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[dodgy geezer]

You may have seen other posts from me as I try to pick the optimum hardware set for little EeZebilt boats. From 10"-20" long, made of balsa - see http://modelboats.hobby-site.com.

What I am looking for is a cheap controller for a small motor. I have just trialed a few, and you might be interested in the findings:

ESC - cheap 25A - this one (only £1.90!) http://www.r2hobbies.com/proddetail.php?prod=rcps51601 . Needs to be started by pushing an arming button.

Motors trialed:

 - Small 240 3v (Mabuchi/KaKo toy) - the sort of motor ususually used for these craft
 - 480 - decent size smallish motor for 18"-24" displacement hulls -
 - Small 12v CD-Rom tray motor (brushed)


4.5v - Servo and receiver work, but all motors cut out shortly after starting

6v - 240 motor runs fast - little response to throttle except over bottom 1/4, where it slows a bit to about 2-3000 rpm.
      480 motor - just on the edge. runs at full ok - good speed range, but hard to start with load, and tends to cut out if any load is applied.
      12v CD motor - Brilliant! Good speed range, down to a 200rpm tickover with a bit of load, and no hint of any cutting out. Top speed is not brilliant, it's a 12v motor on 6v, and the torque is low because it's a small motor...

7.5v - 240 motor runs fast with little variation over the whole range
         480 runs fine, with a fast tickover. But if you stall it it must be manually restarted. That limits the torque you can extract...
         12v CD motor - Runs well as before, but with a much faster tickover. Still not much torque

9v -  240 motor taken off quite rapidly, in a hot condition!
       480 runs fast, more reliably, and is hard to stall. There is not much speed variation except in last 1/4 of throw, and there is no tickover - just fast and medium
       12v CD motor - runs well - still not much torque, but it's very small. Less of a speed variation. No cutout at any point.

One interesting point was that if the transmitter was turned off all motors stopped, and then started again when the transmitter was turned on, without needing the arming button to be pressed. So you could stop a boat on a pond and then restart it. If you weren't worried about leaving a boat with an operating receiver and no transmitter, ready to pick up any interference...

Findings - none of these motors are ideal. The problem is the automatic volt-low cut-out, which means you have to run with high volts or a motor which draws so little that there will be no voltage drop under load. If you run with high volts a small boat will have trouble carrying the batteries, and the motor won't really have a slow speed.

What would be very useful would be one of these ESCs with the low-voltage cut-out disabled. Are there any ESC designers out there who know if this might be a simple mod, like cutting a line, or is it built so deep into the controller circuitry that you might as well buy a more expensive one without the cut-out...?

[DickyD]

The low voltage cut out stops the speed controller from committing suicide and melting down if voltage drops to low, not a good idea to get rid of it.

[andyn]

I think that's an absolutely superb find, can't believe a brushed esc for £1.90

[dodgy geezer]

The low voltage cut out stops the speed controller from committing suicide and melting down if voltage drops to low, not a good idea to get rid of it.

I had heard this, but it's hard to believe it's true, on a low volt/low current installation. When the volts drop, there's hardly any energy left in the system. The controller's BSC was working fine at 4.5v. Remember, this is not brushless, I presume it's PWM. Why should that melt when the volts drop?

I can understand the LiPo dying if it's drained, and that seems a much more likely reason for the cut-off...

[dodgy geezer]

I think that's an absolutely superb find, can't believe a brushed esc for £1.90

It was to be matched with a motor from here, at 30p-70p. http://www.mutr.co.uk/index.php?cPath=13_434&osCsid=a526dab5d90dab3e426fb71fb2afea68

The big problem is the connector - if I want more than a bit of tube I'm looking at £5. The cost for an EeZeBilt looks something like:

Balsa - £1.60
Motor and controller - £2.50
Prop + Rudder - about 50p (solder from a tin can)

Of course, glue and paint will be the high-cost item. And then there's the razor blade. Oh, and the bus fare to the pond...

The idea is to bring back ingenuity and build enjoyment, rather than just buying a bigger motor....

[andyn]

Seeing as the esc is so cheap, could you not just lop off the motor connectors and solder it straight on the motor terminals?

