Vehicles like Segway

[quade]

Originally Posted by citivolus

I don't think all-electric regenerative brakes are adequate for stopping a highway speed vehicle. Resorting to a little quick math, as I am wont to do, consider a very light 1100 lb vehicle going 67 mph. Converting to metric, because I picked numbers that look nice that way, gives 500 kg and 30 m/s. In order to stop this requires either storing or dissipating 225,000 Joules. If we assume a normal stop to be 0.5 g and a panic stop to be 1.0 g, this gives us stopping times of 6.12 seconds and 3.06 seconds respectively. Since a Watt is a Joule / second, we find through simple division that the normal stop has go get rid of 36,765 Watts and naturally the panic stop is going to be double that. While you might get 50-100 HP out of batteries, putting it back in is somewhat harder.

The Segway is rather different. Assuming the total weight of a fully loaded Seg is about 150 kg (~330 lb) at it's top speed of 5.6 m/s (~12.5 mph) has 4704 Joules to eliminate. Again, using the same 0.5 and 1.0 g standards just for comparison, stop times are 1.14 and 0.57 seconds meaning the power is a much more manageable 4116 and 8232 Watts. That still isn't to say that you can jam that much power in a battery just that it is much more manageable. Now, I don't know the real numbers but I'm sure the actual stopping time of a Segway has been discussed here before and anyone really interested can perform the experiment themself.

Who says that all that energy has to go back into the batteries during a panic stop?

Why couldn't it be shunted off to a big chunk-'o-wire and a heat sink?

[hellphish]

Originally Posted by quade

Who says that all that energy has to go back into the batteries during a panic stop?

Why couldn't it be shunted off to a big chunk-'o-wire and a heat sink?

Where inside the sealed platform would you suggest they put it?

[bystander]

Originally Posted by hellphish

Where inside the sealed platform would you suggest they put it?

Quade was responding to citivolus. And citivolus was talking about both EVs and PTs. So maybe Quade talking about electric vehicles in general.

On a PT, there may be a way to add braking circuits externally. I know it's a bit of a reach. I still haven't done anything about it but think. I was thinking that there may be a way to make the augmented braking system with a few less brains by having the variable load proportional to it's own revolution rate, instead of trying to sense the current going to the PTs battery packs.

By adding this ("HBS"-type) accessory brake, it allows for additional EMF braking without putting further strain on the motors. After all, one of the limiting factors in regenerative braking is the peak power limit of the motor's windings.

[quade]

I was absolutely referring to the EV portion of the quote since the PT part of it doesn't really require any more of an energy sink than it already has.

citivolus had been talking about an energy sink for use during panic stops.

[hellphish]

Yeah, sorry about that. Now I see.

[citivolus]

Originally Posted by quade

Who says that all that energy has to go back into the batteries during a panic stop?

Why couldn't it be shunted off to a big chunk-'o-wire and a heat sink?

Oh, I didn't mean to imply the extra energy couldn't simply be dumped into some sort of power resistor only to wind up as heat. But if it's just going to wind up as heat, why not take the easy way and do it mechanically and not worry about heating the electronics and motors thereby reducing the efficiency?

That said, Karl's idea of charging the body shell does sound like it could have some rather "hair raising" applications.

[Five-Flags]

Originally Posted by citivolus

... That said, Karl's idea of charging the body shell does sound like it could have some rather "hair raising" applications.

And we're back to Tesla again. Amazing how that name keeps coming up...