Model Boat Mayhem
Technical, Techniques, Hints, and Tips => DC Motors (Brushed) and Speed Controllers => Topic started by: npomeroy on January 27, 2021, 02:18:28 am
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Motor choice can be a bit baffling especially as motors are often described by brand and number and the suppliers may provide limited data.
I'm looking at an MFA 540LN 5-pole motor (pair) for a 1/32 scale Damen 1907 tug of 5 kg displacement with 50mm props. This motor's data shows a no-load speed of 6000 rpm at 12v and 250 g-cm torque. This sounds ideal specs, provided the motor has enough torque to turn that sized prop at appropriate rpm (which I understand to be 2 - 3000 rpm). (Elsewhere I suggested 540-45T crawler motor and was told would get too hot trying to spin a 50mm prop.)
It seems to me that the torque required to spin a given size (and pitch, blade no. etc) propeller in still water i.e. doing a static pull, may be known. It would be a torque-rpm curve. While due to the number of variables it's probably too much to expect full published data, perhaps someone has experience with a motor of "x" max torque in its specs, and they find it is "too little" or "plenty" for a similar application.
It would take some of the guesswork out of motor selection if you could base it on published specifications. I do a bit of irrigation work and water pumps for instance have flow-pressure charts that allow you to match one to the job. The trouble is of course that with pumps the propeller is integral with the motor whereas we select motors and props separately.
Cheers
Nelson
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Firstly let me comment on the 50% load speed v free running speed. I would say 50% is as low as I would ever want to go. At anything less than 50% the motor is increasingly inefficient and is actually producing less power (or so I understand). I aim for well above 50%.
Props v Motors.
I have asked this question several times and there is not much interest in the scale model boat world. I can give you the exact data for pretty well any brushless motor and any prop in the model aero world but nothing similar for model boats. The argument seems to be that in scale model boats weight is not such a penalty and thus you always fit a bigger motor and battery than you need. In this world efficiency is not very valuable.
This combined with experience and a tendency to use a limited range of motors seems to allow a consensus. The lack of real data doesn't impress me but short of buying an awful lot of propellers and motors to test them there is not much you can do. Notice how infrequently rpm and amps/watts are quoted when motor /prop combinations are discussed and how infrequently any real detail is given about any aspect of the power train apart from the battery.
Having said all that it is me that is out of line with almost everybody else and they produce some beautiful models that are way better than anything that I can achieve with powertrains that work for them.
I hope that someone who has used a 540LN with 50mm props on 12v can report real results. My back of the fag packet calculation suggests 3.5-4.0 amps. We will see.
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Nelson,
This has always been a tricky subject as there are so many variables and unknowns. Back in the 1950s modelling magazines did publish things like torque curves for motors but the general public has become rather less scientifically minded since. (or less technically educated!)
I have been working on an article for Model Boats magazine on the subject of selecting motors and props (and batteries) but it is aimed at the less experienced modeller and beginners and discusses basic principles and testing techniques followed by a selection of 'setups that work' and could be used as benchmarks for broadly similar models. It is very much an empirical approach but it is what a lot of people need judging my the many enquires received by the magazine and on the internet forums.
Colin
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Colin
Isn't your article shown for the next issue of Model Boats?
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Yes, that's the one. It has been split into two parts. It is actually based on the article I did for the 2011 Special issue and has been updated to include more on brushless motors and LiPos with some input from the late Paul Freshney. There are additional typical model setups as well.
The Special issue was not included in subscriptions and had a smaller circulation than the regular issues. Recently the new editor passed on requests she was getting for more information on the subject, particularly from people returning to the hobby and new modellers in the current Covid situation. And of course both on here and on the MB website we get lots of queries of the 'what motors and props do I need in my xxxxx boat?' People generally don't want lots of technical info, they just want something that will work OK and won't be too complicated to maintain.
I've also tried to explain the difference between volts, amps and watts! It's basic stuff but hopefully people will find it helpful. Dave Milborn vetted the draft and approved it.
