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Old Sep 11, 2013, 12:30 PM
I like planes
United States, FL, Hialeah
Joined Jun 2012
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Building a 24" lobster boat (need some help)

Well i'm building a boat with a friend and everything is going well. Just need some help with prop size, motor size, KV, pitch and all that good stuff. I know about planes, so I understand how pitch works and KV and all of that but these are inrunners and I am not so familiar with these. Also the props are very different. I have some pics below. It seems like I can get at max a 30mm prop in there. But let me know what you guys think would be a good combination to get this thing moving. Doesn't need to be a speed boat or anything. Thanks





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Old Sep 11, 2013, 03:39 PM
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Lobster boat info

Go to page 4, and check out the post "1/16 scale Lobster Boat Info". The guy's posted some info for me, that would apply to your build / questions. No need for them to answer them twice.
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Old Sep 11, 2013, 04:56 PM
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30mm should be perfect!!

I like to buy Graupner and Robbe plastic props. The 30mm only comes with one pitch option.

I think brass propellers are better for display, not cheap if you damage or lose one.

You can go to these places to have a look.

http://www.cornwallmodelboats.co.uk/...ropellers.html

http://www.harbormodels.com/site08/m...nufacturer.htm

I like the reliability of a 4mm drive shaft. It's a little thick for your small boat, but easier to find plastic props and handle heavy loads. If you're gonna give this boat some good power, a 3mm or 1/8" prop shaft will get floppy at higher rpms.

Graupner makes a 4mm waterproof shaft good up to 10,000 rpm's.

Motor and ESC?

I would try using a 2845-2000kv with a water-cooled 35 amp ESC.

I used two of those motors an ESC's in my 26" twin. A single setup may be fine for you.

http://www.rcgroups.com/forums/showt...1588859&page=3

You could go off the deep end and use a 4042-2000kv like in my Osprey.

That's a lot of power.

http://www.rcgroups.com/forums/showthread.php?t=1948627

I put together a little info thread for scale boaters who want to go brushless.

This thread is filled with haters!! Nobody likes my brushless ideas for a scale boat. This a good thread to go through and see what people you don't want to listen to. I never finished the damn thing because the protesters got absurd!!

http://www.rcgroups.com/forums/showt...1976482&page=2

If anybody approaches you with a private message to sell you running hardware or powertrain parts for your project, it's probably a scam!! We've had some problems lately.
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Old Sep 11, 2013, 05:26 PM
I like planes
United States, FL, Hialeah
Joined Jun 2012
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Quote:
Originally Posted by CaptCB View Post
Go to page 4, and check out the post "1/16 scale Lobster Boat Info". The guy's posted some info for me, that would apply to your build / questions. No need for them to answer them twice.
Thanks for the response

Quote:
Originally Posted by Tollytime View Post
30mm should be perfect!!

I like to buy Graupner and Robbe plastic props. The 30mm only comes with one pitch option.

I think brass propellers are better for display, not cheap if you damage or lose one.

You can go to these places to have a look.

http://www.cornwallmodelboats.co.uk/...ropellers.html

http://www.harbormodels.com/site08/m...nufacturer.htm

I like the reliability of a 4mm drive shaft. It's a little thick for your small boat, but easier to find plastic props and handle heavy loads. If you're gonna give this boat some good power, a 3mm or 1/8" prop shaft will get floppy at higher rpms.

Graupner makes a 4mm waterproof shaft good up to 10,000 rpm's.

Motor and ESC?

I would try using a 2845-2000kv with a water-cooled 35 amp ESC.

I used two of those motors an ESC's in my 26" twin. A single setup may be fine for you.

http://www.rcgroups.com/forums/showt...1588859&page=3

You could go off the deep end and use a 4042-2000kv like in my Osprey.

That's a lot of power.

http://www.rcgroups.com/forums/showthread.php?t=1948627

I put together a little info thread for scale boaters who want to go brushless.

