Heng Long Seaport Workboat with brushless motor

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Heng Long Seaport Workboat with brushless motor

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27 November 2010 at 21:26 #29005
RedPanda
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@redpanda
I’m not sure if anyone will find this useful but I thought it was high time I contributed something instead of always lunching off other people’s expertise!

I fly electric r/c aircraft and during the winter, we have use of a large lake near Upminster in Essex to fly water planes. I usually fly my 54″ Catalina which goes very nicely once it’s up but its water handling leaves something to be desired. Fortunately, being electric, I don’t have to worry about engine cuts but my fellow pilots who fly IC do have problems with this so, I thought, wouldn’t it be fun to send out a tug to rescue a stopped aircraft instead of risking life and limb in the club coracle?

I searched around the net and came across something called the “Dickie Tug” on RC Groups. This is made in China by Heng Long and is also available here as the “NQD Seaport Workboat”. It’s about 590mm (23″) long, ready to run, and is cheap! Mine was £40 from Howes Models.

Apart from the price, the great thing about this boat is that everything is screwed together, not glued, so disassembling it to get at the works is easy, just try and remember which screw goes where! Following the advice in the threads I’d found, I removed pretty much all the original radio and other components except the motor, sealed the holes in the bottom of the hull in what was the fire monitor reservoir and installed a new servo for the rudder. I also put in a Spektrum 2.4GHz receiver and an Mtroniks Viper 20 ESC. Power came from a 6v 4.5Ah gel cell.

I tried the boat in this configuration but the original motor, a 385 or Speed 400 I think, would only just drive the boat and had no reserve for towing. I checked the current draw and it was 2.5A… In the aircraft world, this wouldn’t actually be considered a proper reading as we’re used to currents in the 40-60A range for ‘sport’ models [sorry, must have bust the upload limit, part 2 to follow!]

Edited By RedPanda on 27/11/2010 21:29:01

Edited By RedPanda on 27/11/2010 21:32:23
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27 November 2010 at 21:26 #3669
RedPanda
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@redpanda
27 November 2010 at 21:42 #29006
RedPanda
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@redpanda
Anyway, the boat did look nice on the water

So, easy fix I thought, just fit a brushless motor. Yep, easy…

The first problem is that there are very few marine ESCs that offer forwards and reverse and those that are available are very expensive. Aircraft ESCs can be very cheap but of course don’t do reverse but after some thought, I decided to take advantage of a feature of brushless motors whereby you can reverse their direction of rotation by swapping any two of the three wires between the motor and the ESC. I managed to track down a very neat double relay from Dimension Engineering that is effectively two electrically separate SPDT relays and a radio controlled energising coil, all in one unit. This allows me to ‘swap’ the two wires by flicking a switch on the Tx. This is the radio installation – the smaller relay controls the boat’s lights, again from the Tx.

Edited By RedPanda on 27/11/2010 21:43:09
27 November 2010 at 21:52 #29007
RedPanda
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@redpanda
Now for the motor. I looked up the specs for the 385 / Speed 400 and found a fairly close match with an HXT 2848 of 2100kV (rpm per volt). This motor is the same diameter as the 385, and a bit longer, but with about the same kV. First results were absolutely dire!! The gel cell couldn’t begin to supply the current the motor wanted so I

substituted a 2S 7.4v 4000mAh LiPo. This time the boat nearly took off with water flying everywhere round the bathroom! Current draw was 27A, versus 2.5A of the 385 so I suppose I shouldn’t have been too surprised. Here’s the installation – the foam is to support the back of the motor
27 November 2010 at 21:58 #29008
RedPanda
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@redpanda
I wasn’t sure if it was just the kV rating that was the problem and if so, why wasn’t the 385 a problem? However, I next tried a small Turnigy 2822 outrunner of 1200 kV and this seemed to be a very good match. It had a 7A current draw using the 2S LiPo and what appears to be good performance without being silly. Sea trials await!

Hopefully, I’ve ended up with a setup that has enough power to actually go out and perform its intended function of rescuing stranded aeroplanes. We shall see

Edited By RedPanda on 27/11/2010 21:59:36
10 January 2011 at 16:25 #29399
RedPanda
Participant
@redpanda
Well, it’s been awhile but sea trials are now complete.

The low speed running and handling is good with 360 degree turns of less than 1m diameter. Reverse running is better than with the standard motor and it will hold a straight course backwards after some trimming. It does cavitate a lot when going astern though.

High speed is very odd – over about 2/3rds throttle, the boat starts to rock from side to side about 30-45 degrees each way and becomes very unstable. I guess this is due to the hull being forced to go much faster than it’s supposed to.

Maximum current drawn was 8.9A and maximum power was 73W. 30 minutes of mixed running drained just over 600mAh from the pack so allowing for a 20% reserve (LiPos should never be drained completely if you want decent cycle life) I would expect to get at least 2.5 hours running from the 4000mAh pack.

Here are a couple of shots showing the bow wave it now generates at just over half throttle, not very scale-like I’m afraid:

Overall, I’m very pleased with this conversion and I’m now off to look for stranded aircraft to salvage

Cheers,

Richard
15 June 2012 at 20:01 #34904
Jessica Lee
Participant
@jessicalee31724
Hello.

I have recently purchased this exact boat and by accident lost the propeller in the back.

Would you happen to know where I can buy a replacement propeller or what the exact

measurements are? I never realized there were so many different sizes!

If you could help me out that would be awesome. I only used the boat once and would love to have

it on the water again.

Best regards

Jessica

Edited By Jessica Lee on 15/06/2012 20:01:51
16 June 2012 at 11:53 #34915
RedPanda
Participant
@redpanda
Hi Jessica,

I understand completely your comment about all the different sizes and types of propellors!

I replaced the original propellor on my Workboat with a three bladed Graupner item, 50mm diameter. It turns anticlockwise to go forward so is known as a left hand propellor. I'm pretty sure the prop shaft thread was M4 but it's not easy to disassemble everything to check. Still, that's one thing you should be able to measure.

I'm not certain about the pitch (twist) but when I bought the prop I just told the seller what type of boat I wanted it for and he made the choice. You can get props for fast (planing) boats and slow (displacement) boats and this is definitely a slow boat

Hope that helps,

Regards,

Richard
20 June 2012 at 20:57 #34960
Jessica Lee
Participant
@jessicalee31724
Thanks so much Richard.

I'm sure now I can find the missing part.

Can't wait to use the boat again !!!

Warm regards,

Jessica
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