ex-Gooserider

Hope this a right place - if not mods feel free to move....

I am working on building an electric mountain board for a wheelchair using friend to use while in his chair. (Far as I know this is the first time anyone has tried this, my friend already does regular longboard and snowboard...)

The biggest challenge that makes this project different from boards that are used by able-bodied folks is that he HAS to be able to take off from a dead stop, unlike the able-bodied folks that give it a shove and hit the juice while rolling....

System summary -

Batteries - 3 x 4S2P Zippy FlightMax LiFePO4 4200mAh 30C batteries in parallel (so effectively a 4S6P pack)
ESC - HobbyWing XERUN 150A
RC - HobbyKing HK-GT2 car control Xmitter / Rcvr set (only using throttle channel)
Motor - Turnigy Aerodrive SK3 - 6374-149kv Brushless Outrunner Motor
The motor is mounted via a custom plate onto a kit my friend purchased from the UK which fits on the Paris trucks the longboard rolls on, and drives via a belt drive to one of the rear wheels.

We've done a couple of test sessions, and the last one is working pretty well - just a couple of tuning adjustments and I should be ready to hand it over to him.

I have two significant questions -

1. What is the "AMTS timing" that is mentioned in the ESC user manual? What should I set it for? If it matters, the discussion on the HK website said the motor is 12 tooth stator 14 magnets, and to tell the controller it is a 12 pole. The HobbyWing manual doesn't really say what it is, just pick the 'most suitable value according to the motor used' and that higher values give slightly more power, but less efficiency.

2. When in braking mode, and the motor is turned it screeches LOUDLY - otherwise it is silent or close to it. If the motor is braking and not turning it's silent, but braking from running in either air testing or use testing, or if I turn the wheel by hand it screeches - is this normal???? In free-wheel mode, or when driving forward it just makes the normal mechanical noises you'd expect from a motor turning a belt driven wheel, it only screams when the brakes are on, and the motor is rotated.

For what it's worth, this is how I have the ESC set at present, using the HobbyWing programming box

ESC - as of 5/6 experimenting, updated on 5/16, pending more testing...
Use "Mode 1" or racing mode
1 - For / Brake (No need for reverse...)
2 - Drag Brake 0% (brake setting at zero throttle - so that it can free-wheel)
? 3 - Volt Prot XX 2.8V / Cell (This kicked in WAY early - even after restarting and using the board some more, I only put about 600mAh back into the batteries when recharging. Changed to Custom 10.0V (total for the pack as 2.5 x 4 =10V)
4 - DRRS "Punch" Level 3 (controls takeoff power / equivalent of motor comp, seems adequate, might increase slightly)
? 5 - Brake Force XX #2 / 50% (force at full brake - is it enough - NO! Didn't hold on hills, increased to #3 / 75%, note air testing it didn't feel any stronger than 50% level - needs testing under load....)
6 - Reverse force #1 / 25% (Default, shouldn't matter since don't use....)
7 - Initial Brake #2 / 0% (brake @ start of range)
8 - Neutral Range #3 / 12% (Dead zone on controller, max allowed, he likes it this way)
? 9 - AMTS Timing #8 / 26.25* (most power, lower eff, not sure about this one at all)
NO 10 or 11
12 - Motor Rot CCW (This works - can also change by swapping any two motor leads)
13 - LiPo Cells AutoCalc (S/b 4, and it shows this on boot)

Advice about how best to set the AMTS timing would be most helpful, as I think I have a handle on everything else...

Thanks...

ex-Gooserider

Maj_Overdrive

My Feedback: (11)

Brushless motors do make noise when braking. If you watch some videos of brushless rc vehicles (especially 1/8 and up) you will hear the typical motor wine under acceleration change to something else (don't know how to describe it) under braking. I don't know the physics of how or why it does this but it has something to do with the phases/coils of the motor being energized to brake the motor. Interesting fact some may not know, the beeping you hear at startup is not the esc. The esc energizes the motor phases so the motor actually beeps, so all sorts of sounds are possible it just depends on the programming. I've always wanted to try an outrunner in a land vehicle but haven't so I don't know what it should sound like under braking but it will make a different sound than when under acceleration.

