parallax sumobot or fingertech cobra

lumpus

so I am brand new to the sumo and wondering where I should start out

there is a parallax sumobot for sale on ebay for a reasonable price, everything included
but I also found this fingertech cobra chassis that looks like a better deal
I heard that you can not scale the parallax, and the cobra would have an arduino board

can anyone give me some advice?

thanks

Duane Degn

It would have been helpful to have included links to the products you're asking about.

I did look up the Fingertech Cobra and it looks pretty cool. If I were only concerned about the hardware, I think I'd go with the Cobra over a Sumobot. However, if you want to learn about robotics, no one makes educational material as good as Parallax.

If learning about robotics is your goal, then there's an easy answer, get something with a Propeller. If you finances allow, get an ActivityBot but even if you don't get an ActivityBot, get a Propeller board and turn whatever has a pair (or more) of motors into a robot.

Here's my "Ode of a Propeller Fan Boy" I wrote over on Let's Make Robots.

Since you're asking, I'll throw in my two cents worth of advice (I'll even wave the fee).I'm a big fan of the Propeller chip. It has eight "cogs" (processors) and can make a lot of tasks which would be difficult to perform on an Arduino easy to write by combining a few "objects" (libraries). What is so nice about the Propeller is the various objects generally don't get in each others way. I've seen many Arduino projects mention needing to find some work around to use a servo because the normal library uses an interrupt which is already being used by some other device such as an encoder.

Since the Propeller has eight identical processors, the resources used by one cog don't effect the what's left over for the other cogs, with the exception of I/O pins.

For example my Mecanum wheeled robot, monitors the four quadrature encoders, six RC receiver channels, an UART and an I2C compass while also providing the PWM to the four independently controlled motors. It was nice not to have to worry about the code to monitor one sensor using resources required by one of the other sensors.

Another example of what the Propeller can do is my little hexapod. The IK positions of all 18 servos are computed at 50Hz allowing each pulse sent to each servo to be optimal value for that particular servo at that particular point in time. The program controlling the hexapod uses five of the eight cogs. The control program is divided amoung the five cogs which allows the many inputs and outputs (including debug info being sent to a terminal window on the PC) to be occurring simultaneously. The remaining three cogs could be used to monitor additional sensors and control additional devices.

The Propeller can control up to 32 servos without any additional hardware. If you add some 74HC573 to the mix the Propeller could control up to 144 servos with 1us precision.

Since the Propeller has eight independent cogs, it can control devices with very tight timing requirements such as the WS2812 LEDs. With one cog continuously updating the LEDs, I used another cog to generate fun patterns to send to three of AdaFruit's 16-pixel rings. Since all the cogs have access to the 32K of 'hub" RAM, the cog generating the patterns fills an array of longs with the colors to be used on each pixel while at the same time the other cog reads from this array in order to know which colors are to be sent out to the LEDs. This "at the same time" component is a very powerful feature of the Propeller. As powerful as the Raspberry Pie is, it makes for a bad NeoPixel controller since it can't easily be controlled to the strict timing requirements required by the LED's control chip (WS2811).

I haven't yet tried to generate a map of a room but I have used a SD card with the Propeller to record the servo pulses as a drove my PropBOE-Bot around by remote control. Once I had finished driving the robot in record mode, I switch to playback mode and watched as the robot repeated its previous course.

There are some who are turned off by the Propeller's lack of interrupts. I don't have enough experience programming with interrupts to debate this issue. I will say there are an awful lot of really smart people on the Propeller forums who have lots of experience with interrupts who don't seem to mind not having them. I think the guy who designed the Propeller wanted very timing determinist code.

There are certainly a lot of awfully cool robots that don't use the Propeller but I often think the robots would have been even better is the had used one.

IMO, the Propeller is a great microcontroller for robots. At $25, the Propeller Project Board is probably the best bang for the buck when it comes to Propeller boards (I just noticed it's on sale for $22.49). I use a lot of QuickStart boards in my projects since they're so nice and small (and they used to cost less). I've made a list of some of my Propeller projects here.

I also think the Propeller would be great to use with the RPi. The Propeller could handle the tasks of interfacing with sensors and the RPi would be used for high level decision making.
I hope you give the Propeller some consideration as you enter into the world of robotics.

Edit: I know a lot of people are concerned about uses 3.3V devices with 5V sensors. Usually all it takes for the Prop to interface with a 5V sensor is a 10K ohm resistor on the Prop's input pin. The Propeller has clamping diodes on all its I/O pins which can tolerate higher voltages as long as the current through the diodes is limited to 500uA.

I don't suggest using resistors on the Propeller's output to a 5V devices since the resistor could interfere with the 5V device reading the 3.3V logic. The only 5V device I've some across that doesn't reliably read 3.3V as logic high are the NeoPixels (WS2812) LEDs. I like to use a level shifter with the NeoPixels but I haven't needed to used a level shifter on any other 5V device I've used with the Prop.

You don't need to spend much money to get started in robotics. In this thread I show how to make a robot from some foam core board and a couple of servos (and wheels).

To get back to you're original choices, the Cobra robot looks like better hardware but there's a lot of great educational material to use with the SumoBot. The SumoBot uses a BasicStamp as the microcontroller. While a Propeller can run circles around an Arduino, IMO the Arduino is a more capable microcontroller than the Basic Stamp.

lumpus

Thank you for responding. I decided to go with the parallax because of my extremely limited knowledge and the price was really great. I'm going to go into those links and the article you posted and thanks for the information.

Genetix

Consider the Competition Robot Kit which has 2 SumoBots along with a ring, unless you know someone who has a SumBot. Be sure that ebay kit is complete and works because replacement parts especially the main board are very expensive.
http://www.parallax.com/product/27402