dual esc/motor setup
 

as i have been frying one mmm after another i was wondering if i could install dual setup in my truck?

i have no problem fitting all the stuff but i was wondering if it could be simple as using y connector from the esc's to the rx or would i need to run the rx from external battery?

by going dual setup i will need to run twice the battery so both setups wont be starved or overload the battery when braking.

as going dual setup the twin would be sharing the load wich fried my older single setup. im guessing that the load would be about 30-45% less on each esc instead of 100% on the single setup.

also im wondering witch lipos are the best. not best for the price!! but the best quality. orion.smc? other??

my truck weights 13 pounds with no wheels and each wheel weights a pound so its 17 pounds in total. i mostly run hillclimbs and it will be geared for about 30-40mph top speed.

Welcome to the forum! But, Information overload...

Lets get some background information first:

What vehicle are we talking about here? 13lbs, 17lb rtr, Thats pretty heavy.

What motor/batteries/gearing are you running? MMM combo?


As far as pushing a 17lb vehicle, I'm thinking you may want to stick to a single setup and just use a bigger motor, something like a Neu 1527 or 2215, on 8-10s. A high voltage setup like I just mentioned will move a vehicle of your's weight with much less effort than say a MMM combo.
I'm not trying to steer you away from dual whatever setup you have, but a single is more often than not easier and less complicated.
More than likely, you're straining the setup way too much with 4lbs of rotating mass and 17lbs of total weight. Thats why you're frying MMM's left and right.

Let us know the motor, gearing, battery, truck setup used before, and we'll advise you in a better direct.

Sounds like you need a HV and high amperage ESC along with a 1521 motor! That's a beastly truck.

The trouble is with dual BL is getting them to run perfect. One motor may have slightly different kv, and each ESC may be sending a slightly different amount of throttle. So, the faster motor/ESC will be doing most of the work and heat up more.

But yes, you should run twice the battery. After all, you are theoretically doublinig the power. Current will be higher than a one motor/esc setup, but a little less than two added together (less load on each setup).

Yeah, you'd run a Y cable for both ESCs, although it would be better to use CH3 mixed with the throttle channel so that you can fine tune each ESC/motor if needed. A simple Y cable means any adjustments to an individual setup would have to be done in the ESC programming.

If you use dual batteries in parallel, you'd want to use the "unslow" harness, or something like it, to make sure both batteries are drained equally.

Also, you'll need to remove the red wire on one of the ESC throttle cables (to prevent paralleling the BECs).

the setup

savage xl
neu 1515/1y
mmm v3
polyrc lipo 2s and 3s 4900 mah 25c in series for 5s out

15t pinion 52t spur
gearbox locked in second gear(same gearing as the flux)
cen diffs 2.88 ratio
baja 5b wheels and tires (paddles)6.6 inch approx

gearing was about 15:1 motor to wheels but i have now geared it down to 23:1 by swapping out the 15t for 14t motor pinion and locked it in first gear.

i think that this gearing would be better to keep heat down but i guess the plastic first gear in the gearbox wont be reliable.

i have not tested the lower gearing yet as my fourth mmm is still in the post.

lol i must remember to send the other three for repairs.

I'd definitely send the other 3 in for repairs. Castle is pretty good on that end.

Locked in 1st gear will make one hell of a difference. You may want to try that first, but your top speed will suffer. At 23:1 you'll be geared for 33-35mph. Before, you weregeared for 55mph+, which with a heavy vehicle will burn stuff up as you found out. If you want to go that fast with such a heavy vehicle, like I said, I would definitely move to a 1527 motor on 8s with either a Pheonix HV110 or Lutach 10s esc. You'll definitely want to bring the kv down and up the voltage.

i think one of the biggest problem was that it was way over geared as i never used but maybe half the speed of what it was geared for.

the reason i have been thinking about going dual mmm and motor is that then i would still have brakes and reverse. but i havent found another esc other than mmm or tekin rx8 that are capable of high load and have those functions.

have actually been thinking about if using dual setup i will make some kind of differential and run the motors by seperate spurs so the motors can run indipendant speed but still share the load 50/50.

lol i'm pretty good at fabricating stuff like this but when it comes to calculate the brushless setup im kinda clueless:neutral:

Like BrianG stated earlier, Dual brushless tend to fight each other or one system overworks its self. Its hard to dial the systems in perfectly, which in turn can cause as many problems as before.