This thread is filled with haters!! Nobody likes my brushless ideas for a scale boat. This a good thread to go through and see what people you don't want to listen to. I never finished the damn thing because the protesters got absurd!!

http://www.rcgroups.com/forums/showt...1976482&page=2

If anybody approaches you with a private message to sell you running hardware or powertrain parts for your project, it's probably a scam!! We've had some problems lately.
And you sir have made my day with all of this information. Thanks for taking your time to respond to this thread and know that it is greatly appreciated. I love rcgroups
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Old Sep 11, 2013, 07:38 PM
I like planes
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Will this work?

http://www.ebay.com/itm/4mm-X-14-cab...item20b2da631f

I'm not trying to go for anything professional just want it to work.

http://hobbyking.com/hobbyking/store..._Inrunner.html

This is the engine you were talking about right?

http://www.ebay.com/itm/RC-Radio-Con...item58a23aa4f6

And maybe this prop?
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Old Sep 11, 2013, 08:37 PM
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Generally ,the cable shaft is meant to turn one direction, when reversed you stand the chance of putting a bird cage in the cable.

Consider a solid shaft unless you only want to go forward

http://www.ebay.ca/itm/Raboesch-146-...item5d406d9ffc

This would be a more traditional prop.. however I doubt it would handle the RPM generated by your motor in a direct drive situation.
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Last edited by more coffee; Sep 11, 2013 at 08:44 PM.
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Old Sep 11, 2013, 09:02 PM
I like planes
United States, FL, Hialeah
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Quote:
Originally Posted by more coffee View Post
Generally ,the cable shaft is meant to turn one direction, when reversed you stand the chance of putting a bird cage in the cable.

Consider a solid shaft unless you only want to go forward

http://www.ebay.ca/itm/Raboesch-146-...item5d406d9ffc

This would be a more traditional prop.. however I doubt it would handle the RPM generated by your motor in a direct drive situation.
Where can I find a solid 4mm shaft? I can't find one on ebay nor hobbyking.
Thanks for the suggestion
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Old Sep 11, 2013, 09:18 PM
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That link for the prop is also a link to a E-bay store that will generally ship anywhere ,,SS shafts ..just determine the length of the tube
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Old Sep 11, 2013, 09:29 PM
I like planes
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Nice so I guess it would be something like this?

http://www.ebay.ca/itm/15-2cm-6-ins-...be1db6f&_uhb=1

And then to connect that to the motor I need this right?

http://www.ebay.com/itm/271093961998...84.m1438.l2649

Thanks for taking your time to help a noob out
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Old Sep 11, 2013, 10:54 PM
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I wouldn't use a collet unless the alignment of the motor shaft and prop shaft were perfect.
you will need a universal.
http://www.harbormodels.com/site08/m...propulsion.htm

Theres also various other vendors that can supply a 3mm/4mm universal
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Old Sep 11, 2013, 11:43 PM
I like planes
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Thanks for the input I'll check that out
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Old Sep 12, 2013, 12:42 AM
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Try Harbor Models, they specialize in Scale model boats.
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Old Sep 12, 2013, 05:34 AM
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One thing you must consider when buying the shaft is the diameter of the tube or stuffing box. You already have built your boat with keel and drilling for the tube may be a considerable job and you may have to cut a slot in your outer keel, rather than drill and you also may have to add doublers inside to the keel or your boat may no longer have a continuous length keel. The keel doesn't appear that thick in the photo.
Ideally you want a M4 shaft but if necessary you can go a M3 as long as you don't go to big a motor. I have one 22" lobsterboat that I had to use a M3 shaft because of a fiberglass keel. It works fine with a 400 size motor and turns a good boat speed. you can cut down on shaft whipping by just having enough shaft extending from the tube for the coupler. In other words use a longer tube since there are bearings at each end.
Just something to consider before purchasing something that may not work in your boat.

Bill
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Old Sep 12, 2013, 07:36 AM
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United States, MI, Macomb
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Quote:
Originally Posted by pandamanda22 View Post
Will this work?

http://www.ebay.com/itm/4mm-X-14-cab...item20b2da631f

I'm not trying to go for anything professional just want it to work.

http://hobbyking.com/hobbyking/store..._Inrunner.html

This is the engine you were talking about right?

http://www.ebay.com/itm/RC-Radio-Con...item58a23aa4f6

And maybe this prop?
That's the motor I was talking about.

Like these guys are saying, cable shafts are for racing, you want a solid shaft. The prop you picked is also a high speed prop. I would suggest a Graupner or Raboesch 30mm Left Hand* 3 blade plastic prop.

