Cheap and Easy HK 600 Stretch - RC Groups
Thread Tools
Apr 13, 2012, 05:42 PM
Registered User

Cheap and Easy HK 600 Stretch

I recently set up a HK-600 for Ap, and had plans for stretching it to get longer flight times with a payload. Well, after some snoopin' on the forums, I finally chose my approach.

The HK-600 is belt, which meant either going torque tube, or ordering a custom belt. Being a low-income 16 year old kid, buying all the torque-tube parts was looking a bit pricey . So I ended up calling almost every belt manufacturer in the US, and finally found a place that made custom belts, had no minimum order, AND sold direct, not through a local distributor; So i called them up, and ordered a 736XL018. What that means is, 73.6" long (which means 368 teath), XL pitch (.2"), and .018 inches wide. The total cost was $15.20 after shipping, which is only a few bucks more then a 600 one from Align. The belt was here a week later and looked good!

I then bought a 700 tail boom, which are $8 each, and pretty generic.

And for blades, I went with some 700mm cheapies from Hobbyking... I was happy to find some that had a 12mm grip, not 14mm like alot of 700 blades. They were here in record time for Hobbyking int. wear-house, about 9 days! Here are the blades here...
One thing to note is that although they are plain CF in the picture, they say TURNIGY in large sparkley letters... You'll see in the pics.

Putting it together
I finally had all the parts, and it was go time. I popped off the boom, split the tail block and removed the stock belt. I put the new belt on, and put it together again. After that, I just swapped the blades, and was done! The whole thing took about 45 minutes from start to finish.
I was relieved to find that the custom belt I had ordered, fit PERFECTLY. I didn't have to cut the boom, nor was it too long. It also fit the pulleys perfectly.
Now the blades... Well the mic. reads that they're 12.5mm thick, so it's a pretty snug fit. Even without the screws, the blades don't really wonna turn or move in the grips easily... Well thats ok, I will try to thin them out a bit, but for now, I got them in there. The blades also have a slight imperfection. When looking at them from different angles, you can see bumps and lumps in the carbon. They feel pretty smooth on the surface though and I don't mind. Hey, they were $37!

I got to test hover in my back yard this morning, and after 20 minutes of adjusting the blade tracking, I got that thing flying nice and smooth The thing now hovers with the stick, HALF the distance from center that it used to. I guess that additional 4,556 cm 2 of surface area makes a difference! I can't wait to test this thing with the camera rig, but that will wait. I hope this helps anyone looking to do the same!

736XL018 timing belt from - $15.20
Trex 700 Tail Boom - $8
Turnigy 700mm Blades $37 ($55 after shipping )
Total: $78

The next couple things I plan to do is go flbarless and get 700 boom supports, but that will have to wait until the wallet is refilled

For those wondering my set up...
Hk-600gt kit
Align 600MX motor
Hobbywing flyfun 100A esc
EXI D226F Servos
Align DS620 on the tail.
Last edited by Foam boy; Apr 28, 2012 at 02:03 AM.
Sign up now
to remove ads between posts
Apr 14, 2012, 05:11 AM
Registered User
The Valkman's Avatar
That's a very good write up especially for a 16 year old!
What head speed did you get before you did the stretch and after?
Did you put larger tail blades on?
One thing if I was you I would replace the bolts holding the blade grips on with HT steel ones.

