Torque vs RPM

[lohring]

A little off topic but the reason we built an inertial dyno for our gas engine testing was the acceleration issue. We thought that high speed SAW runs at Legg Lake were more like drag races and the inertial dyno duplicates that. Electric power systems' output can be calculated so I don't see how prerace testing would help. It looks like the ESC capacity is the limiting factor once you got props that would hold up. Is that true?

Lohring Miller

 

[RaceMechaniX]

Yes, the ESC's for me have been the limiting factor up in till recently. The amount of current you can push for several seconds is sky high to be able to accelerate quickly.

TG

 

[Christian Lucas]

Hello Lohring , Tyler ,

yes and no for the esc . We all know the brick that Ralf used in his monohull ,this is the way to go with 3 phase motordesigns . Possible to switch to run 2,3 or 4 esc in parallel . We have run 2 esc on a Lehner ,with spezial wind to get two seperate 3 phase systems and up to 4 esc with YGE controler on outrunner with 12 leg statordesign . At magnetmotor company i designed during my fuelcell reseach time some homopolar motors with permanent magnets that run at low volts and high current of 2000 ampere . This motordesign allow much smaller esc as the current flow only one way ,no switching + and - that makes the use of capasitors in big size a need . I designed that motors with brush and with electronic (mosfet) switch . With fuelcell the smart thing was that we could change rev by controling the hydrogen flow no electronic switching needed .Other to run it like we do on outrunner with seperate 2phase esc for each phase as there can every esc be small ,separate cooled thats good as they have a bigger surface like mice vis elefant . We run flywheel up to mach 2 surface speed . Slefe made from carbon and titanium wire with pre force set on . Yes need some know how to do .

Lohring ,

For high accelerating with a combustion engine lets think about the use of two counterrotating flywheel that are conected with a differential gear.rev them up and clutch then on of the flywheel to the gear shaft to rev up the driveshaft of the propeller . All power from the engine but with a little store in the flywheel for limited time .

Other way is to build switch the power in two propshaft with a Arneson like angle switching drive that has no skeeg . For stearing use a ruder. With this you get a pitchcontrolable propeller surface drive system .

 

[Ralf Moser]

Hi,

The brick is necessary for converting the power of 2p on one shaft. In 1p the smaller one is enough. And 2 esc 1 motor I drove before was poker at that current, i had to select 2 escs out of six.

But even if this power on one shaft is available, and the prop etc holds it-in the end you cannot accelerate faster then what is possible with the specific hull. A mono has way more resistance, which will lead to some heavy torque reactions if you accelerate too hard when you are slow.

Pulling the trigger is something you can do if you are already at high speeds cause there you have enough hydro- and aero-stability and resistance vs propforces is better balanced.

This is why myself would be in principle happier being able to push out of corners then pull up from dead in the line. A single mono want to do cornering, it is its nature.

And twin.... it is only on the paper faster due to the drag style we have now with current speeds and the course. Lot of totally different problems i have found with two twin saw boats i built for testing. For mono I speak.

Riggers are already faster in acceleration with their low resistance. But you need an esc potential of surviving 400a+, which is not easy in size.