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Author Topic: motors for riva  (Read 5017 times)

3838Derrick

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motors for riva
« on: November 25, 2015, 06:18:23 pm »

Just started building a Riva Aquarama 1/10 scale and would like to fit two brushless watercooled motors. what size motors would you recommend & suitable props.
Thanks, Derrick.
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bubbletop409

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Re: motors for riva
« Reply #1 on: December 02, 2015, 03:12:51 am »

If you give some basic specs on your intended build, you will probably get better responses. Overall length, anticipated weight, desired speed, etc., and members will have a better understanding of your goal, hence more intelligent answers.
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TomHugill

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Re: motors for riva
« Reply #2 on: December 02, 2015, 10:04:52 am »

There's a lovely Amati Aquarama build on here, I would think his motor setup would do you ok.
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BenVK

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Re: motors for riva
« Reply #3 on: December 04, 2015, 02:12:13 pm »

For what it's worth, I used twin S2858-2630kv Brushless Inrunners in my Aquarama.
https://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=40948

It's plenty fast enough on 3S lipos.

Not happy with the motor couplers though, they are far too noisy.  >:-o
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bubbletop409

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Re: motors for riva
« Reply #4 on: December 04, 2015, 07:00:57 pm »

Those motors seem to have a very high KV rating for scale boating operation. I currently have two boats powered by brushless motors. The first is a 1/16th air sea rescue boat, 62" OAL, 25 lbs., two Leopard 4064 1050 KV, turning counter-rotating 40mm brass three blades. The second is a 1/20th Higgins Hellcat PT, 42" OAL, 15 lbs., two Turnigy  3548/6  790 KV, turning counter-rotating 35mm three blade brass props. Both boats are capable of far more than scale speed's, the ASR is definitely way over powered, but scale operation is still possible.

My point being it is necessary to do some research when contemplating the move to brushless. Even a motor with a 500 KV rating on a three cell lipo is capable of 7500+ rpm. Both of my boats are up on top of the water with a very realistic planning attitude with less than half throttle applied.
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TomHugill

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Re: motors for riva
« Reply #5 on: December 04, 2015, 08:21:17 pm »

800-1200 kv is what I use but I do run 4s usually
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BenVK

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Re: motors for riva
« Reply #6 on: December 04, 2015, 09:01:53 pm »

My Aquarama is not overly fast with these motors, it runs scale speeds at about 3/4 throttle with 29mm three blade props.

They are only 28mm diameter motors remember so they don't produce as much grunt/power as your bigger can size motors. 

I chose these smaller size motors because:

1. The bigger the diameter of motor, the further forward in the boat you have to mount it to achieve the correct propshaft angle. I couldn't install the motors any further forward or lower in my hull so my choice was limited. 

2. Price. I couldn't find the Leopard 4064 1050KV but the Turnigy AquaStar 4084-1050KV Water Cooled motors are 46 each! http://www.hobbyking.co.uk/hobbyking/store/__31677__Turnigy_AquaStar_4084_1050KV_Water_Cooled_Brushless_Motor.html

3. Price! again!

4. Motors like the Turnigy D3548/6 790KV are fine but its an outrunner and you obviously can't add a water cooling jacket to it. You can buy motor mounts with water cooling but there's not many options and they are quite pricey.

5. To achieve the correct RPM for your boat to get up and plane with a lower kv motor, you might have to use a higher voltage lipo, maybe a 4, 5 or 6 cell.

I already had lots of 3S packs and didn't want to invest in new ones so I over estimated the kv needed to make sure it would get up and go.

Having said all of this, if I could build this boat again, I would go for a single Turnigy AquaStar 4084-1050kv, 100amp ESC and 4S lipos with at least 5000mah capacity with should give you about 30 minutes run time and a single rudder.

Installing twin motors and rudders is a bit of a pain really, it's twice as much work for not that much gain IMO. It looks great and all of that but you can't see them when it's on the water so...


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BenVK

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Re: motors for riva
« Reply #7 on: December 04, 2015, 09:26:42 pm »

Forgot to mention..

If it's not too late, make sure your spray rails are on the chunky size.

I didn't do this and the spray went about a foot in the air. Not good..
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BenVK

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Re: motors for riva
« Reply #8 on: December 04, 2015, 09:41:45 pm »

The one thing that I'm pleased about with my Riva is that I managed to plumb in the water cooling quite nicely. (despite the re-paint needed!)

