3D Printing

pkrankow wrote:Now THIS is a keeper!

If its not obvious, a continuous loop of yarn (first string type I found) laced through the clothing hanger to hang evenly.  The broken propeller half is the plumb bob, held by a second piece of yard the around the hook of the hanger, and passed over the wire, and under the crossing yarns.  A slipped overhand knot secures the prop and allows for easy adjustment of its height to the plane.

Phil

That is a brilliant demonsration of the principle and would suffice for most practical purposes.

However, and this requires some thought, the friction between the yarn used and the coathanger together with the weight of the aeroplane may affect the accuracy.

If you take the set up as pictured an tilt the plane slightly. Does it stay in that position?

If it were heavier, could it remain stationery at an angle?

If it can then because the plane is level on the trapeze it may not mean that it indicating the balance point.

ian1954 wrote:

pkrankow wrote:Now THIS is a keeper!

If its not obvious, a continuous loop of yarn (first string type I found) laced through the clothing hanger to hang evenly.  The broken propeller half is the plumb bob, held by a second piece of yard the around the hook of the hanger, and passed over the wire, and under the crossing yarns.  A slipped overhand knot secures the prop and allows for easy adjustment of its height to the plane.

Phil

That is a brilliant demonsration of the principle and would suffice for most practical purposes.

However, and this requires some thought, the friction between the yarn used and the coathanger together with the weight of the aeroplane may affect the accuracy.

If you take the set up as pictured an tilt the plane slightly. Does it stay in that position?

If it were heavier, could it remain stationery at an angle?

If it can then because the plane is level on the trapeze it may not mean that it indicating the balance point.

Yes, the plane can be tilted, carefully, as the strings do not move and there is considerable friction. The bob remains pointing at the same position. Verifying by supporting the wing from below the balance point is the same position as indicated in the photograph.

I hope this is a little more clear. The string is laced around the hanger braces, down, and back again around the hanger braces. With a light load it won't slip. It also means the plane wing slides on the string, instead of the string sliding on the hanger.



Phil

Ah HA! A "Vanessa" machine!

http://home.mindspring.com/~the-plumber/Vanessa%20CG%20Machine.htm

http://www.rcuniverse.com/forum/tips-techniques-180/708060-vanessa-c-g-rig-how.html#post708060

Phil

Wouldn't this work with a single pulley? Balanced is balanced... right? Extend the pulleys' axle, to hang the plumb-bob.


(edit) I'll expand on that... one string with slip-loops on each end, that cradle the "fuse" fore/aft the wing; would accomplish the same thing, wouldn't it?

Roddie

I see where this is going, a person could make a 2x or 4x scale model of a Babe Bee!

I think we need a mod to split the CG machine portion out to a separate thread, if the OP is onboard.  That way this thread can return to 3D printing, and the CG discussion can continue separately.

feel free to delete this post when a decision is made.

Phil

roddie wrote:Wouldn't this work with a single pulley? Balanced is balanced... right? Extend the pulleys' axle, to hang the plumb-bob.


(edit) I'll expand on that... one string with slip-loops on each end, that cradle the "fuse" fore/aft the wing; would accomplish the same thing, wouldn't it?

Roddie

Don't need a pulley.  All that is needed is a sling to hold the airplane, and a plumb bob from the same support point.  This could be done with a single hook, except it would bind against fancy paintwork, so separation is desired.

The plane in the sling is one pendulum.  The free hanging pendulum is obviously a second pendulum.  The two originating from the same point mean the CG of both systems are in line with each other.

Because the orientation of the suspended object doesn't matter (people use this for race cars and boats too), but the plans are marked in the way they are, usually from the LE of the wing, having the plane level makes it easier.  Leveling the horizontal stabilizer is the most simple manner described in the linked thread on RCuniverse, as when the plane is flying level, with no elevator input, the horizontal stabilizer will be level.

Having the sling adjustable by turning the support rod means re-leveling the H. Stab after adding weights or adjusting components is much easier than sliding against friction.

Phil

Hi Phil,

I tried out the coat hanger approach this morning and it works rather well.

Unfortunately, I tried it out with my "Max Thrust Riot" and the coat hanger snapped. Luckily it was dangling only 2ft above a bed at the time.

Looks like I will have to print a coat hanger around a steel frame   

This resembles my face when the coat hanger snapped!

ian1954 wrote:This resembles my face when the coat hanger snapped!

That is awesomely grumpy. Looks like me before coffee in the morning.

Phil

ian1954 wrote:Hi Phil,

I tried out the coat hanger approach this morning and it works rather well.

Unfortunately, I tried it out with my "Max Thrust Riot" and the coat hanger snapped. Luckily it was dangling only 2ft above a bed at the time.

Looks like I will have to print a coat hanger around a steel frame   

Coat hanger might be a little weak on something heavy...I'm probably going to swap out the coat hanger for something better soon. I see my hanger breaking if I hang something much heavier than this decathlon on it.

Phil

pkrankow wrote:That is awesomely grumpy.  Looks like me before coffee in the morning.

Phil

Or me, after eating a green persimmon.

pkrankow wrote:

ian1954 wrote:Hi Phil,

I tried out the coat hanger approach this morning and it works rather well.

Unfortunately, I tried it out with my "Max Thrust Riot" and the coat hanger snapped. Luckily it was dangling only 2ft above a bed at the time.

Looks like I will have to print a coat hanger around a steel frame   

Coat hanger might be a little weak on something heavy...I'm probably going to swap out the coat hanger for something better soon.  I see my hanger breaking if I hang something much heavier than this decathlon on it.

Phil

I think for a simple approach - a 2" x 2" block of wood drilled through for a broom handle (1" diameter). A really good hook then screwed into the block. That would be strong enough.

Some iphone cases I printed for xmas gifts. The gears are printed seperate then the pins are glued in to hold the gears in place. They turn pretty smooth.

The finish looks superb and the phone case is smooth. My prints are all still rough looking but I am perservering.

Marvellous job Jason.

Now mounted

Looking good. Is that still ABS? What percentage of fill you you normally use. Most of the stuff I print is 40% infill but on large objects I might drop down to 25%.

Might need to build up a boss around the hole for the battery mount to beef it up. Would hate to loose a battery midflight!

In these items the fill is solid. All ABS.

I did a pull test on some sample battery brackets I made and it took some effort to break one.

The rods on the motor mount will have steel thread rods running through - with lock nuts on the engine bracket and blind nuts on the firewall. Length still to be decided when I balance the plane.

Pretty good looking stuff Ian!

The battery hanging off the bottom is not going to be helpful for stunt. It is shifting the CG low. Otherwise looks good.

Phil

Hi,

I just ordered Reprap Pro Ormerod from RS component, still waiting for delivery.

two things which I'm keen to know,
1)temperature of crank case might too high for ABS motor mount. anyone successfully run an engine on printed ABS mount yet?
2)ABS fuel proof?


ew

I have run both diesel and glo engines on mounts made from ABS and they appear to be fuel proof. Only time will tell!

I have seen no engine crankcase heat cause any ill effects but ABS starts to soften at around 90 deg C and melts at 105 deg C. The mounting lugs don't get that hot but the cylinder definitely does.

However, they dissolve readily in acetone and, over time, will absorb water. I can't say how long something printed with ABS will last or if it degrades.