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Search: Posts Made By: Dr Kiwi
Forum: Power Systems 02-04-2014, 04:02 AM
Replies: 12
Views: 439
Posted By Dr Kiwi
12x6 Sport:...

12x6 Sport: http://www.apcprop.com/ProductDetails.asp?ProductCode=LP12060
Forum: Power Systems 02-03-2014, 03:18 AM
Replies: 12
Views: 439
Posted By Dr Kiwi
Whether or not the Motocalc results match...

Whether or not the Motocalc results match reality, the real issue here is the Kv determination.... an intrinsic property of the motor which CANNOT be fudged. If no-load testing indicates 11700PRM and...
Forum: Batteries & Chargers 01-28-2014, 06:11 PM
Replies: 27
Views: 1,385
Posted By Dr Kiwi
It is not advised to cross-post in many different...

It is not advised to cross-post in many different forums. Here is a link to what people have said in answer to the same question posted on RC Groups:...
Forum: Power Systems 11-18-2013, 04:39 PM
Replies: 8
Views: 478
Posted By Dr Kiwi
One useful rule of thumb for glow to electric...

One useful rule of thumb for glow to electric conversions is:

watts = cubic inches x 2000

Thus .020 is ~40W, .049 is ~100W, .15 is ~300W and so on.
Forum: Power Systems 11-04-2013, 08:15 PM
Replies: 6
Views: 341
Posted By Dr Kiwi
Just one pedantic correction.. rule of thumb is...

Just one pedantic correction.. rule of thumb is "input of ~3W/g"
Forum: Power Systems 10-14-2013, 01:17 AM
Replies: 36
Views: 1,012
Posted By Dr Kiwi
Amps? Watts? As Mike has said... IF you...

Amps?
Watts?

As Mike has said... IF you really are getting the speeds you think you are getting, you must be pushing well over 1200W into a 600W max motor..and your 60A must be surviving close...
Forum: Power Systems 10-04-2013, 05:18 PM
Replies: 36
Views: 1,012
Posted By Dr Kiwi
To get 180mph from a 5x5 on 4s you'd need close...

To get 180mph from a 5x5 on 4s you'd need close to 40,000rpm.. to get a 3000Kv motor to reach 40,000rpm under load on 4s (~14v) you'd need to attain "RPM as % of Kv x V" of around 95%... that simply...
Forum: Power Systems 09-02-2013, 04:45 PM
Replies: 16
Views: 510
Posted By Dr Kiwi
Still not strictly correct, 'cos your two 20C...

Still not strictly correct, 'cos your two 20C packs (let's say each has 2500mAh capacity), when joined in parallel, now give the "united pack" a total capacity of 5000mAh... we cannot say your new...
Forum: Power Systems 09-02-2013, 02:16 PM
Replies: 16
Views: 510
Posted By Dr Kiwi
read on heads up on their batteries. they show...

read on heads up on their batteries. they show with almost every single 3 cell that hooking them up in parallel will double the c rating.

Being pedantic again.... the C rating is NOT doubled......
Forum: Power Systems 09-02-2013, 02:11 PM
Replies: 16
Views: 510
Posted By Dr Kiwi
One of the reasons given was that in calculation...

One of the reasons given was that in calculation C rate with mAh gives higher number but battery construction is still only suitable for the lower amp draw. Your example of dragging 100a out of the...
Forum: Power Systems 09-01-2013, 02:40 PM
Replies: 16
Views: 510
Posted By Dr Kiwi
I accept that I only get total capacity of the...

I accept that I only get total capacity of the packs - but I would have expected that 2 x 20C packs could provide more oooomph than the individual 20C rating ... I was hoping for 30C or more as a...
Forum: Power Systems 08-31-2013, 05:44 PM
Replies: 20
Views: 1,574
Posted By Dr Kiwi
A Park 480-1320Kv should not have drawn more than...

A Park 480-1320Kv should not have drawn more than about 15A on 3s with an 8x4... maybe just a faulty ESC.
Forum: Power Systems 08-30-2013, 01:00 AM
Replies: 20
Views: 1,574
Posted By Dr Kiwi
Simply put... the one vital thing the OP omitted...

Simply put... the one vital thing the OP omitted was the Kv of his motor. Without that everyone is in the dark.... but he apparently got antsy when someone asked him to supply that one simple bit of...
Forum: Power Systems 08-28-2013, 01:14 AM
Replies: 14
Views: 1,012
Posted By Dr Kiwi
I'm just nit-picking for the sake of it, but the...

I'm just nit-picking for the sake of it, but the HK meter gives you only a "raw Kv" (no-load RPM/volts)...true Kv will always be somewhat higher. However, if you are using it to match motors, it will...
Forum: Power Systems 08-19-2013, 04:44 PM
Replies: 11
Views: 1,669
Posted By Dr Kiwi
I posted this reply to your post on RC Groups: ...

