Brushless Converters?

[dvdouden]

Just wondering, does anyone here have experience with brushless converters? I was thinking about building one myself but I noticed there are quite a few commercially available already. None of them seem to be able to handle both main and tail motor signals though, nor simultaneously. I'm just looking for some way to go brushless without having to go full separates.

[JettaManDan]

Originally Posted by dvdouden

Just wondering, does anyone here have experience with brushless converters? I was thinking about building one myself but I noticed there are quite a few commercially available already. None of them seem to be able to handle both main and tail motor signals though, nor simultaneously. I'm just looking for some way to go brushless without having to go full separates.

i don't think there is a good system out there right now that will let you do both motors...so you are still stuck on using 2 systems pretty much....

[HELIHANKSTER]

Originally Posted by dvdouden

Just wondering, does anyone here have experience with brushless converters? I was thinking about building one myself but I noticed there are quite a few commercially available already. None of them seem to be able to handle both main and tail motor signals though, nor simultaneously. I'm just looking for some way to go brushless without having to go full separates.

I have experience with brushless converters and the Bee. Unfortunately Brother the experience for me was a no go. I tried my a$$ off a long time ago to get the converter to work with the Bee 2.4ghz 4in1, but to no avail. If you can get a converter to work on a 2.4 ghz 11.1v Bee or make one that will work…YOU WILL BE THE MAN!!!

[dvdouden]

I've read some similar experiences that confirm your story HH. Makes me wonder what the hell Esky did this time... I'll hook it up to a scope this week if I can find some time to spare. The theory behind a brushless converter is really simple (PWM in, servo out) and it's been done a lot before, so I can't really understand why it shouldn't work with Esky equipment.
I also found someone who made a dual converter for coax helis, he published the schematics and source code of his creation, so that should be a good starting point. And the best part is that it looks like it can be done for just a few $.

[dvdouden]

How to ruin a perfectly good 3-in-1 in 5 easy steps:

1. Attach probes to tail motor connectors
2. Apply throttle
3. Realize the probes are connected incorrectly
4. Remove probe without cutting the throttle
5. Short the connector using aforementioned probe

Thank God it was the tail motor, there's already a vacant spot next to it for a replacement MOSFET (of which I have a couple in my parts bin), so I hope I can fix it...

Anyway, I did figure a couple of things out tonight, the most important one being the reason why a lot of brushless converters don't work on the Bee

Technical stuff below, skip to the last lines if you don't care

Both motor connectors have a capacitor soldered between the positive and negative terminals, you can see the main motor one in the photo above, it´s the light brown square above the large square black component that says "SS34". This capacitor is used to filter out electrical noise created by the motor. It is charged when there's a potential difference (voltage) across the terminals and it releases this charge when there's no potential difference (0 volts). But it needs a load in order to do so. Usually the motor will drain the capacitor in a fraction of a millisecond. However, when there is no motor connected the capacitor will keep its charge for a much longer period.

In other words: if you connect a sensor (read: brushless converter) to the motor wires without having the motor connected, the sensor will read a constant voltage. The load caused by the sensor is not nearly enough to drain the capacitor of its charge, so the sensor will keep reading a constant voltage. In fact, the scope I used has such a small load that it takes a couple of seconds for the capacitor to discharge when I close the throttle. Not really what we want, it should drain about 100,000 times as fast.

The solution:
Add a simple resistor across the positive and negative terminals of the motor connectors I need to calculate and verify the required value of the resistor, but first I need to fix that blown 3-in-1

[dvdouden]

It's easier than it looks

Half of the schematics is for the programmer port, so the firmware can be updated afterwards...



And a rough draft for the PCB, that's not even 1" wide, 22 by 11 mm to be precise (about 0.9 by 0.5")

List of components:
6 resistors ($0.01 each)
1 capacitor ($0.05)
1 LED ($0.05)
1 Six pin male header ($0.06)
1 Double row six pin male header ($0.06)
1 ATtiny ($0.50)
2 Motor wires ($0.20)
1 PCB ($3.50)
total cost:
Less than $5 So, who wants one?

