Smoked motor - suitable replacement?
08-05-2009, 12:01 PM
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Smoked motor - suitable replacement?
The motor smoked the first time I ran the boat:
- Boat: Billing Boats, White Star (length of hull 54cm; 3 blade prop 35mm in diameter), www.cornwallmodelboats.co.uk/acatalog/billing_boats_white_star.html
- Battery: LRP Hyper Pack 4000 – 7.2V, www.lrp.cc/en/products/vtec-batteries/stick-packs-6-cells/produkt/lrp-hyper-pack-4000-72v-6-zellen-nimh-stickpack/details/
- Motor: Graupner Speed 400 6V (3321), www.cornwallmodelboats.co.uk/acatalog/graupner_3321.html
Battery is connected to the motor through a plain on/off switch (full speed all time, no speed control, no rc). I control the rudder with a rc taken from a cheap (approx. 10USD) rc car.
What is a suitable solution to the problem?
Thanks,
Anders
- Boat: Billing Boats, White Star (length of hull 54cm; 3 blade prop 35mm in diameter), www.cornwallmodelboats.co.uk/acatalog/billing_boats_white_star.html
- Battery: LRP Hyper Pack 4000 – 7.2V, www.lrp.cc/en/products/vtec-batteries/stick-packs-6-cells/produkt/lrp-hyper-pack-4000-72v-6-zellen-nimh-stickpack/details/
- Motor: Graupner Speed 400 6V (3321), www.cornwallmodelboats.co.uk/acatalog/graupner_3321.html
Battery is connected to the motor through a plain on/off switch (full speed all time, no speed control, no rc). I control the rudder with a rc taken from a cheap (approx. 10USD) rc car.
What is a suitable solution to the problem?
Thanks,
Anders
08-05-2009, 04:03 PM
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RE: Smoked motor - suitable replacement?
I have a White Star. I had a 400 size motor in it at first as well. Min was a 7.2 volt though, and I ran it on an ESC. It was OK at slow speeds but got really darn hot at full power. It look like you did what I did. I cooked my speed 400 and then installed a 550 turbo. Goes really fast. Although it was really heavy and killed the battery fast. I ended up getting another 400 size motor with a 3:1 gear reduction. The thing flies and doesn't get too hot. If I were you id go for a 400 size motor with a gear reduction and run it on 3 cells. Longer run time and wont be too fast. Seeing as you don't have RC speed control the motor will always run at full power so stopping a boat going as fast as mine does cold be dangerous.
Video of my White Star.
http://s214.photobucket.com/albums/c...t=Eyelevel.flv
A couple of cool pics. You can see how running the motor on all 6 cells might not be a good idea.
Cheers,
Video of my White Star.
http://s214.photobucket.com/albums/c...t=Eyelevel.flv
A couple of cool pics. You can see how running the motor on all 6 cells might not be a good idea.
Cheers,
08-06-2009, 04:47 AM
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RE: Smoked motor - suitable replacement?
6v motor and 7.2V battery puts it thoroughly in the crossed-fingers marginal area of component life. Try a motor rated for 7.2V or a bit more, and reduce the prop size.
08-11-2009, 04:23 PM
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RE: Smoked motor - suitable replacement?
As someone who has destroyed my fair share of Speed 400s, I can attest that replacing them with a 500 sized motor is a good idea. First, you should not be pulling anywhere near 15 amps through a little Speed 400. And running a motor rated at 6v at a higher voltage will decrease its service life.
When it comes to actually measuring amps, I have put a high capacity amp meter in line with the battery, but the resistance of the shunt seems to alter the very system I am trying to observe. But it does give me a ballpark idea. Sometimes, if the motor just sounds like it is bogged down or turning too slowly, either the prop is too aggressive or the motor is too small. Changing one or the other could remedy the situation. Seems a bit strange though if the prop came with the kit and you are using the recommended motor.
Though I had just posted another response about recommending products from MACK Model Marine, I am not an salesman, just a customer. They have good quality motors and systems. I recently bought their 5045 motor and it is a gem. A great replacement for any 6V "500" sized motor.
I can not tell how many poles it has, but it clearly has 10 to 12 clicks as you spin the shaft. Most cheap 500 motors are 3 pole, 19 to 22 turn units and relatively inefficient for the number of amps they consume. You may want to consider the 5045 or another high quality 550 or 540 motor to get your boat back in the water.
