Do I have to chop holes in the expansion board for the leads from the I/O expansion board — the space left above the pins is just too small to allow the leads to fit?
Thanks
Bob
Nice work Joe, that looks great — and thanks for the photos — a big help to see how the unit looks with all the bells a whistles. What are you using the LCD’s for?
Thanks Coleman,
I think the longer standoffs would be really helpful — and while you are at it — the screws that attach the gearbox could be a bit longer. There is not enough thread to come through the nut and allow for the standoff on top of that. I’m ending up without nuts — using the standoffs to hold it all together. Maybe that’s why I’m a bit more crowded in there too.
Here’s the magic standoffs you need guys. I found them at amazon
amazon.com/gp/product/B004G5A60E/ref=oh_details_o02_s00_i00?ie=UTF8&psc=1
2" long - female side down onto the bolt — male side up to hold the expansion board into place. Plenty of room for all the cables now.
Bob
Too funny Joe, the first thing I worked on once I got the rover running was to make it go straight. You must be an engineer 
I ended up with some pretty basic code and fiddled with a variable until I have it working fairly well — but it took a lot of trial and error to get the speed error correction to work — and it still fluctuates a bit. But it has been a fun exercise to get me working with the code and programming in general which I have not done for several years.
Your feedback is much appreciated, thanks again.
Bob
Hi Coleman,
I think the design is good so far (still more for me to assemble) and don’t have any great suggestions except maybe to put a bunch more photos of completed projects on the product page or in the manual.
Thanks for your quick and open responses.
Bob
Note that the center four round plates are made to detach (to rout larger wires), same as for the servo slots. We’ll certainly consider adding longer standoffs.
The expansion plate does limit the number and types of shields you can use. However, you can use the IO shield without issue - can you show us a photo of what you are experiencing?
Appreciate the suggestion; longer standoffs and longer screws. Anything about the design itself which can be improved?
Apprecated.
Regarding one motor rotating faster than the other - consider adding encoders:
robotshop.com/en/encoder-pair-tamiya-twin-motor-gearbox.html
You essentially count the rotations and adjust the motor’s speed accordingly.
Can’t quite see if Joe’s has encoders or not.
Maybe use taller standoffs, to push the expansion board up higher?
alec
I had the exact same thoughts initially. But then I realized I wanted as much of the cabling as possible under the platform than over, for aesthetics. Plus I wanted the upper platform clear for a bunch of other things I’ve planned.
I spent ages trying different routings until I was happy. It’s an obsession I developed rebuilding older motorcycles… I hate my projects looking like somebody threw a bowl of spaghetti on them.
I got over my initial concerns about kinking the wires… they’re pretty tough. And once the thing is built, it’s a moot point.
Yes, I found the fit of the ribbon cables to be a bit tight as well. The gearbox has 4 unused small yellow spacers that are perfect for giving a little extra lift… just use them at the top… the screws are long enough to accommodate them.
Bob, the TM1638 gives me a general I/O device for all sorts of things.
For example, using the keys and displays I can manually fine tune my motors “on the fly” to track straighter. Between the encoders and motor speeds I am exploring how precise I can get the Rover to drive in a straight line over a long distance.
I’ve also used it to display sensor readings such as the distances from the ultrasonic.
Basically, anything I would want to push to the Serial Monitor I can see “on board” without need of the computer, and I can alter behaviour with the keys.
And when I’m using it for nothing else, it just displays a “Cyclon eye” effect. Good fun
Bob, I’m an old school “Computer Science” grad from back when the field was more of a cult than a profession.
Now I’m one of the high priests, instructing the new cadre of those who answer the calling.
I’ve been side-by-each with engineers all my career though
Yes, I have the encoders. I’m (and no doubt Bob as well) doing extensive analysis on each component starting with the encoders. I’ve done multiple frequency distributions on the readings to determine their behaviour.
They’re not “high precision” devices, so there’s a certain inaccuracy to their behaviour.
Add to that the fact that the motors are not absolutely equal, so the same power applied to both will always tend to drift one way or another. And finally there’s the unmeasurable factor of the “rumpity bumpity” of the tracks throwing off trajectory.
Driving an absolute straight line over a long distance is more challenging than one thinks
Thanks JoeM, that looks like it will do the trick although I would still prefer to be able to bring the cables directly up through the plate without kinking them.
Bob