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Old May 18, 2012, 07:45 PM
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New - 9104 problems

Hey everyone,

New to the board - I'm a fixed-wing full-scale pilot (FAA commercial airplane single & multiengine land & instrument) but new to the world of RC helicopters.

A friend of mine gave me a DH9104 because, as I've seen from others reading the first 20 pages or so of this thread, it flies like crap! I've improved it somewhat, but I'm looking for some help.

Here's what I've done so far:
1) Added weight in the nose. Later removed it, as flight characteristics didn't improve and it really affected climb performance.
2) Removed the front right-hand fixed link from the swashplate. This appears to have helped somewhat with the left-drift problem (though now it's a left-front drift, but hey, whatever works cheap!)
3) Lengthened the arm from the servo slightly (loosened 5 turns) to help with forward motion, which is acceptable now.

The remaining problem: It spins to the left quite a bit whenever it's out of ground effect. Even with full right trim and full right stick, it just spins around to the left about 1-2 times per second. Needless to say, not very fun that way!

I tried the gyro tests described in post 177 and 257 of this thread. When the main motor is unplugged, the tail rotor does not spin at all. When the main motor is plugged in, the tail rotor does react to yaw (it correctly tries to counteract any yawing I do with my hand). I can't tell for sure if the tail rotor is mixing with the throttle since it doesn't work at all with the main motor unplugged, but it doesn't appear to - As I slowly increase throttle with the helicopter sitting on the ground, it has an increasing tendency to turn left. I have it trimmed so that the turning tendency goes away right about when the heli lifts off.

Unfortunately, once the heli gets off the ground and climbing, it quickly begins spinning to the left. The stick appears to have no effect on the rate of the spin - I can put in full right or left stick and it'll just keep on spinning away at the same rate.

What kind of problem does this sound like? What can I do to fix it? What's the best source for DH9104 parts (US)?

Thanks!
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Old May 18, 2012, 09:01 PM
Crash and learn
United States, PA
Joined Dec 2011
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Quote:
Originally Posted by flyingcheesehead View Post
When the main motor is unplugged, the tail rotor does not spin at all.
You are sure about this? Main motor unplugged, the servo works, red LED on receiver board is on solid, nose flood LED is on, tail motor does not spin when you give it full throttle. The LEDs on tells me that the ON/OFF switch is on and the +5 volt regulator is likely OK.

On the transmitter, turn the "LEFT/RIGHT TURN" knob fully clockwise. That directly affects the tail motor.

The key to the problem is the tail motor does nothing with the main motor unplugged and full throttle. And the tail motor works more or less when main motor is plugged in. Never heard of that before and considering the electronics, it doesn't make sense.

By "turn left", you mean nose left, counter-clockwise?
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Last edited by Ribble; May 18, 2012 at 09:13 PM.
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Old May 18, 2012, 11:43 PM
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Originally Posted by Ribble View Post
You are sure about this? Main motor unplugged, the servo works, red LED on receiver board is on solid, nose flood LED is on, tail motor does not spin when you give it full throttle. The LEDs on tells me that the ON/OFF switch is on and the +5 volt regulator is likely OK.
Exactly correct - I just tried it again and verified all of the above to be sure.

Quote:
On the transmitter, turn the "LEFT/RIGHT TURN" knob fully clockwise. That directly affects the tail motor.
Just did that too. Nothin'.

Quote:
The key to the problem is the tail motor does nothing with the main motor unplugged and full throttle. And the tail motor works more or less when main motor is plugged in. Never heard of that before and considering the electronics, it doesn't make sense.
No kidding... Got me baffled!

Quote:
By "turn left", you mean nose left, counter-clockwise?
Affirmative. I guess I'm used to flying full-scale enough that I think of everything from the pilot's perspective.
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Old May 19, 2012, 01:05 AM
Crash and learn
United States, PA
Joined Dec 2011
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Got to sleep on this one.

Main and tail motor electronics have very little in common on the DH9104. The circuitry is battery (+), motor connector (+), motor, motor connector (-), MOSFET switch, battery (-), and a snub diode across the connector to absorb voltage spikes.

As a quick guess, could be something mis-wired between the orange battery connector and circuit board solder connections, like the main motor is connected in there somehow. Or something with the ON/OFF switch.

The tail motor should always be pushing air to the right. Can you check that?

Also check that the main motor wires are Red and Back on the plug. The tail motor wires are White and Blue on the plug.

On the back right of the circuit board the four soldered wires are Red Black White White.

If you get ambitious, look at the bottom of the circuit board for shorts or something burned open. Would be in the motor connectors area.
---



"turn left" - Orientation is always a problem with RC helicopters. We learn first with "tail in" so the controls match what will happen. And hour after hour looking at the tail, we tend to describe movement relative the tail instead of the nose. "Nose left" avoids confusion. Even "yaw" (rudder caused) gets confused with "roll" (aileron caused).

Nose left spin means the tail rotor is weak. Nose right spin is usually a gyro or main rotor problem, though one of my latest V911 flights had nose right caused by the tail sliding back off the boom which made the tail rotor stronger.

