Maximum Motor Wire Length??

[Kris Flynn]

Hi, (Jay and others who dont use the other forum)

I have a project that requires me to extend the motor wires to a total of 300mm (12") from motor to controller. Now my questions are:

Is this Bad? if so why?

Do i, or should I add more Caps in somewhere? If so, what, how many and where?

Setup is a Hydra 240, 1515 1.5D 3S and Battery wires are only about 100mm (4") Long

Cheers

Kris

 

[Ub Hauled]

Hi, (Jay and others who dont use the other forum)I have a project that requires me to extend the motor wires to a total of 300mm (12") from motor to controller. Now my questions are:

Is this Bad? if so why?

Do i, or should I add more Caps in somewhere? If so, what, how many and where?

Setup is a Hydra 240, 1515 1.5D 3S and Battery wires are only about 100mm (4") Long

Cheers

Kris

I am not Jay but I can tell ya that the 12" are not good. There is something called "ripple current", that will

burn your ESC to a crisp... it happens when there is an inconsistent current flowing due to the long wires...

There are 3 ways to fix that, 1- shorten the wires to no more then about 7" or less (number told to me by a guy that knows a

boat load about this), 2- Add extra caps to the system (they "smooth" these ripples) you can buy them in banks from OSE

(to keep it easy) and 3- My favorite, shorten the cables AND add caps.

just my opinion.

 

[drwayne]

Hi, (Jay and others who dont use the other forum)I have a project that requires me to extend the motor wires to a total of 300mm (12") from motor to controller. Now my questions are:

Is this Bad? if so why?

Do i, or should I add more Caps in somewhere? If so, what, how many and where?

Setup is a Hydra 240, 1515 1.5D 3S and Battery wires are only about 100mm (4") Long

Cheers

Kris

I am not Jay but I can tell ya that the 12" are not good. There is something "ripple current", that will

burn your ESC to a crisp... it happens when there is an inconsistent current flowing due to the long wires...

There are 3 ways to fix that, 1- shorten the wires to no more then about 7" (number told to me by a guy that knows a

bat load about this), 2- Add extra caps to the system (they "smooth" these ripples) you can buy them in banks from OSE

(to keep it easy) and 3- My favorite, shorten the cables AND add caps.

just my opinion.

OMG !

haha

Caps across the INPUT are always a good idea to protect esc and batts from surges.

Input wires...DC...shorter the better..voltage drop over distance can induce flaws to the power supplied.

EG a set of long DC jumper leads probably wont start your friends V8 due lack of endpoint power

Caps, which ones and where? ampba has thread for this.

440uf25V x2 parallel between input rails would be good for your applet

Adding caps to the output will clip out all that wonderful power your race boat wants.

Output wires .. AC .. powerlines run thousands of miles as AC with negligible power loss..keep the wires parallel, apart and not entwined and you will not get induced ripple.

cheers

DocWayne

 

[jayt]

As Jan said, 12" motor wires are not a good idea. You may get away with it using lower Kv motors as these are easier for most ESCs to "see" the rotor position and run the motor successfully. But on motors like your 1.5D Neu with it's low resistance/inductance the ESC will be challenged to read the motor, made worse by the usual higher currents. It takes time to energize the motor coils (that's why we need timing advance) and long motor wires are not good.

I believe that you'd be better off by shortening the motor wires and lengthening the battery leads. Use additional caps to help compensate. Really, the best soution is to position the ESC so you do not need long wires on either end. Can you re-position the packs or the pack leads?

.

 

[Kris Flynn]

Hey Guys,

First, thanks for the replies.

Second, I can't really move the controller further back, they need to be where they are to get the COG right. Attached is a picture of my project They are actually on the COG

As you can see, there is alot of weight hanging off the back, and to get the COG at around 30% (without adding extra weight) I need to layout to be as pictured.

Kris

 

[Ub Hauled]

Hey Guys,First, thanks for the replies.

Second, I can't really move the controller further back, they need to be where they are to get the COG right. Attached is a picture of my project They are actually on the COG

As you can see, there is alot of weight hanging off the back, and to get the COG at around 30% (without adding extra weight) I need to layout to be as pictured.

Kris

Holly crap!!! I can truly say that's the first time I have seen something like it! Me likey! That's "out there" Kris...

You will need extra caps, that is way too far... How heavy is the whole thing, how about bringing the cells closer

and adding weight to the tip if needed? You have 2 "NEUses" hanging at the transom there, I don't think they'll

mind a few ounces here and there (a few more grams like Jay stated, I am metric all the way).

 

[jayt]

Your power wires are fine in length, no caps needed there. The motor wires are pretty long, but you may get away with it. Be very careful in how you connect the jumpers, use good solder joints to reduce resistance. You have plenty of power, an extra half kilo in the nose will do wonders and will help to keep the tunnel on the water....and let you move everything else back a bit.

.

