![Sad :(](./images/smilies/icon_e_sad.gif)
In theory, such controllers should be suitable for use as single-channel reversible ESCs with no further tinkering. I had two such controllers to test, taken from the Dorman RC servos suggested by Ant Ipodean and the FT90R from Feetech (former are ~£1.50 each from AliExpress when bought in ten packs, latter are around £3.00). Both are pretty small boards, though the Dorman's (top of each pic) are smaller:
![Image](https://i.imgur.com/yY9ZJ1s.jpg)
![Image](http://i.imgur.com/siAUlLA.jpg)
The Feetech has the motor soldered directly to the board, hence the odd shape and large solder-through holes.
![Image](https://i.imgur.com/SEZRqDW.jpg)
After careful retesting I basically got the same results noted previously, i.e. the Feetech boards behaved perfectly (clear dead-band with 0v and full voltage at stick limits) while the Dormans showed around 0.5v in 'neutral' and didn't provide full voltage to the motors. These results were the same regardless whether I had a motor connected to the output or just the digital multimeter, so I don't think it could have been a back-resistance issue. Testing with just a motor, the Dormans caused a slow rotation (10-15 rpm) in neutral and were noticeably slower than the Feetechs at full throttle. No idea why I'm getting such different results from Mike with the Dormans boards - possible I'm doing something wrong or maybe I just got a duff batch. If there's anyone for whom the slight size and cost advantages are crucial then it's certainly worth persevering with them but personally I'm going to forget about the Dorman servos for the moment and stick with the Feetechs.
So... on with my efforts to bodge together a "Poor Man's Nano" or PMN as I'm now calling it. Goal is to have a reasonably consistent little package, as cheap, small and light as possible - but also reliable and easy to drive. I noticed with these controllers there is a slight delay switching from forward to reverse but we're talking less than half a second - so don;t think it will impair driveability in real world situations. Other than that, responsiveness seems excellent, with a proper proportional response as you move the stick gradually through its range.
First step, disassembling all the servos was strangely satisfying. They're generally very well put together and dismantle cleanly:
![Image](https://i.imgur.com/kDFEO2Q.jpg)
Removing the boards was pretty easy too - just hold the motor in a mini vice, melt solder on one side while gently bending the other way. All boards came off cleanly.
![Image](https://i.imgur.com/dkiZKch.jpg?1)
Then just cleaned out the old solder using a simple solder pump (very easy with through-soldered holes if you hold the iron on one side of the board and the pump on the other).
So - that's the ESCs sorted, now just needed receivers. In ideal world, I'd stick with the OrangeRx R614XN as they're the smallest DSM-compatible PWM options I've ever found - only they're a bit pricey at around £10 each and currently unavailable. Second best option, which I've come to rely on most of the time, is the Redcon CM421 4-ch Rx from BangGood. These are cheap (just bought a batch of 10 for £4.90 each), rated up to 10v (so no need for a BEC or voltage limiter when used with 2S LiPO) and pretty compact - except for the row of pins at one end. Futaba connectors are no good if you're after a really compact package (I'd rather have nice holes for through-soldering) - so they had to go. Having tried this a few times now, I find the best option is to slide/cut off the plastic 'comb'-like widget that holds the pins together, then clamp the board in a vice and desolder the pins one by one. It's then easy to clean out the holes using the solder-sucker (again - heating the solder from one side of the hole and sucking from the other). Takes me about 20 mins to complete. Here's how they look before and after pruning:
![Image](https://i.imgur.com/77twtix.jpg)
It's then a case of carefully trimming the ESC leads down to length and stripping the ends (with such short leads be very careful not to pull the whole insulation sleeve off, like I did a couple of times!) and soldering them onto the back of the Rx board, along with any other required leads. In my case that's the power supply (red & black) throttle-channel signal pin (white) and bind pin (grey - this needs shorting to GND to initiate binding), plus blue & yellow for the motor leads. I used 24AWG silicone insulated wire throughout:
![Image](https://i.imgur.com/shSak4P.jpg)
After a quick test, then wrapped the individual ESCs in heat-shrink, folded everything into place and wrapped it all up in clear heat shrink (so I can still see the Rx LED).
![Image](https://i.imgur.com/JAQF2J6.jpg)
![Image](https://i.imgur.com/Z2R5bgJ.jpg)
Resultant package is about 31x17x9mm and weighs 5.5g (including wires). So... not quite as dinky as a real Nano but small enough and cost less than £12 to make - so it's good enough for me! Incidentally, that tiny plug & header in the photo is a JST-SH 2-pin micro connector (1mm pitch) which I'm experimenting with for binding - plan is to have a header with the pins shorted so I can just slide that on to put it in bind mode. Weighs next to nothing and less likely than a tiny slide switch to engage accidentally.
Managed to put together two PMN units in one afternoon and both worked a treat.
![Image](https://i.imgur.com/JyJfvjh.jpg)
Tested using 2S LiPO and one motor per controller. Left it running full speed for 5 mins - no noticeable overheating issues. Obviously, this kind of bench testing is no substitute for the real thing, so plan is to make a quick & easy 4WD antweight and let my son thrash it around our test arena for a while. If it survives him an his little friends, it should survive anything.
Cheers,
Stuart