speed controller advice

[Gary BramhamParticipant @garybramham30806]

Hi all, I am going to be running a Torpedo 800 12v motor but I dont know what size or make of speed controller to use. Any advice is welcome.

Gary

[ashley needhamParticipant @ashleyneedham69188]

Gary. The Torpedo 800 is rated at about 5 amps at max efficiency , which i take it means that its using the MFA recomended 50mm 2-blade prop on a "fast" hull. I dont suppose it would draw too much more unless grossly overloaded, and so I dare say a small 15A ESC would do. Its the sort of thing you really need to use an ammeter on to see how much current your setup is drawing . I use the small Viper marine boat speed controllers and have not had much trouble with them. Its a bit down to personal preference. Any purpose made BOAT speed controller will do, ultimately. Some offer a BEC facility, which means that they will power the reciever and so you can eliminate the reciever batteries, however again, some bods prefer to use a seperate reciever pack. What type of boat and propeller combination are you going to use? Ashley

[Gary BramhamParticipant @garybramham30806]

Hiya Ashley,

Thanks for your info, the model I have nearly finished was started 30 years ago by my wifes grandfaher since he passed away it has been stored in a garage and given to me 2 years ago. the model is a Rapier and its lenght is 38 1/2 ins and its beam is 10 3/4 in, the total weight munis the engine and battery is 2.5 kilo. This is the first boat I have built and I am hooked. I will post a pic as soon as i know how to do it lol. I forgot to say the model is a Lesbro Model

Gary

[ashley needhamParticipant @ashleyneedham69188]

Gary. All the MFA boats around your size use a single 850 motor rather than an 800 to get planing performance. The 800 is a slow revver on 12v, the 850 makes double the revs. The MFA Fantome boat at 48 inches (which is something I have on order) uses TWO 800`s to acheive planing performance, although I suspect it may not be quite as fast as the others.   About 10A current draw for an 850, so still well within a  modest ESC`s capability.  The 800 will turn a big prop mind you, so it depends on the sort of performance you want?   Have a look at the MFA site. There was another thread running by Chris Pierce, who has a Sea Commander , another wood 36 inch boat, and it looks as if a graupner speed 600 and 35mm prop may give him a reasonable turn of speed. (once he gets a new ESC) Unfortunately the motors are different sizes so it may be tricky to try the two out, if you were of a mind to.  Ashley

[Gary BramhamParticipant @garybramham30806]

Hi Ashley, I am not after a racing boat ( not yet anyway) but the prop that is already fitted is about 65mm across, I will just have to wait until its on the water to find out the preformance, but as I said I am not that bothered with this boat, as long as it goes, I just want to complete this 30 year build, i wonder if its a record.

Gary

[Penny LeeParticipant @pennylee76979]

Hi Gary.

Don’t be tempted to switch to a Torpedo 850 under any circumstances.

The stall current (>80 amps) will destroy many 15 amp speed controllers which use either relays or small surface mount transistors.

Have a look here .

The one they are tolking aboul is a bit more rugged and was made by the company that supplied my submarine gadgets.

Lee

[ashley needhamParticipant @ashleyneedham69188]

Gary, as above. You could do with a current measurement before getting a speed controller. I imagine your 65mm prop will be ok on the 800 motor, but best to be safe. Dont want to have to buy a second esc after having blown up the first one.  Ashley

[ashley needhamParticipant @ashleyneedham69188]

..Take the current measurement without an esc, just slap the battery and ammeter in circuit and dump the boat in the water (dont forget to hang on!)

When I was building my HMS jersey island class patrol boat (trawler hull) I tried several motors (and this was 25 years ago when I was not that much up on boats) and one of them was, I found out later on, an 850. I had a 50mm prop and just an on/off switch in the boat, and rudder only hooked up to the radio. Bravely/foolishly I turned on the motor switch…admired the vast plume of water generated behind the boat and let it go.   I have never seen such a bow wave in my life…the boat was fairly heavy, as its 39 inches long, but it was going through the water at an angle of 40 degrees..and a vast sheet of water was being thrown up on either side. The stern was actually UNDER the water surface level, and I had to run it up a section of sloping bank to stop it.  Lesson learnt….  also of course it had a displacement hull, and these cruise at the speed they were designed for using relatively modest power, and if you increase the power over what the shape was designed for it simply digs the back end in…more and more in my case. A planing hull simply lifts out the water when more power is applied. You should be all right with your boat, which I take is some sort of cabin cruiser..    Ashley

[Penny LeeParticipant @pennylee76979]

 It took a calculation but I reckon from the link below that the 800 stalls at approximatly 30 amp and the 850 at 70 amp on 12.0 volts.That is worth considering when you chooe an ESC.

http://www.modelflightaccessories.com/products/drive_reduction_800.shtml

[Gary BramhamParticipant @garybramham30806]

Well we will see what my Koi think of the boat tomorrow, after i have fitted an ammeter. I will be interseted to find the results and I will keep you all informed.  Good guess Ashley, it is a cabin cruiser ( well I think it is). Just to be on the safe side, is it better to test the engine whilst it remains in the boat or should I bench test it first ?