 

[pda75]

Very nice boat !

the wire are fine. I would be more upset with the motors being real wet. I assume that you will carrefully dry them after each run and use liters of oil.

 

[DPeterson]

Hi Kris,

Now that is cool. How long is the Tunnel? Will you counter rotate the props or turn the same direction? What kind of speeds are you expecting?

Please keep us up to date with your build and runs. Was thinking of doing something similar only with an Offshore type hull.

Doug

 

[drwayne]

Hi Kris

using one batt source to feed 2 esc's, Id be keen to add a few ballast capacitors between the batts and the esc inputs.. allows for those power surge moments... caps feed the scs, not causing so much esc destroying voltage drop.

nice effort .. love to see it in run Vic sometime soon.

DocWayne

 

[Doug Smock]

Very cool project Kris!!!! B)

Doug

 

[Kris Flynn]

Well, I let the cat out of the bag with this sucker hey? I was hoping to keep it under wraps untill it was finished, but the wire length worried me and I couldn't find anything in the Castle instructions...Although I remember reading somewhere not to make them over 8-10" or something...

Only things I can do to make the wires shorter are move the servo forward and speedies back, but this will only shorten about 2" or so, and make it harder to connect all the wires up...

Now to the questions...

Total weight, around 3.5kgs, hoping speeds of around 50MPH are not un-reasonable?

Doug, the hull is one of my own designs/builds with a HTB cowling and is 33.25" long

PDA, motors get cleanen after ever run with electrical cleaner and some metho

Wayne, 2 complete seperate power systems, 1 3S 6000Mah Poly RC, Hydra 240, Nue 1515 1.5D for each side of hull

Kris

 

[Ub Hauled]

Now to the questions...Total weight, around 3.5kgs, hoping speeds of around 50MPH are not un-reasonable?

Doug, the hull is one of my own designs/builds with a HTB cowling and is 33.25" long

PDA, motors get cleanen after ever run with electrical cleaner and some metho

Wayne, 2 complete seperate power systems, 1 3S 6000Mah Poly RC, Hydra 240, Nue 1515 1.5D for each side of hull

Kris

I think you should get 50mph w/o any problems, hopefully you'll get similar outputs from each motor avoiding

prop chine... are they going to be counter rotating props?

 

[Kris Flynn]

Jan, sorry I missed that one... I was thinking of that, but prop shafts have a left hand thread on them, if I went counter rotating it might unscrew the left one

I also figured that the nitro guys are running Twins with same rotation props with no real dramas that i have heard...

I have been running my 4S tunnel, 1515 1Y old barra 125 and a X637 and I am pretty sure it is pushing 60MPH in heat race trim, can't wait to put the Hydra 240 in it and bigger props LOL OH and the noise is awsome with the motor out in the open air :lol:

 

[Kris Flynn]

OK, an update, I used the advise and moved the servo forward, controllers back and shaved over 2" off the motor wire lengths... They are now a tad under 10" (were 12") So that makes me feel better, there is no real easy way of making them any shorter and still be able to remove the controllers fro mthe boat easily.

My Next question which I hope can be answered is...what props? I have been told I should be able to swing 45mm (building upto it of course) but I can only swing 42mm under the caveplates...any bigger and I need to cut them off, which is not a huge deal, I just dont want to have to do extra work in getting it to work...

Cheers

Kris

 

[Ub Hauled]

OK, an update, I used the advise and moved the servo forward, controllers back and shaved over 2" off the motor wire lengths... They are now a tad under 10" (were 12") So that makes me feel better, there is no real easy way of making them any shorter and still be able to remove the controllers fro mthe boat easily.

My Next question which I hope can be answered is...what props? I have been told I should be able to swing 45mm (building upto it of course) but I can only swing 42mm under the caveplates...any bigger and I need to cut them off, which is not a huge deal, I just dont want to have to do extra work in getting it to work...

Cheers

Kris

use the 42mm props and see how they work then you can try a 642 if things work right with a 442...

 

[Darin Jordan]

Kris,

You are insane dude... and I LOVE IT! Very cool project... That's a TON of motor for such a short boat... Should be a nice handful!

On the cav-plates... On my REKs... I trimmed the cav-plate off to just in front of the props leading edge... basically just about at the drive-dog, then run the water pickups off the back of the sponson... Seems to work fine and I haven't noticed any ill-handling with the shorter cav-plate... My Lawless 3.5 drive that is modified for an OS stub came basically that way... I can put on pretty much any diameter prop I want...

On all my FE tunnels, to combat the wire-length problem, I put my servo WAY up in the nose, and run pull-pull systems. This let's me put the ESC all the way in the back, and leaves the entire center open for batteries, etc... On my WoodStuff, I actually ran the steering cables down the OUTSIDE of the radio box, which leaves the inside totally clear... Kind of like the real boats do...

Can't wait to hear how this boat goes! It's definately going to LOOK cool doing it!