Colin
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Many if not most brushless motors tend to have a suitable aero prop diameter range specified. I find as a rough guide that if you divide that number by five it tends to get you in the right ballpark for a marine prop.
So a 10" airscrew will give you a 2" marine screw. Naturally for some subjects performance may be more spirited than you wish, but calculation of speed for a given prop size is well documented, and can be worked out with reasonable accuracy in advance.
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The big problem with water props is the huge variety of design.
It isn't just diameter and number of blades and pitch, although three parameters are enough to create plenty of confusion. You also have the profile of the blade and its shape and width. With water being some 1700 times as dense as air, very small variations in any one of the design details make for big differences in performance.
For example, the kit prop on my Lindberg tug was the right number of blades, the right diameter and the right pitch. The blades were thick, chunky and blunt edged. It was better at stirring water and pushing sideways than giving propulsion. A few hours with a sanding stick gave blades with a sharp entry and exit, and the tug performed as it should.
In the elder days, motors were sold as "suitable for boats of length x-y". A very limited variety of motors available, same with props, but the models seemed to work. Mostly.
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Hi, it is an interesting subject however this is an area where there are multiple solutions.
I agree motor running speed should not be that low. If you know the stall current, a quite accurate prediction of most efficient running speed is 20% of this figure. So for a 20 amp stall then 4 amps will be a good load for the motor the speed needs to fit in with the load of the prop.
The problem is that there are 4 variables, motor, battery, esc, and propeller size. Most of us have settled for a particular battery size say 6 cell NiMh and the appropriate charger, this then determines the esc parameters. so the only variables left are motor and prop.
There is another aspect and that is your model will only spend 1% of it's time in the water, so is the above all that important?
Nailing your flag to the mast with just one motor could created an unnecessary problem for yourself.
There s a further school of thought that you should not run a prop whose diameter is greater than that of the motor.
My choice when doing this for a model is what prop looks right. Then find a motor to suit I am a bit spoilt for choice. In your case I would look for a pair of Robbe Navy electric motors. I am planning to put the pair I have to each drive a 4 blade 50mm prop in a Kort nozzle running on 7.2 volts All in a Mississippi Towboat 40 inches loa and about 5 kgrms disp.
If I remember right under load it was 3.5 amps at full speed, having 40 watts of power available fills my criteria for being able to stop quickly.
I have one small cargo boat that I control the speed just on the throttle trim control, for me making the right wave pattern makes the boat look right on the water.
Good Luck
Roy
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Thanks for the various comments. One of my issues is down here in the antipodes the local choice is smaller although I regularly import stuff I need. But that has slowed with the pandemic. So a technical description allows an informed choice among what is available,
... In your case I would look for a pair of Robbe Navy electric motors.
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Did you mean this one?
https://www.robbe.com/en/AIRPLANES/ELECTRIC-POWERPLANTS/Motors/ROBBE-RO-POWER-TORQUE-3534-500-K-V-NAVY/5821NAVY
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Given the situation in the UK at the moment I'd give an arm and a leg to be back in Hawkes Bay!
Colin
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Given the situation in the UK at the moment I'd give an arm and a leg to be back in Hawkes Bay!
Colin
Were you just visiting? We're getting tired of 30 degree days lately. Big fuss a couple of days ago - ONE positive case was found outside the managed isolation system. But it doesn't seem to have spread so far.
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Toured both islands back in Feb/March 2013, probably the best holiday we've had. Good weather too but not 30 degrees!
Colin
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Hi npomeroy, I think the motor you show is a brushless one. The Navy motor is a slow revving brushed one.
Just checked the Dumas model boat website and their motor for the American Beauty is £115 each, but they always were expensive.
A 550 size motor with a 2.5 : 1 gear reduction would suit your requirements. I had something similar driving a 50mm prop on 12 volts and that ran at about 2500 rpm with 30 watts power consumption. I will come back to you.
