P questions

[T.S.Davis]

Couple things.

Why no twins in P classes?

Why a single power source for a twin setup?

Please give me an answer smarter than "safety". Pretend like your talking to an FE guy instead of fuel guy please. Not buying "insurance".

A 6s twin on say 6k per bank requires that we bring two parallel packs together and then split them back apart. There is no safety gain but there is a ton more wire. More wire = more ripple current = hard on equipment for no reason I can justify.

Splain it Lucy.

[ray schrauwen]

A 6s twin on say 6k per bank requires that we bring two parallel packs together and then split them back apart. There is no safety gain but there is a ton more wire. More wire = more ripple current = hard on equipment for no reason I can justify.

I've seen twin cats with the packs paralleled with very little wire required. I must misunderstand.

[T.S.Davis]

You can't have a separate pack for each speedo on a twin.

[NativePaul]

I would guess that no twins in P is an attempt to limit power, as the price of high ampage ESC is a deterrent to obscenely powering boats.

With the limited battery weight we have here I have only seen one person racing a twin, he started out with seperate packs for each side and puffed the inside pack several times, on our roundy-round course he was pulling significantly more current on the inside motor. To avoid it he would either have lots of energy left on the outside and an uncompetitive boat, or run the cells in parallel, he chose parallel, his boat sped up AND stopped eating cells. He didn't need any more wire, he just soldered the ESC connectors together, it parallels the circuit and the bridge should only be flowing current in the turns when there is uneven load. In effect it allows the motor that needs it to have a larger capacity battery, which should lower its ripple. I know we have a shorter course, and I believe tighter turns too (ours are 5 meters radius), so it should be less of an issue for you. With your unlimited capacity there is less to be gained from running packs with marginal capacity, so less of an issue for you. Whether the issue is small enough to be inconsequential is for you to decide, as is whether forced paralleling is the best solution, but there is an issue, and paralleling is a solution.

[ray schrauwen]

You could order a custom pack from Revo that is split to start.

It just sucks in cats since the pack has to sit on the tunnel.

I don't run twins anyway but it might be fun.

[srislash]

Terry asked why tho, I would think it is a limiting factor. It is most certainly better if you can muster it efficiently. I have changed a few over and got gains in parallel.

Terry is there a mah limit?

[TRUCKPULL]

Twins in "P" classes

This is the difference between IMPBA and NAMBA
In IMPBA you are NOT allowed twins in "P" classes -WHY I do not know.

This is why I had to sell my "P" Twin Cat and loose money. ( stupid rule)

On a twin I always wire my ESC's together so the drain from the batteries is equal.
That way each ESC see's the 4S2P battery setup.

In IMPBA there is no limit on "mah" So my new Twin "Q" Cat is wired 6S3P for Offshore.

Larry

[Fluid]

I am a bit confused Terry, AFAIK neither organization limits twins to separate or common power for the motors. Separate packs per motor are easier to set up in cats, where there is a lot of distance between the motors. In monos or hydros, not so much. Two motors pulling from a common source insures that both are seeing exactly the same voltage and will run the same rpm in a straight line.

There was a lot of handwringing over allowing two motors in P boats, the worry being that someone would build a P Hydro with two hot motors and blow everyone away. This would then start a spending war and force everyone out of the hobby. No poop, that was a popular argument. Of course it never happened in NAMBA....



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[ray schrauwen]

I am a bit confused Terry, AFAIK neither organization limits twins to separate or common power for the motors. Separate packs per motor are easier to set up in cats, where there is a lot of distance between the motors. In monos or hydros, not so much. Two motors pulling from a common source insures that both are seeing exactly the same voltage and will run the same rpm in a straight line.

There was a lot of handwringing over allowing two motors in P boats, the worry being that someone would build a P Hydro with two hot motors and blow everyone away. This would then start a spending war and force everyone out of the hobby. No poop, that was a popular argument. Of course it never happened in NAMBA....



.

For example. Larry built a screamer p twin using some very inexpensive motors proving it's how well he dialed that hull in to utilize every % of the motors efficiency he could. The guy that bought that boat got a great deal on a very well blueprinted hull. I wish I had the skill and patience to do that.

[TRUCKPULL]

For example. Larry built a screamer p twin using some very inexpensive motors proving it's how well he dialed that hull in to utilize every % of the motors efficiency he could. The guy that bought that boat got a great deal on a very well blueprinted hull. I wish I had the skill and patience to do that.

Thank You Ray

It took me a while to get that Cat dialed in. In NAMBA I was restricted to 10,000mah total on board.
So to run in the Offshore class (Four and a half min. run time) You max Amp draw had to be below 57A per motor.

Now that we are affiliated with IMPBA ( NO MAX mah on board)
The only rule is weight.

"Q" Twin Cat for Offshore 6S3P total 15,000mah

Larry

[Fluid]

For example. Larry built a screamer p twin using some very inexpensive motors proving it's how well he dialed that hull in to utilize every % of the motors efficiency he could....

As I stated, the feared rush to build twin super-hydros never happened. Just like the hull length limits, limiting the number of motors is a solution waiting for a problem.



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[TRUCKPULL]

As I stated, the feared rush to build twin super-hydros never happened. Just like the hull length limits, limiting the number of motors is a solution waiting for a problem.

Your right Jay.

I remember the talks in IMPBA back then. All the scenarios that people came up with never happened.
I was one of the people back then trying to keep the Electric rules the same in both camps NAMBA and IMPBA
NAMBA had there rules set when we started on the IMPBA rules.

This one is one of them that we missed on ( Twins in "P")

Larry

[T.S.Davis]

Jay, page J-2, at the top of the page.

Who wrote this rule? It makes no sense. We allow 47,000+ mah but we want to micro manage how its done. Paul's reasoning is quite plausible but that's not a reason to mandate it.

I think I have the twin P thing figured out though. IMPBA never bought in on the "limited" thing despite the fact that clubs are running the NAMBA version all over the place. No twins in P might have been an effort to deter an arms war so to speak. If you're trying to get in to FE in IMPBA currently you can do the 2s classes and your next stop iP with opethinking back then P. P is already daunting. Allow twins and it could get nutty quick. I should say.....I suspect that was the thinking. Didn't happen in NAMBA in P but we had P limited for entry level guys and vets to hang out together.

[Fluid]

Missed that Terry. How silly, and to refer to ESCs rather than to motors as is used a few sentences later(?). I wonder if that is really what was intended. As you know, sometimes a rule gets written which is not exactly the way it was intended....


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[TRUCKPULL]

Terry
I do think something got mist there.
I do believe it was Randal T. that wrote them up when they were submitted to IMPBA.

I remember at that time he was very concerned about someone building a ESC that would switch packs from parallel to series.
There was a mechanical wiper type control that did this at the time.

He also was very interested about teching stock motors, as you can see in the rules.

As a club we did not see the final draft that he summited until the vote was sent out by IMPBA

We were told that we could fine tune them later.

Larry