Help me Daydream, Offroad Hybrid
 

Let me start by making this disclaimer: I will probably never be able to build this, and even if I could, its at least 10+ years off. I just want to enrich my mind and imagination by figuring out how it could be done. This would never be the cheapest or easiest, that's not the point. I enjoy the design and problem solving aspects of the build, driving it afterwards is just a bonus.

That being said, I want to figure out how to build a small rock buggy. I think I would want to use a hybrid ICE/electric/hydraulic powertrain. It would need to have enough low speed torque, and maybe have a top speed of say 30 mph. Fuel efficiency is not a primary concern, no matter what, 4x4's are always expensive to play with. I think with as little as I know about the specifics of regular hybrid technology, that I would like to run the ICE in series with the electric motor, primarily as a range extender. The electric motor would in turn power a hydraulic pump that would spin hydraulic wheel motors (mounted at the center of the axles). The two primary reasons to add hydraulics is because I feel these can be made survive harsher environments for cheaper than electric wheel motors. I also think that some clever valving could gain several features that might be nice to have in an offroad vehicle.

Perhaps I could try and complicate things by being able to bypass the electrics and run a hydraulic pump directly from the ICE as a sort of "limp mode", but I dont know how necessary that would be, nor how much more complicated it would be (or expensive).

Most of the questions I have pertain to electronics, but include a few other topics:

• Is regenerative braking something I should try and include?
• Aside from trying to recapture energy, can the electric motor be braked electronically?
• Are there motors available with that would allow me the low end torque and high speed without the use of a gearbox/transmission?
• Aside from weight, what are the primary benefits of using more advanced batteries than say AGM lead acid?
• If sticking with a series hybrid, what is the most efficient type of ICE, and what kind of power cycles should it see if all it is doing is basically running a generator?
• Anyway or reason to make the hydraulics do more than simply transmit the energy coming from the electric motor?

Some of the other details about this daydream:

• Smaller than a samurai, larger than a side by side
• two seater with tube chassis
• 33"-35" tires
• hydraulic valving to get park/reverse/neutral/forward
• homemade solid axles
• as quiet as possible

I am very open to different ways to build something like this, what might you do differently?

http://oldironadventure.files.wordpr...rius.jpg?w=474

I kid, I kid.

come on hybrid guys, tell me what i am missing. ive read up on some of the forkenswift data, and maybe something like that is a starting point, especially since I dont think regenerative braking would be effective at such slow speeds.

also, Im starting to read about The DIY motor controller

Im reading about that controller and i noticed something. The wiki says "Regen can be set anywhere from 0 to 300 amps per phase." This is under the "AC Motor Controller Features" found here. Is regen something that can be ramped up, like with a pot? Could this be used as a sort of brake?

Yes, but there's a HUGE gulf between automatic- and manual-control of that regeneration...ie: computer involvement!

i didnt know if it could be rigged up to a pot to act like a brake pedal. manual hydraulic brakes would probably be sufficient though.

I don't know any reason for the electric part, except for Regen, but if your going slow there will not be much of that I'd think. Here is a thought for drive layout if going Hydraulic, it's a Concrete Extruded curb machine. Each of the three legs steer independently and move up and down independently, for rock crawling you'd probably want four, and have wheels at the bottom instead of steel tracks. You would be able to move each wheel up or down to maintain the vehicle attitude, and each wheel would be steerable...it could turn all the way around in it's own length. I am working on a "Light weight" Electric two seat UTV type of machine, which I'd like to add a generator to for onboard charging...a Hybrid. It's story is under the Hybrid section. Good Luck!

I'm not an expert but I think I can help steer you in the right direction. I'll attempt to answer each of your points.
Is regenerative braking something I should try and include? Your hydraulic drive would have accumulators that help control speed both forward and reverse as well as brakeing, much like electric regen.

Aside from trying to recapture energy, can the electric motor be braked electronically? Yes with full control either way. but see above.

Are there motors available with that would allow me the low end torque and high speed without the use of a gearbox/transmission? Absolutely. Electric motors are ideal for huge low speed torque but some also can attain very high speed with enough voltage.

Aside from weight, what are the primary benefits of using more advanced batteries than say AGM lead acid? Yes, sag, lead acid suffers from voltage sag under heavy load lithium based batteries much less so.

