Model Boat Mayhem
Technical, Techniques, Hints, and Tips => BRUSHLESS Motors and Speed Controllers => Topic started by: nick_75au on October 06, 2009, 09:21:42 am
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Data - Brushless motor testing
Going to do some brushless motor tests,
I built a 4 foot by 8 inch barge and I decided it was too narrow for my Springer's, made a prop tube and glued it in using a 4 mm thread for the shaft.
I have just purchased this motor
(http://www.hobbyking.com/hobbycity/store/catalog/dt700.gif)
http://www.hobbyking.com/hobbycity/...?idProduct=6246
Required Voltage: 11.1v
Suggested Battery Capacity: 1300mAh +
Suggested Prop: 10x4.7, 11x3.8 or 11x4.7
Max current draw: 13A (with 11x4.7 prop)
Max thrust: 900g+
No Load Current: 1.2A
Shaft: 4M (perfectly suited to Towerpor/GWS SF Slow Fly props)
Weight: 78g
Diameter: 41mm
Overall length: 77mm
Kv: 700rpm/v
Initial test results on 6 volts which is more appropriate for scale
No load (spinning bare shaft)
on 6 volts 4200 RPM
40 mm Raboesch 3 blade prop AKA springer prop
3700 RPM
Amps 3.3 max, about 3 average
18 watts
More to follow, I have a 55mm prop 4 blade as well, same brand, initial testing shows about 5-6 amps on 6 volts and mega thrust but its dark now
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Ok put a 55mm 4 blade prop, on 6volts
2200 rpm
10 amp peak about 8 amps average
about 50 watts average,
very high thrust though, probably 2-3 times that of the 40 mm 3 blade,I need to set up some form of thrust measurement.
This taxed my 4 amp gel cell and voltage fell off fairly quickly, NiMH or large capacity gel would be more appropriate for this current draw.
still under the motors stated limits
Nick
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Nick,
This is great stuff. When you have gathered more data any chance of you making up a chart for quick reference?
Maybe Martin could then post the chart somewhere easily accessible for everyone?
Ian
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Thanks Ian,
there is more to come, I have a small collection of carbon 2 blades to try as well
A brushed motor for comparison
One of my springers has a brushed generic 540 motor, its probably close to a 55 turn crawler motor, Im not sure, its from Jaycar electronics, it was designed for 12000 rpm at 12 volts so 6000 rpm at 6 volts, just about right for a Springer.
standard 40 mm Raboesch 3 blade prop, same as first test
no load RPM 6500 rpm turning the prop shaft
0.9 amps no load
loaded 4500 rpm
3.7 amps
about 22 watts
Nick
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Going to do some brushless motor tests.....
I've been doing some motor testing as well, for the EezeBilt boat range, so I'm looking at smaller sizes. Early days yet, but I do have a test rig. Some data:
Brushless Tower 2408-21T-3A - KV 1400 this one - http://www.brchobbies.co.uk/?page=shop&action=additem&item=184
9v dry batteries - coarse 30mm prop - thrust 125 gm fine 30mm prop - thrust 67 gm
6v Gell Cell coarse 30mm prop - thrust 238 gm fine 30mm prop - thrust 255 gm
7.4 v Lipo coarse 30mm prop - thrust 395gm fine 30mm prop - thrust 427 gm
Small 3-6V brushed motor - this one http://www.mutr.co.uk/images/mm28.pdf
4.8v NiMh coarse 30mm prop - thrust 75 gm fine 30mm prop - thrust 22 gm (around 1.4A)
6v Gell Cell coarse 30mm prop - thrust 162 gm fine 30mm prop - thrust 192 gm (around 2.2A)
7.4 v Lipo coarse 30mm prop - thrust 209gm fine 30mm prop - thrust 269gm (around 7A)
I have two more brushless - a Tower 2410-12T-3A Kv 1000, and an Emax CF2822 (see Giant Cod) to do, as well as a Graupner Speed 400 6v. I was going to put the data up on the EeZeBilt web site once I had interpreted it, but I probably need to get a bigger selection of props together. What seems to be happening is complicated - sometimes the motor power is limited by the amps it can draw and sometimes it is limited by the drag on the propeller.
All the above figures are from a static test rig (AKA my bathroom). When the boat is actually running the propeller will be unloaded and figures will change considerably. In fact, you need to baffle the water in a bathtub, otherwise it swirls and makes readings vary....
DG
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KA22-20 motor 40 mm Raboesch 3 blade prop
(http://donsrc.com/cart/images/uploads/A2220L1.jpg)
Specifications:
KV: 1020 rpm/volt
Current rating: 26 amps continuous
Weight: 86 grams
Battery: 3 cell lipo
Shaft Size: 3.0mm dia, Length-12mm
Dimensions: 28mm dia,Length39mm
6 volts
5000 RPM
6.2 amps but pulled 4.5 Ah gel to 5.7 volts
3s lipo 12.2 volts under load
9900 rpm
22 amps
Regards
Nick
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Hi dodgy geezer,
how are you measuring thrust, its something missing in my tests
regards
Nick
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Great stuff Nick! Do you have pictures of your test barge... video even?!?!?