It gets picked up just before the propshafts via brass tubes and then exits out the dummy exhaust pipes at the stern.
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TomHugill

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Re: motors for riva
« Reply #9 on: December 04, 2015, 09:50:09 pm »

Hey Ben, love the finish on your Aquarama, I remember the issues you had but didn't see the conclusion. Any more pictures?
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BenVK

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Re: motors for riva
« Reply #10 on: December 04, 2015, 10:04:46 pm »

Yeah Tom, it was a frikin pain!!

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BenVK

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Re: motors for riva
« Reply #11 on: December 04, 2015, 10:16:46 pm »

This was what I bought off ebay, looked pretty good but they must have used a pritt stick to glue it together!!  {:-{ {-)
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bubbletop409

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Re: motors for riva
« Reply #12 on: December 05, 2015, 12:22:40 am »

My Aquarama is not overly fast with these motors, it runs scale speeds at about 3/4 throttle with 29mm three blade props.

They are only 28mm diameter motors remember so they don't produce as much grunt/power as your bigger can size motors. 

I chose these smaller size motors because:

1. The bigger the diameter of motor, the further forward in the boat you have to mount it to achieve the correct propshaft angle. I couldn't install the motors any further forward or lower in my hull so my choice was limited. 

2. Price. I couldn't find the Leopard 4064 1050KV but the Turnigy AquaStar 4084-1050KV Water Cooled motors are 46 each! http://www.hobbyking.co.uk/hobbyking/store/__31677__Turnigy_AquaStar_4084_1050KV_Water_Cooled_Brushless_Motor.html

3. Price! again!

4. Motors like the Turnigy D3548/6 790KV are fine but its an outrunner and you obviously can't add a water cooling jacket to it. You can buy motor mounts with water cooling but there's not many options and they are quite pricey.

5. To achieve the correct RPM for your boat to get up and plane with a lower kv motor, you might have to use a higher voltage lipo, maybe a 4, 5 or 6 cell.

I already had lots of 3S packs and didn't want to invest in new ones so I over estimated the kv needed to make sure it would get up and go.

Having said all of this, if I could build this boat again, I would go for a single Turnigy AquaStar 4084-1050kv, 100amp ESC and 4S lipos with at least 5000mah capacity with should give you about 30 minutes run time and a single rudder.

Installing twin motors and rudders is a bit of a pain really, it's twice as much work for not that much gain IMO. It looks great and all of that but you can't see them when it's on the water so...

Well I stated from the get go my first boat was way over powered, and from viewing your pictures, I believe we are speaking a substantial size and weight difference in our respective boats. In my first post I suggested the member give us some information regarding his intended build. Not all hulls, motors, props, etc. are built equal.

My Hellcat has outrunners that are propped correctly, correct KV for intended usage, and because they are spinning easily with a light load they run cool and water cooling is not necessary. Even the innrunners in my big boat run cool enough where water is not necessary, load produces heat.
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BenVK

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Re: motors for riva
« Reply #13 on: December 05, 2015, 09:48:37 pm »

The OP did mention that he's building a 1/10 scale Aquarama.
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bubbletop409

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Re: motors for riva
« Reply #14 on: December 05, 2015, 11:12:20 pm »

The OP did mention that he's building a 1/10 scale Aquarama.

And that equates to about 1/10 of the information required to make an intelligent suggestion.
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TomHugill

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Re: motors for riva
« Reply #15 on: December 06, 2015, 12:49:19 am »

And that equates to about 1/10 of the information required to make an intelligent suggestion.


Not really, it's reasonable to assume he wants something that will give rapid planing performance, 1:10 Aquarama gives weight and size. That's all I would need to make an informed decision. If you want scale then your prop would be in the 32-35mm range I would think. I think 2s or 3s would be a reasonable battery to go for.
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bubbletop409

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Re: motors for riva
« Reply #16 on: December 06, 2015, 10:16:09 pm »


Not really, it's reasonable to assume he wants something that will give rapid planing performance, 1:10 Aquarama gives weight and size. That's all I would need to make an informed decision. If you want scale then your prop would be in the 32-35mm range I would think. I think 2s or 3s would be a reasonable battery to go for.