I have a 600 Chaos and I am planning at some stage to do AP with it. Not sure yet if i will stretch it yet. Mine is TT though so may cost more to do than yours.
Apr 14, 2012, 10:23 PM
Registered User
Thanks. I bought larger tailblades (some 105 cf from hobbyking) but I ended up just using the 95mm KBDD blades I was already using and they seem to be fine. As for the headspeed, before I was getting just over 1600 RPM, but my mom is in Hawaii for the next week and I used the Helitach app to calculate it. So I can't measure the HS until she gets back! Thanks for the suggestion about the bolts. I will probably do it since it's a cheap and valuable trick. From what I have heard, for TT, You just need the boom and TT. But You need to cut the boom at exactly 1 inch, but I don't think that will be too hard.
Apr 15, 2012, 01:37 AM
Whoops was it always in 2 bits
bionicbone's Avatar
thats fantastic, i've thought about doing this before but always thought it would take much more messing around.
you've done very well with your research and belt calculations, i'll keep this on file as your details will be handy for myself and others.
Apr 15, 2012, 04:06 AM
Registered User
Thanks, and I'm glad I was able to help!
Apr 16, 2012, 06:03 AM
Registered User
The Valkman's Avatar
The Headpseed calculaters are fairly accurate. But get the taco they are cheap.
With the extra weight make sure to keep an eye on the temperature of the ESC and motor.
May 16, 2012, 09:21 PM
PRO BRO #157
daking's Avatar
Thank you very much. Ive wanted to do a 620 stretch but hate align tt. This is perfect.
May 21, 2012, 07:58 PM
Registered User
Glad I could help!
May 22, 2012, 04:24 PM
Registered User
The Valkman's Avatar
So young lad how are you getting on with this setup? Any pics or vids yet?
May 24, 2012, 04:57 PM
Registered User
TexasClouds's Avatar
Nice find on the belt!

You should look into asymmetrical blades for AP / Sport flying. The flat bottom airfoil produces much more lift and lets you run lower headspeeds for these applications.

I have a 450 that I setup for FPV flying. I was using 3D blades at 2600 RPM and getting an average amp draw of 15 in a hover.

After adding Spin Blades 325mm asymmetrical blades and lowering headspeed to amp draw is now 8A! The heli feels lighter in the air and more stable.
Last edited by TexasClouds; May 24, 2012 at 05:20 PM.
May 24, 2012, 05:00 PM
Registered User
TexasClouds's Avatar
allerc has the blades in AZ.

stock 600mm asym blades might give you the same feel you are getting with the larger 3d blades. they also are balanced perfectly and track nice. the long tail boom might be nice to give you more tail authority at low speeds.

The 600, 620, 690, 700 sizes might interest you.
May 25, 2012, 01:19 AM
Registered User
Thanks for the tip! I considered asym blades, but heard that when either flying in wind or having to auto (I forget which), they don't preform real well? Maybe not though. Anyways, I just got my photoshipone 2XPT gimbal from a family friend (in exchange for some photos of his place this weekend.) As for the heli, due to radio malfunction (and an abbreviated preflight check) I had a tip over on take off and nicked my blades good. So its back on the 600's until I get some new 700's. I also just put on a DFC flybarless head (had to cut the main shaft), and a SK-720 for self level/bail out. This weekend will surely bring some flight report!
May 25, 2012, 07:19 AM
Night flier
Hi foam boy i had this helicopter and its a nice flyier. Just a word of warning though. With the tail blades so close to the ground be very careful not to touch the ground as the tail pitch slider will break on the part that goes through the bearing. i had this problem and its broke causing a bad crash. Just keep a close eye in things at the rear. Good luck sir! lol
May 25, 2012, 04:29 PM
Registered User
TexasClouds's Avatar
My 450 heli auto rotates better and does fine in the wind with asym blades. If someone tells you different, ask them if they have actually flown those blades.

May 30, 2012, 06:00 AM
Registered User
The Valkman's Avatar
Thanks for the update. Let us know how you get on with the SK-720.
Asym blades might suit you but you will be working the pitch more if it's windy out due to them giving more lift with their aerofoil shape. But I bet you know that.

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Build Log Trex 600 Stretch Scale Bell 222 Build algroove2000 Large Electric Helis 111 Jul 03, 2017 03:58 PM
Discussion Aircraft fire rocket(from a poor english chinese boy) WimpyKid Multirotor Drone Talk 8 Aug 21, 2012 08:33 AM
Discussion Can a Trex 600 Pro be stretched to a 700? Allan Gibbs Electric Heli Talk 11 Jan 27, 2012 01:46 AM
For Sale stretched trex 600 flbarless $600 ricksmartinez Aircraft - Electric - Helis (FS/W) 2 Sep 13, 2011 07:52 AM
Discussion Instructions to stretch trex 600 elecitric to 700? djdaveq Electric Heli Talk 10 May 04, 2008 07:03 AM