10S custom skate ESC: testers wanted!

[onloop]

just watched one of your other eboard test videos vedder.... it looks like you have 3mm pitch pulley in use already.

on 15mm I wouldn't try it on 9mm. Boosted runs 3mm or 2mm on 15mm width. 15mm would probably work well. You can reach those more unreachable gearing ratios with the 3mm belts. Let us know.

15mm is a bit wide in terms of motor clearance..... i think 12mm wide is good

 

[onloop]

also with higher reduction the load on each tooth of the motor pulley would be marginally reduced, meaning smaller teeth can function just as good as 5mm

 

[torqueboards]

Oh nice.. 6S 20ah isn't too bad. I was thinking 10S 20ah.

21.69 lbs isn't too bad. Evolve - Is the same weight but not 20ah

Sounds good. Let us know on the 3mm. With the longer width seems like it would work well. Boosted uses 3mm. I think. The 1:4 + gearing ratios are much more obtainable.

 

[onloop]

18mm thin 100mm wide 540mm long 20ah 6s batt.....

it would be hard to make higher voltage batts in this size.....

so if we do go higher voltage we now need custom charger BMS solution..... maybe vedder has the skills to build these things as well.....


suppose u are thinking lifep04

 

[torqueboards]

Bought a few custom 29.6v 9ah packs with a one charger solution. Anything more seems to be a lot heavier. Takes a while to make them but hopefully should get them eventually.

Lithium Ion packs. Lifepo4 = too heavy. Lithium Ion - Should be good. I was looking at a 11ah+ but end up needing a 42" board and using the entire board. Adding 10+ lbs of batteries is a lot. It's nice for an option to have for the long distance riders.

 

[austindavid]

also with higher reduction the load on each tooth of the motor pulley would be marginally reduced, meaning smaller teeth can function just as good as 5mm

I expected this, but couldn't get dual 3mm pitch 9mm wide belts to work at 6:1. An idler pulley might help, but 3mm teeth are tiny.

 

[onloop]

@Vedder. Can you discuss in more detail what you believe to be the best setup for eboards and why?

In the end - the question seems more broad than anything. It's kind of tough to have 1 specific setup for an eboard to be lightweight 10-12 lbs, powerful 30+ mph, hill climber (20% steep hills), distance runner (12-15miles).
@Vedder - Still want to hear what you have to say

yes, i suppose my question was not specific.... so let me clarify further.

Your system is designed for higher voltage (so higher than widely used 24v)... I assume thats because you are confident it is likely to be more efficient running higher voltage as opposed to drawing more current. Also It should generate less heat and you can use smaller wires.

So lets say for now higher voltage is generally 'electrically' more efficient. What do you believe is the best way to get the power to the wheels on a skateboard.... to clarify i am specifically referring to Electro-mechanical Efficiency & Drive train Design limitations.... (the question about dual motors / single motors / flat riding / hill climbing /etc... is secondary)


Below are just a few examples of some different setups that all should deliver a similar top speed. So my question is what (in your opinion) is going to be more/most efficient...

example #1
Drive: 14 teeth (any smaller and teeth in mesh becomes an issue - unless you have really long motor mounts which are more prone to flex or need to use idlers)
Driven: 36 teeth (as big as i'm prepared to go on this wheel using 5mm pitch)
Max Battery Voltage (V): 42.0 V - 10S lipo
Motor Rounds per Voltage (kV): 170 kv
Tire Diameter: 3.25 (83mm)

Final Ratio (FDR): 2.571
Engine rpms: 7 140 rpm
Top Speed: 43.13 km/h (26.85 mph)

CONS
1. not many 170 KV motors to choose from. (only two available on hobbyking 6374's)
2. '2.571" is not much reduction - higher peak current draws - more load/stress on motor - maybe not efficient
3. need 10s charger
4. lower capacity battery for size/weight
5. the lower kV motor will have greater resistance in its windings. more heat.