When it comes to actually measuring amps, I have put a high capacity amp meter in line with the battery, but the resistance of the shunt seems to alter the very system I am trying to observe. But it does give me a ballpark idea. Sometimes, if the motor just sounds like it is bogged down or turning too slowly, either the prop is too aggressive or the motor is too small. Changing one or the other could remedy the situation. Seems a bit strange though if the prop came with the kit and you are using the recommended motor.
Though I had just posted another response about recommending products from MACK Model Marine, I am not an salesman, just a customer. They have good quality motors and systems. I recently bought their 5045 motor and it is a gem. A great replacement for any 6V "500" sized motor.
I can not tell how many poles it has, but it clearly has 10 to 12 clicks as you spin the shaft. Most cheap 500 motors are 3 pole, 19 to 22 turn units and relatively inefficient for the number of amps they consume. You may want to consider the 5045 or another high quality 550 or 540 motor to get your boat back in the water.
08-11-2009, 04:59 PM
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RE: Smoked motor - suitable replacement?
Anders,at least get yourself an aircraft [link=http://www.r2hobbies.com/proddetail.php?prod=rcps51601]€2,21 speed controller[/link] and you can overpower the motor for short periods.
These motors don't have a fixed voltage rating carved in stone because there is more than one factor that causes the unwanted heat.
If you do a test like rcshipyard describes,according to the Graupner figures,use a prop at 15 amp for maximum power and 5 amp for maximum efficiency(70%) on 7,2.
You get a longer duration with the smaller prop at 70% efficiency over 50% with the larger prop but that one gives you maximum thrust to do the aquabatics in the photographs.
These motors don't have a fixed voltage rating carved in stone because there is more than one factor that causes the unwanted heat.
If you do a test like rcshipyard describes,according to the Graupner figures,use a prop at 15 amp for maximum power and 5 amp for maximum efficiency(70%) on 7,2.
You get a longer duration with the smaller prop at 70% efficiency over 50% with the larger prop but that one gives you maximum thrust to do the aquabatics in the photographs.
08-11-2009, 05:27 PM
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RE: Smoked motor - suitable replacement?
These motors don't have a fixed voltage rating carved in stone because there is more than one factor that causes the unwanted heat.
Very true. 7.2 on 6v motor is not a big sin. But the lower the quality, the lower the service life regardless of its rating. It is all about the ability of the unit to take the heat. Better components - better motor - regardless of voltage.
If you do a test like rcshipyard describes,according to the Graupner figures,use a prop at 15 amp for maximum power and 5 amp for maximum efficiency(70%) on 7,2.
5 amps for a 6v motor sounds about right. It's all about balance - motor size versus prop. Gearing is great. You lose RPMs, but since the motor can now run efficeiently, you can return to using a higher pitch on the prop.
You get a longer duration with the smaller prop at 70% efficiency over 50% with the larger prop but that one gives you maximum thrust to do the aquabatics in the photographs.
I have a Fireboat that get up and run with just the prop in the water. Scale? No. But I still love doing it!!!
Very true. 7.2 on 6v motor is not a big sin. But the lower the quality, the lower the service life regardless of its rating. It is all about the ability of the unit to take the heat. Better components - better motor - regardless of voltage.
If you do a test like rcshipyard describes,according to the Graupner figures,use a prop at 15 amp for maximum power and 5 amp for maximum efficiency(70%) on 7,2.
5 amps for a 6v motor sounds about right. It's all about balance - motor size versus prop. Gearing is great. You lose RPMs, but since the motor can now run efficeiently, you can return to using a higher pitch on the prop.
You get a longer duration with the smaller prop at 70% efficiency over 50% with the larger prop but that one gives you maximum thrust to do the aquabatics in the photographs.
I have a Fireboat that get up and run with just the prop in the water. Scale? No. But I still love doing it!!!
08-26-2009, 05:20 PM
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RE: Smoked motor - suitable replacement?
Thanks to everyone for your inputs!
A friend of mine gave me a size 400 motor (no specifications, no sticker/label) and a smaller prop (28mm diameter). Also, I added a relay, so that I can turn on/off the motor using the rc.
Result: the boat runs much faster and the motor doesn't smoke. However, the motor still gets so hot that you can't touch it, and after approx 10 runs it died.
I want the boat to go fast. I am impressed by the performance Cadmunkey obtained with a size 400 motor and a gearbox. Can anyone explain why the addition of the gearbox makes such a big difference in his case? Is there any reason why not to use a gearbox?
/Anders
A friend of mine gave me a size 400 motor (no specifications, no sticker/label) and a smaller prop (28mm diameter). Also, I added a relay, so that I can turn on/off the motor using the rc.
Result: the boat runs much faster and the motor doesn't smoke. However, the motor still gets so hot that you can't touch it, and after approx 10 runs it died.
