Build Thread - HeliBug SPARK Conversion

[carey shurley]

Spark conversion came in today.

I'll post some photos of the actual parts, a couple are slightly different than whats posted on the helibug website.

I'll post more stuff as I get to it. The conversion is really very simple to do

[carey shurley]

so here's what comes in the conversion. Very nice materials, the G10 is cut very cleanly however there are a lot of tool marks on the aluminum parts. They aren't rough though.


Spark Conversion Kit

This particular kit is for mounting the RC motor facing forward. The only difference between the forward and rear facing conversion kit is that the bottom plate is cut differently, everything else is the same.


Spark Bottom Plates

Here's the difference between the Spark bottom plate and the std Spectra-G bottom plate. I'll do a weight comparison of all this later.


Spark vs Spectra Bottom Plate

Here's my conversion target. Its one of my custom made heavy duty spectra-g's. Its a blend of a Stratus and a Spectra with heavy duty bracing. Essentially they are "industrial spectra's". For purposes of this conversion though it will work fine. I'll just have to remove all the bracing and the fuel tank and return it to a more stock Spectra format. The critical dimensions and parts are all identical.


Spectra Chassis

The first interesting component is the clutch interface. What this is, is the stock zenoah clutch baseplate from an RC format motor. Its a cast piece, a little heavy but simple. To interface with the stock Spectra driver, Ali has cut a damper/uniball component. Have to see how accurately it mounts up however the tolerances on the bolt holes are very tight.


Spark Clutch Driver Interface

these two motor mounts bolt onto each side of the spectra along the lower clutch bearing block and then the front of the motor bolts to these mounts


Spark Motor Mounts

I won't have the motor until next week but its going to be a prototype TRM 260 motor thats been balanced and ported for this application.

[carey shurley]

here's how the bottom plate mounts to the landing gear. I always use rubber washers between the bottom plate and the landing gear to help prevent any buzz from vibration.


Landing Gear Mounted to plate

there is a minor change required here, because the form factor of the motor is larger than the original PUH, the distance between the landing gear struts needs to be made slightly larger.

The rear strut can stay in its original position and just push the forward one a little further forward. Here you can see how the relationship changes with the original position at the top of the photo.


Difference in Landing gear strut installation

[carey shurley]

so to get ready to install the RC format motor, you remove the 4 bolts that hold the bottom plate to the frame ladders, disconnect the fuel lines, throttle rod and the tail boom supports and drop the plate and motor.

Engine Removed


Mounting the Spark motor mounts is pretty easy, you just remove the 4 innermost bolts on the lower clutch bearing and then install the motor mounts right over the top of the ratio plates.

Left Engine Mount Installed


after the driver adapter is installed on the motor, it will mount up to these two mounts with 4 bolts

Both Engine Mounts Installed

[carey shurley]

So here's the motor, its a prototype TRM-26cc motor thats been balanced and ported for the RPM ranges that this model will be running. I've replaced the pull starter with an ADA air scoop, which will increase the ground clearance of the motor





This is the new one piece driver interface. It mounts directly to the motor and the original dampers install into the two cavities shown.

[carey shurley]

here's how the model looks with the motor mounted. If my model was set up for a rear facing motor, it would be ready to fly since the tank would likely be in the front of the model. Since I only fly it forward facing, I still have to mount a tank. It looks like I can still get the 16oz nalgene bottle tank in the open space. If not a sullivan 12oz fits perfectly.


Note, I haven't updated the photos yet for the newer one piece driver interface hub

as you see it, its CG neutral. The canopy will make it just a touch nose heavy and I expect fuel will make it nearly neutral again

[Greatsteaks]

What are the pros/cons of forward or rear engine mounting?

[carey shurley]

front mounting results in:

• more forward CG (slightly)
• ability to mount a rear fuel tank
• better balances muffler weight with main shaft
• looks more balanced
• different canopy cutouts
• remove canopy to access spark plug

rear mounting results in:

• more neutral CG
• requires front mounted fuel tanks (which are hidden or requires canopy cutouts for visibility)
• more of muffler weight is behind mainshaft
• looks unbalanced
• simpler canopy cutouts
• easy plug access

the stock spectra supports both orientations out of the box. The spark conversion requires that you order a bottom plate for one or the other
no appreciable impact on radio operation regardless of orientation

[kopterkat]

Carey,
This looks really great. Compared to your other is there much weight difference? I'll tell you it looks lighter than my Spectra G. I also noticed you removed the the pull start. Notice cover.
Thanks for the post.

[carey shurley]

Haven't weighed all the parts in an out yet until its flyable

however I expect it to be weight neutral or near so,. I published a weight comparison on another site not too long ago that compared the weights of the RC240, the PUH231, the G20EI and another TRM prototype motor thats about to be released. If you weigh the PUH motor all up (with fan, shroud, coil) and then compare that with the RC motor (which comes out of the box with a fan, shroud and ignition system), they are very close in weight.

I dont like to "pull start" any of these things because of the lateral stresses it puts on the chassis especially when they are new. So I just remove/replace it.

[kopterkat]

I remember the post. I'm really looking forward to your flight impression. I'm curious to what lateral stress is put on the frame and the effect. The way these frames are joined spreads the load across the frame pretty well. I do however see that the removal of the pull start giving more clearance between the ground and the engine. On your starter do you use a 6mm hex or MA one way?

[carey shurley]

600 & 700 I use the hex start

xcells I always use the newer 2 bearing pro-flex. If you keep the bearings oiled and don't nick up the start shaft the hold up pretty well

[kopterkat]

Thanks.

[carey shurley]

so here's how everything looks mounted up

the stock fuel tank is an 8 oz tank. I've replaced that with a Sullivan RSL 12oz tank which will fit right in to this conversion.

Because this is a hard plastic tank, the one-way valve which is often troublesome with the stock (and other) flex tanks will work correctly.

Sullivan RSL 12oz tank ready to plumb


everything fits right in and can be plumbed neatly.

Completed Install - Right View


Completed Install - Left View

[kopterkat]

I noticed that your setup has 4 fittings were the Spectra G setup has 3. Is the 4th fitting the vent/ filler. Also the T fitting that you have on the capped off line is for what? Carey thanks for your time and sharing this with us all.

[carey shurley]

the stock kit assumes that you're going to put a T-fitting in the fuel inlet line to use as a fill.

the T in the overflow line is for a fill vent, since the one-way valve closes against internal pressure.

I don't like putting ANYTHING in the fuel inlet line so I just add another tank outlet that I use to fill with.

so the fill procedure is to remove the two plugs a the end of the lines and then fuel it.

[carey shurley]

okay so its been flown.

no issues although today was just hovering sessions

very smooth, no problems. This is a prototype TRM 260 balanced to work with the standard 7.15 spectra ratio. We'll see how it does after it gets some time on it and I'm comfortable turning it up

[kopterkat]

Carey,

Anymore flight reports?

[carey shurley]

I did put a coupla flights on it over the weekend, and its working very well

however I'm waiting for a coupla parts from HB before any more detailed report

[kopterkat]

Do you have any more flights on the conversion? How does it compare to your modified Stratus and a stock Spectra G?