E-Wheelie: Homebrew

[bobbygee]

Hi All,
I have decided to build the project from the ground up using the schematic and firmware available through the Elektor Magazine site as my starting point.

I have designed two PCB's; Motor controllers and a separate Logic board.

I have had no problem sourcing all of the electronic components in Australia.

I have access to two 24V wheelchair motors with associated geerbox (25:1) and 14" wheels which I hope to use. May need to tweek the software to accomodate them.

In the schematic published in Elektor, the foot switch is shown with a pull down resistor - should this be a pull up?

There is no clear indication in the articles regarding the orientation of the Gyro chip and Acclerometer chip so I have hazarded a guess and may also have to tweek that in software.

I will keep you all posted as devlopments occur and I am open to any constructive comments or assistance.

Regards - Bob Gilchrist (Brisbane Australia)

[thomas scherer]

Maybe this Foto from an original sensor board helps. But take care: this board is hanging like a bat

[bobbygee]

Thank you Thomas, a picture is worth a thousand words. So if I understand you correctly it is mounted upside down under the Controller PCB, no wonder I couldn't see it in the Elektor article.
Bob

[briany]

Bob, I am also going down the homebrew route but am not quite as far advanced as you. I managed to figure out from the picture on the front of the July / August magazine which way round the sensors go (you can see the "pin one" identifiers for both chips and enough of the board to work out which way it goes!) I think the right orientation is that the Y axis is across the board (side to side) and X is front to back. The sensor daughterboard sits on top of the bottom left of the main board which itself is upside down (like a bat as Thomas says!) so it's been rotated around the X axis so that the Y axis is reversed.

For what it's worth you can buy both sensors already fitted to breakout boards (made by Sparkfun I think) which are 0.7 inches square which makes soldering these components a lot easier - some of the resistors and capacitors on the boards are different values - I have changed them although I suspect they probably still work and it is a bit fiddly to resolder the 0603 size SMD devices.

I found a source in China for the 1020Z motors so once these arrive I should be able to put it together. For wheels I'm using electric scooter wheels which came with tyres and tubes for less than £10. I've cut the hubs down to hake the hub thickness much less and these should attach directly to the motor shaft.

Brian

[bobbygee]

I got a little confused re the sensor orientation because the original (prototype?) article shows the control board mounted on the base of the unit normal way up but the final aricle shows it mounted upside down under the cover.
Not sure if there is a difference in the firmware to accomodate the change but I guess it will be easy enough to tweek.
I have sourced some surplus 450Watt 24Volt 550RPM motors from Oatley Electronics in Australia for $129.00 AUD each which I think will be closer to the design criteria than the wheelchair motors that I already had.
Thank you Brian for the heads up regarding the chips on carrier boards, Sparkfun is a very interesting site, where have they been all my life?
I am currently analysing the firmware and note that there are some diagnostic LED sequences, is there a list available with inerpretations.
My next step is to sloder the SMD's to my board - a new experience for me but there have been some excellent articles in Elektor recently so confidence is high!
Bob

[gamri]

how did you find the parts list. i mean ok by reading the circ diagram but for eg the wattage of the resistors, the voltage of the capacitors?

thanks and well done

[thomas scherer]

@bobbygee

please note that the firmware as released by Elektor is preliminary. So you still have to wait a little for the "GM".
In a few weeks' time, have a look at the German Elektor forum, because heavy optimizing will occur (I believe) and the source comment will normally be in English.

@Gamri
wattage is standard (0.25W) - only R16 is preferably 2W. And voltage: unless otherwise noted, standard Cs are rated 60V.

[bobbygee]

All of the PCB components with the exception of the IDG-300 are available from Farnell Electronics. The IDG-300 is available from the manufacturer, Invensense, directly.
I have seperated the motor controllers from the main logic PCB because I have other applications that they will do nicely for - so there is a controller PC Board for each wheel.
The main consideration with respect to the Wheelie design is the Current sense IC which I have included on both motor drive boards and I will modify the ATTiny25 firmware to read the extra current signal on a spare ADC channel.

Regards
Bob

[thomas scherer]

should be no problem. The firmware for the tiny25 is so simple - just do it

[briany]

I have finally got to the stage where I am about to program the AVRs, having got the motor controllers and the sensors working. The firmware available states the fuse bits needed for the ATTiny but not the AtMega - can someone confirm what these should be - I assume the most critical element is setting the 16MHz crystal as the clock, and probably none of the other settings really make a difference, but it would be good to be sure!