[Penny LeeParticipant @pennylee76979]

What’s to test.

If you look at the MFA link and scroll down you get a table of a motor at 12 volts.

If you go to my gallery you get a picture of how a dc motor performs under load.

You would need two motors and a host of test instruments to dry test a motor or a meter,rev counter and a basin of water.

Fling it in a pond and do your current measurement but mind you have to go 100% or your current reading is misleading unless it measures true RMS current.

It’s pointless exercise anyway because the motor does big props.If the model goes faster with a smaller prop then the first prop was too big to start with.What you need is a spanner and some fortitude.

Lee

[Gary BramhamParticipant @garybramham30806]

Well I havent had any luck as yet. my am-meter packed in so I reckon I will have to get another or just buy a larger speed controller. Thanks to all who replied.

Gary

[60wattParticipant @60watt]

Hi Gary.

Check your meter fuse.

I think I’m on record in this forum saying measure the voltage across a resistance to obtain motor current measurements.That is how 10 and 20 amp ranges work on digital meters.

Insert a resistance-calibrated length of cable say 10 cm of 1mm to make a .002 ohm resistance capable of taking 15 amps.The voltage drop at 10 amps is 20millivolt.If your meter is not sensitive enough you can go to a lower gauge and use then recalculate.

The 800 motor does not require a large capacity speed control.Whatever model or make you have should do with a 10 amp fuse.

Tom

[Gary BramhamParticipant @garybramham30806]

Hi Tom do you recomend a 15amp or 20amp viper  speed controller, I am not that good on working out electrics,

Gary

[60wattParticipant @60watt]

Hi Gary.

My opinion is you have a motor that allows limitless choice.I’m sure it was Ashley who recommended Mtroniks.

I have used several makes but never one by Mtroniks.I don’t know whether you can reduce power and that is something I need. All my models run on 12 volts and I don’t have a transmitter span adjust.

I have three I saw on Lee’s link.They’ve never let me down but I don’t. think they are available any more

Tom

[Gary BramhamParticipant @garybramham30806]

Mtroniks and the type I am planning to get, the motor I have says on the box 12v.   rpm 5167. power output 65w. it also says MFA? como drills. I dont know if that the same type of motor they fit in rechargable drills?

[60wattParticipant @60watt]

I don’t think it much matters what you use with that motor.

It is definitely  a Torpedo 800 or Marlin.Not an 850.

It wouldn’t be used in a rechargeable drill.In a drill the gearbox provides drill bit torque and the motor is always one with a high rpm and a cooling fan.These can be found on ebay but are not capable of turning scale boat props without a reduction mechanism.

Tom

[Gary BramhamParticipant @garybramham30806]

it is a Torpedo 800  brand new and in box.

I will have to just connect and see as this was purchased from a model shop with the intention of fitting into a boat. I will let you know what happen. fingers crossed.

Gary

[ashley needhamParticipant @ashleyneedham69188]

gary, you could  always call MFA and ask what they reccomend as a speed controller for an 800 motor??? Ashley

[Gary BramhamParticipant @garybramham30806]

Hiya Ashley its say MFA on the box but there is not any more details and It may sound daft but who are MFA? I have to find there contact number.

Gary

[ashley needhamParticipant @ashleyneedham69188]

Just google MFA…. Model Fligh Accessories, it will show thier website. Ashley (number not to hand just now)    mfa are probly the major importers of small motors used by modellers in the u.k. Its them wot sells the "como" brand of motor. Ashley

[Gary BramhamParticipant @garybramham30806]

Thanks for that info I have contacted them and they recommend a 20watt speed controller so I am now going to purchase one.

Many thanks for all replies to my question,

Gary

[60wattParticipant @60watt]

Gary Bramham wrote (see)

…… they recommend a 20watt speed controller………..

That made my day.

[JC Uknz 1Participant @jcuknz1]

I do LOVE all this discussion about blowing electronics and motors.   I have none of those problems because I make my controller myself with that board with lots of holes in it and strips of brass.  Plus a couple of 5 watt resistors … it is my version of what is known as a ‘Bob’s Board’.   My controller has off slow medium and full bore .. what more do you want.   people can get just too clever and cause themselves so much trouble

[ashley needhamParticipant @ashleyneedham69188]

JC. You have a good point there…….

20 amp ESC it is then. Fit a 20 Amp fuse for safetys sake and dont shove the throttle forward when heading into weed. Thinking ahead, Mtronics Vipers come in 15 20 25 and 40 amp examples i think, and as the difference in price is not great between the 15-25 versions then get a 25A one and you can use it on something else later. There is a big jump in price for the 40A version.

I have just bought an MFA fantome with 2×800`s and the ESC as provided by MFA is a 30A jobbie, so 15A each. ??? As per my original guess!       Ashley

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