[Bee]

In the spirit of the things I think an ESC is over the top, especially as kids only want full speed. Since the radio is the big expense a second servo is often very cheap.
Then making simple servo operatied switches would be educational. first just on off, then add reverse, then add half speed with a bulb as the resistance.
I used to use drawing pins (dome head if still available) made good contacts with which to make a slide switch.

I think your cheapo one has to maintain some speed to prevent the freewheeling prop generating a reverse voltage onto the switching transistor. As it has no reverse it is not much better than a switch and less robust.

[andyn]

Yes but then you have to buy another servo, two microswitches and a light bulb, whereas the esc is £1.90.......

[dodgy geezer]

In the spirit of the things I think an ESC is over the top, especially as kids only want full speed. Since the radio is the big expense a second servo is often very cheap.

You could be right. I was expecting a certain amount of cruising around to save batteries - EeZeBilts are not really designed for speed. And you are right that a radio is £50.

A major advantage of the Esc is that it saves space, and provides a BEC. EeZeBilts can't really take two sets of batteries. I like the idea of making up a drawing-pin switch, and you can probably get them from notice boards. Just as well, because a box of them is probably about £2.50 - the cost of the motor AND esc... What strange times we live in...

Incidentally, Andyn is right about lopping off the connectors. The esc comes with three sets of connectors and a push-button switch. I can't get those individually as cheaply, so I could just buy the escs for the connectors, and throw away the electronics....

[dodgy geezer]

Yes but then you have to buy another servo, two microswitches and a light bulb, whereas the esc is £1.90.......

Don't forget the cost of the drawing pins! Actually, when I bought a handful of these escs they were only £1.84 - I'm not sure I can afford them now they've gone up to £1.90....

[andygh]

Plenty of radios around for much less than £50 

[barriew]

I've just been looking at a 2.4ghz set on www.giantcod.co.uk for less than £27 for a 4 channel TX & Rx.

Plus carriage of course - but it is in the UK

Barrie

[andyn]

I can vouch for them, they're good sets, was playing with Gandalf's one at Llanberis. Same case as all the cheap 4 channel radios, nice comfortable shape.

[andygh]

It's a bit more but I love this 

http://r2hobbies.com/proddetail.php?prod=rcps61207

Haven't tried this one

http://brchobbies.com/?page=shop&action=additem&item=608

[brianc]

Haven't tried this one

http://brchobbies.com/?page=shop&action=additem&item=608

A couple of the guy`s in my club have these and they`re pretty damned good for the money.......
Even going to get a couple myself

[andygh]

Cheers, might try one myself in that case

[andyn]

It's a bit more but I love this 

http://r2hobbies.com/proddetail.php?prod=rcps61207

I was looking at that earlier, all being well I possibly now have a job, and I'd like a tank. A big one. That controller looks perfect for one

Was trying to work out earlier how long it'd take me to save for a 1/6th one of these: http://www.mark-1-tank.co.uk/tiger-1.html , but I realised I'd have nowhere to put it but the shed, and wouldn't be able to lift it through the house. This would mean driving it through. I don't think tank tracks in the Linoneum would go down well...

Sorry to deviate from the thread, had a look at your site, very well done

[dodgy geezer]

Sorry to deviate from the thread...

No problem! I have just come back with a bit of news from the motor test area.

The main problem I found when using this esc with low voltages was that it would shut down if a bit of load took it below the cut-off point. That would be a killer for small boat use - a small glitch like hitting a twig and your motor stops.

I have found, however, that if you hold the button down continuously, the esc does not shut down, and will keep driving the motor with healthy torque even if it is held to stall point. The esc squeaks a bit if you do this, but it does not get warm to the touch. So simply replace the button with an on/off switch, and this esc will drive small 240 sized miniature motors off 4 drycells/6v. I've even had it running off 4 NiCads/4.8v, though if you are running on low throttle the motor noticeably slows down when the servo is operated. Nothing worked on 3 drycells/4.5v, though :(...

Under this regime (low voltage/small motor) the slow running characteristics are good - the motor does about half-speed at half throttle, and ticks over slowly or stops at low throttle. If it's under a reasonable load it will stop. But, with the button replaced with a switch which is closed all the time, it will simply start again when you raise the throttle.

I think that these are going to be the escs of choice for small brushed eezebilts. Unless, of course, the electronics experts tell me that there are unforseen dangers....

