Slo mo Shun

[Phil Winks 1Participant @philwinks1]

Hey  Bob its your thread/blog whatever you want to call it! The more pictures the better . This really is an incredible model detail wise, cant wait to see pics of it on the water, and maybe a video??

[Bob Abell 2Participant @bobabell2]

Thanks Phil

 

I like taking photographs and improving them with the Adobe photoshop feature…….You`d be surprised on what I actually clone out!….lol

 

The motor stuff is now on order but I`ve yet to sort out the prop shaft area……can`t decide on whether to flex etc

 

Glad you like the pix………Bob

[Bob Abell 2Participant @bobabell2]

Trying the twin MMB900 motors and ESC in the space available

 

Laying it out on CAD to make sure it all goes together first

[Bob Abell 2Participant @bobabell2]

Cosmetically, Slo Mo is as good as finished now……………So it`s out with the Vac, goodbye to all the sawdust and an early Spring clean!

Improvised a high level shelf to get Great Eastern out of the way and I think it looks quite nice up there?

 

Now starting the electrickery………………Bob

[Phil Winks 1Participant @philwinks1]

your workshop looks quite usefull Bob a little more so than my 8×10 brick shed (unheated)

[Bob Abell 2Participant @bobabell2]

………”I pity thee, Jack (Phil) in thy precidament…….But I`m doing rather nicely!”

 

Do you remember that phrase?……..It was on the wireless…….in the 1940`s

 

Could have been in …..”Ray`s a Laugh”…….starring my comic hero…..Ted Ray

 

Happy days……..Bob

[Phil Winks 1Participant @philwinks1]

Hard put to remember that Bob only 54 this year bit of a young pup me  do remember Ted Ray (vaguely) though

[Bob Abell 2Participant @bobabell2]

Advice required, please…….. You speed merchants out there…..

 

Having already constructed the rudders, I`ve now realised that some sort of scoop is required to gather up the water for motor cooling.

 

I`ve not got any experience of these gadgets and would welcome a few tips on the subject, please

 

Of course, I could invent something that would do the job, but I`ve got plenty of time on my hands and you chaps out there, could save me a pile of aggro!

 

Bob

[Phil Winks 1Participant @philwinks1]

You’re going to need two pickups I reckon Bob lots of the fast boys use a device built into the rear drive support that is basically a metal tube that runs over the top of the prop and curves round to face for’d directly in the prop wash. This seems to be mostly used on surface props that are on a flexi drive. for simplicity I’d prob install the 2 in 1 inlet/outlet devices and hook a pump to them run the pump via the motor esc so the harder the motors working the faster the pumps run that Graupner 6 to 12v pump I’ve got in the hl24 actually starts pumping at about 4v and by 6v is fair wacking it through. the advantage of this idea is you can fit the inlet/outlet where ever you want and even  at slow speeds there is a good flow through the system. I’d advise a cooling tank on the esc’s too as often these devices work harder at the slower speeds than at full grunt when they are simply an open tap so to speak. The pump by the way draws app 1.6Amps at 7.2v and at 12v will comfortably power a large fire monitor so plenty of l/min also they’re self priming so no need to have it low down I’d recomend as close to the outlet as poss as all the hose joints between it and the inlet are then under suction not pressure reducing the possibility of a failed joint flooding the boat if one is suspect  it will simply draw air and this will show as a stream of bubbles from under the boat or if the exit pont is above the waterline (as the hl24) then this will be seen to sputter, giving you a chance to investigate before any damage is done.

 

Just my thoughts on the subject

Phil

[Dave MilbournParticipant @davemilbourn48782]

Phil/Bob

Dave Jones’ experience with the P98 ESC in his Perkasa (single MMB900 on 24v) was that it didn’t need any water-cooling. If the ali heat-sinks on Bob’s ESC’s do start to get very hot then we can supply a cooling set for them, but I’ve suggested to Bob that he first tries them without. The MOSFETs in those things are good for a helluva lot more amps than the motors are going to pull. No point in making work for yourself or spending money where it’s not necessary (what am I saying??!!)

