Pololu Blog (Page 38)
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.
My robot, Roku, was the champion of LVBots’ August mini-sumo competition. While I didn’t have the time or inspiration to make it look like anything more interesting (like a Star Wars droid) or make use of especially innovative tactics, I think I managed to build a robot that not only is effective but also looks fairly clean and well put together. In addition, it’s a good demonstration of how the Pololu A-Star 32U4 Robot Controller can be used as a standalone main board for a small robot. Continued…
We are rolling out another set of new products here at Pololu: Scooter/Skate Wheels. They are available in 144×29 mm, 100×24 mm, 84×24 mm, and 70×25 mm sizes, offering larger alternatives to our line of Pololu Wheels. They are compatible with standard 608 bearings, so they also work with our Aluminum Scooter Wheel Adapters, which make it easy to connect these wheels directly to an assortment of motors for use in robot drive systems:
You can find more information about these wheels on their product pages:
We are excited to announce the release of the Pololu G2 High-Power Motor Driver 24v13. Like our original high-power motor drivers, this board is a discrete MOSFET H-bridge that is designed to drive large DC brushed motors. As the first of our second-generation high-power motor drivers, the 24v13 can supply a motor with a continuous current as high as 13 A at voltages between 6.5 V and 40 V (absolute maximum).
The G2 driver is designed to be a near drop-in replacement for its predecessor, with an identical form factor and a similar pinout, but it offers a number of new features and improvements over the older version. Reverse-voltage protection on the power supply inputs helps prevent instant destruction if a battery is connected backwards, while basic current sensing and limiting functionality help the driver handle large loads more gracefully. The G2 driver is also compatible with systems running at 3.3 V (and lower), unlike our original high-power motor drivers.
To learn more about the motor driver’s features and capabilities, see its product page.
I got your torque right here ;)
Now that we are carrying Advancer Technologies’ MyoWare Muscle Sensor, it is time to update our demonstration video! I’ve had two whole years to add some mass to my biceps (during which time I continuously worked on those bad boys for a grand total of four weeks), and now I can proudly present to you these sick gains.
The demonstration is basically a redo of the original muscle sensor demo with the new sensor, except for a few small differences (honestly, my biceps are not that much bigger). In this setup, a 6-channel Maestro reads the muscle sensor’s analog voltage output and commands the position of a Power HD servo. The Maestro’s +5 V (out) pin supplies power to the MyoWare Muscle Sensor, and the servo and Maestro are powered by 4 rechargeable AA batteries. On a personal note, I found it really satisfying to use a single power source for this demonstration, which is not something you can do with the previous version of this muscle sensor, as it requires two supplies. (Be sure to check out the MyoWare Muscle Sensor’s product page to read about more ways the new muscle sensor improves upon the older version!)
This Maestro script is slightly more interesting than the script in the last demo, since the servo’s default direction of rotation was the opposite of the motion for a bicep curl (and we were already quite happy with the servo’s orientation with respect to my arm for the planned video footage). To get around this, and make the servo arm movement match the position of my arm during a bicep curl, I did some basic math and came up with an equation that you can see in the code below:
# Sets servo 1 to a position based on the analog input of the MyoWare Muscle Sensor. begin 8000 # put this value on the stack (for why, see line 5) 0 get_position # get the value of the muscle sensor's signal connected to channel 0 4 times minus # y = -4x + 8000 , which is an equation we use to deal with the servo's # default direction of rotation and scale the Maestro's Target # value to roughly 4000-8000 (approximately 1-2 ms) # which is the range of servo pulses that corresponds # to the motion we want. 1 servo # set servo 1 accordingly repeat
You can, of course, use other devices to read the analog voltages from the MyoWare Muscle Sensor. If you have not already, you might try using one of our A-Stars!
If you have a project that uses the MyoWare Muscle Sensor, we would be pumped to hear about it!
Helen Lawson designed and built a one-sixth scale Mark 1 British Heavy Tank replica that is a functional, radio controlled robot. The replica has been a work in progress for around three years and is now reaching completion. Helen designed the main chassis out of laser-cut wood and made other aspects of the chassis from aluminum and 3D printed parts.
