Working Magnetic Motor on you tube??

[FunkyJive]

Quote from: FunkyJive on Today at 02:00:02 AM
Quote
I wonder if these slight discrepancies would lead to the 45g difference between my 303g rotor (HDPE + magnets + two bearings) and the required 258g rotor of the original. Don?t know what the density of HDPE is.

Hi Omnibus.

If I'm sufficiently awake to do the math correctly (almost 2am UK time !), the increased dimensions of your rotor would add a mere 6% to the total weight - though this only being the case if you were comparing like-for-like of HDPE alone. In such a case the extra dimensions over Jason's would only bring it to a tad over 274g.

However, as there are added weights of the bearings and magnets in both cases then the weight contribution of the added HDPE material becomes even less (HDPE clearly being lighter than that of the bearings and magnets), so the extra dimensions certainly don't appear to be the main contributor to the significant weight difference.


All the best,

FunkyJive




Funny. I get approximately 260 grams. What formulas did you use? Seems to me the 258 grams Al posted should be just about right for the materials Omnibus used on a slightly larger scale.
the density of the material should be some 892 grams/liter.

Hi Morgenster.

We know that the volume of a cylinder is Πr²h, where h represents the rotor thickness.

Therefore calculate the volume of the cylinder in both cases from the dimensions given?

Dia = 147mm, height = 20mm, volume = 339433.4mm (rounded)

Dia = 146.05mm, height = 19.05mm, therefore volume = 319145.0mm (rounded)

You could omit Π (pi) as it is simply a multiplication constant for both cases, though I?ve included it for general completeness when calculating cylinder volume.

Now compare the relative difference of Omnibus' rotor to the lighter?

339433.4  /  319145.0  =  1.06

Omnibus' calculated weight would therefore be 1.06 x 100% = 106% of the lighter, or in other words, +6% by weight.

Now assuming for a moment that you are looking at plain un-drilled HDPE cylinders (as in the above), and multiplying the stated 258g of the original (i.e. with the smaller dimensions), then 258 x 1.06 = a tad over 273g.

Already this doesn?t equate if the HDPE in both cases is of the same material density and the magnets and bearings are also assumed to be the same.

Furthermore, if we assume that the fitted bearings and magnets for both rotors have the same weight, which also reduces the amount of plastic weight contribution in the above calculation, then the total rotor weight brought about by the different plastic dimensions alone should actually be something less than 273g, although Omnibus? rotor was weighing in at a total of 303g.

This therefore suggests that the 45g overall discrepancy is unlikely to be in the magnets and bearings (weighing only 27g in total), or the dimensional differences in the rotor (303g >> 273g), so this would therefore suggest differences in the rotor material density as the most likely.


Hmmm... I hope that's right 


FunkyJive

[Omnibus]

@vipond50,

Just tried with the rotor magnets (N35) shifted symmetrically to the left and then to the right, as you suggested. No joy.

[Omnibus]

Will do some more trials (haven't tried the N38's yet) but probably the rotor weight is the culprit.

[Omnibus]

@Charlie_V,

The stators aren't symmetric around the rotor to begin with (they are not the way you've presented them). Recall, there are 13 holes and the rotor where the AGW is to be achieved is outstanding 3 holes from each one of the other two stators. These other two stators are away 3 and 4 holes each from the other two stators.

[vipond50]

@vipond50,

Just tried with the rotor magnets (N35) shifted symmetrically to the left and then to the right, as you suggested. No joy.

@onmi
I tried this also and had the same results, Looking forward to your insertion of the N35's and well hoping for Joy.

Bill