I posted this reply to your post on RC Groups:

Highly unlikely that with 4s, you can use the same 12x6 that you used on 3s. Probably you'll need to go down an inch or two in diameter but unless...
Forum: Power Systems 08-13-2013, 05:33 PM
Replies: 11
Views: 925
Posted By Dr Kiwi
Another useful "rule of thumb".. most motors...

Another useful "rule of thumb".. most motors should be asked to cope with no more than 3W/g... so your 56g motor is probably good for ~180W max.
Forum: Power Systems 08-13-2013, 05:21 PM
Replies: 10
Views: 654
Posted By Dr Kiwi
My Hobbico has proven to be accurate and...

My Hobbico has proven to be accurate and bullet-proof for over 10yrs .. I use if extensively in motor testing (including for multi-blade impellers on EDF motors [with a bit of math!]), yet I think I...
Forum: Power Systems 04-01-2013, 02:15 AM
Replies: 2
Views: 701
Posted By Dr Kiwi
http://www.draneer.com/OlympicFlying/200709_Extra3...

http://www.draneer.com/OlympicFlying/200709_Extra330L_Dendron/


He used 15x7x3 on 6s
Forum: Power Systems 03-23-2013, 02:34 PM
Replies: 3
Views: 702
Posted By Dr Kiwi
I use a servo tester for running motors on my...

I use a servo tester for running motors on my thrust stand:
Forum: Power Systems 03-23-2013, 02:29 PM
Replies: 11
Views: 1,106
Posted By Dr Kiwi
Just to be unutterably pedantic, centripetal...

Just to be unutterably pedantic, centripetal force (or lack thereof) is the key here:

According to Newton's third law of motion, for every action there is an equal and opposite reaction. The...
Forum: Power Systems 03-01-2013, 03:42 PM
Replies: 35
Views: 1,936
Posted By Dr Kiwi
Just for grins - and to see how different the...

Just for grins - and to see how different the results might be - I just ran the numbers on some data from one of my sailplanes.

now imagine how much unloading you might see between static and...
Forum: Power Systems 02-25-2013, 01:25 AM
Replies: 35
Views: 1,936
Posted By Dr Kiwi
What motor is this? Are you saying 55A is the...

What motor is this? Are you saying 55A is the distributor's rated max. (typically optimistic) or is it a "real" number?
Forum: Power Systems 02-19-2013, 11:30 PM
Replies: 10
Views: 675
Posted By Dr Kiwi
Hobby King:...

Hobby King: http://www.hobbyking.com/hobbyking/store/__21478__NTM_Prop_Drive_28_26_1000KV_315W.html?strSearch=2826-1000

Of course this is HK.. so it is rated for 315W, whereas the FirePower 370...
Forum: Power Systems 02-08-2013, 01:09 AM
Replies: 32
Views: 1,296
Posted By Dr Kiwi
Since DriveCalc was mentioned here is a plot for...

Since DriveCalc was mentioned here is a plot for a Turnigy C3530-1100 (the Aerodrive version is not in there).. it suggests that 10x5 APC E loads the motor appropriately (about 70% efficiency and...
Forum: Power Systems 02-04-2013, 09:30 PM
Replies: 28
Views: 1,247
Posted By Dr Kiwi
Certainly brushed is easier, but do you really...

Certainly brushed is easier, but do you really want to stay in the dark ages.. in a few years it might be very hard to even find brushed gear (motors/ESCs).

Brushless with multiple ESCs and long...
Forum: Batteries & Chargers 02-03-2013, 02:27 AM
Replies: 2
Views: 448
Posted By Dr Kiwi
Are you sure you set the voltage/cell count...

Are you sure you set the voltage/cell count correctly?
Forum: General Electric Discussions 01-17-2013, 01:33 AM
Replies: 22
Views: 962
Posted By Dr Kiwi
Mike, I'm puzzled... my typical test series for...

Mike, I'm puzzled... my typical test series for motors [and I've bench tested hundreds] comprises bursts to WOT for maybe 15 secs (just enough time to record the data..volts, amps, watts, rpm,...
Forum: Power Systems 01-11-2013, 06:26 PM
Replies: 8
Views: 781
Posted By Dr Kiwi
I think that the 9x6 APC E is heavier than that...

I think that the 9x6 APC E is heavier than that 52g motor might like... a 9x6 APC SF would be a better choice, though it might put you close to the motor's limit for amp draw (rated for 13A: 9x6 APC...
Forum: General Electric Discussions 01-08-2013, 03:21 PM
Replies: 9
Views: 619
Posted By Dr Kiwi
I'd ask the RC Boat guys.. I imagine a...

I'd ask the RC Boat guys.. I imagine a "water/boat prop" would be better than an "aircraft prop", wouldn't it?
Forum: Power Systems 12-19-2012, 12:42 AM
Replies: 3
Views: 501
Posted By Dr Kiwi
Or use your left thumb judiciously.

Or use your left thumb judiciously.
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