DM

[Bob Abell 2Participant @bobabell2]

Thanks Phil and Dave

 

I`m very pleased to hear that the P98 ESC`s may not need a cooler afterall, Phil`s pump system sounds a bit OTT  to me!….Sorry Phil, got to keep the weight down at all costs.

 

The motor sound system will be fitted later, for the same reason

 

Not much progress on Slo Mo at the moment……Awaiting props and shafts

 

Thanks for your response, chaps………..Bob

[Phil Winks 1Participant @philwinks1]

I totally agree with Dave there Bob just going on my experiences however it does suggest to me that the motor in the HL24 may have issues its a 550 turning a 55mm direct and pulls nearly 40amps in a tethered test some how I get the feeling I should be considering a different  power plant I could get up to 12v worth of sub C nimh’s in there but that would necessitate a circuit change for the bty indicator what do you think Dave any suggestions on a motor/bty/esc combo

[Dave MilbournParticipant @davemilbourn48782]

40 Amps??!!! O yes, Mr Winks – you’ve got a big something amiss there! First off, a 55mm prop on direct drive would better suit a 900 motor and 12volts; a 550 just hasn’t the guts for one that size without a reduction drive. My rule of thumb for direct drive is not to use a prop whose diameter is more than that of the motor case. It’s not scientific and it doesn’t apply to brushless motors, but it seems to work.

Is the prop a 2-, 3- or 4-blader? 2 blade props are often too “pitchy” for slower craft like HL24.

If you wish to stay with 7.2v and a big  prop then I might suggest a geared motor e.g. MFA Torpedo 500 2.5:1. I reckon a 900 would also be fine on 7.2v; certainly in a sedate model like yours. If you want to go to 12v with a different motor then we can come up with a revised battery monitor for you; it’s simply a case of changing the resistor values. PMK has also designed a variable version so you can set the different drop-out voltages with a couple of on-board pots and a DVM.

You know where we are!

DM

Edited By Dave Milbourn on 16/01/2010 15:24:56

[Bob Abell 2Participant @bobabell2]

Dave

 

You did say that Stavross made his motor coil from car brake tubing……..So therefore, I refer to my original post about the water scoops.

 

If I omit the motor pipes……….will the fuse protect the motors should they get too hot?

 

 

Like to keep it simple…….Bob

[ashley needhamParticipant @ashleyneedham69188]

The Seahawk (mfa 8590/50mm 2 blade prop) gets fairly well warm, but not particularly hot, and the 800s stay only just warm with their 3 blade 50mm props.

 

Assuming the 900 is of a similar size and power I should think they will run ok. 

 

If you want to cool them, them a water scoop very near the prop will be required.

 

I will echo a post against my Fantome by the Fat Controller and say… the motors dont look very big in your hull…..

 

Ashley

[Bob Abell 2Participant @bobabell2]

Hello Ashley

 

We`ll just have to wait and now……….I`ve thrown me arra!……….fingers are crossed!

 

Bob

[Dave MilbournParticipant @davemilbourn48782]

Posted by Bob Abell on 16/01/2010 15:42:49:

Dave

 

You did say that Stavross made his motor coil from car brake tubing……..So therefore, I refer to my original post about the water scoops.

 

If I omit the motor pipes……….will the fuse protect the motors should they get too hot?

 

 

Like to keep it simple…….Bob

 The fuses are there primarily to prevent the wiring from catching fire if the current drawn gets too high. If you fit the coils to the motors then they should not overheat. Put a drop of light machine oil onto the end-bearings occasionally. Make sure that you keep the outlet from the coils as short as possible; ideally through the side of the hull right next to the motors. The earlier suggestions about the type and position of the pick-ups are all fine.

The 900 is far more powerful than a MFA 800.