One distinguishing feature of a MK 1 British Heavy Tank is the lack of a central turret. Instead, it has a sponson on each side. This proved challenging for Helen’s build since most electronics made for RC tanks only allow for a single gun and turret. To make the sponsons functional, Helen used a combination of an RC receiver, an RC switch with digital output, an RC switch with relay, a Micro Maestro servo controller, a few servos, and a Taigen gun flash unit. You can find more detailed information about this part of the system (including a wiring diagram and Maestro script) in her post on our forum. The images below show each side of one of the completed sponsons:
She also made a 3D-printed case for the Maestro (shown in the photo on the right) and a few of the other electronic components, which she made available on her Thingiverse page.
You can see a video of the robot in action on this Portsmouth Model Boat Display Team Armoured Division Facebook page, and even more information on her build, including many more pictures, in Helen’s forum thread at landships.net.
Our 37D mm metal gearmotors now have fitted plastic end caps over their encoders that neatly protect the assembly and keep stray objects clear of the magnetic disc. The pictures below show the previous version (without end cap) next to one of the new ones:
The end cap is easily removable if you need to access the encoder or want a few more millimeters of clearance for your gearmotor, but there is a little bit of base plastic that will remain (as shown in the picture below), so removing the end cap does not quite make these new ones identical to the previous versions.
37D mm metal gearmotor with 64 CPR encoder (with end cap removed).
These gearmotors are available in six different gear ratios and with or without encoders, and we also carry the motor and encoder assembly by itself with no gearbox. The following table shows all of our 37D mm metal gearmotor options:
@ 12 V
@ 12 V
@ 12 V
|1:1||11,000 RPM||5 oz-in||5 A||motor without gearbox|
|19:1||500 RPM||84 oz-in||5 A||37Dx52L mm||37Dx52L mm|
|30:1||350 RPM||110 oz-in||5 A||37Dx52L mm||37Dx52L mm|
|50:1||200 RPM||170 oz-in||5 A||37Dx54L mm||37Dx54L mm|
|70:1||150 RPM||200 oz-in||5 A||37Dx54L mm||37Dx54L mm|
|100:1||100 RPM||220 oz-in||5 A||37Dx57L mm||37Dx57L mm|
|131:1||80 RPM||250 oz-in||5 A||37Dx57L mm||37Dx57L mm|
We are pumped to announce that we are now carrying Advancer Technologies’ MyoWare Muscle Sensor!
This sensor features a number of improvements over the older Muscle Sensor v3 including single-supply operation (no need for a negative voltage supply) and built-in snap connectors for electrodes. Other new features include a raw EMG output, reverse power protection, a power switch, LED indicators, and two mounting holes.
For a fun example that shows how you could use the muscle sensor, take a look at this blog post, which uses one of our Maestros to monitor a bicep while it is flexing, and command a servo to imitate the motion with a tiny cardstock version of He-Man’s arm. (Note that the project uses the older Muscle Sensor v3, not this new product.) You can also head on over to Advancer Technologies’ website for more project ideas.
Before I started designing my entry into this year’s LVBots mini sumo competition, I watched several videos of other competitions. I noticed a majority of the victories came from engaging the opponent from the side or back; a pattern I also noticed during the last LVBots mini sumo competition. For that competition, I made a robot that used a blade and sensors on the front and back of the robot (basically making the robot have two fronts and no back). However, my strategy in that competition was to roam the ring and search for the opponent, which I suspect increased the chances of the opponent engaging from a suboptimal angle. This time, I wanted to try having my robot spin in place looking for the opponent and striking once it was found. This ultimately resulted in my newest mini sumo robot, Black Mamba. For those unfamiliar, a black mamba is a snake with a reputation for being highly aggressive and is one of the longest and fastest-moving snakes in the world. A black mamba’s venom is highly toxic, and it is capable of striking at considerable range, occasionally delivering a series of bites in rapid succession. Black Mamba is also Kobe Bryant’s self-appointed nickname (yes, I am a Lakers fan). Continued…
It has been a few months since we introduced our new high-power micro metal gearmotors with longer life carbon brushes. We now have them available with dual shafts, and we have made a corresponding update to our magnetic encoders to let them work with the larger terminals of the HPCB motors.
