Here is a list of all the postings 60watt has made in our forums. Click on a thread name to jump to the thread.
|Thread: Electric motor temperature sensor|
|No I did not refer to Mark Beard.|
I am sure your Mark will be able to get Graupner figures to tally up nicely even if he adopts crudest measures to account for things like temperature and magnetic properties.
He will be able to confirm the 900 that the efficiency at maximum power is a tinkle over 40% and not the KISS version of 50%.The reason down the very first point I made in this now tired and dog-eared thread....significant iron losses in this motor which is what Barzo is getting with his small props.
I also did tests of many d.c. motors and found the results to match the manufacturer data.That is why I implicitly trust results from MFA,Graupner etc.
Joe Public might use a DVM reading of the motor free running and with a locked rotor and think he has got Mabuchi's Io and Istall. figure.That does not provide meaningful information and is why it is not used.
Telstar I designed cores and windings all day.I know what I am talking about even if you don't.I don't need it misinterpreted.
Edited By 60watt on 08/10/2011 01:31:07
Barzo,I'll repeat my conclusion that, if you stick with that motor,you must increase the prop until you have between 1/4 and 1/2 the stall current and then alter the voltage.
If iron loss and copper loss is so much smoke then I practiced the black arts when all day long I designed windings and cores.I can do this in my sleep.
If you remove a flux ring you do the opposite of adding a pair of Neodym magnets to boost the field of the motor magnets.It makes the no load speed increase,it raises the peak of the efficiency curve and shifts it to the left.It then suits a smaller prop.You could do that but it would only nudge you in the right direction.
You will have to ask Mark the source of his own data.I am using the Graupner data and I can make all their figures add up.As I said in my last post,the key points that make the graphs are obtained graphically.
First published data given was they were different motors and hint from Dave was not to run the Ebay vendor(Graupner ones) above 12 volts.Modelboatmayhem posts recently state they were exactly the same motors from the same source.That I believe.
See the Mabuchi graph.
Whatever the voltage the ideal prop should cause a drain of between 1/4 and 1/2 the stall figure.That should be the peak efficiency and peak power points for this one.
At 12v the target area is 13 to 25 amp
At 6v it is 6.5 to 12 amp
1. How does the iron copper ratio affect the heat generated.
To get torque you need a strong magnetic field.
You need iron to make a strong magnetic field in a confined space
That makes that particular motor inefficient if you don't use a substantial prop.
2. What is a torque ring?
Sheet metal sleeve around the outside which changes the torque/speed characteristic.
3. Given that the particular model is supposed to go quick, how does reducing the motor voltage help it go fast?
It does not.
4. My intuition tells me that by increasing the prop. size it throws more load on the motor and it will get hotter?
It will but you have to get the right prop first.
5. If I were to use 6volts at 7 amps - 42 watts, I don't think the boat would get up onto the plane?
No but I am suggesting that you could do your prop experiments at 6 volts.
What current measurements do you get with your props at full throttle?
6. The amount of energy the boat needs to reach the speeds of which it is capable, is approx. 700 watts. Even using compensated, Froude's scaling rules, it requires 400 watts to match the scale speeds.
You can only get Pin x Vin x Efficiency out of the motor.
1. 12 volt Motor Data from a vendor (A stall current of 50 amp is missing).
Your blue peak is around 6-7 amp @ 6 v,around 13 amp @ 12 v and 22 amp @ 20 v
Red peak is a tiny fraction over half the stall current at each voltage.
In reality that motor has strong core magnetics so its key data points are derived graphically.
P.S. Just try bigger and not smaller props.that's all!
Edited By 60watt on 07/10/2011 12:08:27
Barzo you are now heading in the wrong direction by reducing the prop size.
It is all down to the large ratio of iron to copper.There is a big iron core,strong magnets and a narrow air gap which gives the motor its large torque in the small size.The trade off is high iron loss and low peak efficiency.
