'Low Cost' Hurri 425 build

[Jerrymac]

I recently decided to go on a quest to build an affordable priced Hurri 425/550, but without using cheap 'knock-off' electronics. I have a couple reasons for starting this project.

First, I have been in this hobby for about 3 years( started at the age of 50 ) and my flying skills seemed to have stalled out due to my fear of crashing one of my "babies". I have practiced rainbows, backward flight, and inverted flight on the sim with pretty good success, but, I just can't seem to bring myself to trying them at the field for fear of crashing.
So, I am going to build a lower cost 'trainer' in the hopes that it will give me the ability to progress without the fear of crashing.

Second, with the 425 basic kit selling for under $80 I think it makes a great helicopter for those moving up from a smaller size heli, but many get turned off by the higher cost of electronics. Hopefully this build will help those looking to build a nice low cost "500" sized helicopter.

Although I have enough spare parts to build a complete air frame from scratch, I decided to get a basic 425 kit from RCDumbthumbs since that is what most others will be starting out with. I also decided to take the time to search around for decent quality, 'good used', or 'previously owned' electronics, instead of cheap knock- offs.

This endeavor is just getting under way so I will update this thread as the journey continues.

Here are a few of the ingredients in the pot so far;

Basic 425 kit from RCD= $75
3 DS821 cyclic servos and DS20-GMD tail servo coming from one of our members here, PTcaflyer= $80 - Thanks Paul
Have a couple of used Spartan gyros coming from Scott, one of our admin here, Thanks Scott, $80 for the Quark.
Spektrum RX from a guy over at RCUniverse that had a package deal on 4 for $100 dollars (used) 1=$25
HobbyWing 5A ubec, purchased last year on sale at HeliDirect for $22

Total so far, $282 without motor and esc. Will continue to search for a good used motor and esc for this build. Stay tuned.

Jerry

[Jerrymac]

Update

First update. The gyros, and spare blades (for my 550) that I bought from Scott arrived Saturday. Thanks Scott!
The servos that I bought from PT arrived Monday. Thanks Paul!
I picked up a used (hopefully good, as I haven't received it yet to test) Align 75A esc from a member over at HF for $55 shipped.
Pair of Pro 3D, 430mm FRP blades from HeliDirect. $13

Total so far, $350 without motor, which should be the only thing left that I need to get.
I have a good motor with 5mm shaft in my 'spare parts' box, but don't know what kind, or KV rating it is as it came included in a package deal with some other stuff I bought a long time ago, so not sure if I can use it or not. Was thinking about looking for a Scorpion 3026-1400, or Z-Power Z20-1470, so I know for sure what I have for a motor.

More to come.......

[dunkonu23]

Sounds good Jerry. I'm looking forward to your build notes!

Scott

[Jerrymac]

Brief update,
I haven't been able to find a good used Scorpion or Z-Power motor to suit this build, so I might have to just buy a new one, which I was hoping not to, just to keep this a 'budget build' as intended.

HeliDirect and Flying Hobby are both out of stock on the Z-Power (Tonic-X) Z20-1470 so I might have to get a Scorpion 3026-1400 to finish the build, although I still have that 'mystery motor' in my stash that I don't know what it is, lol.


The build crew has been patiently waiting. Every time I walk down to the basement, they run down and sit on the stair landing just above the build bench discussing the new helicopter build.

Attachments:

[dunkonu23]

My build crew constantly goes to the door wanting out. I think he feels left out.

Scott

[Jerrymac]

Hehe Scott, I guess your helicopters must scare the 'crap' outta him huh.

[dunkonu23]

Yeah, they do. Especially after the BH500 hit the ceiling fan! He has memory issues.

Scott

[Jerrymac]

Another brief update......
After a minor set back due to a health issue, I was able to at least get online and do some more searching for a motor today. I found what was described as a 'good used' Scorpion 3026-1400 for $45 so I bought it. The seller said he also had a spare set of bearings and shaft for it that he would include, although he said the motor worked fine when he removed it from the helicopter that he was parting out.

So........... It might be a little while before I feel well enough to start on the build, but I will update again as the build starts.

Total so far= $395 without batteries, but I have a bunch of 6s 2500 and 6s 2650's for my other Gaui's so I really won't need to buy any more right now as they should work fine in this one too.

