New POPbot - Arduino Based Robot available on Robosavvy

[PedroR]

Robosavvy will soon start selling a new Wheeled Robot based on the popular Arduino Open Source Platform.



Pricing starts at 59 GBP ( 67.85 incl VAT ) for the POPbot Lite and you get the Arduino Board, Serial LCD (it's on the back of the Robot), 2 infrared reflectors for line following and serial cable for programming.
You can extend and customize the robot with any analogue sensor using a JST connector for a quick and clean setup.

For 95 GBP (109.25 incl VAT) you get the POPbot Full Version which adds an infrared distance sensor, a servo and replaces the serial cable with a USB cable for programming.

Both robots can be extended with a wide variety of sensors available form Robosavvy: http://robosavvy.com/store/advanced_sea ... nex+sensor

The POPbot should be available within the next couple of weeks.

[savuporo]

Guys, this thing needs a version with wheel encoders preinstalled, and 1-axis gyro/2-axis accelerometer option.
These wheeled platforms are great for general experiments, but with dead reckoning you cant build precise navigation algorithms.
So It would be really great if there was a preconfigured wheeled platform that ships with preinstalled navigation package ( implementing "gyrodometry" for motion tracking for example )

[PedroR]

Hi

1)

The kits are already in store. The prices in this release phase are slightly lower than the ones advertised:

POPbot Lite: 61.50 GBP inc VAT
POPbot Deluxe: 98,90 GBP inc VAT

You can view the full products list here: http://robosavvy.com/store/advanced_sea ... ds=pop-bot

A complete list of activities, videos, and kit contents (including difference between the two editions) is available in the product pages (please follow the link above).

You can also check the preliminary version of the users and activities manual here http://robosavvy.com/RoboSavvyPages/Ine ... minary.pdf

It includes a full list of all activities with introduction to the various subjects and parts included. (The manual is a great resource for those who are learning and also for those who are teaching )


2)
With regards to the wheel encoder I am confirming the availability of this part. I know the manufacturer sells them so I'll check.
As for the Gyro and Acc sensor, I don't really understand the purpose of it in a wheeled platform but ARE available in our online store here ( http://robosavvy.com/store )

For navigation my I suggest the exploration of different approaches instead of a wheel encoder?
You can use an I2C compass (here http://robosavvy.com/store/product_info ... cts_id/394 ) to make sure you are on a straight line and you can also use a miniGPS serial module to know where you are at all times (here http://robosavvy.com/store/product_info ... cts_id/535 ).
I believe it takes the concept of "navigation" on step further

Regards
Pedro.

[savuporo]

As for the Gyro and Acc sensor, I don't really understand the purpose of it in a wheeled platform but ARE available in our online store here ( http://robosavvy.com/store )

For navigation my I suggest the exploration of different approaches instead of a wheel encoder?

Look up "gyrodometry"
http://www.google.com/search?q=gyrodometry
"This method, called Gyrodometry, is exceedingly easy to implement, yet it appears to be very effective in reducing odometry errors due to non-systematic "catastrophic" errors such
as those caused by bumps or other large irregularities on the floor."

The idea is to combine readings of two cheap and individually unreliable sensors ( wheel encoders and gyroscope ) into a reliable one by tuned fusion of readings. This results in a very precise navigation, and should basically be cornerstone of every cheap wheeled mobile robot navigation. ( Unless a more advanced method like Kalmann filter of different types of sensors is employed, of course )

[PedroR]

Hi

Thanks for the tip. I found this info http://www-personal.umich.edu/~johannb/ ... aper63.pdf

You also mentioned acceleration sensors but I still don't understand the purpose of these.

From my understanding the use of the gyro has these princples: we assume we will be travelling on a straight line. If he hit a bump, the gyro will tell us that and from that information, using triangulation techniques, we can now how much have we travelled exactly on the horizontal axis.

It makes sense

However I did not understand how you address the issues wheel slipping. If for example, one wheel slips and other does not we would have diverted from our straight line but would not know about that.

I still like the idea of using a Compass to address this issue. What is the alternative approach here?

FYI there are wheel encoders available for this robot. We do not stock them yet and there is not sample code but the manufacturer has confirmed the availability so we should be getting them in the future.

[savuporo]

I still like the idea of using a Compass to address this issue. What is the alternative approach here?

I dont have time for full explanation, but compass is notoriously sensitive to tilt, meaning any irregularities in levelness of ground will screw up compass reading big time ( i know, i have tried that )

Of course, compass coupled to gyro through a Kalmann filter can compensates for gyro drift, so compass in the system can improve absolute positioning over long term somewhat, but this is a complication to otherwise relatively simple navigation method.

In addition to compass, you can have inclinometers, various accelerometers, even 6-axis IMU and/or GPS attached, but none of the sensors alone provide 100% accurate navigation in all situations without checking external references.

Gyrodometry is simply a very good bang for relatively little buck in navigation accuracy.

[PedroR]

Hi savuporo

Thanks for the input.

I still don't understand the purpose of an accelerometer.

Is it to test for lateral acceleration (centrifugal acc) when one of the wheel slips and the bot deviates sideways?
If so, then you need a very sensitive one...

As for the compass, assuming, you have a gyro the simplest approach would be to ignore or be cautious about compass readings when the the bot is not levelled.

I also think a 6 degree IMU might be an overkill for this. This is a base kit that focus on being very accessible in terms of cost.
It's a nice foundation so you can add all that mention on top of it though.

[savuporo]

I found what i was looking for here:
http://www.e-puck.org/
Has encoders on board

[PedroR]

Hi savuporo

I'm glad you found what you were looking for.

I checked it out and it looks really really nice.

However, price wise it costs almost 10 times more than our Arduino Robot (According to the info here http://www.cyberbotics.com/order/ the price would be 542 GBP) so they're not really comparable/competing robots I guess, since they aim at different market segments.

Nevertheless it seems like an amazing product.

Our less expensive POPbot is really aimed at a different audience but feature wise, based on what I see from this e-puck robot, it seems that our POPbot offers a nice price/features relation.

With regards to the encoder I will keep following up with the manufacturer to see what they will do.

Cheers
Pedro.