Dealing with ultra-steep downhills

I want to talk about a problem I noticed when going down ultra steep hills (much steeper than the board can possibly climb) - think halfpipe or 45 degree ski slope

Let’s set a baseline first:

  1. The steepest angle a onewheel without torquetilt can handle is around 21-22 degrees with standard rails, with torquetilt we can add another 5 degrees or so
  2. A good VESC board usually can go up pretty much any slope it can go down (excluding the tailscrapers)
  3. A very short ultra-steep slope can be managed with momentom and a soft (Mission like) tune

(1) and (2) I would consider moderate slopes

A long ultra-steep slope is any slope steeper than the Onewheel can handle in theory or climb with momentum, so going up is basically impossible no matter how light you are and no matter how strong your VESC/Motor is - think black diamond ski run

How does VESC handle ultra-steep slopes today (stable 5.3) ?
Imagine a 42 degree slope: if the tail is scraping the board will be angled ~20 degrees forward. If the torquetilt setpoint is 8 degrees then the net angle is 12 degrees forward

So what happens?
To the VESC logic it looks like you are asking it to accelerate really hard (12 degrees forward!) so it will send pretty much max amps to the wheel. So now you have gravity + max amps = a onewheel rocket shooting out from underneath you.

This behavior is worse than with the board turned off!

What do we want to happen instead?
Ideally we want to be able to go down slowly, without acclerating at all.
If that’s not possible if the motor is too weak, we can hope for “controlled acceleration”, meaning the motor is fighting against gravity (but losing)
And if that’s not possible we definitely don’t ever want positive amps sent to the motor in this situation

How can we achieve that?
In theory we could set the max angle for ATR to a much higher value (most people have 3-8 there now), possibly as high as 70 degrees

Alternatively/additionally we could have a logic in there that only allows braking amps when it detects that you’re going down a steep hill. So at worst it will be similar to pure gravity.

Thoughts? Comments? How does an FM Onewheel handle steep downhills?

I haven’t built my vesc yet, but I can answer the last part. My FM XR and steep hills. I’m a heavy rider and there’s a steep hill nearby approx 40m length, I can make about 1/3 the way up before the board gives out, but no problem descending as long as I don’t apply too much brake or let it go too fast. If I brake too hard it overwhelms the motor and cuts out, bad news on a steep descent. I believe going too fast might have a similar effect, too dangerous to test. If I apply a modest amount of brake to slightly slow my descent then I have no problem descending with some control, there’s no tail drag, but I have to be careful as there’s no way to stop, besides jumping off, if suddenly an obstacle blocks the path.
p.s. the hill is too sleep to slow to a stop, this does overwhelm the motor and cause the board to cut out. It’s a matter of finding the balance, not too slow, not too fast. The goldilocks zone of descent.

Echoing Tao, my experience on the XR & GT is that when a hill is too steep for the motor to fully stop you on a descent, if you commit to having some speed, the tail stays up and you don’t drag. It’s as if the wheel can tell you’re on a hill and the tail becomes stiffer to dipping, up until the moment where you approach overpowering it, then it gets softer.

To not tail drag on a Onewheel, you just have to be willing to commit, which isn’t a problem when you have a nice clean trail.

I’ve just recently started playing with torque tilt, and I have yet to install the ATR firmware (currently on stock 5.3 stable), but I definitely experience tail scraping on my VESC when my XR/GT would otherwise clear it. Just gotta work on learning what to tune!

Okay, both you and Tao appear to be focused on the “not being able to stop” part - XRs have many inclines they can’t get up on and they can’t stop on - but I’m talking so steep that it’s not powerful enough to even slow you down or maintain constant speed… I’m thinking about managed acceleration, where the motor helps you accelerate slower than gravity (aka better than a board with no motor)

I think I have identified a few grassy 30 degree+ hills which I will use to test this on… And I’ll bring my Plus, my XR, and a VESC board…

You’re talking about tail dragging, where the hill is too steep to keep the tail off the ground while braking. On a FM onewheel you end up on the ground real quick. The board has no way to tell the difference between you leaning forward and intending to accelerate and the tail bottoming out. I notice this going slowly down multiple short wide stairs. If the stair height is just high enough to keep the tail tipped up when the wheel hits the next lowest stair, the board will shoot out from under you as you’re trying to lean back and brake. You could detect this condition if you had pressure sensors in front and back to determine where the rider is leaning. Relying only on board tilt I think you can’t do it.

Interesting, you’re now throwing stairs into the mix - I agree that there’s no good way to handle this with the current hardware - but what I am talking about is a lot more straightforward and quite easy to detect - you’re applying very high braking amps, yet you’re still accelerating, so the controller can easily conclude that we’re dealing with a steep hill (well, I guess you could also be being pushed by a bus… but let’s ignore that case)