Pololu Blog (Page 5)

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.

Kevin's mini-sumo robot: Roku

Posted by Kevin on 18 November 2015
Kevin's mini-sumo robot: Roku

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…

New products: Scooter/Skate Wheels

Posted by Brandon on 17 November 2015
Tags: new products
New products: Scooter/Skate Wheels

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:

A 25D mm gearmotor connected to a 70 mm scooter/skate wheel using a 4 mm scooter wheel adapter.
A 37D mm gearmotor connected to a 100 mm scooter/skate wheel using a 6 mm scooter wheel adapter.

You can find more information about these wheels on their product pages:

New product: G2 High-Power Motor Driver 24v13

Posted by Kevin on 12 November 2015
Tags: new products
New product: G2 High-Power Motor Driver 24v13

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.

Video: MyoWare Muscle Sensor demonstration with Maestro servo controller

Posted by Jon on 6 November 2015

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!

One-sixth scale Mark 1 British Heavy Tank by Helen Lawson

Posted by Brandon on 6 November 2015
One-sixth scale Mark 1 British Heavy Tank by Helen Lawson

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.

37D mm metal gearmotors with encoders and end caps

Posted by Ben on 3 November 2015
Tags: new products
37D mm metal gearmotors with encoders and end caps

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:

Gear Ratio No-Load
Speed
@ 12 V
Stall Torque
@ 12 V
Stall Current
@ 12 V


With Encoder


Without Encoder
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

New product: MyoWare muscle sensor and electrodes

Posted by Jon on 30 October 2015
Tags: new products
New product: MyoWare muscle sensor and electrodes

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.

The MyoWare Muscle Sensor does not ship with electrodes; they are available separately in packs of six.

Brandon's mini sumo robot: Black Mamba

Posted by Brandon on 28 October 2015
Brandon's mini sumo robot: Black Mamba

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…

HPCB micro metal gearmotors with extended motor shafts

Posted by Ben on 25 October 2015
Tags: new products
HPCB micro metal gearmotors with extended motor shafts

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.

Magnetic Encoder Kit for Micro Metal Gearmotors (old version; not compatible with HPCB micro metal gearmotors).
Magnetic Encoder Kit for Micro Metal Gearmotors (HPCB compatible).

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:

Motor Type Stall
Current
@ 6 V
No-Load
Speed
@ 6 V
Approximate
Stall Torque
@ 6 V


Single-Shaft
(Gearbox Only)


Dual-Shaft
(Gearbox & Motor)
high-power,
carbon brushes
(HPCB)
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
high-power
(HP)


(same specs as
HPCB above)
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
medium-power
(MP)
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!

Prototyping hexapod motion with a Maestro USB servo controller

Posted by Jon on 23 October 2015
Prototyping hexapod motion with a Maestro USB servo controller

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:

New Products

5:1 Micro Metal Gearmotor MP with Extended Motor Shaft
Addressable RGB 8x8-LED Flexible Panel, 5V, 10mm Grid (APA102C)
Raspberry Pi 3 Model B
Wixel Shield for Arduino, v1.1 + Wixel Pair + USB cable
210:1 Micro Metal Gearmotor MP with Extended Motor Shaft
Addressable RGB 16x16-LED Flexible Panel, 5V, 10mm Grid (APA102C)
75:1 Micro Metal Gearmotor with Extended Motor Shaft
MP3 Trigger V24
Wixel Shield for Arduino, v1.1
DRV8880 Stepper Motor Driver Carrier
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