MudbugnTX

I have already posted this question in another website, but I would like to gather all the information I can. Sorry for some of you seeing this twice. Thanks everybody for any help or insight.

I want to build an electric foam airboat for retrieval purposes. It will be used to bring back a 55” fiberglass boat. I have never built and airboat, but I was leaning towards making it out of foam since this is easy to get locally. I have some questions and I will list them as follows:

1. I was wondering which epoxy or resins you recommend to seal the hull or bond the foam together.

2. I do not have a clue about which electric motor would be best for this project, so any advice on picking the motor, prop and accessories will be helpful. I rather use NiMH than Lion or Lipo.

3. What is the best way to determine what amp ESC I need? Do you go for what the manufacturer list or figure out the amps yourself?

4. Could you list motor, prop, ESC and battery setups in some of your airboats?

Here is the basic design I was going with.

luckytempo93

i know nothing about electric rc but what about taking the electronics out of an electric boat like a tyco or nikko. and making a foam retrival boat. i think it would be mor efficent cause i dont think that air woule be strong enough to push. but a prop in the water might be.

Simon.O.

Great minds think alike.
I am about to build a twin hull recovery vessel myself.
My FE's are up to 30" so it will not be as big as what you are after.
I will be running brushed 550 motors, one on each hull.
I have been told that a 8x5 prop will be the go.
I have built one Airpowered vessel before and believe that twin 550's will give me plenty of power to bring my boats back in.
The plan is to eventually fit a lifting sling so that I can lift the boats a little and bring them home quicker.

I chose air power because one of my local ponds has duck feathers and weed in some areas that can foul wet props. It will also make for a very simple build without the hassle of stuff tubes, alignment, cooling etc.
I hope to have a rough sketch on "virtual paper" soon so that you can see what I am on about.

If a Mod ar Admin thinks that this thread should go to the General Discussion then go for it, it may get more exposure and some different ideas too.

shack10

to mudbugnla, ive built a retrieval boat similar to what your planning and as long as the stranded boat was still right side up in the water it worked ok. if the stranded boat was up side down my hull just wanted to push the hull deeper and float over the top of it. i ended up scrapping it in favor of a twin hull design similar to what simon.o. is planning. i also had a submerged net that i could pick hulls out of the water with. i took a net from an old fishing net. cut it to the width of the two sponsons on my hull. i tied the left side of the net straight to the hull and added about 12 inches of heavy stringto the right side. those two ends connected to two winch servos connected with a y harness. i also put fishing wieghts in the middle of the net to help it sink under the boat. i would put the net in the water just before i got to the stranded hull and when i was over it i just hit a switch and winch up the other hull. worked great as long as there wasnt alot of weeds and ther stuff blocking the hull. ive used it to pull my supervee nitro and shockwave 26ep out of the water with maybe 6 inches to spare so.....hope this helps.

ekim1940

The best foam glue is made for modle rail road it is FOAM TACK GLUE sold by Woodland scenics .www.woodlandscenics.com part # st1444

asmithnc

I started this build but never finish it. Almost the same design as above.

deslok113

RyanT 888 in the speed electric wrote this: I hope it will help you.

POWER SYSTEM
The 5 key components that make up a complete Power System in a FE hull are the following:

- Cells
- Hull
- ESC
- Motor
- Prop

bThe most successful order in which these components are selected is

1) Hull
2) Cell Count
3) Motor
4) ESC
5) Prop


HULL
The hull is selected out of personal preference based on appearance, speed and handling goals. There are several different types of hulls.

Mono Hull – Most common, consists of a single hull usually in a V shape. Excellent in rougher conditions, weaker in speed and handling

CELL COUNT
The cell count of a boat is best selected depending on the total length of the hull. Following this general chart will determine a cell count for a specific hull length while providing best speed, performance and handling for the power.

22”-27” / 55cm-68.5cm > 2 cell LiPo or 6-8 cell NiMh
27.1”-34” / 69cm-86cm > 4 cell LiPo or 12-16 cell NiMh
34.1”-40” / 86.5cm-101.5cm > 6 cell LiPo or 18-24 cell NiMh
40.1” + / 102cm + > 8-12 cell LiPo or 28 + cell NiMh

1P recommended for the smaller length in each range
2P recommended for the larger lengths in each range

P = Parallel – typically used for LiPo only. Paralleling packs will extend run time, increase maximum continuous draw, increase reliablilty and decrease pack heat accumulation.

This is only a general guide chart and does not mean you can’t use 8 or even 10 cell LiPo on a 35” hull vs the spec’d 6s.

LIPO
LiPo Advantages over NiMh
- Cheaper cost in the long run
- Life of up to 3 years
- Long run time
- Higher Performance
- Better Discharge Rate
- Lower Internal Resistance
- Lower amount of Waste Heat
- Less chance of Dead Cells

Now days Prices of LiPo’s have greatly dropped. In some cases LiPo cells are just as cheap as higher end NiMh cells.

It is highly recommeded to use high capacity cells with C ratings of 25 or higher from a high quality manufacture.

Using LiPo batteries are as simple or more simple than using NiMh cells. As long as manufacture warnings and instructions are followed use of LiPo is very safe.

