Magmotor S28-400 with 8 inch prop direct drive.

Discussion in 'Hybrid' started by klick, Jul 3, 2008.

  1. Guest625101138

    Guest625101138 Previous Member

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  2. klick
    Joined: Apr 2008
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    klick Junior Member

    Rick, I see the propeller you're talking about, it almost seems to be to be halfway between a propeller and an impeller. I almost thought about ordering an impeller (for a jet ski or something) and trying to adapt it to see what kind of thrust output I could get. However with impellers I would definitely have to create some type of gear down mechnism because I can't find anything close to an appropriate pitch for the RPM's i'm generating with direct drive. I wonder If I could find an impeller, and basicaly make a jet drive unit, I wonder how that would perform.

    I'm not sure pictures or videos would be the impressive, I really haven't built anything yet except a tube with a propeller on the end that I do tests with. At this point i'm just experimenting with thrust output, if I can't obtain what I want then there is no reason to build the rest of the device.

    As far as static thrust I realize that it's quite useless in the overall scheme of things for a standard boat design, but I have a spefic reason for wanting good static thrust. It's hard to explain why ehehe, so we'll just leave it at that. One day i'll hopefully show you a video that will explain why i'm doing so many static thrust tests.

    I might be interesting to do tests with a more impeller like prop, not sure I want to continue throwing more money into propellers. The 5 inch seems to work alright, I dunno, the kaplan prop looks nice, but I can't find anywhere that sells one anywhere near the size I need. Building a propeller from scratch also seems like it would take probably at least a month, and would be cheaper/easier to buy a larger motor then put so much investment into the prop.

    Also, I forgot to ask, the shroud I created was about 3.5 inches long, and the propeller was placed in the middle of it. Is that to long? to short? Should the prop be placed more towards the front? more towards the rear?

    Thanks,
    Ross
     
  3. Guest625101138

    Guest625101138 Previous Member

    Ross
    Making a prop is about 4 hours work if you can weld and use a small angle grinder. The value of this is you can create props much more suited to the application.

    I have attached a picture of one I fabricated from 40mm flat bar and also an image of one milled from my 3D drawing file. The latter cost CAD550 without the spinners and bearing housing - CAD700 complete.

    Rick W.
     

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  4. ASM
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    ASM Senior Member

    Rick / Ross

    I have read this thread with interest and one simple question remains..... how do you get to read your ammeter during testing to get actual 'consumption' and settings at a certain speed ? does it have a memory function or do you have to pedal along your model ? O, provided that one would use such a device in model testing....
     
  5. ASM
    Joined: Sep 2005
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    ASM Senior Member

    As for shrouded propellers like the michigan wheel, a friend of mine has develloped a shrouded prop system as well, using a PU based 'shroud' and he always uses special shaped props for tight fit in the shroud. Furthermore he recommends not to use shrouds beyond ~16 knots as their drag becomes too much and you loose performance
     
  6. Guest625101138

    Guest625101138 Previous Member

    I actually sit on my models. That is why I started building pedal boats as they are a scale that allows me to get on the water.

    I use GPS for measuring speed and these typically have ability to download the data. My latest GPS has inbuilt cadence and heart rate so these are all logged simultaneously.

    The easiest way I have seen of getting current readings off a model is using a digital multimeter with a nice large readout. Do passes at constant speed and simple note the current reading as it goes by. The on-board GPS can be used to determine speed after the test.

    Another feature of a pedal boat is that it can be done hands free so you can skim along beside a model steering it by radio control to keep pace with the pedal boat.

    The video on this link provides a good record of speed and current during testing of a small electric drive:
    http://www.boatdesign.net/forums/attachment.php?attachmentid=17436&d=1196419301
    The little multimeter cost AUD16 at Tandy. It indicates up to about 14A.

    I know you can get radio linked miniature cameras as well as I have seen them used on small helicopters for spying around the suburbs. Could be another option for recording hard data without going to exotic recording devices for each function.

    I had a friend who developed input devices to mate to PDAs for all manner of input but he sadly passed away last year and the development has not been taken up by others. There are probably commercial variants of this available.

    Rick W.
     
