Forum

Fast attack craft

".....it seemed to generalise without mentioning the the decisive parameters involved, including cost difference!..." Um. Tricky to cover everything, in a 4 sentence comment! There seems to be a grave shortage of balanced advice in all aspects of modern life - though no shortage of advice per se at all! In a field where technological change is proceeding it is even harder to gather a useful view. Comparisons which were true one year are incorrect the next, and I suggest that it would be very useful to update any advice on the board which covers batteries.... Luckily there is one reasonably independent place we can go for a balanced view - the market. Although it is not perfectly unbiased, we can deduce that if some battery technologies are surviving in that marketplace there must be a demand for them, and hence that these technologies are likely to be the best available ones for some specific task. We only need to determine what that is. As a quick example, if you look at a major UK battery supplier to the model hobby - Component Shop - you will find available: NiMH - both standard and low self-discharge LiPo LiFe Lead Acid (sealed) Alkaline (probably Manganese) Silver Oxide All of these will be the 'best choice' for some application. Our interest is probably mainly with the first four. There are many battery features to take into account. The energy capacity that the battery contains is one common figure, usually measured in amp-hours, but most people do not realise that that is only correct for a particular delivery rate. To make a motor go fast you need a battery with a high current delivery rate - able to put out a lot of amps over a short time. Dry batteries, for instance, do not usually have a high delivery rate - hence the poor performance available to us in the 1960s! My top-of-my-head generalisations are below, though I am sure exceptions can be found in all cases! 'Robust' refers to a mix of physical strength and resistance to misuse, such as over-charging or excessive drain. I will try to use the words 'capacity' for the amount of energy stored in a battery, and 'delivery' for the maximum rate at which that energy can be released... SLA Very robust. Cheapest for high amp-hour capacity at 6 and 12V. Can do high delivery as well, Very heavy. Use for displacement boats, where the ballast weight is a positive benefit. Can do heavy discharge as well, but many small SLAs are designed for emergency equipment use, and expect to support a discharge over 10-20 hours. NiMH Fairly robust. Quite cheap for medium amp-hour delivery, and reasonable capacity. Low self-discharge costs are dropping and that technology seems to be expanding in the market, though they tend to be low amp delivery types. Some types can compete with Lipos for high amp delivery in the 30-40A range. Fairly heavy. Make sure that you buy a high-delivery type if that's what you need for motors. Low self-discharge types are good for emergency flashs and RC transmitter/receivers... LiPo - Less robust. Best current choice for high amp delivery with low weight. Only readily-available type offering current delivery in the 100+ Amps range. , and available in very small sizes. More expensive than NiMH, high capacity very much more, and you need a special charger, though these can be quite cheap nowadays. You should really be using a charger optimised to your battery type anyway. Remember that each LiPo cell is 3-4V, not 1.2V... LiFE - Similar to LiPo, but more robust. Sly lower voltage, but very flat volt delivery. Typical current delivery in the 30A range rather than 100+. More expensive than LiPo at the moment, but may displace them eventually. LiPos are essential if you are using a very high consumption motor - perhaps a racing boat? But when using such currents you usually require cooling systems and quite a specialist drive train. Brushless motors can take high currents, so LiPos are often associated with them, but you can use any battery with any motor if you want - just so long at it delivers the amps! There is no reason why you should not use brushless with SLAs, or LiPos on a low-drain application - though a LiPo may be more expensive than you need for that... NiMH are perfectly capable of making a boat plane - IF you ensure that the max amp delivery is adequate. You can, for instance, buy NiMh batteries designed for wireless phones with max output 500mA or less - these will disappoint you if you try to use them for motor power! A handy rule of thumb for estimating optimum battery discharge is to look at the capacity in Amp-hours. A low-drain battery is probably designed to put that out over 20 hours, so divide the Ah by 20 to get an estimate of optimum current draw. A high-drain battery is usually designed to output over 1 hour - so divide the Ah by 1 to get optimum amps. That's only a generality, of course, and the battery spec sheet is the definitive place to look... "...more likely that HE had shares in a LiPo company to be able to afford them back then..." When it comes to electrical equipment I do have connections. 😊 If you think LiPos were expensive in the 2000s, you should try buying NiCad pen cells in the 1960s. Probably the most unusual battery I have used was a pack of saline/manganese oxide cells from ex-RAF life jackets, where the battery was open to the water underneath the boat and you could speed it up by scattering salt in front of it....

5 years ago by DodgyGeezer

Forum

46'' RAF Crash Tender

Hi Elsrickle, Those are the same drawings that I posted 6 days ago. if I remember correctly Martin (Westquay) sent them to me a year or so ago to ask me to enhance them a little so we could decipher the text describing the paints used. Thanks for blowing up the text 👍 It confirms as I had posted; decks, cabin sides and tops were all the same shade of grey. https://www.e-paint.co.uk/Lab_values.asp?cRange=BS%20381C&cRef=BS381C%20631&cDescription=%20grey Decks non-slip, cabins smooth. No white anywhere. But if you like white - Why not?😉 Cheers, Doug

5 years ago by RNinMunich

Forum

46'' RAF Crash Tender

Dodgy - if you build a squadron of PT Boats you will surely have to add an E boat to the 50+ collection ! And then build a few as well as a few F ers ............ Unless you were thinking of the Pacific theatre.