If sticking with a series hybrid, what is the most efficient type of ICE, and what kind of power cycles should it see if all it is doing is basically running a generator? With hydraulic drive a small diesel may be used to pressurize the system or recharge the battery.

Anyway or reason to make the hydraulics do more than simply transmit the energy coming from the electric motor? Hydraulics are very flexible systems. you could do almost any thing you imagination dreams up.

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.

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

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?

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

I don't understand, which assertions?

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.

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

Timed event?

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.

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.

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

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.


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...

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.

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

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 :)

Consider what kind of performance a Bobcat Skid-steer style loader has, this will give you a Weight ( though some of that can be done away with removal or the counterweight), a Horsepower, and performance. These machines will spin all four wheels on pavement, so power to the wheels is plenty. Top speed is the limiting factor according to your parameters. CAT 216B Skidsteer: HP...51, Top Speed....7.9, Weight...5690.

Sorry I have taken it upon myself to try to steer the discussion towards actual engineering details, but I think you mean torque. power would be a function of torque * rpm. A slow turning wheel may not have much power (which is why I'm not balking at light rock climbing with a 10hp engine).

an ironic example, that you see on may rock crawlers is a winch, 4 hp and can pull it straight up a cliff. So in a way, they are already electric hybrids :)

Yes and no! To get get a 5+ thousand pound skid steer loader to spin the tires on pavement, one must have the throttle wide open, using all the horsepower!

P-Hack, you obviously have some strong feelings about this, tell us how you really feel? Did you even read the first sentence of the first post? I dont know if you are intentionally trying to be Debbie Downer, but you are being very antagonistic.

The biggest reason I like electric for this application, is because I think it would be fun to design and build, period. The second biggest reason is because in my experience, most ICE's don't produce sufficient torque at idle, which is where the majority of the time is spent. Instead, they have to be oversized.

No where have I said this would be practical, or cost efficient. I have also not said that gearboxes would not be used, I had just asked a question about the electric motors having both sides of the spectrum.

lol, you have a lot to learn, so you might want to get started. physics is fun, daydreaming is a waste of time, on a tech forum anyway.

the problem isn't impossible, things have weight, they make torque, they fly apart at a certain rpm (or torque, or volts/pressure/current/???), things have different energy/power densities (volume/weight), tires make traction based on weight, instantaneous. For any idea you have in your head, you should be able to figure out how fast it can go and what kind of slope it can climb and for how long.

There's no reason, or excuse, for wishful thinking, or disregarding experienced answers that you happen to not like.

Punching a few numbers into the calculator on this site.

A few assumed figures that should be somewhat close

frontal area 25ft^2
Cd 0.6
Crr 0.1 (Wiki has Crr for tires on sand at 0.3, but that would requre all of my engine power to do 35, and I can hit 50+ on sand so I went with something more reasonable.)
4000lbs
Drivetrain efficiency 75% (full 4x4 transmission and all)
500w of paracitic load (probably quite a bit low)

All of that gives a requirement of 35hp.

One site listed hydraulic pumps as having 80% efficiency X2 gives a 64% conversion efficiency. So you would need an engine that could put out 54hp continuously to hold 30mph, or up to 27hphr of storage for the 30 minutes.


Efficient, most likely not.

What he would gain would be a butt load of low end torque, exactly what every rock crawler wants more of.

As far as weight, my rig is pretty light at about 3200lbs, with an engine that weighs in at 650lbs (210ftlbs at 1800rpm, and 115hp at 3200rpm). Depending on how he builds his rig and how big even with hydaulics he shouldnt be over 4000lbs.

Edit to add: I am rarely even at 1800rpm, often below 1000. When I do run above 1500 on the trail I am also feathering the clutch to control the speed.

Now if he was able to keep the weight down to 2000lbs with a 2 seat tube buggy the hydraulic motors/gear reduction at the wheels etc the engine would only have to produce 30hp to maintain 30mph.

that sounds like a reasonable approximation. Now if we add hydraulic storage:
per: http://www.hydac.com/fileadmin/pdb/p...0140000011.pdf
A 50 litre accumulator
with 400 bar maximum
pressure can supply
approx. 360 kJ = 0.1 kWh
(adiabatic).
50liters is about 100 pounds.

plus it needs a low pressure tank, so that is roughly 100lbs of fluid for 100watt hours of energy, plus tanks and stuff. It's enough energy to run the headlights for an hour maybe. to make 25hp (plus 10 from the ICE) for a half hour would be like 10,000 lbs of fluid. And you would have to sit there going nowhere for over an hour to charge it first.

