Peter Wallers Robot Ramblings

[MarkR]

I'm looking at the NCV7708B chip, which can be configured as 3x H-bridge, and would give bidirectional control to three motors (or three channels)

https://octopart.com/ncv7708bdwr2g-on+s ... M-qcsFmFlA

But it uses the SPI interface for communication, the microcontroller would need software changes to support this and it might be complicated.

Mark

[peterwaller]

That's an interesting chip but it is only 0.5 A continuous so would be a bit near its limit.
Also I normally need the third channel for a servo or brushless .
I had a further play with the other layout I had tried with components on both sides and have got it down to 30 x 23 mm all be it with an increase in thickness. Small size while always nice wasn't the main consideration for this design or I wouldn't have used drivers that were 4 time larger than my existing ones. Mind you it does bring the boards down from £4.77 to £3.54 each when buying 10.

[Lincoln]

you can get pcbs made very cheaply from china using pcbway. the Autobot board, 100,75mm cost £50 for 10. and they actually gave us 13.
i see why you have that size now, seems pretty compact for all the constraints, like the though hole connectors. have you tried using smd versions of the connectors (if they are even available, I've not looked) then you would gain more of a size decrease from using both sides.

Mark, that chip while nice that its 3 channels, is as Pete said 0.5A is a little low, and most people use the third channel as a servo not another motor.

Has anyone played with the encoders available on polou for the micro metal gear motors, you have to get special motors that have a little bit of shaft sticking out the back. we have 2 but haven't played with them yet, been to busy.

[peterwaller]

You can get the connectors surface mount but with the various loads and vibrations I prefer the added strength of through the board joints that can if necessary be soldered on both sides. Finally settled on the double sided layout and actually ordered the PCB's this afternoon. I know the current requirements are no where 5 A even with four motors but I do like to run my spinners from 3 cells and the existing drivers I am using can't take that.

[peterwaller]

While waiting for the PCBs I have designed the case and with an old piece of PCB material mocked up the new 5 A controller.
Here it is with all the cables plugged in next to the old 1.2 A and it is a very similar size.
The old is 38 x 24 x 11 mm and the new 32 x 25 x 12 mm.

[AntRoboteer]

Wow, that looks excellent Pete. Great job getting those so small.

[peterwaller]

The boards arrived today the Royal Mail took 3 days to deliver them first class which was a bit annoying.
I have built one up and it all seems to work as expected with only a couple of minor problems.
The two new power driver chips were a little to close together as the plastic IC case sticks out more than I thought so I had to sand it down on one edge to make sure they fitted centrally on the pads.


The receiver stands up slightly higher than I thought due to a capacitor so I shall have to add about a mm to the case thickness.

[peterwaller]

Also looking at a version with the drive motors included.

Incorporating a 12A Afro brushless controller is another possibility as it does fit.

[peterwaller]

Here are a couple of variants of the new controller with motors incorporated.

[Geoffreybath]

Very nice design and nicely compact.