View Full Version : Problems with Axi's in twin.

10-19-2005, 12:49 AM
A friend has built a DH Caribou from scratch & has two supposedly identical small Axi brushless motors in it through seperate ESC's from one 3s litho pack. One motor runs about 600 rpm slower than the other, controller cuts out occasionally & needs to be brought back to idle & started again. He tried swapping the motors from one side to the other to determine if it was the ESC or the motor, the same problem was then on the other side so it must be the motor. Ideas? Faulty motor? - John.

10-19-2005, 01:34 AM
Hmm strange... from your description It sure sounds like a faulty motor. I assume you have disabled BEC on one controller.

I flew a BN-2 Islander with two AXI 2208/34 on a TMM controller each without problems.

10-19-2005, 03:28 AM
Yes, only one controller is supplying the Radio. - John.

Matt Kirsch
10-19-2005, 01:25 PM
Frankly, I would go with the faulty motor angle until someone comes up with a better idea... especially since the performance hit followed the motor.

If the motors are fairly new, start with the vendor you bought them from. I believe Hobby Lobby is the exclusive distributor, so they may be able to help you out regardless. Sending the bad motor back to the Czech Republic will take a while...

10-20-2005, 11:11 AM
Thanks for the advice guy's, I'll pass it on to the victim!
If the motor is faulty he is about to discover the down side of shopping on ebay! - John.

Matt Kirsch
10-20-2005, 02:29 PM
That looks like a B-36 in your avatar...

10-20-2005, 06:46 PM
If he bought them used, One could have been over amped or heated and not performing as it should.

10-21-2005, 04:02 AM
Ok: I too am having trouble with synchronizing two AXI 2820`s.They run about 3-400rpm different from each other. They are new, bought from Hobby-Lobby. I`m using Castle Creations 45 amp ESC`s, and are mounted in a Top Flight DC3. I have gone over all the wiring, connecters, and re-programed the ESC`s. WHAT? Buck

10-21-2005, 09:09 AM
Yep Matt, it's a B-36. There's a thread on it in the scale model section.
eal, I'll find out what motors & speedy's he's using, not looking good :( . - John.

Matt Kirsch
10-21-2005, 01:30 PM

You'll never get the two motors running at the exact same RPM for sure. With my limited twin experience, and no electric twin experience, I'm not sure what an acceptable difference is. 3-400 RPM sounds like a bit much for electric motors, but I'm not 100% sure.

Are you using separate batteries? Are the timing settings for both ESCs set the same? Cutoff style? If there's only one battery, are the ESCs in series or parallel?

You're not running counter-rotating props, one tractor, one pusher, are you? The props aren't exactly the same, so there will be some difference in performance. Plus, it's not scale for a DC3 :)

I know you checked, but check again for good solder joints. One bad joint could cause enough of a voltage loss to do this.

10-22-2005, 04:02 AM
Your right: I re-soldered the three ESC to motor on one motor, and re-balanced the props, and am with in 100 rpms now. I noticed that just spinning the props by hand, one turns a little longer than the other. ???. The props are Groupner three blade props, both turning the same way. The batteries are three, three packs, wired in parallel. These are not the batteries I will end up with, because I need a little more power. I beleive they will fly the DC-3 in low performance. though.

Matt Kirsch
10-22-2005, 05:45 PM
100 RPMs should be close enough for government work... :D

I'd dare say you probably had a slightly dodgy connection there.

10-22-2005, 09:11 PM
Yes, only one controller is supplying the Radio. - John.

I would suggest that you get rid of the BEC and use a separate pack so that both ESC's are operating the same at least.

10-22-2005, 10:23 PM
I just let both becs operate. It has worked so far on two planes and was recommended by Astroflight.


10-23-2005, 03:40 AM
Iflew the DC3 today for the first time, and it went beautifully, on three cell batteries. I didn`t think it would do as weel as it did, even though It only flew for about 6 min. I intend to go to 2 four cell x 4000 LiPo`s. I LIKE IT! Buck

Matt Kirsch
10-24-2005, 12:43 AM
Nice :)

Yeah guys, there's normally no trouble with having both BECs active, and in fact there may be an advantage to that in a larger plane where they'll share the servo load. Both produce a regulated 5 Volts DC, so there's no "fighting" going on.