I'd shoot for the light side first. Say two drivetrains out of a couple of Zero Turn riding lawn mowers, use a frame from one of the 2 seat adult go carts. Wide'n the suspension to get more wheel travel, use one engine and have an extra drive motor geared for the desired top speed. Keep the weight to 1,000 lbs dry would vastly increase climbing ability. My old go cart went 30mph with 3 HP, though it was not hyd. drive.

According to an online sizing calculator

35hp at 5000psi = 10gpm

The engine would definitely have to be powerful enough to maintain speed on its own.

It wouldn't be efficient, but I would likely be able to be a good slow steady crawler.

The reason I prefer hydraulic to electric is that when you bind up your drive train and stall the motor. The electric motor draws way much more current when stalled greatly increasing your chances of burning out your motor controller, batteries, motor, wiring etc. Burn it out with no spare and your rig gets dragged out, which so far I have been able to avoid.

You could have a pto shaft off of the front of the engine to drive the wheels mechanically on the fast areas, and 35hp would get you 30mph easily. I'd use a high output MX bike engine, say a YZ 450 4 stroke, 50HP, 8500 to 11,000rpm. Less than 100 lbs.

well a high rpm motor will only have more losses on the conversion to torqe.

and the hydraulic motors are basically turning all the time, bolted straight to the wheel, so lots of fluid moving around going nowhere at 30mph.

I like hydraulic, as seen on construction equipment and other crawlers (like that thing that moves rockets at 1/3 a mile/hour) but it loses if you want hydraulic energy storage.

An electric motor controller that can monitor current/temperature/etc and minimize breakage isn't that hard to conceive (and liquid cooling can help). But there are lots of design limitations and compromises in that direction as well.

These are very high efficiency engines withe the torque curve remaining virtually flat from 5000-10000 rpm.

Smaller engines aren't usually terribly efficient, but there are atv sized rock-crawlers, but how does the hybrid part play along without being the worst of both worlds?

well this isn't exactly what was described, but an interesting machine anyway, electric drive 4x10hp (peak 200hp total), some large honda generator looking thing, wheelbase can be lengthened/shortened/widened/narrowed/raised/lowered hydraulically. And can go pretty fast, for a little bit.

But it doesn't have much storage, aside from the fuel tank "batteries give it corvette power for 5 seconds". So technically a hybrid (as counting the winch as a hybrid didn't seem to get much traction).

also didn't see any vids of it climbing, mostly dancing around in the parking lot, so nothing conclusive about it performance wise. It might be so expensive he is afraid to climb with it, or it breaks easily, or too heavy with batteries or not geared right for climbing or? But I would think there would be some real climbing vids if it were that good, rather than leave it to your imagination.

green rock dawg
https://www.youtube.com/watch?v=QlaPenxgSvU

"Efficient", by what metric, HP/CID... In the past a Cox .049 2 cycle won that one hands down, today I don't know. These MC race engines are pretty good for what they are designed for, we now have 4 stroke motors beating two strokes in the same class, and P/W is King!

Wow, there you go! That looks like the I believe V8 powered machine that each wheel is on an arm which can be pivoted up or down, chain drive as I remember. Articulation is Crazy!

efficient when discussing an engine can surely be assumed to mean bsfc(well, around here anyway). power to weight can play a role in system efficiency, esp in a vehicle, but an engine by itself cannot go anywhere. The smaller the engine the worse it is at turning fuel into horsepower, typically.

edit, pic:
http://image.slidesharecdn.com/perfo...?cb=1363253456

Here it is in action, way to buisy keeping everything adjusted, more of a can I do it kind of thing. I could see hitting a lever the wrong way and flipping it on its lid.

https://www.youtube.com/watch?v=7GugdJc-O7I#t=121

Don't forget extra friction losses due to high RPM. Not to mention I would need at least one extra gear box to convert RPM based horsepower to torque, and I am already geared higher than I like with an engine that can chug along at 500 RPM.