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Old Nov 14, 2012, 06:29 PM
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Newnan, GA
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GMP Cricket T Copter Conversion - Need some help.

I have an idea for my next project but don't really know what its going to take to make it fly. What are the concerns of a T Copter Design like this where the COG is right over the front of the T booms?

What I am wanting to do is modernize a GMP Cricket that I have. I love the vintage and super simplistic nature of the GMP and the old styling and I think this captures that pretty well but it should give me some better performance than the old fixed pitch under powered nitro that they generally where.

So far I have been modeling it some in Sketch Up and will fine tune it later.

Like I said earlier, I have no experience with this style of T copter. I have only build and tuned traditional T's and Tri's where the COG is still center of the prop triangle.

Can any of you lend some experience or insight as to what I should expect? I plan on flying this with a Copter Control Board.

Thanks.
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Old Nov 14, 2012, 07:02 PM
<Marty>
United States, KY, Springfield
Joined Jul 2011
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one way you could test out how a T would fly or react is to take one you have and place the battery up front enough to simulate a CG in the general area you are asking about...
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Old Nov 15, 2012, 12:34 PM
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Newnan, GA
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No one else has done this before?

I guess I need to try another forum for help with this one.
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Old Nov 15, 2012, 12:58 PM
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Quote:
Originally Posted by Matt Chester View Post
I have only build and tuned traditional T's and Tri's where the COG is still center of the prop triangle.
So take one of those T's and move the battery up to where you want it and try it out!
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Old Nov 15, 2012, 01:19 PM
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I guess that's what I am going to have to do, experiment until I find the solution.

I suspect that I will need to set the CG slightly behind the front arms so that it is a tail heavy situation and then put a smaller motor and prop on the rear to control the pitch and roll of the aircraft. I think the tail would need to be smaller because it is now lifting very little percentage of the load of the machine compared to the front two motors. What I wonder is if any special mixing in the radio needs to be done or if the standard tricopter set up for my copter control will be all I need.

I was hoping to short cut this by hearing someone else's experiences and solutions so that I don't have to wad up a good frame or equipment during experimenting.
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Old Nov 16, 2012, 11:50 AM
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United States, OH, Medina
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I have flown a nose heavy T-copter before. It was one of my prototypes, and I just stuck the nose on the front for a quick flight. Not very fun to fly. It had tendancy to nose forward on takeoff and would not hover well.

Ideally, your cog should be at that black clamp where that brace comes up and meets the tail-boom. You do not want a smaller motor on the rear. Keeping the same size motor as the front 2 will help balance out the tail. You could always add some lead weights to the tail to get the cog right.

Since the boom is long, it gives you a good moment arm to put some weight on. I think it could work, but it still wont fly as good as a heli with it's mass centered at the cog, and very midpoint of the craft.

Darn you, now I kinda wanna do somthing like this.
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Old Nov 17, 2012, 11:38 AM
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Bif,

If you simply fly as a nose heavy typical T or Tri, then yes, it will not fly correctly. However, I believe that if it is set up like a tail heavy Bi-copter, then it will fly just fine as long as everything is set up correctly.

What I am planning on doing is putting large motors and props on the front of the T and set the CG to apply approximately 85-90% of the over all load on these motors and props, then I will put a smaller motor and prop on the rear to carry the other 10-15% of the total loading. This will allow the front two motors to do the lifting and the rear motor to take careof the pitch and roll stability of the aircraft.

If that is successful, I am going to venture further into this by putting adjustable pitch blades on the rear and a fixed pitch heads on the front two motors and place the CG directly under the center of the axis for the front two motors. Then it would not need to tail heavy because of the rear motors ability to apply negative pitch when required to maintain overall pitch stability of the aircraft. This will also make the Cricket conversion more helicopter like by eliminating the airplane propellers, which will keep the Cricket more true to its origins.

I think this is going to end up a really killer project in the end if everything goes well.
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Old Nov 17, 2012, 12:58 PM
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United States, OH, Medina
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Well where are you planning on putting your battery? Can you move it back any? What if you hang the battery from the boom with a custom mount - kinda like the slow stick battery mount that radicalrc sells.

I'm not sure I see the difference between a nose heavy tri, and a slightly tail heavy bi. Basically, when I flew that nose heavy tri, the COG was at about 1" back from the T-intersection, with the overall t-copter length being 15in. This is pretty similar to what you want to do it appears.

I'm sure your idea should work, but if you can get your cog more spot on, it would fly better. A tricopter should outperform any bi-copter (or bicopterish tricopter)
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Old Nov 22, 2012, 09:07 AM
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Powell TN
Joined Jan 2008
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if most of your weight is on the front arms , you might consider using a varible pitch unit on the rear... Copter Ritchie done this on a couple of rigs , and it look very stable..JMO

Terry (love the canopy...)old school

heresone example of a variable pitch T...



http://www.rcgroups.com/forums/showt...267172&page=12
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Old Nov 25, 2012, 08:19 AM
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Terry,

Yep, I found that thread and it gives me hope that this thing will fly and fly well. I have the frame all prepped and ready for the modifications to begin. I will update this thread with photo's soon.

Thanks,
Matt
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Old Nov 25, 2012, 07:17 PM
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Powell TN
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sounds good Matt , I love the T's , tri's ,..... bi's (currently my passion) Wow , talk about a balancing act..... Oh well , keep us informed ....

Terry
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