Removing the torque ring would only nudge it in the right direction.You want to reduce the voltage and use a much larger prop or choose a motor with a higher no load RPM.
A test on six volts you should see the best matched prop draw 6 to 7 amps flat out.
|Thread: Advice needed for a beginner|
It does not look like you opened your message box with the number for Model Flags.
It contains the phone number and the instructions of the reversing esc. You have to log in and Click on "My Account" >"My Messages".
Little Models of Grantham have been trading flags,boat fittings and electrics since before the days of the internet.Mike is still trading under the banner Model Flags but does not have a website.I'll send the Model Flags telephone number to your message box.
Try looking at the local events that Mobile Marine sponsors or attends.
|Thread: Caldercraft "Peggy" electric motor options?|
...and you can use a six volt battery
...and some speed controls allow you to turn down the maximum power,though some don't.
Edited By 60watt on 03/03/2011 19:53:54
Here is one advertised Graupner 900 equivalent on Ebay
When that item expires look for an item in his Ebay shop
A walloping great 1000mNm of stall torque on 12v
Body: 52mm dia 85mm long
Shaft: single end 5.0mm dia ballraced
Commutator: 12 pole, low noise
Voltage: 12v DC
No load RPM: 6700 1.2A
Max efficiency: 5250rpm, 1500g cm, 80w, 12A, efficiency 55%
Max power: 3200rpm, 3500g cm, 115w, 24A
|Thread: Receiver Battery|
He was referring to either the thermal (175 c) or the current cutout mechanism within the BEC.
|Thread: Submarine hardware/electronics|
I just want someone to figure out how to measure how much there is above the waterline and come back with a figure.
David,did you follow Ashley Needham's point about how he would do things differently if he did his Oberon over again?http://www.modelboats.co.uk/forums/postings.asp?th=39666
If the Gato superstructure plastic is not too thick you might get away without a tank.
It would make life simpler.
Edited By 60watt on 12/08/2010 21:04:45
|Thread: Adverts on posted pages.|
|Foggy,if it is of any comfort,I saw such a post recently.|
Edited By 60watt on 04/08/2010 16:49:31
The question has come up before and Colin Bishop has answered in his own fashion.
I prefer the poster broke the page by posting a long hyperlink rather than hyperlinked text.
View > Page Source in Firefox
Page > view source in Internet Explorer
or give Colin Bishop a shout to edit the post.
|Thread: How do I make my battery last longer?|
Possibly the very same mfacomodrill one.
£1 will cover a vero circuit consisting of a 10% to 90% mark/space speed control based on a common 555 timer circuit beefed up up with a power transistor and diodes.
What information do you have on the prop,motor and battery?
If you get 2/3 minutes then your current drain is about 20-30 times the battery amp hour figure. I suspect using a smaller prop will increase speed and duration.
|Thread: Pump for bow thruster - advice wanted.|
If the reversing valve has a high operating voltage then fully proportional operation will not be possible.
I've just used a pump for a fire monitor so I am not sure which is best.I would have thought most suitable pump would be low pressure high flow rate used in caravan plumbing.Just a notion.
If you already use a servo+microswitch to engage the pump then use the servo to pinch silicone tubing,left or right.
Colin,you say bow thruster but if the battery and centre of gravity happens to be up front and you want steering -not docking,site the exit as far away from the COG
|Thread: battery life|
Kevin,whether you are trying to get more power,more efficiency or longer duration,the job is made easier if you understand the science.
The factors that determine current for a given motor are voltage and load torque (prop size,pitch)
Here is a Flash demo from Mabuchi
|Thread: Problems with electric drive|
The value (10,000 uF ) suggested by Mtronics was not a mistake and has the same remedial effect as in a particular auto application.See Maplin A07GU
The suggestion would have been made on incomplete or erroneous information.
Your boat,on the other hand, could do with ferrite suppression(see picture) on your motor cables and connecting the motor case to the battery -ve.For safety's sake I would use a 22 ohm resistor to make the link.
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