Regards
Roy
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Nelson,
A brushed motor of the "500" size can directly drive a 50 mm diameter propeller. I know this and have done it successfully a few times. You do however need to match the motor, battery and propeller.
If I were you, I'd set the model up so that "500" motor types can be easily installed and removed, then test a few. Assuming that the propellers you plan to use do not have a massive pitch, then something like a 70-80 turn Rock-crawler type might be a good starting point.
Also, be prepared to change the battery voltage, something that is grossly overloaded on 12 Volts might be perfect on 6 Volts (Yes, the voice of experience!).
But, do search around before buying anything as some motors can be horribly expensive but with no obvious gain for our models.
Also try to keep the loaded motor speed around 75% of its free-running speed (i.e. not connected to anything). This will keep it happy in the good efficiency region and prevent it from becoming a very inefficient electrical heater inside your model.
Glynn Guest
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Hi, I checked up on my Robbe motors they are Starmax 48 navy 6 - 12 volts 0.7 - 9 amps.
Do not see them on the Robbe web site so may no longer be available.
I noted a Forum comment that the MFA gearbox motors might be a bit noisy, I have not used them so cannot judge.
Good luck with your decision.
Roy
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Today I did some testing with the 45-turn 540 crawler motor. I bought a 48mm clear plastic prop for initial testing (too stingy to get the brass ones yet), and mounted motor+shaft+prop on a wooden strip with the end submerged in a tub. I'm powering it with a 12v lipo. It is way too fast on full power, but throttled way back (the voltage delivered by the ESC was around 3v) it draws around 4A , stirs the water with ample thrust, and is just below cavitation speed. The motor gets noticeably warm to touch after several minutes but I wouldn't say it's overheating to concerning levels.
These motors were only US$17 plus $6 postage from Amain in California and I'm thinking the 80T version https://www.amainhobbies.com/yeah-racing-hackmoto-v2-540-brushed-motor-80t-yea-mt-0017/p529875 (https://www.amainhobbies.com/yeah-racing-hackmoto-v2-540-brushed-motor-80t-yea-mt-0017/p529875) may be just the ticket.
Edit: As Glynn wrote above "Assuming that the propellers you plan to use do not have a massive pitch, then something like a 70-80 turn Rock-crawler type might be a good starting point."
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It would take some of the guesswork out of motor selection if you could base it on published specifications...
As a valued customer of theirs, they might at least tell you if it is the same motor in different turn options.
I think this is the case here, which means they all suit the same prop at the same torque & rpm at a voltage proportional to the number of turns.
Google MABUCHI RS-555-3255 (https://www.google.com/search?&q=MABUCHI+RS-555-3255)
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As a valued customer of theirs, they might at least tell you if it is the same motor in different turn options.
I think this is the case here, which means they all suit the same prop at the same torque & rpm at a voltage proportional to the number of turns.
Google MABUCHI RS-555-3255 (https://www.google.com/search?&q=MABUCHI+RS-555-3255)
Do you want to elaborate? I am aware that the 45T and 80T "Hackmoto" branded motors vary only in the windings. And that more turns results in higher torque and lower rpm for a given voltage.
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Do you want to elaborate? I am aware that the 45T and 80T "Hackmoto" branded motors vary only in the windings. And that more turns results in higher torque and lower rpm for a given voltage.
Unfortunately that is a common misconception and isn't correct. :(( :((
When you double the number of turns and halve the cross sectional area of wire it results in the same copper weight with four times the impedance.
If you then double the voltage on the higher turn wind the current is half but the product of (amps x turns) is the same so the magnetic field and mechanical force is the same. You'd see that if you could get a 90 turn wind.
I'm not capable of working with insufficient data any more than anyone else.
With enough correct data I can crunch the numbers (and print here on Mayhem and compare for you) but it means I can quickly spot a motor with a higher (torque/amp x turns) ratio which drives a bigger propeller.
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Unfortunately that is a common misconception and isn't correct. :(( :((
When you double the number of turns and halve the cross sectional area of wire it results in the same copper weight with four times the impedance.
