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As some would know, David recently re-tooled the business end of the 3.5" Subdriver for both twin shaft and single shaft submarines. Back in January, I ordered through Mike, two of these newer motor end cap units of the single shaft variety. Herein is a basic review following installation into a new WTC and some test sails around my local waterway.
Here is the unit - photos from Caswell site:
I have recently (last weekend) been able to get my Collins (which is almost finished) out for some fun in the local lake and test out this unit.
Here is HMAS Rankin (Collins class) on the bench with one of the units I ordered. Note in the photo that I have extended the equipment tray using styrene plastic card (white colour). I find I don't make use of the supplied metal tray. However, the longitudinal tray supports, their connections to the endcap, the supplied screws for the tray, and the horizontal round support, make IMO installation a simple straight forward job.
It could be easily suggested from this photo that a 3.5" SD is the wrong fit for this model as it virtual occupies the whole boat's beam. There is still around 3/4 of an inch to the bottom of the boat and around 1 1/4" to the deck, and its a tight fit. But, its a necessary fit for this boat. Why? Well sure I could have fitted a 3" or even 2.5" diameter WTC, but this would have meant a much longer ballast tank, so long in fact that there would be extremely limited possibilities of fitting the new torpedoes. In addition I have been wanting to try out a new pump and solenoid from Jim Russell, and the pump is so large it just scrapes inside a 3.5" lexan tube. (ref: http://forum.sub-driver.com/showthre...st-tank-system). The boat was of course tricky to ballast with thin layers of high density foam packed high but below the water line, but nonetheless she is stable and ballasted true.
Ok getting back to the motor unit.
Why did I buy it?
Because whilst I like tinkering with new ballast systems, one thing I have little interest or time for is setting up the basics of the motor gear/box, push rod seals, tray supports etc. I want something I can buy for this with most of the thinking and assembly done. For this the $200US price tag was a logical choice. In fact, as stated I bought two.
Apart from completeness and ready to install servos etc there were a few other things I liked being:
1 - The gear box in this unit is internal.
This is a substantial change on the older 3.5" WTC / SD that David has produced over the years. I like the idea of ease of servicing the thing and IMO this make this easy. The mesh of the new internal gears seems smooth and effortless, whereas I have found the previous bolt on wet g/box, could at times be a bit clunky and rough.
2- The shaft output is centered. Most would recall the old 3.5" SD external g/box was offset. Given my need particularly with Rankin to use a large diameter cylinder, had I used the old 3.5" offset gear box, I would have not been able to mount the cylinder offset below the centre line and have any ballast below the WTC. Had I mounted the old WTC with the offset gear box above the centre line, I would have started to run foul, not of the deck of the sub, but the upward contour of the upper casing. The only alternative I had for a 3.5" cylinder was building my own WTC with a centre output shaft.
3- The supplied and installed push rod seals are 1/16". Whilst previous SDs I have had came with 1/16" push rods, I have had one that came with 1/8". For the time poor, the 1/16" push rod seals you will find are great. Most servo horn holes are 1/16" precisely (at least Futaba ones are), meaning you simply cut 1/16" brass rod to the length you need - push them through the WT seals bending the route as required to limit any seal binding, and then simply z bend them through the servo horn holes. Whilst David has supplied previously 1/8" push rods - I found that there was always work to do if these rods were too short.
4-The tray supports Again AFAIAK - another time saver.
The whole setup of the this engine room side of the SD decked out with the basics of servos, ESC, leveler / fail safe, and RX, and all the connections took about an hour.
The twin motor -some testing
One of the unique features about this new unit is its twin motor, which I must say I though was going to be overkill in this model. In 1/72 scale a Collins sub is 1075mm or 43 1/3" , and has a screw size of 55mm with 6 scimitar blades. My initial tank tests showed the speed was ridiculous for such a small sub who's real world counterpart being the largest diesel subs in the world - run at flank speeds of 25 knots, and typical full speed submerged is more like 21 knts.
