OS GT15HZ Conversion

[Sowa]

I had a few questions wondering if any of you can help me.

I'm looking at installing an OS 15gthz. O.S will be coming out with a 600 class version of this motor but it will still require a gearing change as well as a different fan and shroud.

I saw a video of a 91hz in a velocity 50 on youtube, does anyone have anymore info as to what parts he used?

Velocity 50n2 with OS91 hz, 7.16:1 gear ratio, 2250 head speed (4 min 21 sec)

[ggwatt]

I am also looking to put an OS91HZ-R in a velocity !

Have a look here :

http://www.avcom.co.za/phpBB3/viewto...?f=16&t=114721

[Sowa]

Thanks for posting that! If the original clutch is holding with a .91 nitro it should do fine with the less powerful gt15hz.

Does anyone know what pinion gears are interchangeable with the velocity 50n2? I'd like to find a 16t pinion. That would put me at 8.06 which is a good ratio for that motor swinging 640mm blades.

With some rough calculations I figured out I can keep the same disc loading that the model currently has with the .55hzh/funtech b323 swinging rail 606s by moving up from 606 to a 640mm blade. If this bird turns out identical in power and disk loading I will be very happy.

I found this thread that allows you to switch over to a mod 1 gear but its only a 100t gear set. I did however fine the alees rush main gear which is 112t. Using the align 14t it works out perfect at 8:1


Fusion 50 mod 1 conversion
Clicky

I'm sure for the 91hz he used this pinion : Clicky

Alees 112t mod 1 Main gear: Clicky

[Sowa]

Anyone have a velocity 90 on hand? I'd like to know how wide the frame is.

[Sowa]

Gt15 600 confirmed, looks like this may happen...

[Sowa]

Well I decided to push forward with the conversion and decided to take a certain route.

I will be modifying a stock pinion to gear the model properly. I ordered a velocity 90 engine mount and fan shroud, I will modify the two hopefully to make them work with the gt15hz.

Fyi, frame halves on the velocity are 28mm while the velocity 90 is 35mm. So the parts will not fit out of the box.

[JasonJ]

Good luck with your conversion. I will be watching closely. I would love to gasserize my Velo 50. I love the helicopter but am not loving the nitro prices and general pain in the butt factor. I have to drive over an hour each way to get fuel but a gas station is literally on the way to the field. That and I am building a big gasser plane, it would be awesome to be able to just haul a couple gallon jug o gas for my flying fun. I am wanting to ween nitro out of my hobby, I just hope the gt15 is past it's issues.

[Sowa]

I've been talking back and forth with Thomas Muller, he is the gentleman who figured out the big block conversion in the velocity first off. Here is all the data I have gathered.


Gearing:

I didn't inquire about the different gearing he changed to but as far as the 7.16 gear ratio is concerned a stock velocity 50n2 pinion is modified, and a kyosho caliber pinion gear was modified and pressed on a stock velocity pinion. See attached pdf and cad models*

Kyosho Caliber 18t counter gear: Part #CA3022

The Gt15hz will work with a ratio anywhere between 6:1-- 8:1 with faster headspeed recovery closer towards 8:1.

A break down of gear ratios
Stock 15t pinion / 129t main = 8.6
129/16 = 8.06 => I don't think this is achievable without manufacturing a new pinion gear.
129/17 = 7.58
129/18 = 7.16 => Kyosho Caliber Pinion

7.58 right now feels like the right ratio as the motor makes peak power @ 14k

14000/7.58 = ~1850

To Achieve 7.58 ratio a similar method would be used although of modifying a stock velocity pinion and pressing on a kyosho pinion. I have been trying to get information about the pinons before I purchase one or both.

Kyosho VZW215-17 1st Steel Gear (0.8M/17T for RRR)
Kyosho VZW230-17 1st Hard Gear (0.8M/17T/RRR Evo/SR)

Carey Claims the motor is happier around 16k but he also runs it with a hatori pipe which makes the power peak a little later.

16000/7.58= ~2110

I feel like this puts me in the right range for head speed with that gearing. But I will never know without trying out both.

With 7.16 gearing the head speed would range between depending on motor rpm:

14000/7.16 = 1955
16000/7.16 = 2234

Motor Mount:

Thomas went ahead and manufactured his own mount, I have attached the pdf drawings of the mount and also the cad model. The engine mount drawing already moves the center of the motor forward by 1.2 mm for the 18 tooth pinion, remember if you are changing gearing this distance will be different.

I picked up a velocity 90 engine mount to hopefully make things easier. The velocity 90 engine mount will need to be milled down 3.25 mm on each side and new holes drilled in the frame along with some sort of cutting. I haven't decided on which engine mount to use. Either one will require a mill which I have access to at school. But Thomas's mount seems less intrusive on the frame and it looks like it sits the motor back further.

Fan Hub and Crankshaft (regarding nitro .90 install):

Regarding installing a .90 big block the hub must machined to accept the larger crankshaft of the .90. You must shorten the crank of the motor to be flush with the nut that clamps the hub onto the motor. So the crankshaft will have to be cut on the 90.

With the GT15hz we will see when it shows up, but I believe its sized to accept a standard 600 fan hub. So no modifications will be necessary there.

Frame modifications:

You will have to cut about 5mm from the frame by the motor's head for it to fit. I assume this will be the same with the GT15hz as the crankcase between the 50 and 90 class is the same. In order to get the correct mesh you will need to slot the holes in the clutch stack by that 1.2 mm the motor is shifted to accept the 18 tooth pinion.


Fan and Fan Shroud:

Gathering info from Thomas it sounds like he had good luck running the stock fan and shroud with the .90 nitro. Gasoline engines run a little hotter so I opted to purchase a velocity 90 fan shroud to hopefully fit to the velocity 50 frame. Off first glance I don't think that the velocity 90 fan shroud will work as I would have to cut too much material off the frame. In which case I'd feel safer picking up a velo 90 frame set but that just adds a lot more parts onto this conversion. So I will try my hand with the velocity 50 fan and shroud with the gt15hz 600.

Hopefully this info helps others as much as it's helped me!

*Looks like I can't upload the CAD files, shoot me a PM with your email and I can get those out to you.

[Sowa]

Another update,

I went ahead and ordered a 16t 0.8mod pinion. This pinion is from tamiya.

With a 16t pinion my ratio will be 129/16 = 8.06

[Stevin]

What ever happened with the conversion