PROS
1. USE 5mm pitch pulley


example #2
Drive: 17 teeth (any smaller and teeth in mesh becomes an issue - unless you have really long motor mounts which are more prone to flex or need to use idlers)
Driven: 60 teeth (as big as i'm prepared to go using this wheel with 3mm pitch)
Max Battery Voltage (V): 42.0 V - 10S lipo
Motor Rounds per Voltage (kV): 245 kv
Tire Diameter: 3.25 (83mm)

Final Ratio (FDR): 3.529
Engine rpms: 10 290 rpm
Model Speed: 45.29 km/h (28.19 mph)


CONS
1. you will need to use 3mm pitch pulley to allow this to physically fit - 3mm is not widely tested and maybe won't work well. - 3mm is maybe not suitable for such high RPM, i think for the torque we have on eboards to use 3mm pitch RPM needs to be under 10,000RPM)
2. decent reduction but still not great when in compared to some experienced ebike builders who talk 7:1 or greater for efficiency.
3. need 10S charger
4. lower capacity battery for size/weight

PROS
1. 245KV motors are fairly common



example #3
Drive: 17 teeth (any smaller and teeth in mesh becomes an issue - unless you have really long motor mounts which are more prone to flex or idlers)
Driven: 60 teeth (as big as i'm prepared to go using this wheel with 3mm pitch)
Max Battery Voltage (V): 33.6 V - 8S
Motor Rounds per Voltage (kV): 290 kv
Tire Diameter: 3.25 - 83mm

Final Ratio (FDR): 3.529
Engine rpms: 9 744 rpm
Top speed: 42.88 km/h (26.69 mph)

CONS
1. you will need to use 3mm pitch pulley to allow this to physically fit - Also 3mm is not fully tested and maybe won't work well. - I THINK 9700 RPM IS GOOD FOR THIS 3MM BELT
2. decent reduction but still not great when compared to some experienced ebike builders who talk 7:1 or greater for efficiency.
3. need 8S charger
4. lower capacity battery for size/weight

PROS
1. 290KV motors are fairly common


example #4
Drive: 17 teeth
Driven: 60 teeth
MAX Battery Voltage (V): 25.2 V - 6S
Motor Rounds per Voltage (kV): 390 kv
Tire Diameter: 3.25 - 83mm

Final Ratio (FDR): 3.529
Engine rpms: 9 828 rpm
Top Speed: 43.25 km/h (26.92 mph)

CONS
1. you will need to use 3mm pitch pulley to allow this to physically fit - Also 3mm is not fully tested and maybe won't work well. I THINK 9800 RPM IS PROBABLY GOOD FOR THIS 3MM BELT
2. decent reduction but still not great when compared to some experienced ebike builders who talk 7:1 or greater for efficiency.
3. not many 390KV motors to choose from
4. slightly higher peak amp draw

PROS
1. lots of chargers to choose from
2. larger capacity battery / lower weight


example #5
Drive: 14 teeth (any smaller and teeth in mesh becomes an issue - unless you have really long motor mounts which are more prone to flex or need to use idlers)
Driven: 36 teeth (as big as i'm prepared to go on this wheel using 5mm pitch)
MAX Battery Voltage (V): 25.2 V - 6S
Motor Rounds per Voltage (kV): 270 kv
Tire Diameter: 3.25 (83mm)

Final Ratio (FDR): 2.571
Engine rpms: 6804 rpm
Top Speed: 41.10 km/h (25.58 mph)

CONS
1. '2.571" is not much reduction - MUCH higher peak current draws - more load/stress on motor - maybe not efficient

PROS
1. USE 5mm pitch pulley
2. chargers readily available
3. motors are readily available



SO VEDDER...to get to my point!... there are probably several other setups (and 1000's more PROS/CONS) that we can discuss that will give us a desirable top speed / performance... so what do you believe to be the most efficient..

Once we can all agree I suppose we must then agree what setup is the most cost effective / feasible! then we must agree on the best balance between efficiency, reliability, cost, performance.

 

[vedder]

Since there are so many questions about the speed/efficiency/voltage/current relation, I will write a detailed post about that on my homepage today. I'm not an expert on the mechanical part, e.g. the acheivable reduction ratio and highest speed using pulleys, but I will assume that any ratio is possible and explaing how motor properties and electrical properties relate to the efficeincy.