On the bench both motors flat out were eating 4 amps off a fresh 7.2 volt battery.
Having a Electronize Speed Control on board, I was able to retard the speed via a trim pot to around half the top end rpms, and the drain fell to around 1.9 amps at this new high speed level. The moderate RPMs I tend to potter about at would be far less.
After several hours ballasting in the safety of my test tank, I headed the short trek down the street to my local fresh water dam. I ran the boat through large circuits of surface running when the boat was out from shore about 30 yards, and as I would turn to shore and run parallel to the water's edge I would be in a dive at PD. The acceleration of the twin motors was phenomenal. I setup a measured distance between two points around 40m apart and timed the boat at PD across this at max speed and also started the boat from a stationary position to flat out across this distance.
After about an hour I went home. I opened the motor end cap up, removed the upper motor via simply cutting the wires (can re-solder back on later) and unscrewing the 4 main WTC bulkhead screws and the two motor screws. I measured the weight of the motor being 200gms and re ballasted the boat for this change, -which actually involved removing more weight (apx 150gms) from a location from the bottom of the hull. - A little foam was also removed, as she sat higher in the water with the weight out.
The motor endcap with the upper motor removed. A very quick job - about 15 minutes turn around to get the motor removed and the SD reassembled and back in operation.
The upper motor being weighed - 200gms
Going back to the lake with a fresh battery and about apx 350gms (about 12.3oz) lighter, I repeated the tests.
What I found was, for this boat, was that the twin motor setup was only marginally faster at the high speed run over the measured distance -about 4 seconds quicker. (Bear in mind the twin motor setup had a 350 gm weight penalty).
The biggest difference was the standing start to full speed ahead. The twin motor setup accelerated at a much faster rate, covering the measured distance around 9 seconds faster. Probably a function of increased torque.
In an ideal world you test a couple of identical boats side by side save for the motors (one would have the twin, the other the single), but nonetheless the comparison shown here I hope does illustrate that there is indeed a noticeable difference between the two setups. One thing that I also found was that at my walking pace, the single motor required many more RPMs to match my walking pace than the twin motor setup. Hardly precisely scientific -there is no way of knowing that I walked at exactly the same speed, but it would have been pretty close to the same, both times the boats were at PD, going along the same patch of the dam. The twin motor was just ticking over, whilst the single motor was at a noticeably higher clip.
For the tests of both single motor and twin motor setups, you will note I turned down the ESCs top end speed. I think that the observed marginal difference in top end speed of the twin motor over the single could well have shown a more significant result with the ESC set to the highest speed setting.
What was apparent thinking retrospectively about the tests, is that the Rankin's handling and turning circle were significantly improved with the weight loss. The weight loss was quite a lot, the motor weight was significant, but given the height of the WTC within Rankin, and therefore the height of the upper twin motor, more ballast weight down low was required to help stabilise the model, offsetting this motor weight high in the hull. With the upper motor gone, some ballast weight could be removed.
I was going to run Rankin with the twin motor setup, but in this case, I'd think I'd rather take handling over acceleration.
Conclusions:
Whilst the twin motor setup does give you greater torque, the other features of the motor end cap and its completeness (readiness to install) were the primary selling points for me. If you don't need the extra grunt of two motors, simply disconnect and remove one and you have a spare. I have two of these units, with the other one dedicated for Joel's 1/72 Permit kit that I am putting together, I am thinking that I'd probably run that unit with both motors. I love the smooth operation of the new internal gear box, a vast improvement IMO over the previous 3.5" SD version. The end cap with its precisely engineered components is a quality bit of kit, and the speed of changing from single to double or back to single motor is a direct result of intuitive functional design. Indeed you could probably double duty this back end unit in multiple subs - varying from one motor to twin setup (or the reverse) in around 15 minutes. At $200US the unit is priced to seriously get you re-evaluating the costs of putting it all together yourself -even if you only need the one motor. I am going to be buying a third unit for my 1/72 Seawolf on order with Joel, which will no doubt benefit from the twin motor setup. Time to start saving!