If you then double the voltage on the higher turn wind the current is half but the product of (amps x turns) is the same so the magnetic field and mechanical force is the same. You'd see that if you could get a 90 turn wind.
I'm not capable of working with insufficient data any more than anyone else.
With enough correct data I can crunch the numbers (and print here on Mayhem and compare for you) but it means I can quickly spot a motor with a higher (torque/amp x turns) ratio which drives a bigger propeller.
Sorry but I find I find that obscure. Published motor data clearly shows that motors (of the same physical size) with more turns run at lower rpm, and I understand, higher torque. Are you saying this is wrong? Are you saying that replacing a 540-45T motor with a 540-80T motor is not advantageous in my application?
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Re post 15, I would not run a motor with the amps 4 and voltage is 3. You are getting good technical information elsewhere. If you think about how the losses in a motor are calculated then using I squared times R (= watts) will show you that the losses across the brushes are too high.
The load is too high and for that motor, I would suggest that a 2 or 3 to 1 gear reduction or a smaller prop load i.e. reduced pitch or reduced diameter.
I do not think that buying a cheap prop, probably of different pitch, from the one you will eventually use is going to help you solve the problem.
It is best to start from a fixed point i.e. prop, motor, esc or battery voltage and work your way forward. I like big props running slowly 1 -2 thousand rpm they are very efficient.
I have a smaller cargo boat which travels just at the right speed and you can watch the prop go round.
For your boat I would allow just 20 watts per motor 7volts at 3 amps max or 12 volts at 1.5 volts will give you a nice cool motor and a good running time. You do not have to be at full throttle all the time.
If any item in the drive train gets hot then the heat is generated by battery power. So if something gets hot you have got wasted power that needs correcting.
Good luck, just do not get too over complicated!
Roy
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Sorry but I find I find that obscure. Published motor data clearly shows that motors (of the same physical size) with more turns run at lower rpm, and I understand, higher torque. Are you saying this is wrong? Are you saying that replacing a 540-45T motor with a 540-80T motor is not advantageous in my application?
No it isn't advantageous and you would see exactly this with the pair:-
If you were to run the 80 turn motor at the same voltage the torque would be lower.
It would run the same load at lower rpm only because the current and the torque is reduced. ( lower not higher)
By keeping the voltage in proportion to the turn number in the motor series you get the same power, rpm and torque with the 45T and 80T.
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The motor that you linked is a generic Chinese motor that is available with lots of different brand names. Don't let that put you off as they are good motors.
The good bit is that you don't need to go to the USA to get one.
Go to Amazon and/or ebay and search for "80T motor". You should get lots of hits for this motor. The obvious giveaway is all the colours around the brush gear.
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No it isn't advantageous and you would see exactly this with the pair:-
If you were to run the 80 turn motor at the same voltage the torque would be lower.
It would run the same load at lower rpm only because the current and the torque is reduced. ( lower not higher)
By keeping the voltage in proportion to the turn number in the motor series you get the same power, rpm and torque with the 45T and 80T.
Then I wonder why higher turn motors are quoted as "high torque". And why have various advisors suggested a high T-number? I understand the total power must be lower because the R is higher and the I is less (at unloaded running). My 45T motor is way too powerful if I allow anything like full voltage (judging by the speed and volume of water displaced). I suspect I only need a fraction of that power. The trouble is even if I reduce the voltage to slow it down, it draws a fair amount of current. If a higher turn motor is nearer to its unloaded rpm with my prop then I would think it would run more efficiently, or more to to the point, not heat up so much. I understand (now, on reflection and further reading) that the stall torque will be higher in the low-turn motor, but I'm interested in the torque at the rpm I need.
Edit - Also the load on a motor is proportional to the prop rpm. Low rpm = low mechanical load. Discussions about what size motor for a given sized prop must take into account whether it will be fast or slow revving.