[Jerrymac]

Well, the build has begun.
First order of business was to use a Dremel to trim the plastic from above the lower OW shaft bearing mount and below the upper OW shaft bearing mount on the frame. The reason I do this is because the OW shaft bearings are known to fail prematurely, and I don't like to have to split the frame to replace them. Simply loosen the frame screws a little and push the lower bearing up, and the upper bearing down to remove them. During assembly, I put the OW shaft in place with both washers to hold the bearings in place, then, after assembling the frame, I pull the OW shaft back out and remove the upper washer to get the proper clearance.

Next, I found the elevator arm was not assembled properly from the factory. When installed, the large side of the ball end was facing away from the ball on the swash plate, so I pushed the pin out and rotated the upper part of the elevator arm 180 degrees and put it back together.

The rest of the build has been pretty basic so far. Frame is assembled, head is assembled , tail and boom installed, cyclic servos installed with the large JR servo wheels to get spacing and offset right. Gyro installed ( I decided to use the DS760 that I got from Scott instead of the Quark ). Tail servo is installed in the frame and gyro set up.


The motor arrived today, so hopefully soon I can install the motor, esc, and bec, and tidy up the wiring. Still need to cut out and assemble the 'milk jug' canopy and splash some paint on it. I have a couple of stock Gaui FG canopies for the 425, but will be using the cheapie one for the first few flights.

More to come as the build progresses......

[dunkonu23]

I bet you didn't use the quark because it needs an extension, right?

Sounds good so far, bro!


Scott

[Jerrymac]

Ha, you are right Scott, I mounted the Quark and the wires weren't long enough, and I didn't have any extensions. So, I used the DS760, and the wires on it are way too long, so I need to wrap them up and tie them neatly somewhere.

Mounted the motor and set the gear mesh, which is a real PITA. Mounted the esc and checked motor rotation. Still need to install the bec, tie up wiring, and install the main blades and finish the head set-up. Was hoping to maiden it this weekend, but, I don't think it will happen due to other more important obligations. Hopefully next weekend.

[Jerrymac]

Well, the build is basically finished, except for cutting out and painting the 'milk jug' canopy. I installed a stock Gaui FG canopy for now just to check the CG, and hopefully get in a test flight Sunday to check/adjust blade tracking, set gyro gain and trim it out.

I ended up reducing the default radio swash mixes from 60-60-60 to 56-56-55. With the default settings, I had some binding at full negative pitch and full back elevator which caused the swash plate to 'push up' a little. I ended up with +- 12 degrees collective pitch, and 7 degrees cyclic pitch, so should be good to go.

I might take some pics and post them, although this was just a basic Gaui 425 build that looks like any other one. My main reason for this build was to show others that they can build a nice '500' sized helicopter at a reasonable cost if they want to take the time to look for some good deals on the electronics needed to finish the build.

I will let everyone know how it flys when I get it in the air.

Jerry

[Jerrymac]

It has rained steady here the last couple of weekends, so I haven't been able to maiden this new build yet.
I did take some time to cut out and glue the canopy together, then spray it with some rattle cans. It doesn't look all that bad, although I certainly didn't take the time to fill and smooth out the seam, since the plastic canopies tend to crack a little on the edges after putting them on on off a few dozen times anyhow.
Will take a few pics as soon as I can find the camera.

[Jerrymac]

The weather was great today so I finally got to maiden the new 425. Blade tracking was spot on, and 2 trim clicks of forward elevator kept it in a perfect hover. Power was pretty good, although the Scorpion motor runs much hotter than the Tonic-X motor in my other 425, and is a lot harder on batteries, even though it doesn't have as much power as the Tonic-X does.

The tail was terrible though. It held fine, but the piro rate was so slow it took nearly 3 seconds to do one complete piro at full rudder stick. Even worse, several times while attempting a piro, it would turn about 90 degrees, then just stop there even while holding the rudder stick full right.

I have JR G770 gyros on all 3 of my other Hurri's and the piro rate is blurry fast. I also run 45% rudder expo on them because they respond so quickly to stick inputs. No expo on this one. I tried a larger set of .30 sized tail blades and it made no difference at all in the piro rate.
Since this is the first Spartan gyro I have ever used, I am thinking that I must not have something right in the programming or set-up. The tail held fine in a hover, and forward flight, but turning it was like turning a school bus. It did blow out on full collective punch-outs though.