I want the boat to go fast. I am impressed by the performance Cadmunkey obtained with a size 400 motor and a gearbox. Can anyone explain why the addition of the gearbox makes such a big difference in his case? Is there any reason why not to use a gearbox?
/Anders
08-27-2009, 04:22 PM
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RE: Smoked motor - suitable replacement?
ORIGINAL: anders_r_r
Is there any reason why not to use a gearbox?
Is there any reason why not to use a gearbox?
You can increase your output power and reduce the heat simply by putting on the 28 mm prop.
The maximum power you get on six volts is (0.7A + 25A) x 6.0/2 @ 9,000 rpm
To put it plainly,you want to get your rpm back up above 9,000 rpm at 6 volt or 10,800 rpm at 7,2 volt
Code:
Specification Nominal voltage 6V Operating voltage range 2.4-7.2V No-load rpm 18000 No-load current drain 0.7A Current drain at max. efficiency 4 A Current drain when stalled 25A Max. efficiency without gearbox 70% Length of case, excl. shaft 37.8mm Diameter 27.7mm Free shaft length 13.8mm Shaft diameter 2.3mm Part No: G3321
08-27-2009, 04:26 PM
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RE: Smoked motor - suitable replacement?
Can anyone explain why the addition of the gearbox makes such a big difference in his case? Is there any reason why not to use a gearbox?
When hooked up to a large diameter or a high pitch prop, electric motors can not spin as freely as they should. And electric motors in this situation tend to draw far too much current for the gage of the wire in their windings. This resembles a problem often encountered in electric motors called the "locked rotor" effect.
The locked rotor effect is often seen when a prop is unable to turn due to weeds or grass and the electronic speed control melts down. This is because the locked rotor caused the current draw to exceed the ESC's rating and the poor boater realized he either did not fuse the motor or installed too large of a fuse.
The gear is like a lever and you are multiplying the torque available. Naturally as in all things, you don't something for free and what you lose is RPMs. So if you simply gear down, you get fewer RPMs and you lose thrust. But you've also cut your current consumption. Now you have some spare amperage to play with.
To restore top end performance with fewer RPMs, you now want to push more water by using a more agressive prop (either increase pitch or increase the diameter). Then you will be taking advantage of the increased torque available from your gears.
It may seem is if you are back to where you started by not quite. What you have gained is efficiency. Once the motor is allowed to spin at a higher RPM, courtesy of the gearing, the motor draws a reasonable amount of current that in turn greatly reduces heat. And the big aggressive prop you need for high end performance is not longer a challenge for the motor to turn.
Gearing is great but is does take up valuable room in smaller boats and adds to the cost of the project.
Think about it this way. If you took a small motor and wanted to spin a 100 foot diameter prop, you expect the motor to either die trying or require gearing. While this example is highly exaggerated, you can tell that without gearing, the motor is going to get smoked. What your original prop did was to scale down the 100' prop to a size where the motor was able to hold out for a few minutes.
When hooked up to a large diameter or a high pitch prop, electric motors can not spin as freely as they should. And electric motors in this situation tend to draw far too much current for the gage of the wire in their windings. This resembles a problem often encountered in electric motors called the "locked rotor" effect.
The locked rotor effect is often seen when a prop is unable to turn due to weeds or grass and the electronic speed control melts down. This is because the locked rotor caused the current draw to exceed the ESC's rating and the poor boater realized he either did not fuse the motor or installed too large of a fuse.
The gear is like a lever and you are multiplying the torque available. Naturally as in all things, you don't something for free and what you lose is RPMs. So if you simply gear down, you get fewer RPMs and you lose thrust. But you've also cut your current consumption. Now you have some spare amperage to play with.
To restore top end performance with fewer RPMs, you now want to push more water by using a more agressive prop (either increase pitch or increase the diameter). Then you will be taking advantage of the increased torque available from your gears.
It may seem is if you are back to where you started by not quite. What you have gained is efficiency. Once the motor is allowed to spin at a higher RPM, courtesy of the gearing, the motor draws a reasonable amount of current that in turn greatly reduces heat. And the big aggressive prop you need for high end performance is not longer a challenge for the motor to turn.
Gearing is great but is does take up valuable room in smaller boats and adds to the cost of the project.
Think about it this way. If you took a small motor and wanted to spin a 100 foot diameter prop, you expect the motor to either die trying or require gearing. While this example is highly exaggerated, you can tell that without gearing, the motor is going to get smoked. What your original prop did was to scale down the 100' prop to a size where the motor was able to hold out for a few minutes.
