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Comments by Brandon
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Brandon's line following robot: The Chariot
- 8 December 2020Hello, Sultan.
The main reason I used a voltage regulator was to keep the motor voltage consistent even when the batteries start draining or get freshly charged. I noticed with my previous line followers that I would spend a good deal of time increasing the speed and tuning the robot, only to have the performance get worse when I recharged the batteries. I prefer a regulated motor supply voltage to keep the robot's performance predictable, especially during a competition when you might not have time to fully charge your batteries between each run.
I have not tried a swivel caster with a robot of this scale, but in my experience with larger robots, swivel casters tend to re-direct the robot when attempting to turn since they are directional. The benefit of using a ball caster is that it can freely move in any direction at any time. Since your robot will be on a carpeted surface, you might consider using a larger ball caster than the 3/8" one I used. We carry some all the way up to 1" diameter.
Brandon
New product: Pololu Dual MC33926 Motor Driver for Raspberry Pi
- 11 September 2020Hello, Alex.
I am glad you found the example Jeremy posted for how to drive a stepper motor using the MC33926 Motor Driver Shield for Arduino. However, please note that a few posts later, he posted an improved version that fixes a mistake and adds the ability to limit the maximum coil voltage to prevent damage to your motor if you are using a stepper motor with a rated voltage lower than the MC33926 shield's.
Additionally, while it is possible to drive a stepper motor with this shield, we generally recommend one of our many dedicated stepper motor drivers. or controllers instead. They offer more advanced features like current limiting, multiple step resolutions (some down to 1/256), and come in a much more compact size. Some of the drivers have higher level interface options like SPI, and our Tic stepper motor controllers offer many interface options including USB, TTL serial, I2C, hobby RC, analog voltage, and quadrature encoder input as well as the more standard STEP/DIR inputs. They also have settings that can be configured to control the speed profile, limit switches, a homing procedure, and much more.
Brandon
PID line follower with 5" robot chassis
- 28 August 2020Hello, Matty.
You could add your own reverse voltage protection circuit to the Vcc pin. By the way, just to be clear, reverse voltage protection is to prevent damage in the situation where the Vcc connection is accidentally made with the wrong polarity (e.g. connecting ground to Vcc and your logic voltage to ground). So, if you put together your system in a way that the Vcc connection is made through a keyed connector, that might also be a solution.
If you have additional questions or concerns, please post on our forum, which is more suited for technical discussions, and we would be glad to continue the discussion there.
Brandon
New products: Discrete addressable through-hole RGB LEDs
- 22 May 2020Hello, Paul.
Thank you for sharing your solution to the problem you encountered!
Brandon
Brandon's line following robot: The Chariot
- 18 November 2019Hello, Chester.
Unfortunately, my code ended up fairly messy by the time of the competition, and I have not cleaned it up since then, so I do not think it would be very useful in its current state. If you have never programmed a line following robot before, you might find the line following example for our 3pi robot helpful as starting point for understanding how the PID algorithm works.
I do not currently have a wiring diagram to share, but the connections are fairly simple. The power from the battery runs through the rocker switch and to the input of the voltage regulator. If I were building this robot again, I would probably use a pushbutton power switch instead of the rocker switch. The output of the regulator goes to the VIN of the A-Star and VMOT on the Qik motor controller. The A-Star's 5V output (from its onboard regulator) supplies the VCC power to the Qik as well as the power to the reflectance sensor array. I used digital pins 2-7 on the A-Star for the 6 reflectance sensors and pins 10 and 11 for communicating with the Qik via software serial. There is also a common ground connection for all of the boards.
Brandon
Brandon's line following robot: The Chariot
- 17 September 2018I do not have a schematic diagram for this robot, but the connections are fairly straight forward. The rocker switch is wired between the battery and the input of the regulator. The output of the regulator is powering the Qik motor controller and A-Star 32U4 Mini. The QTR sensor array is powered from the 5V pin on the A-Star 32U4 Mini. The rest of the connections depend on what pins you are using to read the sensors and send serial signals to the motor controller. If you have more specific questions when you start your line follower, you can post a request for help on our forum, and we would be glad to help there.
You should be able to swap an Arduino Uno in for the A-Star 32U4 in this system, but it is much larger, so you would probably need to find a different way to mount it.
Brandon
Brandon's line following robot: The Chariot
- 27 August 2018I noticed you posted similar questions on our forum; I have responded to it there. We can continue the conversation in the forum thread you created since it is probably a more appropriate place for a detailed discussion.
Brandon
Brandon's line following robot: The Chariot
- 24 August 2018It sounds like you have it correct, except I powered the whole system (including my microcontroller) from the 7.5V D24V25F7 step-down regulator. I used a connector to attach the battery to my robot so it could be removed and charged separately. The positive wire from the connector runs through the rocker switch and to the voltage regulator, and the ground wire goes straight to the regulator. The output of the regulator providing power to both the Qik 2s9v1 Dual Serial Motor Controller and the A-Star 32U4 Mini LV.
I did not use any low-voltage cutoff circuitry. I was careful to not run the robot for too long between charges, and in general it only runs for a couple minutes at a time, so it was easy to check the battery regularly. I considered adding a simple voltage divider from the battery to one of the free pins on the A-Star 32U4 Mini to alert me (with an LED) when the battery voltage dropped too low, but it did not seem necessary for the short run time.
Brandon
Brandon's line following robot: The Chariot
- 28 February 2018Hello, cpod.
The Chariot and Mostly Red Racer (the winner of the competition) both used PD control (no integral). The integral term is useful for counter-acting some external force consistently working against the robot. When following a line, you do not typically have that kind of constant force working against your robot's goal, so in most cases you can simplify by leaving out the Integral term.
I find it easiest to start tuning at a somewhat slow speed and gradually increase your speed once your P and D coefficients are working fairly well. At slow enough speeds, you probably don't need a D term at all, especially for a relatively straight line. If you want to be able to drive quickly around sharper turns, you will need your P term to be large, which will likely cause an overshoot. This is where the D term comes in to compensate. Essentially, the D term takes a history of the error and reacts to the change accordingly. If the error is getting smaller, it acts to weaken your robot's response to avoid overshoot. Similarly, if the error is getting bigger, the D term should act to increase your robot's response. There are a lot of good tips for tuning in Ben's posts in this thread. You might consider creating your own thread on our forum if you run into more specific questions when tuning your robot.
Brandon
Video: Setting the Current Limit on Pololu Stepper Motor Driver Carriers
- 29 January 2018Hello, servane.
When setting the VREF voltage, you can connect the driver as shown in the minimal wiring diagram found on the product page for each stepper motor driver carrier, excluding the motor connections. Once the current limit is configured appropriately, you can momentarily remove power and then connect your motor as well.
If you have additional questions about using one of our stepper motor driver carriers, I recommend posting a request for help on our forum.
Brandon