  7. klick
    Joined: Apr 2008
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    klick Junior Member

    ASM,

    Well, I do have an ammeter which I haven't officially used yet, I showed a link earlier I think, it's this one: http://www.rc-electronics-usa.com/ammeters/dc-amp-meter.html

    One feature I like about it is that it saves the max watts/volts/amps in it's memory, so that I wouldn't have to watch it while using it to determine at least the maximum amount of current pulled. I was planning on using it with someone else on the boat to read the data as i had the unit in the water. I can do this because at this point I don' thave batteries or the controller onboard of my unit, therefore it would be easy to place it in the boat. Once I have everything put inside the unit it may not be that useful, except of course for the max load memory, that might be nice to have. The unit however is rated at a max of 100 amps, and in reality I don't see the wires they are using as handling 100 amps for much more then a few seconds. So i'm not sure how much power it really can handle. I'm guessing 2.2HP maximum, but once again it would only be useful for the maximum amp recorded in it's memory, which is useful to me.

    The interesting about the shroud, that after 16 knots it creates a lot of drag, this of course is good news for me, as if I hit 16 knots i'll be throwing a big *** party :) 16 knots underwater is probably going to be very difficult, but it would be a hell of a ride :)

    My (first) shroud is just wood, cut to 3/10th's of an inch thick. It's 3.5 inches long I think. Also it's of course epoxied, poorly at tihs point, but it's just a mockup for testing. I was wondering if 3/10th's of an inch is to thick, that this might cause issues, and really I don't know, it may. I think the beneifts of the thrust increase are much larger then the drag I will incur on my vehicle.

    I think I may try to do a simple static load ammeter test today, after all I bought the ammeter to do that. I'm gonna have to test in my little blowup pool on the porch, making the data not that accurate, but it'll be some amount of data. Technically I believe the voltage will somewhat tell me the RPM of the motor (knowing the windings/rpm per volt data provided by the manufacturer) because even if you apply 36 volt, it's gonna drop down to whatever rpm it maxes the motor out at. I've read about others using this theory and some people who do electric cars go as far as using this technique to basically make an RPM gauge. Perhaps not, but it might give me a lot of data i've been looking for, at least the total watts data.

    Ross
     
  8. klick
    Joined: Apr 2008
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    klick Junior Member

    Well I finally did some testing with the ammeter, interesting results.

    I tested the unit out of the water to determine how much of the power is needed to overcome friction, bearings, flaws in the design.. etc... granted some power goes to moving air, but hardly any. This time around I did all my tests at 24 volt.

    So with the unit out of the water:
    Total watts at 24 volts is: 454 watts.

    Now for the remainder of the tests i'm going to assume the motor has an efficiecy of 75%, which based on what someone did with a dynometer, they got a peak efficiency of 82% at a specific RPM. Now I have no idea what rpm i'm doing, and surely am not getting the exact perfect efficiency rpm, so i'll just assume 75%.

    So 454 * .75 is 340 watts towards spinning the device. A little more then I expected, but the PSS (www.shaftseal.com) is big and takes some energy. Also I believe there may be a balancing issue which the unit did vibrate a little, this of course could add to the issues. I also realized that in the water the RPM would be lower, so I tried to get it going the same rpm, which ended up pulling 320 watts, equating to 240 watts of wasted energy (well not wasted, not having a shaft seal would be bad eheh).

    So I put it in my awesome $9 inflatable pool and ran 24 volts at full throttle. Now I was surprised to find that it pulled in 2240 watts. With 75% efficiency that means the motor was outputing around 1680 watts, and calculate in my mechanical friction above (subtract 240 watts) that means 1440 watts went to the prop. Basically 2 Horsepower. More then I expected. Perhaps 75% efficiency is completly wrong, maybe it's more like 50% at these rpm's, unfortunatly I dont' have a dynometer to determine what it is at my rpm, and i dont' even know what my RPM is... so this data will have to do.

    Now, these tests I did at 24 volt, I did run on the lake at 36 volt so i'm interested how much power it pulled them, but the little ammeter i'm using maxxed out on the 24 volt supply, so i'll have no real way of knowing with that.

    This is the first time I tested in my pool with the shroud, it really does help out with thrust (plus it's much easier and safer, don't have to worry about cutting the pool or my fingers off). I need to get a fish scale thing or something, i could probably test it pretty easily in the pool.

    Really I think this all comes back to the pitch of the propeller, is it still to much for direct drive? I think it may be, but then again these are static thrust tests (which i know are not all that useful) and once I start moving perhaps it's the perfect pitch, I dunno. Moving to that level of testing is expensive and much more difficult, but I guess that's my next step.

