ryan_t888
Posts: 4152
Joined: 7/24/2005
From: Hamilton,
ON, CANADA
Status: offline
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INTRO
The biggest mistake a new FE boater can make when building their first boat is choosing a power combination that is not properly matched. In most cases this leads to excessive heat with in the system. Heat is electronics worst enemy, too much will certainly destroy any electrical component.
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
Catamaran – Consists of 2 Outer Sponsons with a tunnel in the center section. Improved Speed, and handling, Good in rougher conditions
Tunnel Hull - Consists of 2 Outer Sponsons with a tunnel and cowl in the center section. Powered with an Out Board Motor. Good Speed and handling, Average in Rough Conditions
Sport Hydro – Full bodied hydro – Designed for speed/handling
Great Speed and handling, Average in Rough Conditions
Out Rigger – Designed for least drag. Consists of narrow center tub section with booms and sponsons offset a distance from the tub. Excellent Speed/Handling. Poor in rough conditions
All FE hulls have a hatch. To properly keep water out of your hull, tape the hatch shut and check for leaks in the tub. Having a sealed hull will keep the water off your electronics. I use Clear Renfrew Hockey Tape.
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 best FE information.
Happy Boating
Ryan T
< Message edited by ryan_t888 -- 7/30/2008 4:07:25 PM >
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A theory may be so rich in descriptive possibilities that it can be made to fit any data. - P.J.L.
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