As for motor timing, yes higher timing generally gives more power with less efficiency increasing motor temps. I'm actually surprised the esc can be set for that much timing as a typical 4 pole inrunner doesn't need anywhere near that much timing. The esc was obviously designed to run outrunners though as outrunners like lots of timing. Some say motors with 8 or more poles should be set for 30 degrees of timing. So while your 26 degrees is lower and some power is being left on the table your motor temps should be a bit lower than they would be at 30 degrees too.

Maj_Overdrive

My Feedback: (11)

Brushles motor timing works like this. While the motor is rotating EMF is created in the motor phases that aren't being fired by the esc. The esc reads these emf signals coming back through the motor wires to determine the motors position and when the magnets align with a phase that phase is energized. If you add timing you're energizing the phase sooner in terms of the magnets position within the phase.

Think of it like ignition timing in a car. The EMF signal coming back through the motor wires is like the distributor. It's what signals when to fire the spark it's or in this case the phases of the motor. The magnets coming into position within the phases of windings is like the piston of an engine reaching top dead center on the compression stroke. In an engine you want the spark to occur before the piston reaches top dead center in order to start the combustion process as it takes time. If timed right combustion pressure will peak at top dead center providing the most pressure to push the piston down. Same principle applies to electric motors and the more poles the more advanced timing they like.

ex-Gooserider

Many Thanks Maj_Overdrive, this helped me a great deal in feeling comfortable with the way I've got things set up.

I did another test session this afternoon, and it went really well, so I ended up turning the board over as finished...

Your explanation of the AMTS timing is better than anything that I've found elsewhere, and makes a lot of sense. The 26.25* value I have it set to is the highest the ESC supports, so I can't get it any higher. However the startup is very smooth and controlled, and it seems to have plenty of power, without getting the motor to hot. Probably helps that the motor has a built in fan, and isn't enclosed at all.

The boost to 75% brake force seems about right as it now stops on hills, but doesn't hit so hard as to be a problem for staying on the board.

Power consumption seems reasonable, this afternoon we had the ESC running for about an hour and a half, with about 30 minutes of actual riding time, that included a lot of starts and stops - partly for testing, and partly to deal with all the folks that saw us and thought it was super cool to see a guy in a wheelchair riding a powered longboard - it is seriously impressive as it involves holding a constant wheely with the chair, and shifting the balance point to steer...

After all that, the charger the pack only took about 800 mAh to charge it back up, which is pretty trivial considering the pack is 12,600mAh.

We are also happy with the top speed, which we haven't measured, but estimate at around 10-12mph - fast enough to be fun, but 'survivable' if one crashes...

I've attached a few build shots - the motor setup, the board as it's ready to roll, and the inside of the electronics box...

ex-Gooserider

Maj_Overdrive

My Feedback: (11)

Glad I could help. Wait a sec though. A constant wheely with the chair and shifting the balance point to steer the board? So he's got the chair facing to the side of the board and has to adjust his chair wheely to steer the board? That is seriously impressive!! Kudos to him for not being held back and being able to pull that off!

ex-Gooserider

Exactly - the board has those aluminum angles along the edges that act as chocks for the rear wheels of his chair, and he balances on those while facing sideways and rolling forewards. If you Google for 'Erik Kondo skateboard' you can find some videos of him doing the same basic technique on a regular non-powered longboard and a snowboard... He also is on Facebook...

It is totally mindblowing to watch - especially as I'm also a paraplegic with about the same level of injury, and I can't hold a wheely in my manual chair for more than a few seconds. (partially because by choice I use a power chair most of the time)

ex-Gooserider

EXT2Rob

My Feedback: (1)

That is incredible! Awesome. Good on you guys.