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The motor that you linked is a generic Chinese motor that is available with lots of different brand names. Don't let that put you off as they are good motors.
The good bit is that you don't need to go to the USA to get one.
Go to Amazon and/or ebay and search for "80T motor". You should get lots of hits for this motor. The obvious giveaway is all the colours around the brush gear.
Yes but Amazon/ebay are no closer than USA when you live in New Zealand.
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Then I wonder why higher turn motors are quoted as "high torque". And why have various advisors suggested a high T-number? I understand the total power must be lower because the R is higher and the I is less (at unloaded running). My 45T motor is way too powerful if I allow anything like full voltage (judging by the speed and volume of water displaced). I suspect I only need a fraction of that power. The trouble is even if I reduce the voltage to slow it down, it draws a fair amount of current. If a higher turn motor is nearer to its unloaded rpm with my prop then I would think it would run more efficiently, or more to to the point, not heat up so much. I understand (now, on reflection and further reading) that the stall torque will be higher in the low-turn motor, but I'm interested in the torque at the rpm I need.
Yes. :-)) Your observations tally
Can you rotate the brush gear? That would help.
Stall torque is higher in its lower turn version at the same voltage but it is the same when the voltage is kept in in proportion to turns.
Some high turn motors in the exact same can size are better but not because a change in turns.
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Don't they have Amazon in New Zealand?
Lots of ebay sellers ship from China to everybody.
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A higher turn motor will produce more torque, but it will only do so at a higher voltage. At the higher voltage, because of its lower KV, it turns at the same speed, but produces more power, which is seen as torque.
Just dropping a high voltage motor in as a replacement for a low voltage motor will give lower rpm, but will not give more torque with the same battery. It will run cooler because it is not dissipating as much power, but at the same time it will be offering less power to the shaft.
It's a sound engineering principle to remember that what comes out of a system, must have gone in. What you get out of a motor, depending on its design and how it is used, is turning force, rpm and heat. All of this comes from the charge in the battery. A good combination gives the rpm wanted with the torque to do the job with the minimum of waste heat. Finding a motors comfort zone does not equate to looking at a data sheet and going for "max efficiency". Running a motor in that condition usually results in a short lived motor. Its the point where practice trumps theory every time.
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I repeat that the higher turn, 80T in this example,will produce less torque and that the 45T motor does. It will be lower until the voltage to the 80T motor exceeds voltage of the 45T motor by the ratio 80/45 or by 1.78, rounded up.
More turns and a lower kv does not help this prop overload. To run the test prop these motors need gears or a change to the timing, and if the end stock can be rotated. Even if the back of the motor is fixed, it may show a different kV in the reverse rotation.
I've suggested a 540 sized motor that is in the ball park. It is nearer than the 540LN
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I've suggested a 540 sized motor that is in the ball park. It is nearer than the 540LN
The motor you suggested (Mabuchi 555PH-3255) has very similar specs to the 540LN in terms of rpm @ 12v. I think both are 5-pole. I can get the 540LN locally https://nz.rs-online.com/web/p/dc-motors/8347679/ datasheet: https://docs.rs-online.com/cbd9/A700000007082505.pdf
Is there a good reason to prefer the 555-3255?
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Greater torque at broadly equivalent RPM, I believe a bit over a third more. That'll help keep the prop spinning and prevent the motor bogging down.
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Greater torque at broadly equivalent RPM, I believe a bit over a third more. That'll help keep the prop spinning and prevent the motor bogging down.
OK. Good enough for me. I've ordered a pair of the RS-555PH-3255 over ebay from California. I already have a pair of HobbyWing 80A(!) ESC's. Seemed to work fine with the 540-45T motor and I've programmed my Tx to give forward/reverse with switchable rudder mixing.
Cheers
Nelson
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Hi anyone following this thread and wondering what all the numbers mean then a quick look at this website may help.
Roy
https://www.mabuchi-motor.com/product/knowledge/classification/
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Hi anyone following this thread and wondering what all the numbers mean then a quick look at this website may help.
