Das Mikro - £12 dual channel speed controller with mixing

[Roboteernat]

I had bought 2 of these boards as they looked interesting and the manufacturers are also making (copies?) the small Deltang RX modules i use too - hence why i saw them, but saw this page had been linked to on Facebook Ant pages. mine should arrive in the next day or so, looking forward to it, although it would take up more surface area than my current setup of Rory boards and separate RX but i'm working on that should be good though when the program is looked at too.

[Shakey]

I did some thinking about how to get a centre brake onto these ESC's that's super easy without reflashing the firmware. Something that could be done by a beginner without having to have another roboteer as a middleman flashing them and adding postage onto the cost. So I racked my brain and found a solution.

Resistor Braking
Centre braking is connecting the two terminals of a motor together to create the brake effect. I decided that a carefully valued resistor placed across the motor terminals would provide a brake effect when the ESC is not powering the motor. I experimented a bit and settled on ~50 Ohm as a good value resistor.

The important thing to understand is that this resistor adds extra load to the ESC, I chose ~50 Ohm as it provided a good level of braking with only ~0.17A of additional load at full power. A smaller value resistor would provide a more aggressive brake but would load the ESC more and heat itself up more (~50 Ohm on 2S got warm but no where near enough to worry).

Pros
- Adds Centre braking
- Cheap and Easy to do

Cons
- Resistor heats up
- More load on ESC
- Higher Power Usage

Testing
You can't say crazy stuff like this without a test!


This is 'Why do I exist?', my temporary testing bot. It has a 180mah 2S LiPo, an Orange RX, 2 30:1 motors. The two switches on the back can be used to switch the resistors in and out (turn the brake on and off). It has for an ESC a TinyTwo Rory ESC (I'm so sorry), it is one of rorys early ESC's that doesn't have centre braking so perfect for testing.

And a Test, first with centre braking off, then on, then on on only one side to show it doesn't affect the speed.
https://youtu.be/PubybLylBOs

A neat implementation would look something like this:

[Rapidrory]

I'm interested to see if these can drive beetle motors on 12v, seeing as there are few good options for beetle ESCs atm.

[Rapidrory]

Thinking about it, it may be impossible to program centre breaking on the Mikros if there're connected the same way as the TinyTwos; the processor only has 4 free io pins and there are 8 fet gates, meaning the gates are connected in pairs. Given it has no center breaking as is, they are likely connected so that one pair does forwards, one pair does reverse. If you switch both pairs on it catches fire, and if you switch both pairs off it coasts. In that setup there's no way to switch on the FETs in such a way that it brakes the motor, so reflashing them would likely not solve the problem.

[UserFriendly]

Loved your write up Joey.

Nice jumper too.

Great idea about the resistors Alex!

You guys are all geniuses. This is why I love this community!

[Andrew_Hibberd]

I have started playing with my own speedos as a little side project. Is someone with these boards able to read what the h bridges on these boards are?

Thanks.
Andy

[Rapidrory]

According to Joey, 4 x SH8M14 N/P dual MOSFETs...

Another thing they supply that could be useful is £7 Deltang knock offs: http://www.banggood.com/DasMikro-DSM2-5 ... 84913.html
Certainly be helpful for Nanos!

[Andrew_Hibberd]

Hey Rory

I bought some of these RXs a couple of months ago, the 6ppm input is really nice to free up an IO pin.

Not the best chip with no logic protection on those banggood boards, still on the look out for a nice H bridge for 2 cells. I have the A4950 in my first test board. I got it nice and small 14x11x6mm with RX.

[Rapidrory]

Those look good. I used the A4950s for the N2HV ESCs, but found they had a habit of cutting out if you change direction too fast, and didn't like 2S unless the battery was fully charged..

I've been thinking of redesigning my Nano ESCs to go with those RXs since they've proven themselves driving Wedge Wedge Wedge and Bad Idea, and can be made the same size as those RX.. Probably wouldn't sell them but they'd be a useful mini 2S ESC

[Danieljr1]

Did anybody try this on 3s?