Motor Performance in BOT

[dcarmack]

I haven't been thrilled with the climb performance on my BOT.  My current setup is Multiplex 480/4G,  4.4:1, 45A ESC, and 14x8 prop, the plane weighs about 60 oz w/o battery (if I remember correctly).  This combination performs OK but not well enough for competition, and definately not good enough for the 30s motor run.  I've flown this plane exclusively with the Flight Power 2170 3cell since it is 25C continuous and also heavier than my other batteries (and I needed a little more nose weight).  Someone suggested checking the batteries to see if that was more of a contributor to performance so I connected my wattmeter and here are the results:

TP 2100 15C - current draw was 33.92A peak
Flight Power EVO25 2170 - surprisingly it peaked at 22.6A
Dymond LiPo 2100 20C - 35.4A
DN Power 2150 15C - 29.5A (my oldest pack)

I don't understand the huge reduction in current for the Flight Power Battery.  Would this mean it's more efficient, or more indication of a problem pack?  I do seem to recall that the last few times I charged this battery, my cell balancer took a long time to balance the cells, so maybe I have a weak cell.  But regardless I may not get much better perfomance.  Seems the literature speaks to a 480/4G use on a plane weighing up to 32 oz and mine is twice as heavy.

I ran the multiplex calculator on this motor with different props using a 4cell but I didn't see any improvement in thrust since I need to prop it down to a 12x6 and this even looks like it reduces the thrust. 

Any thoughts on this?

I took a look and multiplex does not offer a larger motor so would need to look at different brands.  I looked at NESP and looked at the motor recommendations on similar weight sailplanes and Sal is recommending a Medusa MR-028-056-1900 with a 4.4:1.

[francsm]

For all you power mongers out their...  More Power.. More Power... More Power...

I suggest a Maytag 35001057 electric motor that can be found on Ebay for $49.95.  Most of the time these motors last for ever and ever and ever with no maintenance at all. 

[dcarmack]

Difinately needs a new plane and different power source...... maybe something at the st mary's airport... oh, and thanks budy... :-)

[n1lul]

Hey,

I put my Cox Dust Devil in hard, so I pulled the stuff out of it.  I have the motor and ESC just sitting around if you are interested.

Here is the link to the motor.  http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=3888

The ESC is also Turngy 45 amp, I think.

Let me know.

The main circ water pumps here at the plant have HUGE brushless motors, Like 6 feet across and about 8 feet high.  They only turn at 150 rpm so you would need a prop with a lot of pitch.  Each pump has 1250 hp, and moves 200,000 galons per minute.  Only problem is that they are 4160 V motors so that is like a 1040S LiPo pack

[dcarmack]

Thanks Ray,  I'm not sure this would perform better than my existing motor.  My 480/4G is a real screamer for a 2M plane at about 30-40 ozs.

[BigTilly]

Dale, if you have ever seen my Castor climb, it is a 480 4G on a 4S flightpower pack turning a 12.5x9 prop.  The plane AUW is 42 oz, which is much much lighter than your BOT.

Two considerations for you might be to look at a 2S setup using a motor like a hacker B50 or a Neu 1506.  That would minimize weight gain, but you are still looking at a 15 oz power train, which makes the wing loading of the BOT quite high.