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Feb 20, 2004, 08:49 AM
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vintage1's Avatar
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Can motors on 3s LIPO.


I am going to be doing a fe comparaive tests between cheapo motors on 7 and 8 cell packs, and on 2s LIPO in order to be able to work out what sort of combinations work well.

Having FINALLY got a tacho in teh post today, the first comparison I have done is bteween a pair of 6v motors, driving 8x6 props.

The first setup is geared 2.33:1 and normally runs happily in a high wing trainer on 7x600AE.

On testing it, although the pack was falling quite rapidly, I got something like 7.6A at 7v dead - in input power of 53W - and the prop was clocking 5850 RPM.

The second setup was geared 4.09:1 and run off 3s1p E-tech 1200. It sounded smoother and the actual figures were

4.8A 10.1v and 5970 RPM. An input power of 48.48W.

So its pulling 10% less power, and delivering another 120 RPM on the higher voltage setup.

The motor in the higher voltage setup is a permax 400, the other is a graupner. The same make of ESC and gearbox (RipMax Xtra 12,MPjet ball raced) was used in both tests.

So the frst point - that operatting the motor at lower current, and higher voltage to get better efficiency seems realised.

The second point, to find a series of setups that suit 3s packs, is also realised. 4C on the e-tech 1200 is a nice gentle pull, and will give a mimimum of 15 minutes flight. Probably nearer half and hour, at far less weight.

compared with 5 minute of so on the Nicad pack, or 8-9 minutes on equivalent 7 cell KAN 1050 pack.

I am hoping to compare a DD 6v 400 and 7.2v 400 on 8 cells/3s LIPO next, as time permits. I am also running out of cans

Plus DD 480, and geared 480.
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Feb 20, 2004, 12:07 PM
know it all
I tried the AE dcm-189 johnson motor, with the flux ring, with a GWS 3x2 prop.. a very reasonable current of 6.5A with an etec 1200 3s1p pack and an ungodly high rpm sound .. my tach will not even try to measure the rpm. Motor does not seem to heat up much. Lots and lots of thrust..

Yeap, two of them are going into a GWS A10, either pusher or tractor.. tractor will just clear the wing/fuse with the 3x2 prop.

Could you do me a favor and tach one of these setups?
Feb 20, 2004, 12:36 PM
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Dr Kiwi's Avatar
Vintage - I am a bit concerned that you are comparing apples and oranges using two DIFFERENT 6v 400's. You need to do a series for each battery pack, using the same motor, for each gear/prop combo, then, by varying only the gearing and prop, find the optimum (thrust or prop speed, I don't know exactly what you are gunning for) for EACH pack.

I have some figures for 6v and 7.2v Graupner 400's in DD with a 6x3 folder if they are of interest to you for comparative purposes.

6v Graupner 400, 6x3 Graupner folder

2s TP 2100:
11.9A*, 6.5v, 78W, 11000 rpm, 248g (8.73oz), 3.18g/W

8-cell KAN 950:
13.6A*,7.2v, 100W, 11800 rpm, 284g (10.00oz), 2.84g/W

3s TP 2100:
18.0A*, 9.1v, 170W, 13250 rpm, 380g (13.38oz), 2.24g/W


7.2v Graupner 400, 6x3 Graupner folder

2s TP 2100:
8.0A*, 6.6v, 56W, 10080 rpm, 188g (6.62oz), 3.36g/W

8-cell KAN 950:
9.2A*, 7.8v, 73W, 10800 rpm, 230g (8.10oz), 3.15g/W

3s TP 2100:
12.6A*, 10.2v, 128W, 12510 rpm, 326g (11.48oz), 2.55g/W


Obviously the 6v gives you more thrust and higher rpm, but with lower efficiency (g/W or rpm/W), than the 7.2v. In this Direct Drive scenario, it is also obvious that lower voltages mean lower currents and therefore greater "efficiency", than higher voltage/higher current. But once you start to change ratios and props you will presumably find that you can do better on the higher voltage packs than at lower voltages.