---

Two versions of DH9104 PCB. If the copper (green enamel coated) is burned open on the left edge between upper white line and lower solder joint of the photo, that would cause the tail motor to only work when the main motor plug is plugged in.

A shorted snub diode, the large one between the motor connectors, would cause the copper to burn open.
.
.
Right click the photo and open new tab to see the photo better.
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Old May 20, 2012, 05:00 AM
still a lot to learn!!!!
Auflyer's Avatar
Australia, NSW, Laurieton
Joined Jan 2012
306 Posts
Quote:
Originally Posted by Tumppi T View Post
Finally my DH is 4 channel

MJX transmitter + PCB functions perfectly. I really suggest them. Feels like my DH has now much more power and there is lots of trimming options.





Looks great, I'm keen to know more about how you made this work. My 9117 fried it's pcb after three flights however it's flight performance was garbage so not sure what to do with it
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Old May 21, 2012, 04:21 PM
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Hello Tumppi T,
Hello everybody else that can help me,

I am planning to mod my son's 9104 in the way you did it, as it seems to me it is the easiest and for European cheapest way.

I found a place to order a combo of MJX Transmitter and PCB for 50$ (the one before the last):

http://feala.com/mjx-F645-F45-RC-hel...-F45-parts.htm

I think, they will send it from China, but without shipping cost.

I think I also need an additional servo. You seem to have bought two new ones, would it be sufficient to take one of those on this list? And then the smaller or the bigger?

So this PCB does include Receiver, Motor Power Unit, Mixer, Gyro, and all other things like the famous 4-in-1, which is a 9-in-1? Nothing else needed?

Coming to the swashplate setup: you used the original swashplate, just put in the screw in the mentioned position. Did you drill a hole before?

Can you make some closeups of the wiring (or description) and the swashplate mod?

I think the servo mod is documented very well. Did you use a paper clip fpr the metal part? And where did you get the plastic T-like thing.

Sorry for so many questions. I am still fuzzy after reading 62 pages of this marvelous thread, where people from all over the world mod a heli!!!

BR,
Carsten.
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Old May 22, 2012, 12:30 AM
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Tumppi T's Avatar
Finland, Tuusula
Joined Mar 2012
181 Posts
Quote:
Originally Posted by carsten12 View Post
Hello Tumppi T,
Hello everybody else that can help me,

I am planning to mod my son's 9104 in the way you did it, as it seems to me it is the easiest and for European cheapest way.

I found a place to order a combo of MJX Transmitter and PCB for 50$ (the one before the last):

http://feala.com/mjx-F645-F45-RC-hel...-F45-parts.htm

I think, they will send it from China, but without shipping cost.

I think I also need an additional servo. You seem to have bought two new ones, would it be sufficient to take one of those on this list? And then the smaller or the bigger?

So this PCB does include Receiver, Motor Power Unit, Mixer, Gyro, and all other things like the famous 4-in-1, which is a 9-in-1? Nothing else needed?

Coming to the swashplate setup: you used the original swashplate, just put in the screw in the mentioned position. Did you drill a hole before?

Can you make some closeups of the wiring (or description) and the swashplate mod?

I think the servo mod is documented very well. Did you use a paper clip fpr the metal part? And where did you get the plastic T-like thing.

Sorry for so many questions. I am still fuzzy after reading 62 pages of this marvelous thread, where people from all over the world mod a heli!!!

BR,
Carsten.
Hi Carsten and Auflyer,

I try to answer all the questions

The MJX F45 PCB includes all. I didn't do any other electrical modifications than swap wires of both motors (main & tail). They run wrong way with the MJX PCB. Its very easy to swap the connectors from the plugs.

About the swashplate modifications......only the small screw in the front part...and yes...i drilled a small hole first. Also took the left-front arm away.

The servo link was made from paperclip....and the white T-link came with my new servos. I put two new blue 9g servos only for visual reasons. You may use the original servo as well. Only add one new 9g servo (same size as the original).

There is no place for main switch in the MJX PCB.....so i took the original switch away from my DH. You don't need it. You may use the battery connector as main switch.

The black plug that is loosen (see the picture) is for my navi-light system (the yellow unit under the PCB). I get power for that system from the third servo place of the MJX PCB.


Hope this was helpful,
- Tumppi


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Old May 22, 2012, 04:10 AM
Micro Heli mods
Tumppi T's Avatar
Finland, Tuusula
Joined Mar 2012
181 Posts
Quote:
Originally Posted by flyingcheesehead View Post
Hey everyone,

New to the board - I'm a fixed-wing full-scale pilot (FAA commercial airplane single & multiengine land & instrument) but new to the world of RC helicopters.

The remaining problem: It spins to the left quite a bit whenever it's out of ground effect. Even with full right trim and full right stick, it just spins around to the left about 1-2 times per second. Needless to say, not very fun that way!

