Here is a list of all the postings Mark Beard has made in our forums. Click on a thread name to jump to the thread.
|Thread: Discussion on Motors and Props|
I fully agree with Chris E’s comments (which I received as email notifications and for some reason are yet to appear here), that specific data are needed for motor and propeller combinations to enable good mathematical modelling of boat performance. The kv parameter and motor count are key for motors, and drive voltage for the battery. Gear or belt speed reduction ratio is key for the drive system. Diameter, blade count, blade pitch and prop count are key for the prop(s). The most difficult to enumerate is the hull shape, as there are enormous performance differences between, say a full displacement hull, such as a tug, and a fast planing hull as in an MTB, with everything in between. The aim should be a mathematical model which accurately predicts scale performance for a model boat, as easily as is achieved for model aircraft. Notwithstanding the fluid dynamic difficulties of hull characteristics, our field should not be inferior!
Edited By Colin Bishop on 18/09/2020 14:03:56
|Thread: Exciting development!|
I understand the disappointment of not having as much footage aired, but I thought the slot did a good job of illustrating the historic cable laying and many of the technical issues involved, and included a reasonable show of you and the GE. I think you and her ladyship equipped yourselves rather finely actually, even if there was more shot than shown. I thoroughly enjoyed seeing it. Well done to you and all who contributed to such an exciting adventure and an opportunity to show what fine scale model engineering can achieve.
All the best,
Alas a very busy work and family life have got in the way (both are enemies of modelling), but it's a long weekend so I'll be off to pick up my copy
Oh wow, will definitely be watching that! Have you got your dinner jacket and black tie ready for your premier performance? The wife'll need a smart new frock too!
|Thread: Precedent 34" Huntsman|
Sounds like you have some powerful kit there!
You have come up against the biggest downside of outrunners: the fact that the heat is generated on the inside and needs to get to the outside. This is the equivalent thermal problem to brushed motors.
In a brushed motor, the windings where the heat is generated are on the rotor on the inside. To dissipate, that heat must pass through the bearings to the stator and either free air or a water jacket.
In a brushless motor, the windings are on the stator not the rotor. The outrunner has the stator on the inside. So the heat still has to pass through the bearings to dissipate. The other complecation of the outrunner is that you can't put an effective water jacket on a spinning outside rotor. Some outrunners, (and the Turnigy 35-42 seems to fall into this category) have non-rotating cases around the rotor. This adds an enclosed layer of insulating air to the outside which makes thermal management harder still.
The inrunner brushless motor has the stator on the outside and here the windings are coupled to the outside by a thermally conductive metal sleeve. This allows heat to dissipate very easilly to air, or better still to a water jacket.
As far as I know, the only practical and effective way to cool an outrunner is a high flow of air over and (if possible) axially through the motor. I guess that's why they're used so much in model planes and helecopters!!! So if you can engineer forced air cooling over the motor, then this will probably be the best plan.
|Thread: Exciting development!|
Lol! Just as well GT seems to be used for safety regulations and berthing fees, rather than for loading!
It seems that Tonnage is a measure of cargo carrying capacity and displacement is the maximum weight of the loaded vessel. So in simplistic terms, GE would have an unloaded weight of 8,000 tons and was able to carry a load of 19,000 tons, making her 27,000 tons fully laden.
According to the wonderful Wikipedia, Gross Tonnage is now a standardised calculation based on the volume of the vessel, as Kimo describes. GT is not quite the maximum weight of cargo in tons though, but is an approximation based of the volume of the vessel.
Does this help or make sense?
Happy New Year!
|Bob, thanks so much for keeping us all up-to-date and involved with your fascinating project! Wishing you and yours a very happy and peaceful Christmas, as well as success in your new-found celebrity status in 2012! Mark|
|Thread: Electric motor temperature sensor|
Hey, you've got a 44% speed reduction in the water, (albeit static and not moving through the water), which is close to perfect for a performance hull. IMO, you're now getting the most from the 900 motor so if it isn't fast enough now then you need a higher power motor.
I seemed to have missed the excitement when this thread was current!
