I was posting in another thread and It made me think of an Uneven drive board I built recently.
the build was a total accident, I was making a DR for a friend with parts he provided and he accidentally bought 2 motors of different size.
so I have by total accident probably pioneered the dual uneven drive board.
I figure no one else has probably been stupid enough to try this, but I was actually really interested to see how it turned out.
so I had one motor which was around 200kv and one with about 400kv
would it work?
would it explode?
Or,
would it work like some sort of sequential twin turbo system where the torque from the 200kv would assist getting the board off the line and up to the top where the 400kv would take over and boost the top speed?
well turns out it was the twin turbo option. who knew?
seriously, the low down is taken care of by the extra torque of the 200 and the 400 kicks in and boosts acceleration and top speed!
each motor is powered from its own individual ESC so the loads on each motor are different but shared slightly, handled by different electronics so there is no real feedback or connection from one motor to the other.
So what happens when the 200kv motor exceeds its theoretical RPM limit?
think of it this way: whats your theoretical top speed?
mine is about 35km/h but we have bombed hills right? i have had my board up to ~38km/h-40km/h which is already exceeding the max RPM of my motor.
So you could say its just the same as going down a hill, the load on the 200 will be reduced.
Wow - sounds like a fun thing to test with full protective gear!
What voltage are you using for them? My first dual motor (5065 200kv on 8s) did 30mph with a tailwind. Would do 25mph easily the rest of the time. I actually didn’t realize how fast i was going (first run in the neighborhood the night i got it finished), and typically moderate the speed a little better now. I try to gear mine so that it’s top speed is around 22-25 max. Keeps me out of trouble that way.
As for the motors i’m surprised it works well and wonder if the gearing works out to be limited by the fast or slow motor? What gearing, wheel size and voltages? I’ll calculate both and see which one it seems to be limited to.
I have done the maths, the theoretical top speed of the 200kv with 2.5:1 gear on 70mm wheels is 35km/h and the theoretical top of the 400kv with same ratio and wheels is 54km/h.
I say theoretical because I have never ridden it to the top speed, I run out of balls at upwards of 40km/h
thought it was doomed when I read the title, but as I look at what you are saying, it actually seems pretty sweet!
I think if done right, this will be super sweet, but consider some of the following:
you would need some way to switch to the second motor after picking up speed- you could possibly use the second channel on your rc remote (the steering wheel) to do the switching between motors- I don’t know how you’d actually get it to switch though… the only thing I can think of is a servo on a switch which changes which esc goes to the throttle pins on the receiver. I just wouldn’t connect both esc’s to the throttle at the same time… it seems like a recipe for disaster. also, I think the 200kv motor will be fine exceeding its RPM limit so long as it’s not powered when it exceeds it… if its just freely spinning because the other motor has taken over at that point, I don’t see any reason for it to just blow up.
in all, I think it will work as long as you don’t have both spinning at the same time, because they will want to go different speeds.
@cmatson - he’s running dual now w/ different kv. Seems to work without toggling power to either. Kind of amazing it works really!
lowGuido - cool! I wanted to compare setups with the calculator i have, but it needs motor gear # teeth, and wheel # teeth.
Looking at typical gearing around 2.5:1 - 16/40 = 25kph @ 200kv, 50kph @ 400kv (simple math at least). I guess i’m close to your actual gearing.
Honestly i never thought i was going all that fast, but in hindsight 30mph was pretty foolish.
If you ever want to use a good gps app for this, i really like strava for miles ridden, avg mph/kph, elevation gain, and top speed.
This is a amazing. I never would have even thought about a hybrid kv system like this, but it makes total sense.
I think you’ll be just fine without actively switching between motors. In fact i kind of wonder what kind of performance I would have if i took one of my 270’s and replaced it with one of my binned 245’s.
Have you noticed any sort of torque steering issues? 200 to 400 is a pretty big gap.
yeah, there is no active switching, as i said, once the RPM ceiling is exceeded the lower kv motor just has less load and acts in the same way it would as if you are going down hill.
All the electronics are separate anyway.
I’m with most of you guys, I wouldn’t have thought it would work either, but I guess that’s why I tried it.
I’m also not saying this is a perfect system and that I have all the answers, cause I don’t. i’m just relaying my findings with you guys to perhaps open new avenues.
and there is no torque steering issues. look at a single wheel drive board, they the the most differential possible, all and none, and yet they don’t have any major torque steer problems.
in fact you are probably best to look at it as two separate 1 wheel drives on the same board.
This would work better if the rear pulleys were on ratchets (like the rear sprocket on a bike) and you had a nice brakeboard truck on the front. You would lose regen braking though.
well I tried a top speed run today on the UDR drive.
Results were pretty good.
so I took my board with a single motor down the road and peaked the speed at 30 as a control run.
then I took the UDR board down the same road and it was noticeably faster. however I only made it to 37 before I got a bit of a wobble up and slammed. not too hard fortunately, but I could feel that there was more in it.
I might have to try it again another day when I get the balls to give it another shot LOL.
30km/h.
don’t get me wrong, I have had it up to 40km/h but on this particular road on this particular day I peaked at 30km/h
may have had a slight incline or my 40km/h run had a slight decline, or perhaps a bit of both.
but for the purpose of back to back testing, the peak of that board on that day was 30km/h.
also worth noting is that my single that I was testing against is a sturdy board with a kick tail that I’m very much used to riding. the UDR board is a flexy bamboo board with no kick tail and just slightly different physics that make it a little uncomfortable for me to ride hence why I slamed towards the top end.
bottom line is that the UDR really easily pulled an extra 7km/h with more in the tank before I slammed. that’s quite a substantial difference when you break it down.
Nice! I’ll be running a dual diagonal setup(if I can fix my first vesc) with different motors. Rear will be Enertions big rspec and front will be a Tacon 160. It will be fun for sure!
@lowGuido This is so cool! I’ll mention something obvious, but not yet noted; this approach might allow dual-rear configs with more motor can options. Maybe you could use different motor can sizes, one large one (63mm) and one smaller one (50mm) without running out of room on your trucks!
Ok, so here’s my question - what if you put a brushed DC motor on one truck and a BLDC on the other? Brushed motors have maximum torque at zero RPM, which would give you great take-off power and then as the power on the brushed motor diminishes with increased RPM the BLDC kicks in and pulls you the rest of the way.
Also you wouldn’t have any of the issues with over RPM drag since the brushed is not a “timed” motor.
