I totally agree on the different wheel speed when turning. the inner wheel will always be slower than the outer wheel.
however I do not agree on your bottom diagram. in real world situations it simply doesn’t happen.
maybe if you try riding a DD you will change your mind.
Yeah I know… I can’t really talk cause I have never ridden that way… But i have ridden single drive and it happens, DD is basically two single drives.
I think it would be more noticeable during braking, but like I said easy to counter by tilting the other way.
But YES this is just my theory… have not done real world test…
Someone with a DD should setup a test, load up the deck with a “dead” weight drive it off down the street at full speed then slam on the brakes and see if it tracks to one side. Of course as a rider you will counter it with tilting, but a dead weight cannot.
I can prove it. Keep in mind I’m talking and thinking about a skate truck. You are talking about a vehicle. Because the skate truck turns only from the center it acts like one wheel. Picture a truck that holds one 10" wide wheel at either end of the board. When you lean both wheels turn in toward the side you’re leaving to right? The board will turn in a circle. Now ask yourself this. Does the outside of that one wheel turn faster than the inside of it? It can’t. It’s impossible.
YES IT DOES.
Its not impossible it actually happens. the truck twist does change things a bit so yeah you cant compare a car to a skateboard… let’s stop doing that. but the inside wheel does always turn less that the outside.
I agree with @lowGuido in real world situations to a certain extent.
Just so you know: I have never ridden Dual diag, or dual rear… only single drive on a couple different builds.
I rode my first build for almost 6 months with the back left wheel always being the powered one. Back then, I’d swear that it wouldn’t turn when you accelerate or brake, and that one wheel drive was fine. Then, when I got the new enertion motor mount, and put it on the back right(of a different board., I was genuinely shocked at how different it felt: not saying back right is the best, and back left sucks… I just got used to the feel of back right and switching threw me off. Of course I immediately switched it to the left after than… You just get used to it quickly, and automatically correct without thinking. Try switching your dual diag setup to the other side, and see how it feels- it’ll be way different.
also, as far as one wheel spinning faster than the other, @onloop and @lowGuido are correct. Tomorrow I will put a black dot on my skateboard wheels (an old pair I have on one of my normal boards), loosen the trucks, and show it turning slowly. starting with the dots in sync, and then, showing them going out of sync as it travels through a turn.
Also, Onloop’s diagram actually represents skate trucks- not cars
On paper, in diagrams related to automotive tech you are absolutely right. As soon as you introduce a kingpin none of it matters. Just because onloop drew skate trucks on the diagrams doesnt make it a skate diagram…
This concept applies no matter if we talk about cars or skateboards or anything else with wheels that need to turn in an arc.
It also does not matter how the steering system works, wether it pivots on a king ping or each wheels is turned on its own axis or tilts to turn… it really doesn’t matter.
The fact of the matter is the ID of a turning arc/circle has a smaller circumference to the OD.
So even if you just had a one wheel vehicle. For example a monocycle & it had one really wide skateboard wheel of 30cm width. If you make that wheel turn any arc from just a few degrees through to 360 degrees the outside edge of the wheel has further distance to travel then the inside edge…
If you created a machine that spun this wheel in a continuous circle (like a big clock with a wheel assembled onto the tip of the second hand) it would begin to wear out unevenly as one part of the wheel is being forced to travel across an area quicker OR slower then what it is actually rotating.
The thinner the wheel the less it will wear out.
The only way to stop a wide wheel wearing out (if it was attached to the second hand of a clock) is to make the wheel a cone shape, with the outside edge having the greater circumference than the inner edge. This way the outside edge can travel a greater distance in the same time as the smaller inside edge without skidding.
In car racing on oval or circle tracks they call it “tyre stagger” for more info this article explains it. http://iracing.wikidot.com/components:tire-stagger
Yup I know all about Sprint cars as I used to work at San Jose speedway…do you guys have any other comparisons other than cars or geometry books?
So with that concept, because the inside of your outside wheels can’t turn faster than the outside of the wheel…all of our wheels would ware funny right?
Basically YES, that is why all wheels eventually wear down.