Roy
https://www.mabuchi-motor.com/product/knowledge/classification/ (https://www.mabuchi-motor.com/product/knowledge/classification/)
Wonderful. Thanks.
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Excuse me resuming stirring this topic...
What IS IT about number of turns that makes higher turn motors recommended for applications that operate at low revs?
Is it all about kV, i.e. the (unloaded) rpm w.r.t. voltage?
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Excuse me resuming stirring this topic...
What IS IT about number of turns that makes higher turn motors recommended for applications that operate at low revs?
Is it all about kV, i.e. the (unloaded) rpm w.r.t. voltage?
No excuses are due since it is a good question.
If you examine a servo motor you find it is wound with more turns than the equivalent sold as a propulsion motor.Rock crawlers, like servo motors operate at low revs and stalled while energised ( albeit with reduced throttle). That's where the name comes from.Many turns of smaller diameter wire effectively makes a higher voltage version of the motor which is what both applications need.
Both have a large ratio reduction gearbox.
To help with the mental picture of torque:- Magnetic strength is proportional to amp x turns.
You could wind more turns on a bobbin of wire to increase the magnetic strength of the core, limited by core saturation.
There is no space to do that on a motor.
If you wind more turns of a smaller diameter wire you have to increase the voltage proportionally for the same rpm, torque and power as before.
At the same voltage there are more turns but the amps (and amp x turns ) falls.
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So the motors - Mabuchi RS-555PH-3255 you recommended have arrived, and seem to give ample power on a brass 2" prop drawing less than 1A. They are very directional, i.e. weak in "reverse" as driven by my allegedly fwd/rev ESC (https://www.hobbyhangar.co.nz/hobbywing-30112750-quicrun-wp-crawler-brushed-program-card). But if you manually swap the polarity they are strong in the reverse direction. So is this likely to be an issue with the ESC design? You'd think with an H-bridge type circuit you could get equal power in both directions. The throttle channels in the Tx are 0 to 100%, not -100 to 0 to + 100% but I don't see that should matter.
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Looking a bit further it seems Rock crawler ESC's typically have a lower reverse than forward output. I didn't expect this. I'm sure some model tanks can rotate on their tracks and you'd think that would require equal forward and reverse power. Maybe the ones specific for boats are like this too? Any ideas?
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Read the instructions that come with the esc.
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Read the instructions that come with the esc.
I did this. There is a programming box that allows different power levels to be set forward and reverse. When both are 100% the reverse is still MUCH weaker. The max variation that can be set is 25% fwd and 100% reverse. This is still very weak reverse comparatively. A google search in crawler forums suggests it may be common for these ESCs to have weaker reverse. Please let me know if you you suspect I have overlooked some other facet.
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Is this the ESC? https://www.applianceelectronics.co.uk/viewproduct/15971/hobbywing-quicrun-hw30112750-1080-80amp-wp-brushed-crawler-esc
The problem with crawler motor ESCs is the brake feature which on a boat needs to be switched off. Some early ESCs did feature reduced reverse output, but I never found that arrangement in any way satisfactory. It was probably done for reasons of economy in manufacture, and because "they" had to buy a truckful of the components to get the right price, never changed later when better parts became available because the skip with the original parts in still had lots left over. If the basic ESC is designed to give 25% max in reverse, it doesn't matter how the parameters are fiddled, 100% of 25% is still 25%. Proper marine ESCs are symmetrical in output - they give as much in reverse as forward.
Noted that in the link, the ESC is "Programmed via". Via what is unstated.
Weak reverse (which is your brakes when you need to stop) might be made worse by the design of the prop. Depending on the shape of the blades, it might not be able to grip and move as much water in reverse as forward. Most land vehicles do tend to be slower in reverse, apart from the WW2 Italian tanks of legend.
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So the motors - Mabuchi RS-555PH-3255 you recommended have arrived, and seem to give ample power on a brass 2" prop drawing less than 1A. ......................