[stallspeed]

I had heard this, but it's hard to believe it's true, on a low volt/low current installation. When the volts drop, there's hardly any energy left in the system. The controller's BSC was working fine at 4.5v. Remember, this is not brushless, I presume it's PWM. Why should that melt when the volts drop?

I can understand the LiPo dying if it's drained, and that seems a much more likely reason for the cut-off...

The voltage failsafe is essential for a park flyer to get theplane/helicopter back down in one piece but the esc would self destruct on 3 pencells,no voltage failsafe,running a 380 motor.

When you "document scan" both sides of the esc to pick up the voltage failsafe part which needs modified,you will see the esc's "voltage controlled resistors" are made by an outfit like Alpha & Omega
If you manage to modify the voltage part,the finger thermometer will show the controller is probably safe with a low power motor on three cells but not with a 380 motor.

[Proteus]

It sounds like it is not a fully proportional controller but an on off switch with idle.

from there advert

This ESC is perfect for scale planes, as it operates in a scale like manner. The motor starts when you press the button and will only shut down when the voltage level drops below 5 volts. So cutting off the throttle lets you idle the motor, simulating a real airplane engine (or glow engine).

You should install the button on the side of the plane, where you can press it just before launching your plane.

Once you start the motor by pressing the arming button, the motor will not stop until the battery voltage falls under 5v - cutting the throttle will have the motor rotating at low rev. simulating engine idling


Proteus

[nick_75au]

I take it to mean that like an IC engine it will keep the prop rotating at tickover speed when the throttle is pulled all the way back, its still full proportional between idle and WOT.
Nick

[dodgy geezer]

I take it to mean that like an IC engine it will keep the prop rotating at tickover speed when the throttle is pulled all the way back, its still full proportional between idle and WOT.
Nick

Nick, you are right regarding the design when used with a big motor at high voltage - it does provide idle-full proportionally, just like a glow motor throttle.

I am seeing how it behaves with small motors and low voltage. The general answer is that it cuts out a lot, but this can be avoided by substituting a switch for the push-button. If you do that, the small motors will generally run from stop to full in quite a reliable way. Here is a shot of the test bench...

[portside II]

I am having trouble finding the esc on the bench  ,
 is it the one from the C cell pack  or the bit of heat shrink just behind the motor  .
But all in all an esc for less than a couple of quid , brilliant  .
daz

[dodgy geezer]

I am having trouble finding the esc on the bench  ,
 is it the one from the C cell pack  or the bit of heat shrink just behind the motor  .
But all in all an esc for less than a couple of quid , brilliant  .
daz

It's the black heatshrink on the wires, close to the yellow motor mount. If you look carefully, you can see another one next to the multimeter. There are a couple more out of picture to the right, and the rest are waiting to be unpacked :)

The blue one on the C cell pack is the brushless one I got together with the motor for £12 - so it cost about £6? That counts as incredibly expensive for this application. I'm wondering whether to buy some more of the escs - it's a cheap way of buying wire with connectors on. The electronics are an extra bonus....

[dodgy geezer]

If you manage to modify the voltage part,the finger thermometer will show the controller is probably safe with a low power motor on three cells but not with a 380 motor.

Stallspeed, what would the worst regime be for running at low voltage?

I have the esc on the bench at the moment, running a 480 motor with a bit of load on, with 4 nicads. Their off load is 5.3v, but with the motor running they drop to 4.8v. If I press the arming button and then leave it open, when I drop the throttle, the motor stops and the esc needs re-arming to start it again.

If I do my trick of holding the arming button closed, however, the motor is quite reliable down to tick-over and stop. When I raise the throttle again the motor re-starts happily. When I put a stalling load on the motor, the voltage at the battery drops to 3.5v, and the esc begins to make unhappy noises on fuill throttle - a peep about twice a second. But it does not get hot, and the motor starts again happily as I let it go.

Interestingly, under this low voltage running, the servo seems happy. But if you operate the servo while the motor is running slow, you see a distinct drop in motor speed while the servo is operating.

Am I right in assuming that this is the worst treatment I can give it under low voltage running? If so, it has survived so far. I will treat it like this occasionally for a week or so, to see if it will crack....