Need some advice. Worthwhile project or white elephant?
08-29-2016, 08:54 AM
#26
Thread Starter
Correction, it seems I was a bit off in my estimation of prop size, they are 4" (100mm) diameter. Now I am considering a beast of a motor, so we'll see what happens. I am now kicking around the idea of using 4 12V batteries in series to run 48V since most of the true torque motors work in the higher voltage range.
Mark
Mark
08-29-2016, 10:49 AM
#27
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Looking at the numbers in my Janes Fighting Ships, and assuming a scale of @ 1:64, running the numbers gives a model weighing in at 280lb needing about 100-150 Watts to drive it a an actual speed of about 5 ft/sec which will look right. It was a 1916 design, not a WW2 greyhound.
4, possibly geared, motors would probably be a much simpler install than a distribution gearbox and would give the chance of better control. Something that weight needs all the control it can get at 5 ft/sec, there is a LOT of inertia there. Suitable motors can be found in most cars. Window winder motors, fan motors and such, all capable of being controlled by quite ordinary ESCs.
4, possibly geared, motors would probably be a much simpler install than a distribution gearbox and would give the chance of better control. Something that weight needs all the control it can get at 5 ft/sec, there is a LOT of inertia there. Suitable motors can be found in most cars. Window winder motors, fan motors and such, all capable of being controlled by quite ordinary ESCs.
08-29-2016, 02:19 PM
#28
Looking at the numbers in my Janes Fighting Ships, and assuming a scale of @ 1:64, running the numbers gives a model weighing in at 280lb needing about 100-150 Watts to drive it a an actual speed of about 5 ft/sec which will look right. It was a 1916 design, not a WW2 greyhound.
4, possibly geared, motors would probably be a much simpler install than a distribution gearbox and would give the chance of better control. Something that weight needs all the control it can get at 5 ft/sec, there is a LOT of inertia there. Suitable motors can be found in most cars. Window winder motors, fan motors and such, all capable of being controlled by quite ordinary ESCs.
4, possibly geared, motors would probably be a much simpler install than a distribution gearbox and would give the chance of better control. Something that weight needs all the control it can get at 5 ft/sec, there is a LOT of inertia there. Suitable motors can be found in most cars. Window winder motors, fan motors and such, all capable of being controlled by quite ordinary ESCs.
08-30-2016, 11:35 AM
#29
Thread Starter
I only need one motor, there is a very over-engineered transmission already in it, with a .85 reduction to 4 output shafts. It's staying put and is part of the novelty of this old design. I'm surprised the wattage requirement is that low.
Thanks
Mark
Thanks
Mark
08-31-2016, 12:41 AM
#30
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A look at a copy of an old Janes might remove some surprises. It might equally create some. Most destroyers of the period had engines with more than twice the output power.
4 of 4" props turning together roughly equals one 7" prop for the purpose of shifting water, it needs to move some 5000 cubic inches a distance of about 100 inches every second for the scale performance which, not knowing much about the props guesstimates at about 1500 RPM.
If a lack of close control is not a requirement, one motor would be fine, just a question of finding one that has the right power input and speed characteristics for direct connection to the gearbox input, or looking at toothed timing belts and matching pulleys to gear the right power of motor to the speed required. To repeat, a large, heavy model like this needs all the help it can get when maneuvering in a restricted area (like when bringing it in to recover it) to avoid damage to either the boat, the surroundings, or the operator.
4 of 4" props turning together roughly equals one 7" prop for the purpose of shifting water, it needs to move some 5000 cubic inches a distance of about 100 inches every second for the scale performance which, not knowing much about the props guesstimates at about 1500 RPM.
If a lack of close control is not a requirement, one motor would be fine, just a question of finding one that has the right power input and speed characteristics for direct connection to the gearbox input, or looking at toothed timing belts and matching pulleys to gear the right power of motor to the speed required. To repeat, a large, heavy model like this needs all the help it can get when maneuvering in a restricted area (like when bringing it in to recover it) to avoid damage to either the boat, the surroundings, or the operator.
08-31-2016, 10:48 AM
#31
Thread Starter
mfr02,
That was an extremely informative breakdown of what I need to accomplish. I am proceeding with a tentative test motor and ESC, worst that could happen is it's a slug in the water, or I burn them up. 5000 cubic inches being moved 100 inches sounds quite daunting, I hope in practice, it will work with what I am doing. Momentum will definitely be a key factor, courtesy on the pond will keep me from doing great harm to my fellow boaters. With a steel hull, I doubt I will lose any contest with others.
Thanks
Mark
That was an extremely informative breakdown of what I need to accomplish. I am proceeding with a tentative test motor and ESC, worst that could happen is it's a slug in the water, or I burn them up. 5000 cubic inches being moved 100 inches sounds quite daunting, I hope in practice, it will work with what I am doing. Momentum will definitely be a key factor, courtesy on the pond will keep me from doing great harm to my fellow boaters. With a steel hull, I doubt I will lose any contest with others.
Thanks
Mark
09-26-2016, 10:02 AM
#36
Thread Starter
Sorry for disappearing for a bit, life has kept me from updating what's happening on this end. The hull is gutted, I am in the process of stripping, sealing and priming the inside of the hull. The motor and ESC are in hand and the second (first was way too large) planetary gear reduction is on order. I should be real close to the speed of the original motor hopefully. I won't get too much done this week because I have been asked to display it this weekend at the Maker Fair at Balboa Park in San Diego, so I can't do anything that will have it laid up. There has been quite a bit of interest from the local RC boat group, so I will have some people to bounce ideas off of and grovel for help with modeling details.
Mark
Mark
09-27-2016, 04:13 PM
#37
I've seen scale ships this size and larger. Years ago a scale ship club used to hold a regatta 3 miles east of my house. Someone brought a 14-foot ship that was incomplete but ran. They used power seat motors with 12-volt deep-cycle batteries to power it. I don't know what else they used for electronics however. They seemed to move it along at scale-like speeds
09-29-2016, 08:42 AM
#38
Thread Starter
I'm still working on the single motor/planetary reduction, if that goes south, I will look at 4 individual motors. If I'm doing my math correctly, with the current plan I will have a final prop speed (no load) at right about 1000RPM.
Mark
Mark