 

[makepeace]

http://file.lasersaur.com/docs-thirdparty/The_World_of_Timing_Belts.pdf

So far the best resource I've found on timing belts. All the profiles, their ratings and all of the relevant calculations.

Correctly tuned timing belt setups have between 0.95 to 0.98 efficiency, so wouldn't too much about that.

What do you believe is the best way to get the power to the wheels on a skateboard.... to clarify i am specifically referring to Electro-mechanical Efficiency & Drive train Design limitations.... (the question about dual motors / single motors / flat riding / hill climbing /etc... is secondary)

This is entirely a function of your motor data (efficiency, speed, torque curves) and your required operating conditions. You have P_elec, P_in (to the drive), P_out (of the wheel), and their associated efficiencies. Assuming an ideal ESC, everything else can be calculated providing that you have your motor data and operating conditions (desired efficiency, and speed @ torque).

Unfortunately motor data is very few and far between. I actually find it unbelievable as to how the motor sellers don't give enough useful information (even empirical) of their motors. As far as the last 2 weeks have shown me, it is the missing link to designing an optimal setup. We need comprehensive motor performance graphs!

It could also be cool to make an app like DriveCalc, but suited to skateboards.

 

[vedder]

I just put together some of my experiences regarding motor KV/battery voltage/efficiency/gear ratio in a post here:
http://vedder.se/2014/10/chosing-the-right-bldc-motor-and-battery-setup-for-an-electric-skateboard/
I will probably update it several time in the coming days to make it more clear, but hopefully it is a bit useful as it is now.

Also, I just made an outdoor test with the longboard kit I got form Dexter and Austin:
[youtube]7T3aDo8o1ZE[/youtube]
I have limited the maximum speed to 30 km/h in software because I feel safer that way while holding my camera. In this video, you can hear how quiet the brake is. Note that the regenerative braking current and torque is the same as for the acceleration, so it feels quite natural. Also, wiiceiver seems to work glitch-free so far

 

[psychotiller]

Just out of curiosity I tried starting from a standstill on my uphill driveway with my "woody cruiser" and I discovered that with almost no cogging I was able to start and ride away. I didn't really know that was possible because I always push off.

ESC mamba monster2
Motor Tacon Bigfoot 160 245kv
2:1 ratio
22.2v 6s packs
75mm Wheels
Wiimote/Kama

 

[makepeace]

Funny you mentioned reterminating to star, I was just reading all about it this morning. I think that's what we need to do as a matter of course to get the best out of these motors for skateboards. It's also (mostly) more efficient. Think I'm gonna have a crack at it when I get my NTMs. Will require a 1.5 RR for 37 km/h which should make life quite a lot easier (and lighter).

 

[torqueboards]

Sweet write up Vedder. Thanks!

@psychotiller - Do all your setups start up without cog? It seems to start up fine if the motor kicks properly and there isn't nothing holding it. Does it start up fine on carpet when the wheels sink in?

As for mine it's on and off.

@Vedder - For the new esc - How is the start up on grass? Is it able to start up in grass with those 83mm wheels or would it not work? Can it start up going up a hill without a kick start or running start?

 

[psychotiller]

@Torque, Its really the first I've ever tried to take off cold. I'll try it a few more times with each board and let you know.

 

[onloop]

Well....... that was the first time i have ever read an electric skateboard specific analysis of what would make a highly efficient skateboard.....

I don't know who you are vedder!.... but I now have a serious e-boardie-man-crush on you. (assuming you're a male)


> So based on your conclusions it seems it would be basically impossible to design your ideal system with gearing reduction of 4:1 using, 5mm pitch pulley & belt OR #25 chain & sprocket... there is simply not enough diameter on an 83mm wheel to fit the driven pulley.

So one of the only options left is 3mm Pitch pulleys & belts!

I'm not a scientist but if my calculations are correct: Say at 8000 rpm & approx 1.2kw (not sure what average amps you draw at 10s so I guess 30ish) the 1.4nm of torque at the drive pulley is at the upper limits of the published specifications of a 3mm HTD belt.. BUT STILL WITHIN THE LIMITS OF THIS BELT

Maybe this explains why boosted use it. Even with a 9mm wide belt it should be able to handle the torque. The wider the belt & the more teeth you have the more torque it is rated to handle.