I tried the gyro tests described in post 177 and 257 of this thread. When the main motor is unplugged, the tail rotor does not spin at all. When the main motor is plugged in, the tail rotor does react to yaw (it correctly tries to counteract any yawing I do with my hand). I can't tell for sure if the tail rotor is mixing with the throttle since it doesn't work at all with the main motor unplugged, but it doesn't appear to - As I slowly increase throttle with the helicopter sitting on the ground, it has an increasing tendency to turn left. I have it trimmed so that the turning tendency goes away right about when the heli lifts off.

Unfortunately, once the heli gets off the ground and climbing, it quickly begins spinning to the left. The stick appears to have no effect on the rate of the spin - I can put in full right or left stick and it'll just keep on spinning away at the same rate.

What kind of problem does this sound like? What can I do to fix it? What's the best source for DH9104 parts (US)?

Thanks!
I think that the tail motor has reached the end of its life.
I got same kind of problems....replaced tail motor....and now it works fine.
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Old May 22, 2012, 08:37 AM
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Thank you Tumppi T,

that helps me a lot. unfortunately, I now have some shipping cost, but I found
another seller, where it's 33,33. Deal!

BR,
Carsten.
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Old May 22, 2012, 10:08 AM
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Tumppi T, just another short question. I know you had to construct a new lever for
the new servo, but you wouldn't hafve had to change anything on the old servo, didn't
you, if it weren't for the blue stylish one?

Also, How did you manage to change the polarity of the plugs. Pulling them gently out
and putting them back in the other way round?

Ah yes, and did you have to bind the transmitter and the PCB somehow?

BR,
Carsten.
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Old May 23, 2012, 01:36 AM
Micro Heli mods
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Finland, Tuusula
Joined Mar 2012
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Quote:
Originally Posted by carsten12 View Post
Tumppi T, just another short question. I know you had to construct a new lever for
the new servo, but you wouldn't hafve had to change anything on the old servo, didn't
you, if it weren't for the blue stylish one?

Also, How did you manage to change the polarity of the plugs. Pulling them gently out
and putting them back in the other way round?

Ah yes, and did you have to bind the transmitter and the PCB somehow?

BR,
Carsten.
Hi Carsten,

I was have to move the original servo to upper place to get enough space for the lever and also cut the lever little bit shorter.
I didn't cut any new holes to frame....just bolted the servos to places that already exists.

The polarity of the plugs was easy to change. There is small white clips on the plugs...just lift them little bit and then pull out the connector....and then put them back other way.

No binding needed with the transmitter and PCB. Just connected the battery to PCB...then turned transmitter on ....pulled the throttle min - max - min.....and it was connected

BR,
- Tumppi
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Old May 23, 2012, 01:40 AM
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My next project is to get brushless motor to my DH....

I'll try to find motor and esc that are bolt-on with my MJX F45 PCB and 7,4V battery
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Old May 23, 2012, 08:43 PM
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Quote:
Originally Posted by Ribble View Post
Quote:
Originally Posted by flyingcheesehead View Post
When the main motor is unplugged, the tail rotor does not spin at all.
You are sure about this? Main motor unplugged, the servo works, red LED on receiver board is on solid, nose flood LED is on, tail motor does not spin when you give it full throttle.
Whoo, this is odd. So it wasn't the other day, still wasn't when I verified it. I played around with it some more, then charged it up and let it sit for a few days, and then it did start working as desired with the main motor unplugged. By "as desired" I mean that moving the helicopter manually in the yaw axis varies the speed of the tail motor (gyro is working), and both the throttle and the left/right stick change the motor speed as well.

Then, just now after pseudo-flying it (in ground effect, mostly) I unplugged the main motor again to do some experimentation on the tail motor, and when I advanced the throttle, it started working for just a few seconds and then cut out. I turned both the transmitter and receiver off and on a few times, nothing made it work again until I plugged in the main motor, whereupon it started working immediately. Unplugged the main motor, and it works again.

So... What could cause the tail motor to always work when the main motor is plugged in, but occasionally stop working with the main motor unplugged, until the main motor is plugged in again?
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Old May 23, 2012, 08:44 PM
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Originally Posted by Tumppi T View Post
I think that the tail motor has reached the end of its life.
I got same kind of problems....replaced tail motor....and now it works fine.
Thanks Tumppi... Did yours exhibit the odd behavior I described in the previous post (just a minute ago)? I'm wondering if it doesn't need a new PCB as well.

What's a good source for DH9104 parts in the US?
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Old May 23, 2012, 08:55 PM
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Ribble,

Thanks for the detailed reply. In addition to the other observations of oddness from the last couple of posts, I'm noticing two things with the tail motor:

1) At full throttle, the tail rotor doesn't spin much faster at full right stick than it does with the stick centered. With the stick full right, the speed of the tail motor does not vary regardless of the throttle setting (as long as it's spinning at all). Tumppi might be right about the tail motor...

2) There's a slight vibration to the tail rotor. It's not noticeable at fast speeds, but near idle with the stick to the left it's easy to see.

More later - Gotta enjoy the sun while it's still up!
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