I think for your truck and what you want to do, hill-climbing and 35ishmph in a heavy vehicle, I say gear it down and try it again. The 1515/1y is a strong motor and geared down to 35mph, it shouldn't have a problem.
Otherwise, a HV system is in your future.

here is my idea of using dual 1500 kv motors connected through a differential so they can each run at their own pace at the same esc settings but still give all they got to the wheels.
gearing is two 14t pinions four 52t spurs and two truggy differentials.

i have already bought most of the components needed for the gear setup and im working on a mock up of the gear carrier frame.

and the upside is that i have always wanted to put a mid differential in there.
by using mid differential there will be allot less stress on the front and rear diffs while crashes and this setup should be allot stronger than the original gearbox setup and it all uses the same bearings as are used at the wheels so it should be plenty reliable.

here is a quick sketch up of the concept.
the bearing carriers for the spur bearings (blue) are not drawn in at this point and the diff bearings are hidden under the grey carrier plates.



http://img17.imageshack.us/img17/5442/gearboxsavage.png

Hmm, it might be tough to maintain a consistent gear mesh since the motors aren't mounted to anything. :smile: :wink:

Dual BL = bad.

Single big BL = good.

The weird center diff idea is interesting, but I forsee it not going too well, as two seperate systems driving the front and rear diffs at the same time via a diff is just gonna cause them to fight eachother still, and cook the diff too probably; just say no to Dual BL...

I would not be trying a dual BL setup. You are going to start smoking the controllers twice as fast as you are now.

Man you guys are being a little tough on Mr Snuggles (I want to squeeze him myself!)

I like the dual center diff idea, save for the rotating weight that it will involve. Using plastic spurs, like the 44t kyosho will help with rotating mass. Using 30-50k oil in the lower center diff (lets call that the output diff) will allow good turning that any center diff vehicle has. And something much thicker in the upper diff (lets call that the motor diff), like 100k so that the motors are connected almost solidly, but have some freedom. This way that cannot fight as bad as if they were connected to each other via driving the same spur.

I would like to see this done,but there are some engineering issues that you will need to figure out. I would say that placing the spurs inside the bulks against the motor diff, that way the bulks can also be the motor mounts. Also place the motors next to the motor diff, and the output diff centered below that. This will help you access the motor mount screws and keep the setup simple and compact...

If you must go dual BL, I would like to see this drawing come to life, I thikn this setup would take the fighting each other out of the equation...

Have you run it locked in 1st gear, geared for 33ish, yet?

You're whole issue was being geared for 55+ mph and trying to do hill-climbs in a 17lb truck with over 4lbs of rotating mass. That is a total AMP HOG. You must have some pretty solid batteries to hold up to that...

If you regear for mid 30's, you'll be fine. The MMM's are super tough, but if you draw 5000amps through them, yeah, they're gonna die.

The twin diff thing looks interesting. The thing I would be worried about though is if for some reason one motor (say motor #1) doesn't start up (cogging etc) as soon as the other (motor #2), and instead of it driving the car forward it spins motor #1 in reverse because of the diff, then motor #1 tries to start up while spinning in reverse, which can be bad for the esc. I burnt my year and a half old quark by hitting the throttle while still rolling backwards. Don't know how much chance there is of that happening, but something to consider. The thicker the "motor diff" oil the less chance of that happening. And obviously use exact esc settings.
That made sense in my head, but not so much in writing.