 

[makepeace]

It must be noted that as you step down to 3mm pitch, not only the more teeth you have to transmit x amount of power, the more teeth you require to transmit x amount of power (because they are smaller, duh). Take a look at table 44 in the pulley manual I posted above. @ your estimated torque of 1.4 Nm and 8000 RPM, you need between 50 and 56 teeth on your small pulley at 9mm width to transmit the power (and looking at the pitch diameter this equates it to about a 32 tooth 5mm pitch which can transmit about 2 Nm torque @ 8000 RPM). So we're going backwards here..

In any case, the GT2 profile is much better suited to this kind of power transmission, and can actually transmit the power you're talking about with a reasonably sized pulley 9mm wide and 3mm pitch, and no warnings of belt slip or high service factor. Why aren't we going with that? both smallparts and SDP/SI have a huge range of GT2 stuff.

 

[onloop]

yes, 5mm pitch can better handle the torque, but trying design a drive train using a 32T 5mm pitch drive pulley, with 4:1 reduction on a 83mm wheel is actually impossible....

so i guess i'm just trying to work within the restraints that are present....

Basically it would seem we must sacrifice something to get the holy grail of efficiency OR use a slightly inefficient system to ensure everything is working within its limits.....
1. using a power transmission system that can't handle the MAX torque load = maybe some slipping & early failure of belts!
2. using electrickery to limit the torque? = BORING!
3. Limiting the power output electronically, something like 900w & 8600 rpm = BORING!
4. Lowering the power output by lower voltage batteries = Not efficient!

>>> I think if vedder could write some software that can control/monitor the torque load & make torque output variable that might be nice... so then if the torque load is too great where some slipping might occur the system will be monitoring this and electronically limit the power output to ensure no slipping occurs, I can only assume the torque load on the belt is reduced as speed is increased....

For me the option of the GT tooth profile doesn't have enough benefits over HTD to warrant using it..... Also there are some commercial reasons why i don't use it..

 

[vedder]

For the new esc - How is the start up on grass? Is it able to start up in grass with those 83mm wheels or would it not work? Can it start up going up a hill without a kick start or running start?

It does not start on grass with the single motor and 83mm wheels with 1:2 gearing. Even if I kick-start on grass, it will come to a stop because the load is too high and the torque is too low with this gearing. That means: if it cannot run under a given load, it cannot start either. The same would be the case for a sensored setup. The dual-motor longboard starts perfectly on grass, carpets and uphill with my ESCs. The problem when starting uphill is if you begin to roll backwards too fast before you use the throttle, where the transition through zero speed can become a bit jerky.

My ESC will start cogging when the load is too high as well. The difference with my ESC from the other sensorless ESCs is that my ESC is able to consistently produce (approximately) 95% of full torque during startup; other ESCs also produce torque at startup, but it is only a fraction of full torque and inconsistent, depending on how lucky you are with the first alignment.

Basically it would seem we must sacrifice something to get the holy grail of efficiency OR use a slightly inefficient system to ensure everything is working within its limits.....

Regarding my example with 1:3.9 Gearing, keep a few things in mind:
* If you design for higher top speed than 35 km/h, you can use a lower gear ratio.
* If you use smaller wheels, you can also use a lower gear ratio. The larger wheels you have, the more reduction you need.
* Even if the setup is not fully optimal, it will still work well. 1:3 is better than 1:2, and even so, my setup with 1:2 also does the job, even though I cannot take too steep hills.

Also, regarding the use of 12s batteries: The ESC is very efficient, so the heating bottleneck is the motor and not the ESC even on my 8s setup.

I think if vedder could write some software that can control/monitor the torque load & make torque output variable that might be nice...

I already use current control, which is equivalent to torque control. You can set both positive and negative (braking) current limits, thus torque limits, individually.

 

[Jan Christian]

vedder wrote:

I already use current control, which is equivalent to torque control. You can set both positive and negative (braking) current limits, thus torque limits, individually.