You might see similar-looking motors elsewhere, but no one comes close to our offering, from the quality of the gears to the variety of winding options to the selection of gear ratios, all in stock for shipment the day you order. By bringing together Pololu’s exclusive features of high-power windings, long-life carbon brushes, and encoders for closed-loop feedback control into a single package, these latest motors and encoders really demonstrate our continual investment in this popular form factor. With ten gear ratios available, from 10:1 through 1000:1, our total selection of micro metal gearmotors has grown to nearly 70 options:
@ 6 V
@ 6 V
@ 6 V
(Gearbox & Motor)
|1600 mA||3000 RPM||4 oz-in||10:1 HPCB||10:1 HPCB dual-shaft|
|1000 RPM||9 oz-in||30:1 HPCB||30:1 HPCB dual-shaft|
|625 RPM||15 oz-in||50:1 HPCB||50:1 HPCB dual-shaft|
|400 RPM||22 oz-in||75:1 HPCB||75:1 HPCB dual-shaft|
|320 RPM||30 oz-in||100:1 HPCB||100:1 HPCB dual-shaft|
|200 RPM||40 oz-in||150:1 HPCB||150:1 HPCB dual-shaft|
|140 RPM||50 oz-in||210:1 HPCB||210:1 HPCB dual-shaft|
|120 RPM||60 oz-in||250:1 HPCB||250:1 HPCB dual-shaft|
|100 RPM||70 oz-in||298:1 HPCB||298:1 HPCB dual-shaft|
|32 RPM||125 oz-in||1000:1 HPCB||1000:1 HPCB dual-shaft|
(same specs as
|1600 mA||6000 RPM||2 oz-in||5:1 HP|
|3000 RPM||4 oz-in||10:1 HP||10:1 HP dual-shaft|
|1000 RPM||9 oz-in||30:1 HP||30:1 HP dual-shaft|
|625 RPM||15 oz-in||50:1 HP||50:1 HP dual-shaft|
|400 RPM||22 oz-in||75:1 HP||75:1 HP dual-shaft|
|320 RPM||30 oz-in||100:1 HP||100:1 HP dual-shaft|
|200 RPM||40 oz-in||150:1 HP||150:1 HP dual-shaft|
|140 RPM||50 oz-in||210:1 HP|
|120 RPM||60 oz-in||250:1 HP|
|100 RPM||70 oz-in||298:1 HP||298:1 HP dual-shaft|
|32 RPM||125 oz-in||1000:1 HP||1000:1 HP dual-shaft|
|700 mA||2200 RPM||3 oz-in||10:1 MP||10:1 MP dual-shaft|
|730 RPM||8 oz-in||30:1 MP|
|420 RPM||13 oz-in||50:1 MP|
|290 RPM||17 oz-in||75:1 MP||75:1 MP dual-shaft|
|220 RPM||19 oz-in||100:1 MP||100:1 MP dual-shaft|
|150 RPM||24 oz-in||150:1 MP|
|75 RPM||46 oz-in||298:1 MP|
|25 RPM||80 oz-in||1000:1 MP||1000:1 MP dual-shaft|
|low-power||360 mA||2500 RPM||1 oz-in||5:1|
|1300 RPM||2 oz-in||10:1|
|440 RPM||4 oz-in||30:1||30:1 dual-shaft|
|250 RPM||7 oz-in||50:1||50:1 dual-shaft|
|170 RPM||9 oz-in||75:1|
|120 RPM||12 oz-in||100:1||100:1 dual-shaft|
|85 RPM||17 oz-in||150:1|
|60 RPM||27 oz-in||210:1|
|50 RPM||32 oz-in||250:1|
|45 RPM||40 oz-in||298:1||298:1 dual-shaft|
|14 RPM||70 oz-in||1000:1||1000:1 dual-shaft|
You can see all ten of the new versions below, and if there are any versions we do not yet have that you would like to see us carry, let us know in the comments!
Chris Barlow posted this interesting write-up about how he is using the USB connection of a Mini Maestro servo controller to prototype motion control for his hexapod robot. He has been going over the build in detail on his blog, so check it out over there, and be sure to take a look at this short video below: