Brutus

[Gareth JonesParticipant @garethjones79649]

Bob,

Tomorrow looks OK for us now. I have a range of adapter leads for my wattmeter but it would help to know what type of battery connector you are using now. Is it still a Tamiya type?

Gareth

[Bob Abell 2Participant @bobabell2]

Well done, Gareth

I`m still using the Tamiya plugs

The show opens at 10.00am

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. I would suggest filling in the small gap between the shaft exit and the long "skeg", to stop excess turbulence.

40mm props eh?? should be ok.. if you get more overheating I should go down a size.

Ashley

[Bob Abell 2Participant @bobabell2]

Ashley

The props are the correct size for a Brushless jobbie, going at 20,000 rpm….we've now got a pair of brushed motors, going at 14000 rpm

it seems only natural to go a size larger?

I'll fill in the gaps you've referred to shortly

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. Not sure I can agree there about the props. The props must match the motor and if you are getting excessive amp consumption (and overheating) I would say go smaller on the props. I would see what Gareths wattmeter says.

Try a range of props from too small to too big and see what the current draw is, Obviously you need to get the current draw to the motor recommended max, and also listen to see that the motor is revving out ok.

Another ploy might be to go to X pitch props but in the same size, or use a size smaller X pitch. I would not confuse size of boat and size of prop; big boat, not necessarily a big prop…

It is tricky this. I tried over a dozen props in the Ecranoplan and am still not sure I have the right one yet!

Ashley

[Bob Abell 2Participant @bobabell2]

Ashley

What makes you think we are getting excessive heat?

The original wires melted because they were too thin!

That's stopped you in your tracks!….eh?

Bob

.

[ashley needhamParticipant @ashleyneedham69188]

fair comment. I thought there was mention of overheating, but with thin wires of course there would be!! (in the wire department and connections area)

Ashley will pay more attention to posts next time before opening keyboard.

[Kimosubby ShipyardsParticipant @kimosubbyshipyards]

Hi Diede and Bob, doesn't this thread hurtle along, 5 pages in 3 days…………..

thank you for correcting my false memory Diede, indeed the yellow XT60 connectors as shown are the ones I'm now using. (Where did JST come from? – old age)

Kim.

PS  and no offence meant here, but how can anyone do electrics (even in a model boat) without a simple multimeter to check voltage, polarity, amperage (current) and continuity of connections.

 

Edited By Kimosubby Shipyards on 15/06/2014 09:56:36

[Diede van AbsParticipant @diedevanabs87670]

Hi Bob,

Good to hear your wiring problem seems to be sorted. I cannot wait to see a movie of Brutus at (near) full speed, on a big pond! Let us see how this beast performs!

And Kimmo, indeed… A simple multimeter is about the least you'd need when working with electrics.

@ Invisibleman: You certainly don't need a PhD for this, it's fairly basic math (which you actually don't need that often too!) and once you come close to the limits of the components it is even simpler: Stay below the limits and you're fine, go above it and find a nice fire going on on the water…

Edited By Diede van Abs on 15/06/2014 11:18:36

[ashley needhamParticipant @ashleyneedham69188]

I must say I dont often resort to a multimeter (but obviously i DO have one), I do have a small car type ammeter on leads that does + and – 30A and this is useful for seeing if you are in the right ball park for loading motors and also to check and see what size ESC you can get away with.

Ashley

[Colin BishopModerator @colinbishop34627]

An ammeter is also useful when you are lining up a motor with the propshaft. When the amps are lowest then that is the sweet spot.

Colin

[Gareth JonesParticipant @garethjones79649]

Elizabeth and I had an entertaining day out in Lyme Park today, lots of banter with the Etherow Club members especially when Nessie was attracting the attention of the passing public.

Brutus was opened up on the table to reveal a maze of hefty sized wiring and connectors, no problems with excessive voltage drop there, but finding the right connectors to insert my wattmeter took a little while. Initially Bob and I checked the right hand RX15 Plus motor and unloaded, boat out of the water, the motor was taking 3.8 amps, 7.4 volts and 28 watts and the propshaft was achieving 16500 rpm. According to the MFA website the free running speed of the motor should be 22500 rpm at 7.2 volts but the lable on the motor said 20000 rpm so there is a bit of confusion there.

The next step was to put the boat in the water and hold it steady while Bob went to full throttle. However the power readings on the wattmeter barely changed and there was no discernible propwash. After a bit of investigation Bob diagnosed a slipping coupling between the motor and propshaft.

We decided to try the same checks on the LH motor and unloaded it ran at 16400 rpm, taking 3.5 amps and 25 watts. Putting the boat in the water Bob gradually increased the thottle setting and this time we got a healthy propwash but with the wattmeter reading around 70 watts the motor died completely, quickly diagnosed to be the result of the main 10 amp fuse blowing. We replaced that with a 20 amp fuse and put the boat back in the water. This time we reached full power with the motor drawing 21.6 amps, 5.8 volts and 125 watts and the propeller speed reached around 7300 rpm.

At 5.8 volts, the free running speed of the motor should be around 18125 rpm. Under load it is running at 7300 rpm which is about 40% of the free running speed. The motor will deliver maximum power at 50 % of the free running speed and maximum efficiency at about 75%. Hence the first conclusion is the propeller, a 40 mm 2 bladed plastic unit is too large in diameter and/or too coarse in pitch. I think the optimum size for these particular motors is probably 30 or 35 mm diameter. The second conclusion is that a fuse rating of at least 20 amps will be required. Thirdly Bob needs to check that the speed controllers are rated for at least 20 amps.

Overall I think the motors are a bit on the small size for Brutus, the complication is that the propshafts are close to the bottom of the hull so a bigger diameter motor won't fit. The options seem to be either an inverted belt drive, something like the MFA toothed belt system which would be expensive, or go back to experimenting with twin brushless motors and get them to work. Bob, if you would like me to have a go at playing with your twin brushless gear I would be willing to give it a go and could perhaps pick it up at Colwyn Bay next month – its up to you but the offer is there.

I suggest fitting the two RX15 Plus motors in Slo mo with 30 or 35 mm propellers, 20 amp fuses and suitably rated speed controllers, capable of at least 20 amps continuous rating. If you stick with Mtroniks ESC Bob, remember to set the speed controller to recognise the transmitter full forward and reverse settings when you first set up the system.

Slo-mo had its first outing on the lake, running on just one of the brushless motors. The mechanism by which the driver operated the steering wheel and rudder was absolutely brilliant, totally realistic and good enough to persuade small children that the model was being driven by a real, but very small person.

Gareth

[David WooleyParticipant @davidwooley82563]

Just been following this thread and it bring to mind the time I was actively involved with fast electrics . In the 60s and 70s when the whole concept was one big leaning curve . One of the tricks we used to ascertain the operating current was to attach a ammeter to the model and simply read off the amps when using various types of props on a know size of course . We found that restraining any model for load tests produced distorted reading , especially when evaluating props as ,prop size and pitch was critical to help efficiency and ultimately produce better performances . Also the material of the prop became important as plastic propellers under load would distort and the readings would also be distorted. .metal became the preferred material as distortion was very low but these type of props where easily damaged so it was often trade off. Batteries , motors all of which added to the equation , as it does today. although I must admit I know little of Brushless motors . For those that may remember that far back I produced an MAP book devoted to Fast Electrics but technology has made some aspects of the book rather stone age but Ohms law remain exactly the same . Motor efficiency was the holy grail and many of the best motors where actually hand made . Also we tended to work with Watts which is amps x Volts remembering that 1BHP = 746watts . As for wiring I tended to use thick multi stranded copper wire for all the power connections as I seem to recall that electricity flows around the strands and not through it, the thinner the wire the more heat generated with an accompanying loss of power and efficiency .

Dave Wooley

[Bob Abell 2Participant @bobabell2]

Many thanks Gareth for your splendid attention to detail during the Brutus tests and apologies to Elizabeth for the constant joking and leg pulling……All great fun though

The tests were very interesting and very tortuous for the poor old motors!

It was a great surprise to us all, to be told that the props were over loading the motors!

The final test with the 20 amp fuses did show a very impressive backwash from the prop and was encouraging enough to continue with the setup……Although the fuse blew in the end

My verdict is that the props look too small for the model and so did the motors!……The motors are sold as small motors with a powerful punch and their size may be misleading?

Next move is to run the boat again with the same motors, bigger fuses, if the ESC can stand the load or finer pitch props…..Then put the motors in SloMo and reinstate the Brushless motors in Brutus

A few pictures taken today……..There will be also a video, shortly

What a dismal start to the day?….But it didn`t dampen our spirits……..Plenty of fun and laughter all day and just look at the scenery!…..Beautiful!

We were promised a Marquee, but it failed to materialise

No sooner had we unloaded the stuff…..The rain came dawn!

Duckie having a well earned rest

As Gareth says, the Animated driver was an eye opener!……..He looked splendid turning the wheel in a most realistic manner……The kids were gobsmacked! and highly delighted

Another crowd pleaser!…..Nessie in the Steering Comp!

The kids loved it!

I hope the Lyme Park organisors saw this, as it is worthy of a mention in their publicity brochures

SloMo had to be rescued with a flat battery, by Martin`s Eskimo Kayak. much to the amusement of the onlookers!

[Diede van AbsParticipant @diedevanabs87670]

Now now, Bob, where are the videos of Brutus?

If I were you I'd gladly accept Gareth's generous offer to look into your twin brushless setup again, I still believe that is the solution to the power issues for Brutus.

I also think Slo-Mo could also use a nice brushless outrunner…? Although it looks NICE on the water… Is that photo flat-out?

And Gareth, KUDOS for Nessie! I had good fun reading the article in the mag, and seeing pictures of her always make me smile.

[Bob Abell 2Participant @bobabell2]

Hello Diede

Thank you, for your comments

Duckie has made two video's of the SloMo and Ellie, but we are having trouble posting links for some reason

Will try again

Bob

[Bob Abell 2Participant @bobabell2]

The SloMo video….

**LINK**

The model has only one Brushless motor and this is the maiden voyage to test the balance etc

Will probably fit the two MFA RX15 RV700 motors next

Bob

[Andy CParticipant @andyc56856]

Hi Bob and crew, including the guy on the bike.

Cool video, but I have a feeling you know what is coming. As Clarkson would say "MORE POWER".

Cool driver movements too. I think your next electrical set up will do it far more justice.

Andy

[Bob Abell 2Participant @bobabell2]

Thank you Andy

Compare SloMo with the latest Ellie video…..Same motor, same hull

The sponsons must be creating too much drag…….Now removed for the next test

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. Brutus video clip good, nice fine bow wave but woefully slow I think. Personal opinion regarding how fast it should go of course. The bow would be more impressive at speed. As usual, looks huge on the stand with the others but "ordinary" once out.

Also needs to be as designer intended, flat or matt black. Another personal opinion probably not shared with anyone except myself.

Great unusual shape, good execution of the designers plans Bob. Nice.

Ashley

 

Edited By ashley needham on 16/06/2014 18:48:05

[Bob Abell 2Participant @bobabell2]

Thank you, Ashley

I have mentioned the removal of the sponsons, somewhere on the forum already

I like the leg pulling banter, where someone mentions that SloMo is the winner compared to Nessie!

There was quite a lot of similar leg pulling

Bob

[ashley needhamParticipant @ashleyneedham69188]

Bob. I was trying to keep post about ellie and slo-mo OFF the Brutus thread!! Thats why I have just posted twice!!

The thread paths are a bit tortuous at the moment. Sorry if I have just reiterated something you commented on earlier (sponsons)

Ashley

[Bob Abell 2Participant @bobabell2]

I've been doing a bit of thinking…..Oh dear, not again!……..Yes, as I can hear the cavalry, not far away

If we had power to spare, big motors and ESC's etc, Gareth's static water test would have proved just that!….We have power to spare!

But we are struggling with the present set up and I don't wish to abandon the gear just yet

With the prop almost resembling a paddle wheel rather than a prop, the static test is too much of a strain on the system, as the prop is struggling to drive static water, out the back like a fireman's hosepipe?

As Dave Wooley commented on…….Hello Dave

With the more than generous rearward propwash, still fresh in my mind, from Gareth's final test, I think we stand a chance of achieving an acceptable performance……As Paul expected

We are not looking for outright speed, but something just above sluggish!

At the moment, the fuse rating for the ESC's is not obvious from the literature, but since the unit survived the 20amp fuse blowing, I'll try a pair of 20amp fuses

When the boat is at speed. The props will have less work to do, as the water is not static, but flowing past the prop, compared to starting from rest. So I reckon, that with some careful intelligent driving, Brutus and I could save some face?

Does that make sense?…….Yes!……..Three cheers for Bob, clutching at straws as he eats his eggs

Challenging tests are more fun, to me, than simply dashing about the lake

Great story, Bob…….Make 'em 'ave it!

Capt Bob would have come up with a similar optimistic story, had he been on the Titanic!

[Bob Abell 2Participant @bobabell2]

Good news chaps!

Just phoned Howes to ask about the RV11 ESC`s and they are rated at……Wait for it……..50 AMPS!

Wow!………Now we`re talking!

Bob…….With a huge grin on his face!

Many thanks Gareth for your kind assistance

[Gareth JonesParticipant @garethjones79649]

Bob,

What is the rating of the speed controllers in Brutus? Please also have a look at the bit I have just written in the BEC thread.

Gareth

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