Help me Daydream, Offroad Hybrid

[Frank Lee]

It's gonna be heavy with a battery pack. I'd go with ICE.

[Donahue]

Thanks for the suggestions, keep em coming. The ptomato reason for wanting electric over ICE is instant torque, which means the power system can be smaller with less total power than required ICE because it makes said power right away. I also like that it's silent and smooth. Would a hydraulic system require accumulators?

[P-hack]

I don't think any of those assertions are true except in your daydreams.

[Donahue]

Originally Posted by P-hack

I don't think any of those assertions are true except in your daydreams.

I don't understand, which assertions?

[hamsterpower]

Originally Posted by P-hack

It is a function of the size of the motor, so yes, but it is gonna be heavy IF YOU HAVE NO GEARS!!!

The tesla roadster has about 8.25:1 gear ratio IIRC. But you are not going to find a motor that can drive a single speed gearbox AND lift a heavy homebuilt thingamabob offroad rock climbing AND push it down the hiway. Multiple gear ratio choices certainly would be a good call there.

electric motors arent magical. And adding volts adds weight for a given torque, so less climbing.

He said top speed would be about 30mph, so no highway speeds needed. He also is talking about a rock crawler so the range only needs to be a few miles per charge. so no big battery packs needed. With a diesel genset and a reasonable lipo pack and a small tube frame it could be fairly light and compact. Accumulators would help, its a way to regen and brake with hydraulics instead of the EV parts. Also with hydraulic drive that eliminates the need for mechanical gearing.

[P-hack]

ok, if range and top speed limited, then sure, though I would assume it is a timed event and more power is better to a degree (as is less weight), and batteries/accumulators have really bad power/energy to weight compared to fuel.

plus a 10hp ish engine running a generator running an inverter running a motor pushing a rock crawler geared to be able to climb rocks sounds very unlikely to be able to maintain 30mph. I'm thinking maybe 8mph, especially if the tires are a bit deflated for traction.

fyi the hydrodynamic rock crawler has been done:
HydroDynamic Rock Buggy - Four Wheeler Magazine

[Donahue]

Originally Posted by P-hack

ok, if range and top speed limited, then sure, though I would assume it is a timed event and more power is better to a degree (as is less weight), and batteries/accumulators have really bad power/energy to weight compared to fuel.

Timed event?

plus a 10hp ish engine running a generator running an inverter running a motor pushing a rock crawler geared to be able to climb rocks sounds very unlikely to be able to maintain 30mph. I'm thinking maybe 8mph, especially if the tires are a bit deflated for traction.

I'd probably be satisfied with 30 mph for up to 10 minutes every hour or something like that. That speed would mostly be for traveling to and from the trailer to the trail head.

fyi the hydrodynamic rock crawler has been done:
HydroDynamic Rock Buggy - Four Wheeler Magazine

I remember watching that guy build that on pirate years ago. It is vastly different from what I would want. That's like saying that nobody should be building EV's, because its already been done by some other guy. Its really kind of a silly point to try and make.

[P-hack]

Originally Posted by Donahue

Timed event?

many rock crawling events are timed, quickest one to the top and all that.

Originally Posted by Donahue

I'd probably be satisfied with 30 mph for up to 10 minutes every hour or something like that. That speed would mostly be for traveling to and from the trailer to the trail head.

Well, you will need to understand the engineering compromises involved. No gears and rock crawler and 30mph and 10hp diesel, pick 2. Daydreaming isn't very pragmatic I recon. But you could do some research and some maths instead of wishing.

Originally Posted by Donahue

Its really kind of a silly point to try and make.

Why do you think I was trying to make any other point than "here is a working example you might want to borrow some ideas/operating points from"? Oh, wait, that IS a silly idea apparently...

[TheEnemy]

Timed events are only seen in competition, the vast majority of rock crawling is done just for the challenge or fun of it.

Seasoned rock crawler here, with a few notes first. I have very rarely seen above 25mph on even the access roads to the trail so 30mph max is very reasonable. Since it is a trailer queen that helps simplify the design. I have daydreamed about building one, but that I could take on the highway for short distances, that really added to the complexity of what I needed to build.

With what you are wanting I would suggest hydraulic powered by a small gas engine 10-25hp should be all you need if you are actually crawling and not bouncing.

The biggest reason I suggest hydraulic is the opportunity for motor stall. Face it you will bind up and stall the motor at some point. The stall current of an electric is insane, while the fluid draw on a stalled hydraulic is near 0. And hydraulic also produced max torque at 0RPM.

As far as an accumulator, yes you would need one, otherwise there would be little point in converting to hydraulic asside from the torque advantage. Also regen would be usefull particularly when you are going down a long steep slope. I had figured I would do my regen control using a lever (like a bicycle brake handle) on the stick shift.

[P-hack]

Originally Posted by TheEnemy

...while the fluid draw on a stalled hydraulic is near 0. And hydraulic also produced max torque at 0RPM.

Hydraulic is a good choice if driven by an ICE, plenty of construction/mining/etc equipment uses it. Has its advantages.

Originally Posted by TheEnemy

As far as an accumulator, yes you would need one, otherwise there would be little point in converting to hydraulic asside from the torque advantage. Also regen would be usefull particularly when you are going down a long steep slope.

hydraulic accumulators have good power density, but the energy density is horrible. start and stop seems to be about the practical limit, and on bus-sized vehicles. Long descents or expecting it to help on a serious climb, or make much difference in 30mph for 30 min is probably in dreamland.

I guess I'm wondering what the point is myself. gasoline/diesel have terrific power and energy density, exactly what a rock crawler needs. And if it is trailered everywhere the efficiency isn't a concern.

The main focus of the hybrid stuff is to save fuel. It always adds weight and complexity (both bad for a machine that occasionally tumbles over).

I imagine if you ever get to the number crunching phase, you'll see that there isn't much difference how you do 30mph for 30 min, it still takes about the same amount of energy. And for that application I'd trade gas for batteries/accumulators any day.

When you compare the cost of implementation, and the hit in performance due to the extra weight, and compare that to the fuel you saved with a bit of regen, let me know