40 V reverse voltage protection MOSFET with a 20 V one for slightly improved efficiency if your input voltage will always be lower than 20 V. If you are interested in customization, please contact us for more information.
Comparison to other regulators
D36V28Fx and D36V50Fx Step-Down Voltage Regulators.
The D36V50Fx regulators are larger and more powerful counterparts to the D36V28Fx family we introduced last year, with the same input voltage ranges and mostly similar characteristics. What distinguishes the two families in performance is that the D36V50Fx regulators can provide roughly double the output current! (At the high end of the input voltage range, the difference is generally less dramatic.)
Comparison of the maximum continuous current of Step-Down Voltage Regulators D36V50Fx and D36V28Fx.
Comparison of the maximum continuous current of 5V Step-Down Voltage Regulators D36V50F5, D24V90F5, and D24V50F5.
As usual, we are offering an extra introductory special discount on these new regulators, to help share in our celebration of releasing a new product. The first hundred customers to use coupon code D36V50FXINTRO can get up to 3 units of each version for just $11.95 each!
We have expanded our line of micro metal gearmotors to include versions with a 15:1 gear ratio. As with all of our other micro metal gearmotors, these units are available with five different motor options:
- Motors with precious metal brushes
- Motors with longer-life carbon brushes (HPCB)
Each motor is available with or without an extended back shaft, which rotates at the same speed as the input to the gearbox and offers a way to add an encoder, such as our encoders for micro metal gearmotors (see the picture above). This makes ten new versions in all:
(Gearbox & Motor)
|(kg ⋅ cm)||(oz ⋅ in)|
|0.75||0.06||2200||0.25||3.5||1.4||15:1 HPCB 12V||15:1 HPCB 12V dual-shaft|
|1.5||0.10||2100||0.25||3.5||1.3||15:1 HPCB 6V||15:1 HPCB 6V dual-shaft|
|1.6||0.07||2000||0.30||4.2||1.5||15:1 HP 6V||15:1 HP 6V dual-shaft|
|0.67||0.04||1400||0.20||2.8||0.70||15:1 MP 6V||15:1 MP 6V dual-shaft|
|0.36||0.02||860||0.17||2.4||0.37||15:1 LP 6V||15:1 LP 6V dual-shaft|
More detailed specifications for all our micro metal gearmotors can be found in their datasheet (2MB pdf).
These new versions bring our total micro metal gearmotor selection to 130 options, with gear ratios ranging from 5:1 to 1000:1! To see them all, visit our micro metal gearmotor category, and visit our metal gearmotor category to see all of our metal gearmotor options. Keep in mind if you don’t see an option that suits your application, for sufficient volumes, modifications such as customized output shafts are available.
Once you find the perfect gearmotors for your project, don’t forget to check out our great selection of accessories. These were all designed either specifically for our micro metal gearmotors or with their compatibility in mind:
- Wheels and tracks
- Universal mounting hubs with #2-56, #4-40, or M3 holes.
- 12mm Hex Wheel Adapter for 3mm Shaft
- Mounting brackets in white, black, or extended options
- Magnetic and optical encoders
Our Black Friday Sale has come to an end. As we ship out the last of our Cyber Monday orders, we’d like to point out our Specials category where you can find great deals on Pololu products any time of the year! For the last couple years, we’ve released most of our new products with special intro coupons. If you see a product’s intro banner listed in the specials category, its intro coupon is still active! There’s lots of great deals waiting to be used up, so make sure to have a look before you place your next order!
Our Black Friday / Cyber Monday sale is going strong, and we have been working hard to make and ship the products that people are getting great deals on. Most of the sale coupons can be used on backorders if we happen to run out of stock, but you should still get your orders in early since lead times on some popular products can get long.
Please note that our usual same-day shipping guarantee is suspended during the sale, though so far we have been able to keep up with orders as they have been coming in, and we are closed Thursday, Nov 28th (tomorrow) for Thanksgiving. Happy Thanksgiving!
26 November Update: We are no longer accepting doorbuster submissions. If you submitted wishes for doorbuster coupons, thank you! You should receive an email from us soon. All the sale details are now up on the Black Friday sale page.
What’s this? A 400-Point breadboard with mounting holes! We know you’ve been waiting for this your whole life.
Okay, maybe not. But hey, mounting holes are awesome, and now you can pick up some of our new 400-point breadboards and mount them all over the place!
This 3.2″ × 2.1″ breadboard is fairly standard in many ways. It has four bus lines spanning the length of the board and 30 rows of pins, enough for up to four 14-pin DIP ICs or three 16-pin DIP ICs. The rows and columns of tie points are conveniently labeled, multiple units can be connected for larger projects, and it has an adhesive backing for those of you who like sticking breadboards on things.
But this breadboard is also a little special. It has eight mounting holes for M2 or #2 screws spaced evenly down the center on a 1 cm pitch. Now you can do stuff like mount your breadboard to a Romi Chassis (or any robot chassis) with some standoffs like this:
Wow! So convenient! And they’re just $2.49 each! But, even better, we’ve got a special discounted price for the first hundred customers. Get up to 10 boards at just $1.75 each using coupon code 400PTBBINTRO!
Everyone wants encoders on their motors, but not everyone wants to solder a bunch of wires to a tiny encoder board. That is why I am excited to announce that we are now offering two new versions of magnetic encoders for Micro Metal Gearmotors that feature JST SH-type connectors:
- Magnetic Encoder Pair Kit with Top-Entry Connector for Micro Metal Gearmotors, 12 CPR, 2.7-18V
- Magnetic Encoder Pair Kit with Side-Entry Connector for Micro Metal Gearmotors, 12 CPR, 2.7-18V
These encoders are easier to get up and running than our previous design that requires soldering to through-holes with a 2 mm pitch. With these new encoders, you just have to solder the board to the two motor tabs (sorry, that part is not going away yet), put the magnetic disc on the backshaft, and plug in your cable (available separately in a variety of lengths)!
We think that the “micro” aspect of our Micro Metal Gearmotors is one of their coolest features since their small size make them useful in a wide array of projects. We designed these encoders with this in mind, making them within the profile of the gearmotor on three sides (the side with the connector extends a few millimeters past the motor). Since everyone’s constraints are different, we decided to make two encoder versions, one with a top-entry connector that lets the cable come straight out of the back, and one with a side-entry connector for applications where there isn’t much space past the rear of the motor. We are also continuing to offer encoder boards with through-holes, which allow wires to be soldered to the board for especially compact installations.
In case you are not as excited as I am yet, our intro special might help. Right now, you can get up to five of our new encoder pair kits for just $4.95 each using the coupon code MMGMENCINTRO! (Click to add the coupon code to your cart.) But you better hurry, this offer is limited to the first hundred customers to use the coupon code.