The new 3.5" Subdriver motor end cap is well worth considering and is adaptable to many different WTC ballast setups.
Best
John
Here is the unit - photos from Caswell site:
I have recently (last weekend) been able to get my Collins (which is almost finished) out for some fun in the local lake and test out this unit.
Here is HMAS Rankin (Collins class) on the bench with one of the units I ordered. Note in the photo that I have extended the equipment tray using styrene plastic card (white colour). I find I don't make use of the supplied metal tray. However, the longitudinal tray supports, their connections to the endcap, the supplied screws for the tray, and the horizontal round support, make IMO installation a simple straight forward job.
It could be easily suggested from this photo that a 3.5" SD is the wrong fit for this model as it virtual occupies the whole boat's beam. There is still around 3/4 of an inch to the bottom of the boat and around 1 1/4" to the deck, and its a tight fit. But, its a necessary fit for this boat. Why? Well sure I could have fitted a 3" or even 2.5" diameter WTC, but this would have meant a much longer ballast tank, so long in fact that there would be extremely limited possibilities of fitting the new torpedoes. In addition I have been wanting to try out a new pump and solenoid from Jim Russell, and the pump is so large it just scrapes inside a 3.5" lexan tube. (ref: http://forum.sub-driver.com/showthre...st-tank-system). The boat was of course tricky to ballast with thin layers of high density foam packed high but below the water line, but nonetheless she is stable and ballasted true.
Ok getting back to the motor unit.
Why did I buy it?
Because whilst I like tinkering with new ballast systems, one thing I have little interest or time for is setting up the basics of the motor gear/box, push rod seals, tray supports etc. I want something I can buy for this with most of the thinking and assembly done. For this the $200US price tag was a logical choice. In fact, as stated I bought two.
Apart from completeness and ready to install servos etc there were a few other things I liked being:
1 - The gear box in this unit is internal.
This is a substantial change on the older 3.5" WTC / SD that David has produced over the years. I like the idea of ease of servicing the thing and IMO this make this easy. The mesh of the new internal gears seems smooth and effortless, whereas I have found the previous bolt on wet g/box, could at times be a bit clunky and rough.
2- The shaft output is centered. Most would recall the old 3.5" SD external g/box was offset. Given my need particularly with Rankin to use a large diameter cylinder, had I used the old 3.5" offset gear box, I would have not been able to mount the cylinder offset below the centre line and have any ballast below the WTC. Had I mounted the old WTC with the offset gear box above the centre line, I would have started to run foul, not of the deck of the sub, but the upward contour of the upper casing. The only alternative I had for a 3.5" cylinder was building my own WTC with a centre output shaft.
3- The supplied and installed push rod seals are 1/16". Whilst previous SDs I have had came with 1/16" push rods, I have had one that came with 1/8". For the time poor, the 1/16" push rod seals you will find are great. Most servo horn holes are 1/16" precisely (at least Futaba ones are), meaning you simply cut 1/16" brass rod to the length you need - push them through the WT seals bending the route as required to limit any seal binding, and then simply z bend them through the servo horn holes. Whilst David has supplied previously 1/8" push rods - I found that there was always work to do if these rods were too short.
4-The tray supports Again AFAIAK - another time saver.
The whole setup of the this engine room side of the SD decked out with the basics of servos, ESC, leveler / fail safe, and RX, and all the connections took about an hour.
The twin motor -some testing
One of the unique features about this new unit is its twin motor, which I must say I though was going to be overkill in this model. In 1/72 scale a Collins sub is 1075mm or 43 1/3" , and has a screw size of 55mm with 6 scimitar blades. My initial tank tests showed the speed was ridiculous for such a small sub who's real world counterpart being the largest diesel subs in the world - run at flank speeds of 25 knots, and typical full speed submerged is more like 21 knts.
On the bench both motors flat out were eating 4 amps off a fresh 7.2 volt battery.
