Baby Orangutan and 25D motor ... advice appreciated

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I’m new to robotics and am trying to design a robot that will perform step-function velocity and acceleration profiles while moving in a straight line, and also make precise turns while stopped. An arduino with the micro-metal gear motors, 42mm wheels and encoders has been a good learning platform. In addition to getting the hardware and electronics to work together with a PID algorithm for the speed control, I’m now understanding why step up and step down voltage regulators and an encoder with more steps per revolution may be necessary. I’m still hoping to keep the cost of the final design in the $100 - $150 range, so think I want to try out a baby Orangutan B-328 with the 25D metal gear motors and encoders (product #2284), but I have some questions.

  1. The stall current on the motor is 2.2A, which is greater than the 1A continuous rating on the Orangutan’s motor channels. I’m guessing I’ll need to use current sensors to prevent the motors from stalling and burning out the controller. What’s the best algorithm for using the current information to decide when to shut things down? I would want to set the trigger to turn off after the current’s been over 1A for some period of time, but how far above 1A and for how long? Should I keep a running average of current readings?

I really don’t need the extra power of the 25D motor, just the better encoders. Is there a better motor/encoder (with > 1000 steps per revolution) match for the Orangutan?

  1. This is a very basic question that will reveal how new I am. How would I best mount the baby Orangutan (or other PCB breakout boards) on a prototyping PCB like your item #330? Or is this not something I should be thinking of doing? If not, what’s the alternative?

  2. Will the 25D motors mount on the round PCB chassis like the RRC01A or RRC04A? I’m willing to drill holes. If not, what would be a better choice? If so, which version is better?

  3. Once the robot is built and the program is loaded, I want to be able to connect the robot to a computer via USB (while it’s stationary) and transmit velocity and acceleration data to it over a USB/serial interface. This is easy with the Arduino, but will require some additional electronics and work with the Orangutan. What’s the difference between the item 391 USB to serial adapter and the item 1300 USB AVR programmer? Which will get me closest to having the USB port installed on the robot so I can just connect computer to robot with a USB cable and send, as I currently do with the Arduino?

Thanks again for your help. I’m enjoying the learning process. You’ve made it easy to get started, get my hands on and learn as I go. I’ve learned from each of my false starts and dead ends, it hasn’t cost me too much, and I’m hoping I’m at the point where I can ask some more specific, productive questions.

Matt

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Hello, Matt.

It sounds like you are trying a fairly ambitious project for someone so new to robotics. I recommend starting with something simpler, because it will probably teach you a lot of things that would help you make a more capable (and expensive!) robot that can perform the final task you have set yourself to. Just as an example, going in a line is actually a very hard and not well-solved problem in small-scale robotics.

  1. You can do fairly well with our encoders. I recommend trying that first. Beyond the motor actually stalling, it can end up drawing about twice it’s stall current if you change directions quickly.

  2. If you solder female headers into the prototyping board and male headers into the Baby Orangutan, you can create a socket for it.

  3. You could use our 25D mounting brackets to help but I don’t think it will work that well with any of chassis. If you go with smaller motors, you can use the RRC04A chassis.

  4. Item 1300 implements a much more limited serial port than item 391. The USB AVR programmer still implements basic serial, which should be fine for your application and you would need to get it anyway to program your Baby Orangutan, so I would recommend going with that.

You sound like you are interested in learning more about electronics, so I encourage you to look at our President’s Blog and our other resources for more general information about robots.

- Ryan