    As much as I don't want to, I think i'm going to go with quad motors, 2 props conter rotating. So each prop gets 2 of these motors, which i'll line up straight. If for some reason that's overkill for the prop, it'll just let the motors work easier and the heat will be spread out more, which will be easier to disipate/cool. Granted, it will make my dreams of a super compact unit less likely, but i'd rather go fast then slow...

    Ross
     
  9. Guest625101138

    Guest625101138 Previous Member

    Ross
    In a small pool you are not quite doing a static thrust test because you have a stirrer that will set up a flow pattern. That will likely increase power and also thrust over a true open water thrust test. The power reading is about what I expect for the 5" prop.

    You should do a no-load reading on the motor without any connections. There seems to be a lot of power going into things it shouldn't. Did the seal get hot?

    Rick W.
     
  10. klick
    Joined: Apr 2008
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    klick Junior Member

    Rick,

    Unfortunatly for water proofing needs, I sealed the entire thing shut and can't open it quickly afterwards to feel for things that are hot.. Even the PSS would be tough to touch since it goes in a few inches.

    Since i'm moving to a different design, i'm rebuilding the unit to be able to get in and out of easily. The first prototype was just sealed shut to make it easier on me, and i'm glad I did as it wasn't the best design anyway.

    I should say that the "slight" vibration as I put it before was probably more moderate then slight. Ironically the vibration is coming from the shaft seal, there's no way to install it "off balance" but it shakes when the rpms go up real high. I remember seeing this on my workbench int he basement and going "hmm, that seems a bit odd" and that was with no propeller, surpringly the shaft seal doesn't seem to lose it's "seal" when this happens. I honestly think my other tiny pump shaft seal that I have from mcmaster is going to work much better moving forward. Rather then put much effort into testing this inefficiency, i'm going to build the second prototype and see what power this uses. I will test the motor with nothing attached when I get a chance, and with just the shaft (no prop, no shaft seal) and with the shaft and the prop (no shaft seal), basically go through all the variables and test which one is causing the issue. Once it's down in the workshop this will be easy to determine with the ammeter.

    Also I attached a picture of the propeller and shroud, just so you can see what i'm working with. As I stated the shroud was built quickly and epoxied poorly eheh... i never even got around to sanding, re-epoxing, filling, then painting, but it was meant to be a test anyway :) I'd show the rest but it's enclosed in a non-openable container right now eheh... once i crack it i'll get a picture, but then i'm rebuilding it so it won't lookt he same anyway. Really as I said before it's not exiciting, it's just a tube that has the PSS and the magmotor in it, and the wires come out the side and I connect with the motor controller externally, and currently use large lead acid batteries for testing.

    I do have to say I like this little ammeter, for $60 it's nice, upto 100 amps and voltage upto 50, compared to the alternatives it works nicely for the price. I mentioned before I don't see how it could take 100 amps for very long but they use extremly nice wires on here, tinned and high count, they didn't even get warm int he test, but my enourmous jumper cables did get warm... I thought that was quite interesting.

    Ross
     

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  11. klick
    Joined: Apr 2008
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    klick Junior Member

    Oh yea, about the swirrler comment on the small pools, yes I realized this and the tests where done quickly before that occured, once the water started moving the unit would create large vortexes in the water anyway and start sucking in air. So the watts ratings where pulled from when it first started.

    I actually attempted to use the swirl to my advantage to try to see how it woudl react to moving water (the pool is circular, tried to get the water spinning in a circle) but once it stirs it up it starts sucking air and doesn't work to well, so these results weren't very conclusive of anything.

    Ross
     
  12. Guest625101138

    Guest625101138 Previous Member

    The shroud is a nice fit for the prop. Certainly good enough for static testing./

    Once you get this thing moving it will need to have fairing on all leading and trailing faces to get nice clean flow. A lot of power can be lost if the flow is not clean.

    I will have to look into the ammeter. I was keen to get a clamp on to avoid need to wire in.

    Rick W.
     
  13. klick
    Joined: Apr 2008
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    klick Junior Member

    Yea, the ammeter I linked to is alright, the Clamp On you listed before is still nicer, has a higher amp limit, but it 4 times as costly. for $60 the one I got is pretty decent, and the memory function is kinda nice too.