You need to measure the length of the shaft that will be long enough to go from the point of where you want to mount the propeller and all the way to the inside of the boat with enough room to mount your motor and allow room for cooling.

I don't have your hull in my hands to see what length will work, but you do have to consider a few things for mounting the motor. If you are not using a waterproof shaft, you will need to have the end of the shaft inside the boat to be above the waterline to prevent possible leaks. If you want to put it below he waterline, you need a waterproof shaft. Putting the shaft below the waterline will allow you to place the motor in the center of the boat and use a realistic shaft angle, but you may have to cut out some hull framing to make the motor fit and allow room for cooling.

http://www.rcgroups.com/forums/showt...1948627&page=2

The waterproof shafts are at the bottom of this page. One of the shaft models can be shortened to desired length and the rest cannot be altered.

http://www.cornwallmodelboats.co.uk/...ropshafts.html

*Left Hand is a Right Hand when ordering from the UK or Europe.
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Old Sep 12, 2013, 08:52 AM
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Quote:
Originally Posted by sound sailor View Post
One thing you must consider when buying the shaft is the diameter of the tube or stuffing box. You already have built your boat with keel and drilling for the tube may be a considerable job and you may have to cut a slot in your outer keel, rather than drill and you also may have to add doublers inside to the keel or your boat may no longer have a continuous length keel. The keel doesn't appear that thick in the photo.
Ideally you want a M4 shaft but if necessary you can go a M3 as long as you don't go to big a motor. I have one 22" lobsterboat that I had to use a M3 shaft because of a fiberglass keel. It works fine with a 400 size motor and turns a good boat speed. you can cut down on shaft whipping by just having enough shaft extending from the tube for the coupler. In other words use a longer tube since there are bearings at each end.
Just something to consider before purchasing something that may not work in your boat.

Bill
Yes, if you are picking the 4mm shaft, make sure it has a 6mm stuffing tube. Like Bill says, it will probably "bulge out" wider than your actual keel width. You could leave it like that and just fair it in or add "doublers" to bury the shaft in the keel.

The M3 shaft would have a nicer scale look, If I really wanted a scale appearance, the M3 would be my top choice. I would keep the motor rpm's lower and not use more than 7.4 volts. I don't know of a waterproof M3, so you would have to keep the end of the shaft above the water line.

Just so there's is no confusion, Bill referred to a 400 sized motor. The 400 motor is a "brushed" motor, but it's almost the exact same size as the XK2845-B-2000KV I recommended. The XK2845 is pretty much my personal "brushless" replacement for the 400 "brushed" motor. The XK2845 has a lot more power than the 400, but it's the same size.

You can go "brushed" and use a Graupner 400 and maybe Bill can help you choose a good ESC speed controller. He knows more about what better options to use for a "brushed" setup.

Whether you pick "brushed" or "brushless", now would be a good time to decide your battery options. NIMH or Li-Po. NiMH does not require a programmable charger (you should have one anyways) and you can run the battery down until it slows and then limp it back to the dock. NiMH batteries are much heavier though, and this is a little boat, so don't put too big of a battery in it just to get a longer run time. You can use NiMH with almost any setup but if you choose Li-Po, you may have to make a decision.

The advantages of Li-Po are pretty cool, they are lighter and more powerful. You can get longer run times for the same size battery in a NiMH setup. There is also less weight for the same power, that's a nice plus. Turnigy has a line of "Nano" brand Li-Po's that are even more compact than an ordinary Lithium battery pack. There are some drawbacks.

Li-Po batteries must have a Low Voltage Protection. If your Li-Po batteries drop to a certain voltage, you must stop and remove them for recharging. A good "brushless" ESC has this protection feature built in and can be programmed for the proper voltage. If you are using a "brushed" ESC, it is most likely you will need to install a Low Voltage Alarm to let you know when the batteries are getting to a critical level. When using Li-Po batteries in a boat you may have to bring your boat in before the batteries reach that critical level. If the voltage protection stops your boat in the middle of the lake, you may not be able to retrieve it. I have noticed a change in peak performance before this actually happens.

I don't know much about Low Voltage Alarms, but Bill and the Boys at the Dauntless thread are testing some of that tech right now. Maybe you could ask them. Very interesting stuff!! It's a cool combination of brushed motors using Li-Po to save weight and get longer run times.
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