Peter Wallers Robot Ramblings

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MarkR
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Re: Peter Wallers Robot Ramblings

Post by MarkR » Sat Jun 16, 2018 8:46 am

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
Robot: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?

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peterwaller
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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Sun Jun 17, 2018 10:30 am

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.

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Lincoln
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Re: Peter Wallers Robot Ramblings

Post by Lincoln » Sun Jun 17, 2018 11:34 am

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.
Team RobotMad, home of the Smart robots, and very mean pots :)
Chris and Lincoln Barnes

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peterwaller
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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Tue Jun 19, 2018 6:16 pm

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.

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Fri Jun 22, 2018 2:38 pm

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.
Image

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Re: Peter Wallers Robot Ramblings

Post by AntRoboteer » Sat Jun 23, 2018 5:58 pm

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

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Thu Jul 05, 2018 2:09 pm

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.
Image
Image
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.
Image
Image

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Thu Jul 05, 2018 8:01 pm

Also looking at a version with the drive motors included.
Image
Incorporating a 12A Afro brushless controller is another possibility as it does fit.

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Fri Jul 13, 2018 6:35 pm

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

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Re: Peter Wallers Robot Ramblings

Post by Geoffreybath » Fri Jul 20, 2018 9:41 pm

Very nice design and nicely compact.

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Sun Jul 22, 2018 10:08 am

I have put one of the modules into a flipper to do some testing.
Image
Image
It is only in PLA at the moment so not really for full combat but it only weight 107 grams so I might consider it as part of a cluster later and reprint it in nylon.

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Sun Jul 22, 2018 3:59 pm

Here it is in action.
https://youtu.be/bKQQzel9xKU

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Re: Peter Wallers Robot Ramblings

Post by Paulmchurd » Tue Jul 31, 2018 9:53 pm

Really nice drive set up. You should sell a few 😜.

I’m still looking forward to this book you are writing.

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Mon Aug 06, 2018 10:58 am

Yes must make a decision on that soon.
In the mean time I have been playing with an idea for an axe though I probably will not get round to building it.
Basically it is a gear on the end of a standard gear motor which has teeth around 180 degrees. The meshes with a gear on the end of the axe arm and drives it back against a spring until you get to the part of the drive gear with no teeth. This release the arm and the spring fires it forward. The drive gear keeps turning until the teeth re-engage repeating the process.
Here is the mechanism
Image
Here in action
https://youtu.be/EvHLrfhms3s
I particularly like the unusual use of the spring.

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Re: Peter Wallers Robot Ramblings

Post by peterwaller » Wed Aug 15, 2018 2:56 pm

My horizontal spinner Combatant was supposed to be an upgrade on Anticyclone with more power and reach but it has so far been a disappointment.
A combination of too small a clearances and balance problems have made it unreliable and ineffective in battle. I have finally decided to rebuild it and try and address some of these problems. By printing a disc with lathe parting off tools as cutters I seemed to have greatly improved the balance problems and by increasing the wheel diameters the cutters body and ground clearance is improved.
Here is the new unit.
Image
Image
Here is the old nylon body after meeting the new unit.
Image

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