Cheers, Phil
Feb 20, 2004, 06:45 PM
Motors beat engines!

A couple of other cans


8mm retimed GWS eps 400 C ( 2.67:1) w/ 10x6 HD on 8 kan 950's: 6600 rpm HOC and 6100 rpm after 30 seconds. About 11 amps by my VOM. ( not too accurate)

ips A, 3s kokum 340's, 9x5HD: 2.1 amps, 4900 rpm.

ips C, 3s kokum 340's. 11x7HD, 2.2 amps, 3050 rpm

ips S2, 3s kokum 340's, 5x5 carbon gunther, 1.9 amps, 9300 rpm

endo, 8 3000 nimhs, 3.8:1, 12x8 apc-e, 6800 rpm. ( could'nt measure amps this high, likely about 40).

All these setups work very well BTW.


Dean in Milwaukee
Feb 20, 2004, 08:20 PM
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Dr Kiwi's Avatar
Heck Dean - I don't have comparable data for most of those combos, but for the one I have replicated, your numbers surprise me.

IPS A on 3s and a 9x5 GWS HD [I used TP 2100 rather than Kokam 340SHC, so your voltage (and thus rpm and amps) would have been lower under load].

You got 2.1A and 4900 rpm - yet I measured 2.8A* (11.7v, 33W) but only got fractionally more rpm [4950].

Is this due to the inaccuracy of your VOM or my Whattmeter [it's the 100A one and reads only to 0.1A, but 0.7A is a HUGE discrepancy] or is my tach less accurate than yours [it always calibrates exactly to 3600 on household AC].

Cheers, Phil
Feb 20, 2004, 10:16 PM
Motors beat engines!
Not sure Phil, but heres what I do know. My buddies hobbico mini tach also calibrates to exactly 3600 rpm.

I am running amps directly through my VOM which has resistance and will lower the amp number, but on very low draws like ips's its not a big difference. The VOM's internal resistance becomes progressivly more significant as amps go higher. If it was a bigger deal for ips level draws, I would guess both my amps AND my rpms would be low, so since rpms are'nt, I doubt amps are much low either.

Per motocalc , using apc prop constants, it predicts 4900 rpm and 2.1 amps. Just about dead on.

Motocalc also predicted the s2 5x5 combos rpm to within 100 rpm, but underestimates the amps on that one. at 1.2.

It was way off on the ips c on rpm, it said 3500 rpm, but guessed amps almost perfect.

Based on all this, I'm guessing your whattmeter is indeed off that 0.7 amp. That not to bad really though, its only on these really tiny motors where thats enough to even worry about.

BTW, that A and 9x5 combo is VERY nice for small indoor planes. I'm using it on my 400mm drenalyn and it pretty much goes at high speed wherever the nose is pointed.


Dean in Milwaukee
Feb 20, 2004, 10:51 PM
jollyroger

Can motors and Lipoly's


I am getting more confused as this conversation continues.
1) Is the purpose of this excercise to operate the motor at optmum current draw and efficiency?
2) If so is it necessary to utilize a gearbox to do so?
How does one ascertain which ratio and prop size even while using programs such as Ecalc.
I understand the concept but not quite certain how to achieve this goal. John Z
Feb 21, 2004, 05:03 AM
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vintage1's Avatar
Thread OP
Ok, John, that's a good question.

The answer to the first one, is a slightly longer one thatn you might expect.

Asfar as canmotors goes, 'every one knows' that you slap 7 or 8 cxells on, and then use them like that. The curents, props and sop on to work in those setups are well known.

However, with LIPOS we have a whole new ball gaime. For a start there is no LIPO equivealnt to 8 cells, secondly we have severe current limitations on teh packs unless we paralelle thenm up.

My idea was tio try and find setups that delivered the same, or more, power and efficiency, as the same or similar motor on 7-8 cells, on 3sLIPO, and if possible see what 'standard setups' could be arrived at so that if for example you are building a plane that is designed for '6v 400 and 7-8cells' you could slap in 3s LIPO, change the motor, ratio, or prop, and get a good performing model.