Well if you can determine the weight, size, and construction methods from 1/10th, more power to you. Two people can build the same boat, using different techniques, and have a 5 lbs. or more difference in finished weight.

And I will state it again, if you choose motor, prop, battery, AND shaft angle correctly water cooling is un-necessary.

The reason your buddies boat needs gigantic spray rails is the fact the shafts are at such an acute angle the props are trying to lift the stern and bury the bow. This is not to say that spray rails are not necessary, only that the shaft angle is exacerbating the problem. The object is to push the boat ACROSS the surface, NOT out of it.  Prop shaft angle should always be held to 10 degrees or less, not the 20 plus I see in that picture. The object is to push the hull forward, not raise the stern.

And finally since you can determine all the needs from 1/10th, what is your suggestion?
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TomHugill

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Re: motors for riva
« Reply #17 on: December 06, 2015, 11:36:05 pm »

Well if you can determine the weight, size, and construction methods from 1/10th, more power to you. Two people can build the same boat, using different techniques, and have a 5 lbs. or more difference in finished weight.

And I will state it again, if you choose motor, prop, battery, AND shaft angle correctly water cooling is un-necessary.

The reason your buddies boat needs gigantic spray rails is the fact the shafts are at such an acute angle the props are trying to lift the stern and bury the bow. This is not to say that spray rails are not necessary, only that the shaft angle is exacerbating the problem. The object is to push the boat ACROSS the surface, NOT out of it.  Prop shaft angle should always be held to 10 degrees or less, not the 20 plus I see in that picture. The object is to push the hull forward, not raise the stern.

And finally since you can determine all the needs from 1/10th, what is your suggestion?


I agree on the propshaft angle, however the Aquarama hull does seem to be prone to pushing up a massive wake. On my 1:7 scale Aquarama the hulls been slightly tweaked with a deeper v and a small lip which does the same job as spray rails.

I've see very few Aquarama scratch builds in 1:10, usually they're Amati. Any way half a pound wouldn't have much of a bearing on my choice.

Motor wise 3536 outrunner 800-1100kv range. Probably on 3s as I like a bit of poke.

If your boats can get away without using water cooling then power to you. My Tamar uses a pair of outrunners and is ok without. However I usually use in runners so water cooling becomes more important, and a cool motor is a happy motor so if it's not prohibitively difficult I would always water cool.
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BenVK

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Re: motors for riva
« Reply #18 on: December 07, 2015, 08:16:35 am »

Prop shaft angle should always be held to 10 degrees or less, not the 20 plus I see in that picture.

15 degrees actually but I promise to do better next time!  ;D
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3838Derrick

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Re: motors for riva
« Reply #19 on: December 11, 2015, 01:57:24 pm »

Thanks for all the suggestions and useful tips. Plenty for me to think about there. I'll let you know what I decide when I've made up my mind.
Derrick.
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3838Derrick

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Re: motors for riva
« Reply #20 on: December 16, 2015, 01:46:53 pm »

Sorry Guys, another question............
I intend to have contra rotating props. Looking from the stern forwards, which way would you have them turning? i.e. Left hand clockwise. right hand anti clockwise?
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TomHugill

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Re: motors for riva
« Reply #21 on: December 16, 2015, 02:12:30 pm »

As long as you get a left handed and a right handed it doesn't matter which side you put them on.
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aln101boat

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Re: motors for riva
« Reply #22 on: December 25, 2015, 02:12:14 pm »

Sorry Guys, another question............
I intend to have contra rotating props. Looking from the stern forwards, which way would you have them turning? i.e. Left hand clockwise. right hand anti clockwise?
Normal practice is outward turning (at the top), Stbb prop right-handed and Port prop left-handed. This is necessary for manouvering reasons.
Only exception to this, is long passage merchant ships with keels between the props, where inward turning is fractionally more efficient due to interaction with the hull.
Alan
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3838Derrick

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Re: motors for riva
« Reply #23 on: January 05, 2016, 04:59:02 pm »

Normal practice is outward turning (at the top), Stbb prop right-handed and Port prop left-handed. This is necessary for manouvering reasons.
Only exception to this, is long passage merchant ships with keels between the props, where inward turning is fractionally more efficient due to interaction with the hull.
Alan

Thanks for that. Getting close to maiden voyage !!!!!!!!!
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