DM

Edited By Dave Milbourn on 16/01/2010 16:55:29

[Bob Abell 2Participant @bobabell2]

Dave

 

From my school dayz………

 

Watts = Volts x Amps…………..W = 24 x wot?

 

So how many watts are we talking about for a 900 against an 800?

 

 

 

I`ve always wanted these figures!…………….Bob

[Dave MilbournParticipant @davemilbourn48782]

900 = 24V x 15A = 360W

800 = 12V x 5.3A = 63.6W

In theory, at least (Ah ha! Here comes Mr 60 Watt……………….. Now!!!!)

DM

[Phil Winks 1Participant @philwinks1]

Point taken Dave we’ll no doubt speak soon. for the moment though things will stay put till My bank manager recovers from xmas. also according to the motor data sheet upto 45 ish amps is ok and the esc is rated at 80amps my prob is at 40 amps the 5200 bty’s don’t last to long. mind you at half throttle and below she potters round for a good 30 mins so not too bad except for on the river where an upstream run takes best part of 3/4 throttle to achieve its scale 20knots

edit

The prop is a raboesch 55mm 3blade brass and having checked my data sheet it looks like i’m about 50% over peak efficiency and just under half way to stall current so we WILL be talking next month (I do think however that a static test is prob highly inaccurate as suggested by actuall run times, could do with telemetry! I wish)

 

Handing Bob his thread back

Edited By Phil Winks 1 on 16/01/2010 23:41:10

Edited By Phil Winks 1 on 16/01/2010 23:47:13

[Bob Abell 2Participant @bobabell2]

Thanks Dave and Phil

 

WOW!…..63.6 watts against……360 watts!!!!!!……….Very impressive……..eh?…Ashley?????

 

I think that will do nicely!………..We`ll just wait a short time and see what 60 Watt has to say……….can`t wait!

 

45 amps!……. Phil, that sounds more like a short circuit to me!…..lol

 

 

Bob

[Phil Winks 1Participant @philwinks1]

I really must learn not to generalise lol. I believe I said “nearly 40amps”, in fact its 36.5 and I’m convinced that when I’m tootling around at 1/2 to 3/4 throttle its an average of 10 to 15amps or the 5200mah bty wouldn’t still be pulling it around at anything like the 30 min point. (5.2A = 1hr so 1/2hr =10.4A) Which just demonstrates to me how wildly inaccurate a tethered test in the confines of the “domestic test tank” (aka bath) must be. However that test does demonstrate that the wiring and esc are capable of handling a worst case scenario ie: using full throttle to get it of a sand bank or similar  (Done that)

 

Any way 360W sounds like a plan to me Bob. Just look out for the ducks.

[Dave MilbournParticipant @davemilbourn48782]

Phil

I’ve sent you a PM on this one. And that’s 2 x 360W…………………….

DM

Edited By Dave Milbourn on 17/01/2010 09:53:34

[ashley needhamParticipant @ashleyneedham69188]

Well well, Its horses for courses on the motors.

 

An 850 is twice as powerful as the 800, but with an extra  50…i can now see why the 900 is such a   powerful engine!  (did I get that right??) 

 

Yer pays yer money and takes yer choice on these things….power..speed..current consumption..running time per battery.

 

I am not sure that gel cells will like the sorts of current draw we are talking here…they are ok for my boats, but you are talking some big draw with 2×900 and 24v !!

 

Perhaps Bob, you could make some large water cooling jackets to fit over the motors to make them look more impressive when you take the lid off?  

 

OR a couple of false V8 covers..available in the shops is a “Top gear v8 pencil sharpener”

 Which with a bit of work would look quite good, slip over these motors quite nicely and to boot you could have the back end of the 900 motor shaft drive the “radiator fan” and have additional air cooling

 

 Ashley

 

 

##disclaimer## not all the suggestions in this post are …..etc etc

 

 

 

 

 

 

 

Ashley

[Bob Abell 2Participant @bobabell2]

Are we right there……..?

 

360 Watts is approaching a 1/2 HP….?

 

 

Too good to be true!………Bob

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