The reason I think its worth doing, is because these motors - if operated at lower currents and higher voltrage, seem to actually run better. That, plus the fact thet the package weight is down so much due to LIPO, means that they are by no means a sucker choice for planes. The contention being that a can on LIPOS beats a brushless on NiMh, on price and duration, and even power to weight...although that is marginal. And run at lower currets, they last well too.

Anoher point is that with LIPOS and cans, the packs are teh biggest expense, so I am myself trying to come up with 3 or 4 'pack sizes' that will cover a range of power outputs, and then work out which motors used in what way can get the best out of them.

So for example I have a 3s2p Irate 1100 pack, and so far every single 480 motor I have, geared or ungeared, fits that perfectly.

The other pack I am 'standardising' on for these tests is the 3s1p e-tech 1200. Now teh current this will deliver is not great, by speed 400 standards, and I want to produce setups that will draw at most 8A, yet still deliver teh sort of power a 6v 400 will on 8cells/10A.

Gearboxes are helpful, to move on to the second part of the question, but not essential.

What is sjhowing up though, is we can't realistically use - say - a 6v motopr opn 3sLIPO on direct drive, simply because to avoid killing it, it needs to be allowed to rev up to 25k plus RPM and that is not the way to driuve a prop efficiently. In this case I am concentrating on e.g. what can replace a 6v can motor when you move from 8 cells to 3s LIPO, and the short answer is , a 7.2v motor. There is no added efficiency - thet performance is very similar - but at least it runs on the same prop size, and doesn't cane the LIPO pack or the motor.

So there are two or three things going on here, trying to find 3s LIPO setups that work and can be copied, trying to see if we can squeeze a bit more out of a cheap motor and expensive cells.

As far as the use of motocalc goes, I am using it to suggest setups, which are then tested, and results compared. Motocalc is inaccurate in many thngs, but its efficeincy calculators ARE good, and borne out by the fact that my tests show better efficiency on higher voltages just like Motocalc indicates should happen. You might say I am 'feeling' my way towads good setups, using all the test gear and computational softate I can (cheaply) obtain.
Feb 21, 2004, 05:11 AM
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vintage1's Avatar
Thread OP
Quote:
Originally posted by Dr Kiwi
Vintage - I am a bit concerned that you are comparing apples and oranges using two DIFFERENT 6v 400's. You need to do a series for each battery pack, using the same motor, for each gear/prop combo, then, by varying only the gearing and prop, find the optimum (thrust or prop speed, I don't know exactly what you are gunning for) for EACH pack.


Sadly, with MPjet boxes, disaasmebly once all is glued in place is NOT an option, plus the fact that at some level one has to assume that one identically wound and magneted Mabuchi 400 can is very much the same as any other.
As far a I am concerned, the Permax 6v 400 and the Graupner 6v 400 ARE the same motor, obviously the motors vary from one to another due to production tolerances, but not by very much.

Part of the fun in startng this thread was to get cross checks from you anyway. I hoped you would not be able to resist it. Hopefully we can all together build up a table of these budget motors and then when someone asks - well there is the table. Pick your poison!

LIPOS are coming down in price to the point where such a table may be very useful for the newbies who don't have whattmeters and tachs and thrust rigs, or a drawer full of props...or the desire or patience to go out and test them.

For every man out there flying a hacker B50 on Thunderpowers, there must be 50 flying a stock zagi who just want to spend a little, and get some more. That's where I am heading.
Feb 21, 2004, 07:40 AM
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Andy W's Avatar
I've seen very different results with "otherwise identical" (and new) speed 400 motors..
Even when broken in, some just perform better than others.. different brush composition or spring tension, perhaps, or something more subtle..
..a
Feb 21, 2004, 09:21 AM
jollyroger
vintage1, thanks for the reply. It's starting to make sense now and since I have a bunch of can motors I feel I should try this route.
It might be possible to investigate this idea using speed 700 or 800 size can motors.
Do you think this method can be used with cobalt motors?
john Z
Feb 21, 2004, 09:52 AM
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Dr Kiwi's Avatar
Hi Vintage and Dean - You guys have got me hooked now. I just hope my students understand when their Professor's mind is not on the intricacies of fungal reproductive cycles because he's thinking about whether his Whattmeter is consistently over-reading!

