Aeronautic13

I am designing a small boat for a racing project, so my main goal is to maximize the speed of the boat over a short period of time (roughly 30 seconds). Since this is the case, I desire to run the motor continuously at maximum speed until the boat reaches the finish line. I do not need to vary the speed below maximum, and the boat will not actually be remote controlled.

In this scenario, do I actually need an ESC to interface between the motor and the battery?
In other words, does the ESC do more than just regulate the speed?

Thank you!

Rafael23cc

My Feedback: (6)

I'm not an expert in boats, nor an expert in electric powered RC systems. I do recall, before the brushless motors came about, visiting a local RC dragstrip. In there I found that most dragsters had the battery hooked up directly to a BRUSHED motor with just a push button of the appropriate amperage to control the on-off of the motor. This may be the ticket you are looking for.

Rafael

Aeronautic13

My understanding is that brushed motors are less efficient than brushless motors. Since speed is my main goal, I figured brushless would be the way to go. However, since cost is a limiting factor, I have to consider the trade-off between speed and price.

Perhaps someone experienced in finding the best components for a given price range could help out. Given a budget of $50 for the motor and controls, which would be more powerful: a brushed motor, or a brushless motor with ESC and something to run the ESC input (since I won't be using a receiver)?

Any comments would be much appreciated. Thanks!

mfr02

Brushed motors can be used direct off the battery. The brushes and commutator do the technical job of putting the power into the right places at the right time.
Brushless motors are only half of the deal, they need something to distribute the power to the three connections in the right order at the right time. The device that does that is a brushless ESC. No doubt that with a lot of effort you could make a device that would do the job, but the simplest way is to use an ESC and a servo tester to supply the control signal for the ESC.

Aeronautic13

That makes sense. So would a brushless motor with ESC and servo tester be more powerful than a brushed motor at a $50 price point? Efficiency and durability is not particularly important to me as it will only be run for about 30 seconds at a time and for probably 10 or 15 runs total.

Aeronautic13

Actually, I just decided to go ahead and use a brushless motor with an ESC and a servo tester. Do you know if you can run a servo tester, like this one, off a 5V battery?

fly24-7

The input rating of that servo tester is 4.8-6V. So yes, 5V will power it. Also, brushless motors require speed controllers as they energize the motor coils in a sequence to create rotation.

rgburrill

Brushed would be cheaper. Very high current ESCs are expensive.

kmeyers

I think you are going down the right path. The market place is brushless and ESC's (best bang for buck).

500 watts (2/3' of a horse power) should get you going pretty good at your price point.

mfr02

The servo tester wants 5 volts as does the input side of the ESC. If the ESC contains a BEC, no problem. If t doesn't, you need either a separate BEC or a separate 4.8v battery to power the servo tester AND the input/control part of the ESC.
Catching it between runs could be a bit thrilling if it works as well as you hope. Gloves are suggested. Free running boats can be a lot of fun, but persuading them to run straight is a sport in itself, allowing for sidewind just an added interest.

flyinwalenda

My Feedback: (5)

A brushless motor runs on 3-phase AC power converted and regulated by an ESC. A brushed 540 type motor can run directly off of DC power. If you install a brushless motor and you use a cheap ESC that is not waterproof then it will fail when water gets inside the hull and it gets wet. A brushed motor hooked directly to a battery can get wet and will run fine under water.....just dry and oil the bearings afterward. In fact, that is how you properly break-in a brushed motor. Something to think about.

RSEA

I have a 1989 vintage RS-540 Motor, NOS sealed in its plastic bag. It just has a label that says RS-540 32406710 on it. I assume the specs on this motor are identical to the current Mabuchi RS-540-SH motor. Based on the kit my motor came with, it is probably the 7.2V nominal voltage version and not the 9.6V version. The kit refers to the motor as an RS-540-S. The motor itself just says RS-540.

Are you saying that is the best way to break in the brushes, is to run the motor, with no load, while completely submerged in water (distilled or tap water)? How do you properly dry the motor afterwards? I would be worried about rust developing inside it after its submarine like break in.. How do you oil this motor? I don't see a way to get inside the motor casing, or to take it apart..

RSEA

Since the original poster did ask about the not utilizing an ESC at all. I'll mention the non-ESC set up I have. My kit came with an MSC Sweep Arm Speed Control with a resistor. This speed control is mechanical, actuated by a servo. I've never used this type of speed control before.. The resistor must lower the voltage, going to the motor. I don't know if one position goes through the resistor (for low speed), and a second position bypasses the resistor giving the motor full voltage. The instructions say you can vary the speed, by changing the position of the pushrod in the servo horn (changing its position in the different holes to affect its travel). At this point, I don't know if this is a two speed controller, or if you can obtain more than two different speeds by adjusting the pushrod position.

Does anyone know if the high speed setting does indeed bypass the resistor on this type of sweep arm MSC? If it does completely bypass it for the high speed setting, would the motor receive more voltage, than going through a Brushed ESC? If it bypasses the resistor, then it should be a direct circuit to the motor. Can a decent Brushed ESC, match direct hard wired to motor performance?

flyinwalenda

My Feedback: (5)

Water break-in is the best way as it allows the brushes to form without heating up and becoming irregular or cracked. Start slow for the first run, change the water then vary the speed up and down a bit, rinse,lather, repeat until the water stays somewhat clear--------finished. Then drip some oil down the end of each shaft,spin the motor so the bearings get oiled.

What you are describing is an analog speed control. This is all there was before ESC's and some were notorious for catching fire ! I would only use one if I was building a vintage 70's kit for display only !
If you want variable speed then use an ESC.

mfr02

It restricts the current that the motor gets. More resistance, less speed. Full speed happens when all of the resistance is bypassed. Since the resistor(s) are in series, they pass exactly the same current as the motor, but dissipate the energy as heat. Max heating effect happens at half speed.
In the situation described, a brushed motor can be run on rather more volts than the label suggests because it is only intended to run in a short burst, after which it will have a chance to cool before the next run. More volts = more speed. It might need thicker wire. With a brushless setup, a lot of thought needs to go into figuring just how much reserve is going to be needed for the ESC specification to keep within budget.

dontrinko

All IMO; you have to get the boat in and out of the water and if you are looking for max speed you may need to control the power at the beginning to keep the boat from flipping or cavitating. So for me the esc would actually simplify things. Don

mfr02

The OP does say that for the project, the boat will not be controlled, so there isn't really much chance of building up the revs. It's either going to be full on, or off. Since this is a "racing" project, winning requires a combination of skill, luck and money in its various forms (time, swapping parts etc). Practice increases skill, the more skilled you get , the luckier you get.