Having a Electronize Speed Control on board, I was able to retard the speed via a trim pot to around half the top end rpms, and the drain fell to around 1.9 amps at this new high speed level. The moderate RPMs I tend to potter about at would be far less.
After several hours ballasting in the safety of my test tank, I headed the short trek down the street to my local fresh water dam. I ran the boat through large circuits of surface running when the boat was out from shore about 30 yards, and as I would turn to shore and run parallel to the water's edge I would be in a dive at PD. The acceleration of the twin motors was phenomenal. I setup a measured distance between two points around 40m apart and timed the boat at PD across this at max speed and also started the boat from a stationary position to flat out across this distance.
After about an hour I went home. I opened the motor end cap up, removed the upper motor via simply cutting the wires (can re-solder back on later) and unscrewing the 4 main WTC bulkhead screws and the two motor screws. I measured the weight of the motor being 200gms and re ballasted the boat for this change, -which actually involved removing more weight (apx 150gms) from a location from the bottom of the hull. - A little foam was also removed, as she sat higher in the water with the weight out.
The motor endcap with the upper motor removed. A very quick job - about 15 minutes turn around to get the motor removed and the SD reassembled and back in operation.
The upper motor being weighed - 200gms
Going back to the lake with a fresh battery and about apx 350gms (about 12.3oz) lighter, I repeated the tests.
What I found was, for this boat, was that the twin motor setup was only marginally faster at the high speed run over the measured distance -about 4 seconds quicker. (Bear in mind the twin motor setup had a 350 gm weight penalty).
The biggest difference was the standing start to full speed ahead. The twin motor setup accelerated at a much faster rate, covering the measured distance around 9 seconds faster. Probably a function of increased torque.
In an ideal world you test a couple of identical boats side by side save for the motors (one would have the twin, the other the single), but nonetheless the comparison shown here I hope does illustrate that there is indeed a noticeable difference between the two setups. One thing that I also found was that at my walking pace, the single motor required many more RPMs to match my walking pace than the twin motor setup. Hardly precisely scientific -there is no way of knowing that I walked at exactly the same speed, but it would have been pretty close to the same, both times the boats were at PD, going along the same patch of the dam. The twin motor was just ticking over, whilst the single motor was at a noticeably higher clip.
For the tests of both single motor and twin motor setups, you will note I turned down the ESCs top end speed. I think that the observed marginal difference in top end speed of the twin motor over the single could well have shown a more significant result with the ESC set to the highest speed setting.
What was apparent thinking retrospectively about the tests, is that the Rankin's handling and turning circle were significantly improved with the weight loss. The weight loss was quite a lot, the motor weight was significant, but given the height of the WTC within Rankin, and therefore the height of the upper twin motor, more ballast weight down low was required to help stabilise the model, offsetting this motor weight high in the hull. With the upper motor gone, some ballast weight could be removed.
I was going to run Rankin with the twin motor setup, but in this case, I'd think I'd rather take handling over acceleration.
Conclusions:
Whilst the twin motor setup does give you greater torque, the other features of the motor end cap and its completeness (readiness to install) were the primary selling points for me. If you don't need the extra grunt of two motors, simply disconnect and remove one and you have a spare. I have two of these units, with the other one dedicated for Joel's 1/72 Permit kit that I am putting together, I am thinking that I'd probably run that unit with both motors. I love the smooth operation of the new internal gear box, a vast improvement IMO over the previous 3.5" SD version. The end cap with its precisely engineered components is a quality bit of kit, and the speed of changing from single to double or back to single motor is a direct result of intuitive functional design. Indeed you could probably double duty this back end unit in multiple subs - varying from one motor to twin setup (or the reverse) in around 15 minutes. At $200US the unit is priced to seriously get you re-evaluating the costs of putting it all together yourself -even if you only need the one motor. I am going to be buying a third unit for my 1/72 Seawolf on order with Joel, which will no doubt benefit from the twin motor setup. Time to start saving!
The new 3.5" Subdriver motor end cap is well worth considering and is adaptable to many different WTC ballast setups.
Best
John