Charge LiPo's at the rate specified by the manufacture. In most cases this is 1C.
C = capacity. A 4500mAh pack would be charged at 4.5A - 1C

All LiPo cells are also given a C rating. This C rating is specific to the maximum rate of discharge the battery can perform safely. The recommeded maximum discharge is calculated using the C rating and battery capacity. A 20C 5000mAh battery has a max discharge of 5Ah * 20C = 100A. I would recommend drawing at most 60-80% of this. 60-80A

Long LiPo Life
To ensure long life of cells:
- Try to avoid getting them wet. Although the cell is completely water proof, the balance taps are not and can easily corrode from excessive water. If a pack becomes wet one may cut the shrink wrap off, dry out the taps, and re-shrink the pack.
- Discharge a maximum of 60-80% of the spec'd maximum discharge rate. Running 2P will greatly take the pressure off the cells
- Discharge the cells to the manufacture specified voltage when storing.
- Only discharge a maximum of 70-80% off the cells total capacity. This means bring the boat in well before any voltage cut off kicks in.

MOTOR
To select the motor best suited for a hull it is important to know the hull size and amount of cell planned to be used. Size of hull will determine the size of motor needed to push the weight. Cell count will determine the wind (Kv) of motor needed.

Hulls from 22”/55cm – 34”/86cm typically will use a 540 size motor 36mm Diameter by 50-75mm length

Hulls from 34”/86cm – 40”/102cm + typically will use a motor with a diameter around or over 42mm and a length of over 60mm.

To determine the best suited Kv for a motor, the cell count planned to be used is needed. Following this chart will provide a wide-ranging base for proper kv selection.

2 cell LiPo / 6 cell NiMh 3200-5500Kv
3 cell LiPo / 8 cell NiMh 2500-3500kv
4 cell LiPo /12 cell NiMh 1600-2650Kv
6 cell LiPo / 18 cell NiMh 1100-1800Kv
8 cell LiPo / 24 cell NiMh 800-1350Kv
10 cell LiPo / 30 cell NiMh 600-1100Kv
12 cell LiPo / 36 cell NiMh 550-900Kv

A mono hull will run the Kv’s listed on the lower end of the range. (Larger Prop)
An outrigger type hull will run the Kv’s listed on the higher end of the range. (Smaller Prop)

Higher Quality motors will run higher Kv within the range listed.
Lower Quality motors will run lower kv within the range listed.

ESC
An ESC regulates the power from the batteries to the motor. It must be properly selected in order to be able to handle the current draw demanded from the motor.

It is recommended to choose a high quality ESC. The most common ESC is the HV and LV Hydra 120 by Castle Creations. For the most part these high voltage and low voltage ESC’s will handle the majority of setups. Be sure the motor selected will not exceed the maximum continuous current rating of the ESC. If it does a higher rated ESC is needed.

When using more than 4s LiPo or 12-14NiMh cells, it is wise to disconnect the BEC on the ESC and use a 4 or 5 cell NiMh receiver pack or 2 cell LiPo with voltage regulator. To disconnect BEC remove the center wire on the ESC to RX lead. It can be pushed out with a pin and replaced later if needed.

PROP
Choosing the right prop for an application is the hardest selection. Too large of a prop will certainly destroy electrical components. Too little of a prop will not get the boat on plane. It's not voltage that destroys motors, it is current and maximum rotational velocity that destroys motors. Current is controlled by the load placed on the motor.

It is recommended to seek advice if one does not know what a conservative prop would be for their specific application. Every combination is different!

Knowing which prop would work best for a hull, comes mostly from experience.

2 cell LiPo 6 cell NiMh – 30mm - 40mm Diameter
4 cell LiPo 12 cell NiMh – 37mm - 46mm Diameter
6 cell LiPo 18 cell NiMh – 40mm - 52mm Diameter
8 cell LiPo 24 Cell NiMh – 45mm – 55mm Diameter
10 cell LiPo 30 cell NiMh + - 48mm+ Diameter

It is extremely important to understand this chart is very basic, and the best or most conservative prop for any given combination may very well be out of this range.

A larger prop increases load. Increased Load will result in an increased current draw. A smaller prop will decrease current draw. Higher prop pitch will increase current draw, a lower prop pitch will decrease current draw.


IMPORTANT

When the hull is finally completed with a well suited power system it is very important to follow these next few steps.

After choosing the most conservative prop for a given setup, charging the packs and placing the hull in the water run it for 45 seconds. After the 45 second period, bring the hull in and note the temperature of the ESC, motor, and cells. If all components are well under 140F/60C, run the hull for yet another 45 seconds. If temps are under spec run for another 45 seconds and continue this pattern.

If the temperature exceeds the safe limit, one has either exceeded the maximum allowable run time or is using too large of a prop or a combination of both. Reduce prop size or run time.

Following these simple rules will greatly increase the odds for a successful 1st or 100th run.

For even greater safety, make only a few passes totalling 20-30seconds and bring the boat in. Checking temperatures can be a pain but will save loads of money


HEAT

There are several reasons equipment may heat up, if this is the case here are possible causes. Too hot - greater than 140F/60C. Many times there may be more than one reason for over heated equipment. In this case choose the most logical fix.

Motor - too hot
Possible Causes
- No thrust bearing, creating extra resistance when thrust is applied
- Binding within the shaft. When the motor is disconnect, rotating the prop shaft should be done effortlessly
- Too much prop
- Too much run time

ESC - too hot
Possible Causes
- ESC not properly matched to motor - exceeding continuous current limit. A larger rated ESC is needed
- Too much run time

Cells - too hot
- Drawing too much current from the cells. Increase capacity or C rating. Only use a maximum of 80% of the calculated max discharge rate
- Too long of a run time. Be certain to not dump the packs or hit the Low Voltage Cutoff




This guide was created solely on my experience with the hobby as well as what I’ve witnessed. There are plenty different ways of choosing a power system, this way works well and has been successful countless times.

This guide will also continue to be updated to provide the