5 years ago by redpmg

Wiki

Radio Control Wiring

NOT from me (RNinMunich)! I just edited it to delete a previous comment of mine! Wiring Methods Wiring can be a little tricky, especially when there are more functions than just power and steering. To wire correctly you should first check: - What is to be wired up. - What voltages are going to be needed. - if there is any equipment that is not compatible. Receiver Where possible try to have a separate battery for the receiver and not power it through B.E.C. circuits in speed controllers. There is a simple explanation for this. The speed controller works by switching on and off and different rates. Depending on the rate of switching the motor will speed up or slow down. it is this fluctuating current that is not good for the receiver if its using the B.E.C. *Edit* More modern electronics are not affected so much by this, but if you start to experience problems with reception it could still be something to consider. The receiver should be placed as far away as possible from other electrical equipment such as motors/servos. Also DO NOT CUT THE AERIAL ON THE RECEIVER. The receiver aerial is a set length and can affect signal quality if made shorter or longer. All motors should have suppression to avoid any interference with the signal. There is a section in the knowledge base for this if you need to learn more. ing ing equipment is running at a constant current and can be placed off any battery without it affecting anything else... BUT if it is put onto the same battery as say a drive motor, the s will dim everytime power is asked from the motor. If LEDs are being used you will have to be careful about the voltage. Three things can be done to ensure the LEDs are getting the right voltage (usually between 3.0 to 3.5v). One. Use a voltage regulator. Two. Put resistors into the circuit. Three. Put the LEDs in series with each other. Each LED is about 3v so two in series would need a total of 6v. Sound/speakers Speakers generate sound using a fluctuating current through the coil. it is recommended that all sound devices are run off a separate battery to avoid interference. Another problem with speakers is the magnetic field. This can play havoc with the signal, especially analogue radio sets, therefore the speaker should be as far away as possible from the receiver and have magnetic protection if there is no choice. Relays/switches A switch is always a good idea so that the boat or anything else can be switched on and off easily, but they should only be used if the current is low going through them. To reduce the amount of problems that could occur it is recommended to do without a switch if possible. A switch for the receiver is fine as it is only low current. For drive motors it is better to have a straight link onto the battery. Fuses Fuses are always a good idea to ensure they blow up before your boat does! Make sure you use the proper car type fuses for high current applications (blade fuses).

5 years ago by RNinMunich

Wiki

Radio Control Wiring

DRAFT; TO BE REVISED SHORTLY (RN) ;-) Wiring Methods Wiring can be a little tricky, especially when there are more functions than just power and steering. To wire correctly you should first check: - What is to be wired up. - What voltages are going to be needed. - if there is any equipment that is not compatible. Receiver Where possible try to have a separate battery for the receiver and not power it through B.E.C. circuits in speed controllers. There is a simple explanation for this. The speed controller works by switching on and off and different rates. Depending on the rate of switching the motor will speed up or slow down. it is this fluctuating current that is not good for the receiver if its using the B.E.C. *Edit* More modern electronics are not affected so much by this, but if you start to experience problems with reception it could still be something to consider. The receiver should be placed as far away as possible from other electrical equipment such as motors/servos. Also DO NOT CUT THE AERIAL ON THE RECEIVER. The receiver aerial is a set length and can affect signal quality if made shorter or longer. All motors should have suppression to avoid any interference with the signal. There is a section in the knowledge base for this if you need to learn more. ing ing equipment is running at a constant current and can be placed off any battery without it affecting anything else... BUT if it is put onto the same battery as say a drive motor, the s will dim everytime power is asked from the motor. If LEDs are being used you will have to be careful about the voltage. Three things can be done to ensure the LEDs are getting the right voltage (usually between 3.0 to 3.5v). One. Use a voltage regulator. Two. Put resistors into the circuit. Three. Put the LEDs in series with each other. Each LED is about 3v so two in series would need a total of 6v. Sound/speakers Speakers generate sound using a fluctuating current through the coil. it is recommended that all sound devices are run off a separate battery to avoid interference. Another problem with speakers is the magnetic field. This can play havoc with the signal, especially analogue radio sets, therefore the speaker should be as far away as possible from the receiver and have magnetic protection if there is no choice. Relays/switches A switch is always a good idea so that the boat or anything else can be switched on and off easily, but they should only be used if the current is low going through them. To reduce the amount of problems that could occur it is recommended to do without a switch if possible. A switch for the receiver is fine as it is only low current. For drive motors it is better to have a straight link onto the battery. Fuses Fuses are always a good idea to ensure they blow up before your boat does! Make sure you use the proper car type fuses for high current applications (blade fuses).

5 years ago by RNinMunich