I rechecked the tail limits and the slider is moving to the full limits just short of binding. Gonna read through the manual again to see if I missed something. I am pretty sure that my mechanical set up is correct, so I must have something buggered in my gyro programming.

Any suggestions???

Jerry

[dunkonu23]

It's the same as any gyro. Turn up the endpoints. The gyro comes programmed with 50 percent expo already. If you use transmitter expo, there's a chance that can be added to the -50 percent already there. Don't use transmitter expo until you've tried it with transmitter expo. Believe me, the Spartan is capable of blur piros like there's no gyro at all.

Scott

[Jerrymac]

Thanks Scott. I wasn't questioning the gyro, I was questioning my lack of knowledge in programming the gyro properly. It seems that all gyros are not the same. The JR's do not have any expo pre-programmed in them, so the Spartan is different in that respect. Jr recommends adding a minimum of 45% rudder expo, where as, unknown to me, you say that Spartan already has 50% expo programmed in it. I didn't know that.

Also, the JR's are supposed to be set up at full rudder end points available in the TX which is 150%, then reduce for the best piro rate. I think I set up the Spartan the same way as the Jr's, which might be incorrect, I dunno. I set it up with rudder end points at 150% just as I have always done with the JR's, so I cannot increase the rudder end points as they are already at their max.

No big deal. I have another JR G770 on the way. The Spartans will be in the for sale section soon if anybody wants them.

Thanks again,

Jerry

[dunkonu23]

Oh, well. It's your choice, bro. You're supposed to set up the Spartan with +-100 endpoints in your radio. Did you adjust physical throw of the servo/gyro system? For the record, I've never put any TX expo for spartan gyros and they were fine. So, I think your expo settings were added to the default expo on the gyro.

Scott

[Jerrymac]

Well, I am going to go back to the beginning and set the gyro up again. I knew I must have done something wrong. I set it up with the end points at the max so I couldn't increase the piro rate. I will go back and set it up at +-100 and then go from there.

I just had a really "bad tail" day yesterday. First flight with my 200 and the tail locked up then piro'd out of control. A 200 doesn't auto so I ended up crashing it trying to get it down. Second flight was with my BH450 and a minute into the flight one of the link ends on the tail control rod broke. I actually saw the control rod drop off at the tail end before it went out of control. I hit TH and got it down with minimal damage. Then the problem with the new 425 build just put me over the edge, lol.

I was so frustrated that I just packed up and went home.
Yard work and cook out today, so haven't had time to go back through the gyro set up, but I will give it another shot.

Thanks Scott.

[Jerrymac]

OK, so tonight I started all over with the gyro set up from the beginning, just to be sure everything is right this time. I never realized that different gyro manufacturers do things so much differently. I have used about 6 different brands of gyros, and never had one with "built in" expo.

I set it up with endpoints at +-100, set left and right travel limits to the max without binding, and no expo in the radio. After the set up was complete, I re-binded just because it is something I always do after setting up any helicopter, then I cranked up the rudder endpoints to +-150.
This should give me the fastest piro rate that the helicopter can produce. I also put the smaller stock tail blades back on as these work just fine on my other 425 and also on my HH '500'.

The other issue that I had on the maiden flight still baffles me though. Even though I believe I set the gyro up incorrectly causing the slow piro rate, I still don't know why, when holding the rudder stick full right, it would turn 90 degrees, then just stop. I would have to release the rudder stick, then push it full right again to get it to turn, and then it would turn another 90 degrees and stop again. This still has me a little confused so I am going to go back and check all of my connections to make sure that nothing is loose.

Hopefully we will get at least one dry day this weekend so I can take it back out to the field and see how it flys.

[dunkonu23]

I hope so, too. I had that VERY gyro setup at one time to do piro's so fast it was insane. Look at some of Nexgen's early videos with his 550. He had a DS760, too and that thing was fast on piros, too.

I have no idea why it would just stop unless the linkage is not set for full end points. I also always used to setup a spartan gyro in rate mode and adjust the pushrod until I got a good hover in rate mode. Then, I'd switch to heading hold and it worked great.

Scott