Mtroniks versus Bobs board

[Ian RiddickParticipant @ianriddick46987]

Help required please, I have two Graupner Jumbo 540 6volt motors in an eboat circa 1978, I had fitted an Mtroniks speed controller replacing the Bob's board only to find that when the voltage dropped below 6 volts down to 5.6 volts I was experiencing intermittent operation of the esc. I have been informed by Mtroniks that the minimum voltage for operation of the esc is 6volts. Graupner have also confirmed that the maximum voltage for the Jumbo 540 motors is 6 volts. Do I have any alternatives other than refitting the Bob's board?

[Ian RiddickParticipant @ianriddick46987]

[Dave MilbournParticipant @davemilbourn48782]

The MTroniks ESC has battery eliminator circuitry. This means that although you can use the main motor battery to power both the motors and the receiver it requires a minimum of 6v to allow for the voltage drop across the regulator which provides the 5v for the receiver. If you use a speed controller which doesn't have BEC e.g. an ACTion P80, then you'll need a separate 4-cell receiver power pack but you can operate the motors from a main battery as low as about 3v and as high as 12v.

Dave M

[ashley needhamParticipant @ashleyneedham69188]

Ian. What battery type do you have? Using a 7.2V Nimh pack, for instance, replacing a 6v SLA would alleviate these problems straight away.

Ashley

[Dave MilbournParticipant @davemilbourn48782]

Ashley
A fully-charged 6-cell NiMH pack can go as high as 8.5v, which is much more than the 6v maximum mentioned.
Dave M

[Ian RiddickParticipant @ianriddick46987]

Ashley I have only a 5 cell 6 volt Nimh battery which is the problem as the motors are only good enough for 6volts max. I am going to follow Dave M’s suggestion and get a new action speed controller.

Ian R

[Boiler BriParticipant @boilerbri]

I have a few motors, 380's and 540's i always thought they were 12v? Good job i never used them.

What current can i expect them to pull if i use 6v on them? I suppose the prop size will affect it?

This would help with selection of an electronic speed control such as the mktronik range.

Brian

[Ian RiddickParticipant @ianriddick46987]

Brian, my motor picture attached. Is 6 volt and 4.5 amps max. I understand there are different voltages for 540 motors depending on style and manufacturer.

Ian R

[Colin BishopModerator @colinbishop34627]

540s can be all sorts of specifications depending on the motor windings. The only way to check is by using an ammeter on them while on load at various voltages.

Colin

Edited By Colin Bishop on 14/08/2018 22:19:15

[Malcolm FraryParticipant @malcolmfrary95515]

Replacement 540 motors, if not going for "super race" types, are cheap. The worst thing that is likely to happen is that the boat goes faster and runs longer. In all probability, the existing motors will have enough safety margin (they are Graupner) to be quite happy with a 20% voltage boost. For quite some time, anyway. Then fit new motors of the correct voltage rating, or, if they do show signs of getting too warm, try a size smaller prop.

The downside of resistance controllers is that they must, if actual control is wanted, be perfectly matched to their motor and the load on the motor.

Alternatively, run the ESC off the 6 volt balttery, fit a receiver pack to run the radio and servos, BUT DON'T SWITCH THE ESC ON USING THE ESC SWITCH. That way, the control part of the ESC is powered via the receiver and controls the output which is being supplied by the main battery. A non-BEC ESC will do this anyway.

Brian – the numbers 380 and 540 refer only to the length of the motor can, 38 and 54 mm respectively. Often there is a whole bunch of numbers and letters around there. If you have the time and patience, it is possible to find out from them the details affecting performance, and what performance can be expected. Within the can you get differing magnets (strength and size and pole face area), differing armature diameters and profiles, different windings, different commutator and brush details. Literally millions of combinations of internal workings resulting in the same number of operating voltages and load handling characteristics and life expectancy. The only fairly common item is the number of watts that the can is able to dissipate before harm happens. "Surplus" 540s could be anything, thats why it is a good idea to stick with known names. And yes, the load imposed by the prop does make a huge difference to the current drawn.

[Boiler BriParticipant @boilerbri]

Right thank you that explains it. So looking around the named ones of quality start at about £20 for the 540's.

The 10a version of the mktronic should suffice as long as it's a brushed type?

Why fit an extra battery pack. Why not use the connection from the esc to power the radio?

Brian

[Charles OatesParticipant @charlesoates31738]

Hi Brian, there's some very good help in the answers my fellow posters have given, it might be worth reading through them again to clarify things. To highlight a couple of things, battery voltage drops as the battery is used, this stops the bec……thats the power to the receiver from working.

Using a separate battery for the receiver means that if the main battery gets low you still have control. Incidentally, most of us would call a 6 volt SLA battery flat at 5.6 volts, it's never wise to run any drive battery too low.

Decent motors can be obtained from many good suppliers, such as MFA, action etc from around £6.00

Instead of just choosing a 10 amp ESC get to know the power drawn by the motors, and choose one with a big margin over that figure.

If Ians boat was my model, I would run it again with a separate receiver battery. I would check the amps drawn to ensure that the battery isn't overloaded, then knowing that consider a propeller change if its needed.

May I respectfully suggest that you start a new thread  to follow up on your query, it gets a bit confusing for my old brain having 2 sets of figures from 2 people in one thread.

Chas

 

 

Edited By Charles Oates on 15/08/2018 07:58:53

[Boiler BriParticipant @boilerbri]

Hi Chas. thank you for the clarification and clear explanation. Electric is a bit of a dark art at times.

Cheers

Brian

[Dave MilbournParticipant @davemilbourn48782]

This was written for folk such as yourself. **LINK**

DM

[Boiler BriParticipant @boilerbri]

Interesting read thank you. I was not aware of the change for nicad batteries. It also looks like no one used silver zinc anymore🤗

Brian

[Malcolm FraryParticipant @malcolmfrary95515]

The price difference between a 10A ESC and a 15A one is so small that I would only go for the 10A version if space or weight was at a premium. The great thing about modern ESCs is that what can handle a high current will work every bit as well with much lower current, as opposed to the resistance types where the correct one had to be specified first go. As a bonus, there is a huge number of steps in control as opposed to even the best resistance types.

As to running on a very slightly higher voltage than the motor spec suggests – that's where a bit of self control in waggling the stick comes in. That, and with a cheap basic radio, a bit of cunning in setting up the ESC so that stick full forward gives 6 volt performance, stick plus trim gives "flank speed".

[Boiler BriParticipant @boilerbri]

Right im getting there, bought a ripmax charger – dc supply and ac so that should be use full. Bought 7.2v 1200mah battery packs. Bought some capacitors to fit to the motor bodies and terminals.

I went for a Mtroniks 20a unit for the speed control, what will do big will do small. It might physically be a bit bigger but that's not an issue with me, unless i am going to put it in a thimble!

I just need it all to come so i can have a play.

Cheers

Brian

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