Hi
I'm the author of ScratchGPIO
I am very keen to get a low cost wireless Scratch controlled robot into our schools.
Yours is by far and away the best candidate in terms of form factor and sensors and value for money that I've seen so far.
But I think you could be right in that it would be better to design a case for a Raspberry Pi to include a battery and just mate the two together.
I estimate the cost of provding a Raspberry cased add-on to your Robot to be about £40 (Rpi, case, SD card, WiFI) not including battery.
If there was just one case that included everthing then we could save £5-10? And then save £5-10 on your controller??
I think I need to build a non cased prototype with the same features as yours and see if the overall savings would be worthwhile.
But I need to persuade one of my schools to buy one of yours to test out
I think you have built a very very very good device and I thank you for making it open source
regards
Simon