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Electronics / Reality Check Raspberry Pi & DC Motor Control
« Last post by RpiHacker on Today at 07:47:47 AM »
After reading the material on this site, and elsewhere, I believe I have a conceptual framework to proceed with detailed planning to provide locomotion to a Raspberry Pi based robot (Pi-Bot) equipped DC motor driven wheels.

That said, I would appreciate feedback from forum members to confirm, correct, and refine the following conceptual framework to provide locomotion and skid steering control to the Pi-Bot:

RPi  PWM → level shifter → L298 motor driver → DC motor
        ↑                                                                  ↓
PID feedback <--------------------------------< motor encoder

Based on my understanding of RPi PWM I do not believe it necessary to have a microcontroller between the RPi and the motor driver (L298).

My intent is to build-out the Bot slowly adding features, capabilities, support circuits, sensors, etc. after verifying the previous stages work properly.

With this in mind, I must take care to plan carefully for future build-out of the Pi-Bot so as not to do something in the early stages of the build-out that would require major rework to in order to meet the original design specs of the Pi-Bot.

Thank you for any feedback you may provide.

Issue resolved: the proper way to interpret 4k7 on the schematic is 4.7k ohms.

It appears you can teach old dogs new circuit symbol conventions!

Misc / Robot Path Finding Project Home
« Last post by swordmaster2k on Today at 06:57:23 AM »

So I'm brand new to this community which I found via a Google search for "online robotics communities", I also came across "www.communityofrobots.com" but that place seems pretty dead, so I chose society of robots.

Anyway I've been apart of online communities before most notably www.rpgtoolkit.net  where I was the lead software developer for that open source project from 2012-2014, I've now moved into robotic applications focused mostly on navigation. I'm currently working on a year long project as part of my final year in Computer Science and what I m really looking for is somewhere to share my work. It is currently up on Github https://www.github.com/swordmaster2k/botnav the readme is currently lacking...

So, my project is based on path finding for mobile robots (wheeled, tracked, humanoid, etc.) in a 2D environment. It is largely research based but there is a fair amount of software implementation it includes:

  • Grid based path planning routines
  • Reusable software design
  • Autonomous navigation with map building
  • Wireless communication via Bluetooth, Wifi, Serial, etc...

The idea is that I produce a generic navigation system with a graphical program that a user can adapt to any ground based robot with very little effort. This gives the robot some "intelligence" but it requires some means of sensing where it is, a range finder, and communications to a computer. I already have the software running on 2 different systems Arduino and Raspberry Pi.

I'm wondering if this is a suitable home for such a project or are there any others?

Robot Videos / Robot Costume Contest
« Last post by avgrant on October 22, 2014, 01:12:21 PM »
Hey guys! I know quite a few people on here have built their own robots, and just wanted to share our little competition with you if you are interested. We'd love to see some Society of Robots submissions!


Thanks, and let me know if you have any questions!
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 22, 2014, 04:26:22 AM »
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by sdk32285 on October 21, 2014, 02:59:55 PM »
1. Just google "motor brake". Often when you order a motor you can get encoders, brakes, gears, etc.. from the same vendor.

2. For the most part you know the position of your motor from hall sensors or an encoder. And the rate you spin it can change when you start or stop the motor. When you issue a stop command instead of instantly stopping you send the intermediate commands from current speed to 0 based on how fast you want to decelerate. In an extreme case you can imagine commanding the motor to go backwards to reach a desired deceleration rate.

Based on how you are braking or if you have gravity forces on your motor you might also need a shunt regulator in your design.

3. There are a few reasons. The simplest can be to achieve a desired form factor. Another common reason is that certain gear boxes will have a max input speed, so you need another gear box to slow the shaft enough for the second gear box.

Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 21, 2014, 12:52:18 PM »
I've just used the motor sizing calculator on SoR, one of the motors was 16.2 kW but that's just from estimated data.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 21, 2014, 10:16:58 AM »
Hi, thanks. This isn't for a hobby, I plan to start a business using a theory I have with computer architecture. But more to the point:
1. What types of motor brakes are there available?
2. I will have to build the motor driver myself (long story), the digital side of it isn't a problem, but I need to know what it's physically going to do to the motor (which I will also be building myself) in order to accelerate and decelerate at different rates.
3. I've seen a lot of designs where they increase torque and decrease RPM with many gears, rather than just one small one and one large one. Why is this?

Thanks. It's unbelievably hard to find someone on the internet willing to help.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by sdk32285 on October 21, 2014, 09:50:30 AM »
Using gearing to get the high torque low RPM you need is the standard way of doing this. Most people do not make a custom motor for this (even though I know of several exceptions to this).

If you get a professional quality motor driver such as an Elmo or a Copley (I have a post on Copley drives that I am releasing in the next few days) you ca configure the acceleration and deceleration rates (it is just a parameter).

The nice thing wit using a bunch of gearing is that it will give you some resistance so there is a good chance you will not need any active braking to slow down. This should not be confused with a motor brake which you might need if you need to hold a position with the motor unpowered (or when stationary to conserve power). Note that motor brakes are typically only to be used when the motor is not in motion and not to slow down.

If you look on the main SOR site (or google it) you can find calculators for determining motor specs required.

Often harmonic drive gears are used for the compact size with good torque and low (or no) backdriving of the motor (which helps hold position).

A downside to professional hardware (motors, gears, controllers, etc..) is that they are often much more expensive than hobby level hardware. If you can find a hobby level digital motor drive it might be able to do the acceleration/deceleration stuff also.
Electronics / Re: Controls Braking vs Dynamic Braking for Motors
« Last post by Tranq97 on October 20, 2014, 03:35:51 PM »
Large motor, large motor... I'm not talking about one I possess, and I'm not sure how to judge it in kW. Let's just say the nominal dimensions are 150mm/150mm/250mm. That's probably as much as I can give you, sorry.

Now, this thing is going to go at high RPM and low torque, attached to a couple of gears to convert that to low RPM and high torque for the robot's arm. Before, I was trying to design a type of motor which could just run at high torque, low RPM. But, I found that that would hinder it's precision, accuracy and braking mechanisms. So, then I decided to use the gears with a high RPM motor. So, the braking on the arm will have to be virtually instant on the arm (big gear), so I don't know how quickly the motor (small gear) will have to stop to make that happen.

Basically, I'm building the motor and controller myself. The controller I have sorted. But electronic motors have always made me a little confused. With all this back EMF and whatnot. The things I need help with are as follows:
- Calculating motor requirements
- How to build a motor and account for those requirements
- What system can I use to change the acceleration rate?
- What system can I use to change the deceleration rate?
- What system can I use to hold a stationary motor in place?
- How to calculate gear sizes
- Are there any systems which can make the large gear more compact?
I'm 17, I've been interested in robotics for 4 years and it's all been textbooks, internet and college. I haven't had much practical experience at all, and about half of my education hasn't been learning, but rather developing ideas. As for the last point I made, basically I am worried that the large gear will be too big to fit in the robot's arm. So, are there any special gears which have the same effect as a big gear but a more compact? You seem like an expert on robotics, David, so I was wondering if you could give me a hand with these hurdles?
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