[HELIHANKSTER]

Awesome investigational work my brother.

I knew if anyone could figure out why the converters weren’t working on the Bee it would be you. Having a working converter to go full brushless would be off the hook…heck, just having a plug in play brushless tail mod would be amazing. It’s a shame the Bee is fading away…just think, something like this would have sold like hotcakes a couple of years ago.

[dvdouden]

My 3-in-1 is officially half dead now, the tail pins are shorted and I can't figure out why, so I'll have to order a new one. The main motor part still works fine so I'll keep it as a test board, but flying is out of the question at the moment. The weather sucks at the moment so I'm not really missing out on anything anyway

It's a shame the Bee isn't as popular as it used to be, it's still a great learning helicopter for those who don't like to spend tens of dollars on each crash (or have a wife that keeps an eye on the expenditure )

There's still a market for this kind of device though, it should work with any 2-3S brushed heli with either one or two motors (so that includes Coax helis).

I verified a couple of things:
1. there's a clean PWM signal coming out of the 3-in-1's CPU controlling the tail and main motor MOSFETs.
2. When the green light on the 3-in-1 goes red, that's when you've reached full throttle. Strangely enough, this happens at around 75% throttle stick...

[jeffmb]

i am insterested in this setup. I would love to convert my Bee using this setup.

[dvdouden]

Thanks for your interest jeffmb! It´ll take some time before I have a fully functional and tested converter (probably a month or two) but there's plenty of testing and researching to be done in the meantime.

I did some more research tonight, there's some things I found which are worth mentioning. First of all the PWM signal is 4KHz, not 8KHz like I assumed earlier. This is actually a good thing since it means there's more time for the capacitor to discharge before it's charged by the next pulse.
Using a 100 Ohm and 220 Ohm resistor in series will discharge the capacitor quite nicely. There's a small problem though. Combined the resistors pull about 37 milliamps of current (12V / 320 Ohm = 0.0375A). This doesn't seem like much, but it becomes a bit of a problem when you calculate the power being consumed. The 220 Ohm resistor needs to dissipate 8.25V * 0.0375A = 0.31Watt of heat, and I'm using a 1/4W resistor, so that thing runs HOT. It becomes even worse for SMD resistors, those are 1/8W... As you can see, there's a lot of things involved when designing even something relatively simple as this.
So here's the dilemma: using low resistor values will possibly overheat the resistors, but using higher resistor values probably won't drain the capacitor fast enough which makes it impossible to measure the duty cycle of the PWM signal.

There's a solution to everything though. It's possible to put multiple resistors in parallel to divide the load while still keeping enough load to discharge the capacitor. Or, like a colleague of mine suggested, just connect a small 12V car lightbulb, even 1W should be enough.

Plenty of stuff left to figure out! And I still need to order a new 3-in-1, but there's a bit of month left at the end of my budget so that'll have to wait

[sprooce]

Hi Dvdouden,

I'm on a similar quest for signal converters but since I don't have an oscilloscope I'm working in the dark. I bought a double channel signal converter from HobbyKing which matches your PCB layout very closely but I have since discovered that it's set up for an MCPx.

What the difference in motor PWM signal between that and the HBFP is I have no idea.

If you've made any progress I'd love to hear about it.

cheers,

Sprooce

[Chevy2035]

The BLHeli firmware for ESC's might make this a really easy conversion

[sprooce]

Yeah the BLHeli firmware is amazing stuff. Unfortunately I need an Atmel version for my ESC on the HB and I think he switched all his work across to the SiLabs chips. Certainly all the ESCs that are listed in the "suitable for.." list are Silab chips.

I know he started on the Atmel but I can't find any info on whether these MCUs are still supported by the software.

Any ideas?

At the moment I'm experimenting with a full separates setup but with no gyro..... so far I can't get the revo mixing set up right to make the heli even remotely flyable.

I think this might be a challenge too far... the HBFP is not the easiest of helis to fly in the first place and with an unstable tail it's proving to be impossible. Still... it's an interesting project.

Cheers.

S