Yeah, It’s all too much to worry about with as narrow as our foot print is unless you like worrying I guess haha.
i have a small contribution. Math. I suck at it, but this is pretty basic. The diameter of the outer wheel’s circle is greater than the diameter of the inner wheel’s circle making the total distance travelled greater, yet both wheels must spin for the same amount of time during a turn. So if you spin both wheels for a given amount of time, yet give one wheel a larger distance to travel, guess what has to happen? The one with the longer distance has to spin faster or it skids and drags on the pavement.
But the difference is utterly minuscule and with separate drive motors on essentially separate ESCs (even dual ESCs are just two singles getting the same signal from the receiver) then the outer motor will be allowed to spin faster as a result of them not being tied together yet still receiving roughly the same amount of juice. It won’t spin faster because of awesome programming, it will just be allowed to because more pavement is running underneath it as a result of math and since its got the same juice as the inside motor, it can do less work to go that extra distance.
but again, we’re talking 8 to 10 foot turning radiuses here with a difference in circular diameter no more than 360 mm given a 180mm truck. The difference in spin is negligible.
If you want to get into some serious shit, try and have your ESC detect tilt and give the outer motor say 5% or 10% more juice. Might be possible with a VESC, i don’t know.
I have some useful info. I am a qualified snowboard instructor and I have studied the theory of carving and in a toe side carve it is best to have your centre of gravity over your front toe, in a heel side carve you should shift your centre to your rear heel, this gives you a tighter and more controlled turn. With that in mind the DD setup would benefit, as a goofy rider, I would put the front drive wheel under my front toe and the rear drive wheel under my rear heel. Therefore when I am turning, my centre of gravity is above the drive wheel. This would give better traction in turns and help you manage your tourque better. On the other hand it’s more wiring, plus I’m going to have less space under my deck for components. Thoughts?
Hey @Moja. now that there is the first REALLY interesting thing posted in this thread!
as a natural rider I have my DD motors front right and rear left. (front toe, rear heel) I am also an avid snowboarder. this would totally explain the superior carving action that I feel riding the DD setup.
now the real test would be if I was to ride a DD front left and rear right would it then feel weird?
I reckon it would feel real weird, you would probably experience wheel spin during carves as there will be very little weight over the drive wheel. I’m glad you hear that the theory works in practice on e-boards, how does it compare to a dual rear wheel drive setup? I’m going to be building my setup in a few weeks and I’m yet to decide which way to go.
as I have mentioned earlier in this thread I personally prefer the DD setup over the DR setup. perhaps it is because of what you have just mentioned above.
To add my two cents to the argument I have to say I prefer Dual Rear. Now I understand all the mechanics and to be truthful there are both advantages and disadvantages to DD and DR. For me though I prefer the feel of DR and I think this is what it comes down to. Just as some run their trucks loose and some tight, some bomb hills while others carve the flats the setup of the board and how you like to feel the board will depend which you prefer.
My DR preference was because firstly I noticed the pull of diagonal being annoying … not so much in drive but in braking and in my riding hard braking is a common need…and it bothered my most that it varied heelside to toeside then further would annoy because I tend to switch foot and I could never get it in my head that the torquing tendency under breaks would also be flipped because I was. Sure, this is a stupid set of circumstances but it just affected how much I enjoyed my rides. I liked riding a DD electric … I loved riding a DR.
Why I like DR. I am a kid of the 80s with single kick boards and have an inherent reflex to lift the nose from time to time - DD made that harder especially on a pintail (and it’s why I have a pintail not a snub). When I hit a bad spot on the road the DR misbehaved exactly how my brain expected whereas DD would surprise me sometimes with how the board wanted to snake it’s way out. I didn’t want wiring running up my board because I know I will scrape up the top or bottom at some point and I din’t want to be making plasma and possibly frying an ESC if I did.
So I say DD and DR are both good but different strokes for different folks and I sit firmly in the DR camp.
@moja that makes perfect sense and i will definitively be considering this point when asking people about their riding style in order to come up with the best configuration for them.
I’m also in the DR camp but i suspect my affinity for symmetry has more to do with it than actual experience since I have not actually ridden a DD setup before.
Everyone should try both 
Then we have a better basis of comparing.
Been riding both for 2 years but the DD is always the one I give friends to ride 