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MLD 70cc Twin - Starter System - The Project

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MLD 70cc Twin - Starter System - The Project

Old 08-11-2011, 10:41 AM
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Umran
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Default MLD 70cc Twin - Starter System - The Project

Hi All,
Today i received this engine. The owner of this engine requested me to design and build the starter system for this new engine.

mmm... this engine is basically new in the market, performance wise, i do not know yet. But the project must go on.

Some simple weighing just to see how much the weight different after completion of this project - initial weight without muffler and ign unit = 1700grams. Not bad for a twin 70cc.
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Old 08-11-2011, 10:49 AM
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Umran
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Default RE: MLD 70cc Twin - Starter System - The Project

Let us investigate this engine further....

The specs doesn't actually dictate the BORE x STROKE, but after dismantling the engine i found out that the piston is 38mm diameter and the stroke is 30mm. The crankshaft size is 12mm. One thing very perculiar is that this engine is using original wabro carb with pre-install long arm for the throttle input. Quite nice!

The overall casting quality is very good, very clean and smooth external surfaces. But when i open it up, yes the internal surface of the casting also not bad at all.

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Old 08-11-2011, 10:56 AM
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Default RE: MLD 70cc Twin - Starter System - The Project

Okay some basic approach to do this start system,

Piston Diameter = 38mm, Stroke = 30mm
Initial volume, V1= 27285mm^3
Final volume, V2 = 3740mm^3

P1 = ambient pressure = 101325N/m^2
V1 = 27285 mm^3 - calculated volume enclosed after the top of the piston passed the exhaust port.
V2 = 3740 mm^3
Resulting in P2 = P1V1/V2 = 739212N/m^2
Nett pressure acting on combustion face of the piston = P2 – Ambient pressure P1 = 739212-101325 = 637887N/m^2
Piston Area, A = (pie)r^2 where r = 0.019meter, therefore A = 0.001134m^2
Force on the piston = Nett Pressure x Area = 637887 x 0.001134 = 723.4N
Torque = Force x Distant, where distant is between the centroid of piston rod pin (on the crankshaft) to crankshaft center, in this case it is 15mm or 0.015m.
T = 723.4N x 0.015m = 10.85Nm for 2 cylinder = 10.85 x 2 = 21.7Nm, to make 100% confirm that we can rotate this engine, our start system should be having double this negative torque i.e. at 43.4Nm.

Power required (kW) = [Cranking speed (rpm) x Torque (Nm) x 2 x pie]/60000

*P = [120rpm (10% from idle) x 43.4Nm x 2 x pie]/60000 = .545kW = 545W


To those who don't quite catch what was i wrote above, one may browse my other thread, [link=http://www.rcuniverse.com/forum/m_10613348/tm.htm]link[/link] which deal with a more detail explanation. Only this time the parameters being changed.
Old 08-11-2011, 10:57 AM
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Umran
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Default RE: MLD 70cc Twin - Starter System - The Project

enough for one night i guessed, will continue later after some other work being done to it.
Old 08-15-2011, 08:29 AM
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Default RE: MLD 70cc Twin - Starter System - The Project

I'm a bit tight up during the weekend... was busy testing DJI wookong autopilot system... we side tracked a bit... some testing videos that i did for this DJI system...

[youtube]http://www.youtube.com/watch?v=vRrhquZ4d8c[/youtube]

second test...
[youtube]http://www.youtube.com/watch?v=IekUBX1ogjo[/youtube]



Comeback to the actual project...

Tonight i drafted the engine mounting plate and some side profile of the engine, refer attached photo. From here, the length from prop hub to rear plate is 138mm. A typical 50cc engine length from rear standoff to prop hub is 170mm, this leaves us 32mm of extra space at the rear of the engine to mount our start system... that should do.
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Old 08-17-2011, 08:34 AM
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Default RE: MLD 70cc Twin - Starter System - The Project

Some preliminary design was done tonight.... progress is a little slow as my work consuming my time...

We try to make this start system as compact and light weight as possible, since the engine negative torque is not so high, we'll be looking at aluminum as our primary input gear for the main drive...

About the power requirement, something like 500W... mmm... at this moment i'm looking at 750kv motor with 28XX size. With a step down ratio of between 35 to 45, by right it should do the job. We'll see...
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Old 09-20-2011, 03:52 PM
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Default RE: MLD 70cc Twin - Starter System - The Project

Okay gents,

The system finally done. ooooo..... it took me a while to get it done. The basic reason is, the smaller the engine, the tougher the challenges are. Considering the additional weight imposed by this system to the overall weight of the engine, i need to design it as economical as possible in terms weight.

In this video below one can see it work, even that also i under rated the motor for it (weight saving) and resulting in slightly poor performance. I need to get a slightly larger spec motor for it to work as intended.

[youtube]http://www.youtube.com/watch?v=CdrPIfjOb4Y[/youtube]


Anyway for subscribers, thanks for your support.
Old 03-13-2012, 06:26 AM
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cmanios
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Default RE: MLD 70cc Twin - Starter System - The Project

Hello

I enjoyed your comments on this page and your starter system is a beautiful project! You should market it.

Have you tested the MLD-70 for performance yet and if so could you please provide the performance information in terms of:
Temperature - C
Humidity - PA
Elevation - meters
Oil Used
Fuel/Oil Mix
Fuel Octane
Propeller - Pitch and Length used for testing
RPM obtained - Idle and full throttle
Noise Level - dBa and distance from engine
Vibration Level - G Forge in 3D if possible

Any information would help and I hope you produce and share more projects for we modelers!

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