Martin :-))
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Hi Martin,
The barge is not photo worthy :embarrassed: I will endeavour to clean her up a little. Once this is complete I will get some photos up
Nick
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Hi dodgy geezer,
how are you measuring thrust, its something missing in my tests
regards
Nick
I have a range of Correx meters - see http://longislandindicator.com/p10.html
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Yowee, 200 quid, each, bout 450 of our money %%
I was thinking of doing this with the wifes digital kitchen scales.
Nick
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Will that give you indication of possible speed?
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Im not sure, the air-plane guys always have thrust as an important measurement. When thrust is equal to planes weight then flight characteristics are exiting I gather. Speed could be calculated from RPM, allowing for prop slip.
Nick
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Im not sure, the air-plane guys always have thrust as an important measurement. When thrust is equal to planes weight then flight characteristics are exiting I gather. Speed could be calculated from RPM, allowing for prop slip.
Nick
Not all motors can run the same size and pitch prop, but can output the same power,smaller prop higher revs
Peter
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Yowee, 200 quid, each, bout 450 of our money %%
I was thinking of doing this with the wifes digital kitchen scales.
Nick
And what would your wife be doing in the meantime?
You can get the correx instruments cheaper - here's a recent ebay sale - http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=130333734480 They are nice items, of wide application and well worth a few quid. I used to use them in my wind tunnel a lot...
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Not all motors can run the same size and pitch prop, but can output the same power,smaller prop higher revs
Peter
I can confirm that. If you look at my figures you can see that changing the prop results in quite a variation in thrust with the same motor/battery setup. The issue is whether the motor is limited by the amps it can draw from the battery (in which case coarse props will give more thrust, or whether it is limited by the propeller drag, in which case a finer prop might give a better performance.
Nick, how do you measure RPM when the system is under load? There's not much room to use a laser tach on the edge of the motor...
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I use a laser tach, Ive haven't had a problem yet
Oh and the wife, well she aint using them so Ive sneaked them out of the house :D
Nick
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Oh and the wife, well she aint using them so Ive sneaked them out of the house :D
Nick
That works well, right up to the moment when she wants to bake a cake....
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This is interesting stuff ok2
Fishermen/anglers use inexpensive handheld 'hook/hang' spring weigh scales.
If we keep it basic then efficiency is measurable since the amperage drawn is an indicator of motor/prop thrust efficiency.
If a model is tethered in line with the scale and throttled to exert a constant indicated 3kg(?) pull as a benchmark we can measure/note the amperage drawn by the motors using an ammeter//multimeter.
We can repeat the benchmark test with different props till the lowest amps reading is demonstrated.
Bear in mind that hull shape is irrelevant when a model is tethered although the model's mass (size/weight) may be a relevant factor.
My choice of a 3kg thrust benchmark is just a 'guestimate' - different model types may probably need different kg benchmarks to give realistic guides to performanc e.g tugs/mtb/cargo/battleship and their build scales. We could also use this relatively simple method to test/compare different motors/model and combo setups.
The above proposal is a starting point and any other ideas/comments/tweaks are very welcome. :-)
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This is interesting stuff ok2
Fishermen/anglers use inexpensive handheld 'hook/hang' spring weigh scales.
If we keep it basic then efficiency is measurable since the amperage drawn is an indicator of motor/prop thrust efficiency.
If a model is tethered in line with the scale and throttled to exert a constant indicated 3kg(?) pull as a benchmark we can measure/note the amperage drawn by the motors using an ammeter//multimeter.
We can repeat the benchmark test with different props till the lowest amps reading is demonstrated.
Bear in mind that hull shape is irrelevant when a model is tethered although the model's mass (size/weight) may be a relevant factor.
My choice of a 3kg thrust benchmark is just a 'guestimate' - different model types may probably need different kg benchmarks to give realistic guides to performanc e.g tugs/mtb/cargo/battleship and their build scales. We could also use this relatively simple method to test/compare different motors/model and combo setups.
The above proposal is a starting point and any other ideas/comments/tweaks are very welcome. :-)
Interesting proposal, but I think it assumes that the performance curve is a straight line, enabling you to extrapolate all other points from one figure? In reality, I suspect the performance line is a curve, with a best power in/thrust out position. So some combinations which hit peak efficiency at 3kg (6lb 9.8oz!) will look really good, others which may have a better overall efficiency will look poor if they are made to perform outside their envelope...
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I have just tested this motor on a couple of props, its not much.
Its almost a direct replacement for a 785 in speed and power(can handle more)
http://www.hobbycity.com/hobbyking/store/uh_viewItem.asp?idProduct=3887
I only tried 2 props, both carbon racing style props a 50 mm and a 30mm
50mm over 50 amps on 3 cell lipo
30mm 21 amps on 3cell Lipo
Nick
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Heres a video of the C3542 1250 Kv motor
Nick
http://www.youtube.com/user/Nick75au1#p/a/u/0/lYJtODg_hQk (http://www.youtube.com/user/Nick75au1#p/a/u/0/lYJtODg_hQk)
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Hi all, I have 2 similar brushless motors and wired them up to one ESC there was no load on them.
They got up to speed OK, did not like reverse very much sort of shuddered and twitched, and when you stopped one the other one stopped as well.
You hear the myths and I think they were right!
kind regards to all Roy
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Golden rule - One Brushless motor per controller!
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I wonder if this is worth anything to anybody
An Article I wrote for our local club Magazine
I had to remove the pictures, the graph remains :-))
Nick
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Thanks Nick - very useful O0.
Barrie