    I was browsing the web and found something interesting: http://www.whisper-electric.com/motors/whisper-xt.html The Whisper XT, it's a brushless motor outboard that runs at 72 volts, they claim a maximum of 72 amps. Which equates to 7.2HP, calculating efficiency, lets say 6HP. Now, they have a video showing a 22 foot boat with 2 people going like 8mph or knots, not sure which. This seems like dramatically better results that i'm getting with power input.. i don't see 3 times my input getting the speeds they are getting. I don't know how much their boat weighs, but my thruster didn't even move my 2000 pound boat, except for in circles. We tried making it move it straight, but it was really slow.

    If you hit the spec sheet they say they are using a vetus 6 blade propeller, which is made for bow thrusters, based upon their shroud size, which they claim one part of is 12.5 inches, I would assume they are using a decently large vetus 6 bow-prop. I'm guessing it's this prop: http://www.go2marine.com/product.do?no=191488F Which is a vetus 9-7/8" prop, no idea on pitch. Based upon apperance (which can be found elsewhere searching with vetus 6 prop) I would say the pitch is much less then the prop, after all it's meant for bow thrusters. I'm half tempted to get one of these props though, as they seem to be decnet, they are kinda expensive, but the ones i'm getting wheren't exactly cheap either.

    The Whisper XT looks like a direct drive system, although I can't confirm this, and I know there are many inline gear boxes available or could be designed compactly, it just seems like it's probably direct drive as the pitch of those vetus props is probably 3-5 inches.

    Here's another fact sheet of theirs: http://epowermarine.com/pdfs/whisperxt.pdf

    It claims 90% efficiency with the brushless motor... although I can't believe all of their claims, as one of them is "Variable speed control down to 1 rpm"... umm, yea, i'm sure that if I hit the smallest amount of throttle it's going to do exactly one rpm. Regardless though, the video demonstration shows that it's very powerful and moves a boat very nicely. Says it can push a 16 foot john boat at 12.7mph and that it can plane it out.. which is pretty good for a 6-7HP motor.

    I wonder what brushless motor they are using, I highly doubt they are building their own, magmotor will build motors for you that are custom if you have a decent amount of volume. Magmotor already produces some decently large brushless motors which are more ppowerful then they use, so for all I know there is a magmotor in that thing. Be interesting to know what's in there exactly though.

    Not a bad price for $4500 either, I wonder how many of these things they are selling...

    Ross
     
  14. Guest625101138

    Guest625101138 Previous Member

    Ross
    You are restricted using the square props. If you really knew what you wanted to do it would be easy to design you the right prop. Can you weld? Have you got a hand grinder?

    I have a couple of PMAC Mars motors and Kelly controllers. They have phase locking on the magnetic field using Hall devices for feedback so it is quite reasonable to get very low rpm. I guess 1rpm is realistic. Certainly mine will turnover at a pace that is hardly detectable. If you try to stall by hand it will just generate more torque and keep the same pace.

    If you were using the set up in the previous photograph it would not go very well once you get moving. There would be too much drag for water past the motor.

    There is some of my test data on this thread:
    http://boatdesign.net/forums/showthread.php?t=20445&highlight=electric
    There are two videos. One boat has a scooter motor running at about 10A with say 22V (220W) giving 9kph. The other one has the Mars motor. This is set up for 48V but I was testing on nominally 24V. With this I got up to 11.5kph before the batteries started to complain. From memory current peaked at 12A before the undervoltage limit started to kick in. I believe it is set at 22V so 11.5kph (say 6kts) is not bad for 264W.

    The Mars motor should drive my proposed solar-wind boat at about 10kts and the design weight is 1.2 tonne. So you do not need a lot of power to push an efficient hull at a good pace.

    My latest pedal boat design holds 12kph with 150W. There is a video and performance data on this site:
    http://www.adventuresofgreg.com/HPB/2008_06_29_archive.html
    It is a matter of knowing where the losses are and designing them out. With readily available design tools it is possible to get within a few percent of design speed for power input.

    Rick W.
     

  15. Guest625101138

    Guest625101138 Previous Member

    Ross
    I was checking data and realised I did not get 11.5kph using the Mars on the catamaran. I did this speed on my OC1. It was rather cramped and trying to video, adjust speed and steer was more than I could cope with.

    The outboard leg also pushed up a lot of water that filled the footwell on the boat so it was not the greatest of tests.

    Irrespective I am very pleased with the Mars motor and Kelly controller combination.

    Rick W.
     

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