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Ballast shifter.
As you may have seen from previous threads (URL), this is an upgrade to a boat which is a dry hull design but uses a removable tech rack. This which contains all the workings, except the servo’s and drive motor, and can be removed from the hull to potentially be used in another hull. To date the tech rack has functioned flawlessly, but has a drawback which is a function of the single piston tank design. The piston tank control is fully proportional with fine tuning available for the final 20%. I have ballasted the boat to enable me to take the boat all the way to the bottom if needed. However the problem is that with an empty tank the hull is level and with a 90% full tank the hull is level, but at any point in between, or more than 90% the hull does not sit level. For this design of boat the attitude is not so critical, as the real boats tended to pivot about an axis near the stern. However with the tank filling from the bow, there is a tendency for the stern to rise as the bow fills, so when sitting with the sail just breaching the prop is very close to the surface and starts cavitating and chewing the air, especially if attempting a dynamic dive. Also I seem to find varying densities of water in my region and hence a device to fine tune my attitude would be useful (no not that attitude homeboy!!)
Based on a suggestion by Andy (Subculture), back when I originally was building this boat I decided to add on a device to correct the attitude of the sub with any volume of tank fill. The current setup is configured with 2 x 6V SLA to give 12 v operation. In addition to the batteries I had a couple of small pieces of lead attached to the front of the Tech rack. I plan to replace the SLA with 4 x A123 batteries (http://www.a123systems.com/a123/products ) (to give a nominal 13.2Volts. these give me double to amp hours and weigh less than half the SLA’s. the weight difference (as lead) plus the existing ballast lead will then be moved backwards and forwards to balance the boat (well that’s the plan anyway).
Additional Items required
Low speed 380 motor (this was an old one out of the spares box, which I originally got from SWM)
2 small micro switches for end stops
4:1 toothed pulley’s and belt (http://www.motionco.co.uk/timing-pul...-25_35_50.html)
Engel BTS – this is a fairly extravagant item for what it’s doing, but as I had it doing nothing in my box it’s basically free.
Wire.
So about 25 quids worth of bits for the ballast shifting parts, the main expense being the pulleys, plus another 25 quid for the batteries. I already have another use for the SLA’s so they aren’t wasted, and as the mAh was questionable for this boat it was something that was worthwhile doing anyway.
First job was to strip down the battery end of the tech rack, and drill some holes to mount the motor, and for the jack screw. Also some holes in the third bulkhead to allow wires to pass through. Seemed quite simple so far but then realised I need some holes in the second bulkhead to also pass wires through. This meant stripping down the back end of the tech rack, which I was just about able to do without disconnecting anything. I plugged the BTS in, and connected up the system using some old wire. Amazingly considering the BTS has sat around for a year or two, and has been flooded a few times, it all worked :) . Found a small space in the back of the tech rack, and with the wires attached wedged it in, and rebuilt the back end, with the wires running forward. It is a real rats nest of wires in there, but I’m not getting any glitching and all is working fine. At a later date if this is deemed the final configuration I will make the area slightly bigger and remove some of the excess wires (both the BTS, and the tank controller have about 300mm of cables to plug into RX when it is only 50mm away, and the controller has another bundle of cables to connect it to the piston motor, and again its v close).
I next made up a bracket to mount the motor on and a couple more for the micro switches, then it was out with the iron and soldered the system together, and rebuilt the battery end (without the new batteries, which were still on order). Amazingly the system still worked.
Original battery setup and lead weighed in at 711g. The new batteries should be 310g. I found I had a nice lump of lead which came in at 250g. Allowing 100G for the motor, pulleys, jack shaft and fixings gives me 50g to play with for final trimming.
Space was tight up front so I extended the assembly to give more room, and did a final rewire. Everything assembled, everything worked, well it did until I tried two things together!!!!!!
As you may have seen from previous threads (URL), this is an upgrade to a boat which is a dry hull design but uses a removable tech rack. This which contains all the workings, except the servo’s and drive motor, and can be removed from the hull to potentially be used in another hull. To date the tech rack has functioned flawlessly, but has a drawback which is a function of the single piston tank design. The piston tank control is fully proportional with fine tuning available for the final 20%. I have ballasted the boat to enable me to take the boat all the way to the bottom if needed. However the problem is that with an empty tank the hull is level and with a 90% full tank the hull is level, but at any point in between, or more than 90% the hull does not sit level. For this design of boat the attitude is not so critical, as the real boats tended to pivot about an axis near the stern. However with the tank filling from the bow, there is a tendency for the stern to rise as the bow fills, so when sitting with the sail just breaching the prop is very close to the surface and starts cavitating and chewing the air, especially if attempting a dynamic dive. Also I seem to find varying densities of water in my region and hence a device to fine tune my attitude would be useful (no not that attitude homeboy!!)
Based on a suggestion by Andy (Subculture), back when I originally was building this boat I decided to add on a device to correct the attitude of the sub with any volume of tank fill. The current setup is configured with 2 x 6V SLA to give 12 v operation. In addition to the batteries I had a couple of small pieces of lead attached to the front of the Tech rack. I plan to replace the SLA with 4 x A123 batteries (http://www.a123systems.com/a123/products ) (to give a nominal 13.2Volts. these give me double to amp hours and weigh less than half the SLA’s. the weight difference (as lead) plus the existing ballast lead will then be moved backwards and forwards to balance the boat (well that’s the plan anyway).
Additional Items required
Low speed 380 motor (this was an old one out of the spares box, which I originally got from SWM)
2 small micro switches for end stops
4:1 toothed pulley’s and belt (http://www.motionco.co.uk/timing-pul...-25_35_50.html)
Engel BTS – this is a fairly extravagant item for what it’s doing, but as I had it doing nothing in my box it’s basically free.
Wire.
So about 25 quids worth of bits for the ballast shifting parts, the main expense being the pulleys, plus another 25 quid for the batteries. I already have another use for the SLA’s so they aren’t wasted, and as the mAh was questionable for this boat it was something that was worthwhile doing anyway.
First job was to strip down the battery end of the tech rack, and drill some holes to mount the motor, and for the jack screw. Also some holes in the third bulkhead to allow wires to pass through. Seemed quite simple so far but then realised I need some holes in the second bulkhead to also pass wires through. This meant stripping down the back end of the tech rack, which I was just about able to do without disconnecting anything. I plugged the BTS in, and connected up the system using some old wire. Amazingly considering the BTS has sat around for a year or two, and has been flooded a few times, it all worked :) . Found a small space in the back of the tech rack, and with the wires attached wedged it in, and rebuilt the back end, with the wires running forward. It is a real rats nest of wires in there, but I’m not getting any glitching and all is working fine. At a later date if this is deemed the final configuration I will make the area slightly bigger and remove some of the excess wires (both the BTS, and the tank controller have about 300mm of cables to plug into RX when it is only 50mm away, and the controller has another bundle of cables to connect it to the piston motor, and again its v close).
I next made up a bracket to mount the motor on and a couple more for the micro switches, then it was out with the iron and soldered the system together, and rebuilt the battery end (without the new batteries, which were still on order). Amazingly the system still worked.
Original battery setup and lead weighed in at 711g. The new batteries should be 310g. I found I had a nice lump of lead which came in at 250g. Allowing 100G for the motor, pulleys, jack shaft and fixings gives me 50g to play with for final trimming.
Space was tight up front so I extended the assembly to give more room, and did a final rewire. Everything assembled, everything worked, well it did until I tried two things together!!!!!!
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