I do try to apply the "scientific method" by using the same instruments, packs and motors every time - so hopefully the "relative" numbers I get in my comparisons are internally consistent.

I have a Hobbico Tach too, so at least we are on the same page with that. If I were made of money, I suppose I should get a "little" Whattmeter for measuring this IPS stuff - but I've just spent $600 on parts as I rebuild the power-head on my 1964 Johnson outboard motor, so the cash-flow is all "out" at the moment.

Cheers, Phil
Last edited by Dr Kiwi; Sep 07, 2012 at 04:45 PM.
Feb 21, 2004, 11:58 AM
Vintage nice thread, I'm very interested & will be following along
closely. Question: with regard to a basic speed 400 (multiplex)
6V, what are the maximum parameters you would apply to this
motor direct drive at total wot ?

Max amps Max voltage Max rpms

I'm so tired of seeing the "red ribbon" on my tx antenna setting
stright out & flapping !

TIA
Ed
Feb 21, 2004, 12:04 PM
Motors beat engines!
Phil, I would'nt sweat it too much that a device rated to 100 amps can be off 0.5 amps at the extreme bottom of its range.

Back in school in electrcity 101, our teacher taught us to always use a VOM on the lowest range that was capable of measuring what your were trying to do, ie when measuring an expected 18V dc, use the 20v dc scale not the 200v one as resolution and accuracy will be higher. ( this is especially true when measuring resistance). Also, expect highest accuracy in the midrange of what its set for. In the example above in the 0-20vdc range, you should expect it to read closest to reality around 10 vdc.

Your meters locked into 0-100 amp range when you really should be using the 0=10 amp range, plus, your trying to read off the scales very bottom end besides. I think 0.5 amps off is pretty reasonable considering all the above.


I'm pretty much on Vintages page here regarding lipo's and can motors as far as looking for maximum bang for the $$$.

What I mean is, take any apples to apples comparsion of a can / lipo setup and a brushless / nimh setup regarding equal $$$ spent and looking for equal run times, the can/lipo comes out on top.

Its just cheaper to add lipo batt capacity and use that for both added run time and extra amp input than trying to do the same thing with the added efficiency a brushless buys you.

My example above with ips A, 9x5 hd and 3s is a good example.

ips A $18
pixie 7p $32
kokum 3s 340, $34 Total=$84

Motor/batt weighs about 2.2 oz, does 4900 rpm and runs for about 10 minutes wide open.

There are no brushless combo's I'm aware of that can match these numbers, much less beat them without spending considerably more $$$.


Dean in Milwaukee
Feb 21, 2004, 12:28 PM
Registered User
HVLC (higher voltage, lower current) is obviously worth pursuing based on actual results realized by DeaninMilwaukee, Vintage1 and a few other pioneers. The 3-cell lithium pack is an ideal focal point. Tuning is accomplished by varying the gearing and/or prop size. Care must be taken not to spin the motor faster than its physical limits. Beyond those few basic rules, there are many opportunities.

For instance, I'm just beginning a project to make 3-cell packs out of old 830mAh CGR17500 Panasonic Li-ion cells to use with an M100 motor. A 2-cell pack will not spin the motor fast enough to produce good power at the ~2.5A maximum discharge rate of the CGR17500s. A 3-cell pack with the right gearing and prop size will provide much better performance at the ~2.5A limit.

When you have reached the limits on current draw from your 2-cell lithium packs, you can increase voltage 50% by adding a 3rd cell to the pack and adjusting the gearing and/or prop size to bring current draw back down to the max level you were getting with the 2-cell pack. This reduces the requirement for higher-current lithium cells, and extends the life of older generation, lower-current cells.

HVLC has tremendous potential.


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