Is that on 12v?
How many blades on the prop?
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...It seems to me that the torque required to spin a given size (and pitch, blade no. etc) propeller in still water i.e. doing a static pull, may be known. It would be a torque-rpm curve. While due to the number of variables it's probably too much to expect full published data, perhaps someone has experience with a motor of "x" max torque in its specs, and they find it is "too little" or "plenty" for a similar application.
It would take some of the guesswork out of motor selection if you could base it on published specifications...
Published specifications for RS-555Px-3255
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Either your doing something wrong with the programming, or you have a defective esc. That model of esc has an option for full 100% reverse. Default setting from factor, reverse is set to 50%. The programming card is optional for ease of use- you don't need it, you can set the esc up with standard set button provided.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjX1_a--5bvAhWMTcAKHQFYDOcQFjAAegQIAxAD&url=https%3A%2F%2Fwww.hobbywing.com%2Fproducts%2Fenpdf%2FQUICRUNWPCRAWLERBRUSHED.pdf&usg=AOvVaw3vs-L3a0dOOo2LAGp4EV4w
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Is this the ESC? https://www.applianceelectronics.co.uk/viewproduct/15971/hobbywing-quicrun-hw30112750-1080-80amp-wp-brushed-crawler-esc (https://www.applianceelectronics.co.uk/viewproduct/15971/hobbywing-quicrun-hw30112750-1080-80amp-wp-brushed-crawler-esc)
The problem with crawler motor ESCs is the brake feature which on a boat needs to be switched off. Some early ESCs did feature reduced reverse output, but I never found that arrangement in any way satisfactory. It was probably done for reasons of economy in manufacture, and because "they" had to buy a truckful of the components to get the right price, never changed later when better parts became available because the skip with the original parts in still had lots left over. If the basic ESC is designed to give 25% max in reverse, it doesn't matter how the parameters are fiddled, 100% of 25% is still 25%. Proper marine ESCs are symmetrical in output - they give as much in reverse as forward.
Noted that in the link, the ESC is "Programmed via". Via what is unstated.
Weak reverse (which is your brakes when you need to stop) might be made worse by the design of the prop. Depending on the shape of the blades, it might not be able to grip and move as much water in reverse as forward. Most land vehicles do tend to be slower in reverse, apart from the WW2 Italian tanks of legend.
Yes that is the ESC. The brake feature is turned off. It is programmed via a "box" which I have. I understand that props are usually shaped to be directional and reverse will give less thrust but the rpm difference is so great it eclipses this effect.
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Either your doing something wrong with the programming, or you have a defective esc. That model of esc has an option for full 100% reverse. Default setting from factor, reverse is set to 50%. The programming card is optional for ease of use- you don't need it, you can set the esc up with standard set button provided.
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjX1_a--5bvAhWMTcAKHQFYDOcQFjAAegQIAxAD&url=https%3A%2F%2Fwww.hobbywing.com%2Fproducts%2Fenpdf%2FQUICRUNWPCRAWLERBRUSHED.pdf&usg=AOvVaw3vs-L3a0dOOo2LAGp4EV4w (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjX1_a--5bvAhWMTcAKHQFYDOcQFjAAegQIAxAD&url=https%3A%2F%2Fwww.hobbywing.com%2Fproducts%2Fenpdf%2FQUICRUNWPCRAWLERBRUSHED.pdf&usg=AOvVaw3vs-L3a0dOOo2LAGp4EV4w)
Yes you can set reverse and forwards between 25 and 100% in 3 steps but I'm talking about at the 100% setting. I have the programming box.
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In that case it sounds like something may be wrong. Always difficult to assess these things by internet proxy.
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:embarrassed: Duh. OK it's fixed now. The ESC factory default was slow reverse, fast fwd but each was adjustable. I thought I'd changed all combinations but hadn't pressed the correct button to save all my changed settings. So even though it is a crawler ESC it in fact gives pretty symmetrical fwd/rev power.