For what it's worth, iron losses and temperature rises do have real effects on motor performance. But the calculations I've put out there have used the 80:20 rule, to get 80% of the way to a useful answer by applying 20% of the calculations.
60 Watt: My calcs were based on first principles, including T=KtI, E=KvN, Kt = (Kv in v/rad/sec) and Ohm's Law. They match manufacturer's published curves almost exactly. If you're interested, PM me an email address and I'll gladly send you my spreadsheet.
Barzo: IMO I think you're cooking your motor and would do well to run water cooling 100% of the time.
Here are some suggested golden rules for motor-prop sizing, for those without a laser tachometer!:
1 - Use the recommended motor for the model you're building, or if it's a scratch-build then pick a similar hull which performs well and use a similar motor.
2 - Run the motor at, or below, the rated voltage, but NEVER above it, unless you're racing and know what you're doing.
3 - Run your motor at full throttle with the boat out ot the water, (no-load) and listen to the pitch of the motor sound. Now run the boat full throttle on the pond. If the motor pitch on the water is more than one octave below the no-load pitch then you're running on the EVIL side of the torque curve, your motor is over-loaded, is overheating unnecessarilly and delivering less shaft power than it could. In this case, choose a smaller prop or one with a finer pitch. That smaller prop WILL make your model go faster, cook your motor less and make your battery last longer!
4 - For a non-planing scale hull, the best compromise between efficiency and performance is when the shaft is loaded so that on the water it's running at 75% of the no-load speed, or three full-tones below in pitch. (If no-load the pitch is uper C with the throttle wide open, then on the pond the tone should be G below). If not, adjust the prop size or pitch to suit. This will give you around 90% of the maximum motor efficiency and the best battery life. If the performance is inadequate, change to a larger motor and repeat.
5 - For a high-performance planing hull, you need to accept short battery life and a cooking motor. Choose the best water cooling arrangement you can, as hot motors not only have short lives, but deliver less power. Select the prop to give a water pitch just less than an octave below the no-load pitch. (If no-load the pitch is uper C with the throttle wide open, then on the pond the tone should be middle D). If the performance is inadequate, change to a bigger motor as you have already got the most from the one you have.
I'd be delighted to hear how these rules apply to real models in practice. If your scale model runs with a motor pitch more than three tones below the no-load pitch, does your motor get hot?
|Thread: Ads block forum content|
I'm having trouble reading some forum threads as the thread text extends beyond the ads column on right, which blocks the forum text from view. I'm using Firefox 7 and IE8 and have the same problem in both. Is there a fix? Am I the only one suffering this?
|Thread: Exciting development!|
|Bob, you have quite a following for this amazing thread: 400 replies and 10,000 (yes, ten thousand) views! Fame at last, eh? Mark|
|Please let us know when it's scheduled to be broadcast, (I know 2012, but that's all).|
|Bob, what a wonderful day! And great sequence of photos with your inimitable commentary on proceedings. Well done and congratulations on an excellent job! Mark|
|That's great, and so long as the container body is grounded, like a metal framed caravan is, the RCD will work just fine.|
|Ashley, I see where you're coming from with filling the riser tube with oil - the hydrostatic (or should that be oleostatic) pressure from the column of oil in the riser will force oil up the shaft tube. Only trouble is, unless the bottom bearing is sealed that same pressure will dump most of the oil out the prop end of the tube. Reading both your and Colin's advice, if it were me I'd blank the oilers off and oil each end before and after sailing.|
|David, your containerised workshop is an inspiration! Have you thought of insulating the walls? With such a well-conducting enclosure, I do hope you have well grounded the container where the electrical supply comes in, for safety. Best regards, Mark|
|Thread: Exciting development!|
|Should have been SE of course. Glad you passed the awake-test!|
|I guess since the cable was laid east-west, you need to find the bouy, sail a few miles SW then begin traversing North and South across the path of the laid cable until you snag it. If you're far enough from the end, the weight of the cable should keep the end on the ocean bed. Once up on deck, the task of running the cable to its end begins. The weight of cable certainly would need powerful winches and clamps!|
|Excellent! Plus, the bouy must have had at least a mile and a half of chain! How will you manage that?|
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