Help - extension to RX for more motor power?

[Alex Slowfly]

Hi all

this is my first mail in the DIY area and I'm not a born electronic crack although I have some knowledge. I'm looking for an extension board as a general addon to a all-in-one RX board (actually it's the micro-coaxial-heli bladerunner board). The board has integrated ESC for two brushed motors.
I like to expand the possiblities of the board towards more powerfull motors and a higher voltage feed. See my sketch below.
As I have no experience in brushless motors I try to stay with brushed once for a while. I imagine some simple (?) FET addon for the motors but then I have no clue how the circuit would look with all necessary parts.

Any help is appreciated - thanks.

Alex.

[Alex Slowfly]

Ok, one more try:

Is there some simple circuit like a "second ESC" to just add to an existing onboard ESC - the aim still being the use of a more powerful motor?

Thanks. Alex.

[jeffs555]

Alex,
I have never seen a BladeRunner except in pictures on this BB, but if it has the normal N-channel mosfet motor drivers, this might work. Just duplicate the P-channel mosfet circuit twice. No guarantees, and if you blow up your bladerunner I take no responsibility.

Jeff

[Alex Slowfly]

Jeff

Thanks very much for your input! I take all responsibilities.. no problem :cool: ... :eek:
I'll have to check what's already on the board.
Can you give me any indication what mosfet I would use to be on a save side?

Thanks.
Alex.

[JMP_blackfoot]

Okay for the voltage regulator part, even though an LM7805 in a small package would be easier.
The power part looks like the P-Fet will never be turned off properly. I suggest the attached circuit, which should give no trouble.

[Rajesh L G]

Removed.

Rajesh

[JMP_blackfoot]

Oh well, didn't see the 1k series with the base. Rajesh

You didn't see it because it initially wasn't there. I corrected it when I realised the mistake. ;)

[jeffs555]

Since the BR runs off a single 4.2volt LiPoly, a fixed 5 volt regulator like JMP said, would probably work, but it would be safer to use an adjustable and set it to 4.2 volts.

My circuit should work, that is why I showed a negative regulator, so that the +8.4 was common to both boards. I have redrawn it with with actual voltages instead of the battery terminal lables, and have also drawn in the likely output circuit of the BR board. Because you said simple, I didn't include a transistor driver. One advantage of JMP's circuit is that it would work in the very unlikely event that BR used a P-channel on the motor drivers.

As for what P-channel to use, IRL5602 is one that is available in TO220 so you don't have to work with surface mount. This thread has a lot more http://www.rcgroups.com/forums/showthread.php?t=309213

Jeff

[Alex Slowfly]

Jeff and JMP thanks very much for your help. Also the link to the other thread is interesting. Never thought I'll swing that soldering stick again in my old days, but when you get hocked on those flying r/c objects anything can happen.
This is a great place and source.
Alex.

[Alex Slowfly]

Well I managed to read what's next to the 2 motors on the BR board:

I see the diodes parallel to each motor and then there is one of those terrible tiny 8-leged micro monsters.
One reads: 9926 ∆43NG
The other: L9110 CD426

Does this make any sense? :confused:

Thanks for your support.
Alex.

[Bruce Abbott]

"9926" could be a dual N channel MOSFET.

SI9926DY (http://www.fairchildsemi.com/pf/SI/SI9926DY.html)

"L9110" may be this bi-directional DC motor controller?

L9110 (http://www.jinjubao.com/new_page_1.htm)

[jeffs555]

Bruce is probably right about the parts. You would have one section of the dual N-channel for each main motor, and the bi-directional motor control for the tail motor. I had forgotten all about the tail motor control. If you increase the main motor size and voltage, you may also want to increase the size and voltage of the tail motor. Since the tail is bidirectional, this would be much more difficult.

[Alex Slowfly]

Bruce + Jeff
Thanks very much for the details. This all makes sense now. As for the tail motor, I'll try to control pitch by shift of the CG - so I leave those questions for next spring... ;-)
Thanks again.
Alex.

[Zlatko]

Alex,
If weight is an issue, why dont you consider replacing the Dual Fet with a higher curent one and just add a voltage regulator for the remaining circuit.
ie use jeffs negative voltage regulator and inserting it between the Source on the Dual FET and the rest of the circuit and feeding the 8.4V to the Dual Fet Source.
.... or even just put another Si9926 on top of the existing one to double the current, it can cope with 20V ( I think Bruce is right about the devices ) and still separate the rest of the circuit with the voltage regulator .. you can even put a switch to short the IN/OUT pins on the regulator to have it swichable between 4.2 and 8.4V ..
Cheers

[Rajesh L G]

You didn't see it because it initially wasn't there. I corrected it when I realised the mistake. ;)

Ah..., I was thinking I was getting old :D

[Alex Slowfly]

Alex,
If weight is an issue, why dont you consider replacing the Dual Fet with a higher curent one and just add a voltage regulator for the remaining circuit.
. . .
Cheers

Zlatko
Thanks for the advise. This sounds reasonable regarding the weight - but I really have some respect from those very tiny SMD on that board. I just fear to burn some of those little creatures on there... :eek:
So I will start with an addon circuit (I fear a rather big one) - the aim of the upsizing of the design remains, so that means more possible weight as well. :rolleyes:
Thanks for that advice anyway.
Alex.