I guess that means if you limit the amps to say 50 or lower; it can never blow up when pushing it?

 

[makepeace]

For me the option of the GT tooth profile doesn't have enough benefits over HTD to warrant using it..... Also there are some commercial reasons why i don't use it..

This doesn't make any sense. I would think that actually being able to transmit the required power at reasonable pitch diameters is enough of a benefit in itself. Belt slip is less, belts are stronger etc etc. The GT profile is just far superior, end of story.

The only redeeming factor for HTD is availability and price. Anyway, I managed to find the perfect 3mm pitch GT pulley for my future setup for only $6 each.

 

[Svenska]

Hello everybody,

I'm an Mechatronics engineer and skater for 25+ years in the process of building me a Skateboard.

I found the discussion and information posted here VERY valuable, so first up thank you guys!

About the belts. Usually these design tables are meant to give you an indication of what belt to choose for an industrial application. That means a run time of 8 hours a day for the lifetime of the belt. Maintenance on these sort of systems is about once a year. That means that if you follow the tables the belt will be good for 1 year, 8 hours a day, 7 days a week!
That's much more then we need. If you go over the lifetime shortens. Considering how much the belt can take in hours 365*8=2920 hours!
Your feet fall off before the belt gives in...
The important part is to be careful with the amount of teeth that are meshed in the gear as this correlates directly to the amount of torque the belt can transmit before stripping/skipping.
I hope I could be of some help here.

@ Vedder

I'm looking into making some of your ESC's. I'm part of the local hackerspace and we got pick and place available for the assembly and people with all the knowledge needed to get em up and running as well as maybe improving. I wanted to make them before this thread came up. Are you going to redesign the PCB or are you keeping it as it is and only making major changes to the code? Don't want to make a bunch of them and then shortly after finding that there is a much improved hardware.

Cheers, Svenska

 

[onloop]

For me the option of the GT tooth profile doesn't have enough benefits over HTD to warrant using it..... Also there are some commercial reasons why i don't use it..

This doesn't make any sense. I would think that actually being able to transmit the required power at reasonable pitch diameters is enough of a benefit in itself. Belt slip is less, belts are stronger etc etc. The GT profile is just far superior, end of story.

The only redeeming factor for HTD is availability and price. Anyway, I managed to find the perfect 3mm pitch GT pulley for my future setup for only $6 each.

Are you a selling agent for GT belts?...maybe I can employee you to promote enertion products...

Honestly... the claim of slight advantage for me it's not worth it.... if a belt and pulley combination just happens to be $3 or $4 more that's cheap when you buy one unit..... however when you buy 100 you do the math...

 

[makepeace]

Hmmm, I get what you're saying about the belts Svenska, however 2920 hrs is still not a gratuitously long life service life for this kind of product. If you ride for 1 hour a day, that's 8 years - never mind the abuse of an extreme environment with stones, sand etc getting into your drive. That's about how long you'd expect your bearings to last. K, maybe a bit more. As I see it, that's a perfect life cycle for this kind of product. And regardless, it's bound to fail by some mechanism or another way before that anyway. I don't want to have to replace the belt, just like I don't want to have to replace the bearings. Batteries I don't mind, as there's no getting away from that.

Lol. Not an agent. I just like to see things for what they are. When I see in a design table that for the same profile, torque @ speed and number of teeth that 1 profile can transmit 5 times more power than another, I'm going to say something about it. I don't really see it as a slight advantage. And of course I know about economies of scale, but you presented a problem and I gave you the solution. You can't get more performance out of your equipment by wishing it was better, or pretending it's not much worse. You need better equipment.

 

[onloop]

. if you can please show me how 3mm gt2 belts can deliver 5 times more torque then 3mm htd you win...

 

[makepeace]

Ok maybe not 5 times. A bit of an exaggeration sorry , but by my calculations for 6000rpm, 24.83 PD, 9mm width and 270mm belt length its at least 1.5 times.. And that's excluding the fact that HTD belts always seem to be in the blue range that says "reduced service life to be expected", which would suggest some or other multiplication factor to put them on par with GT2.

Regardless, it's still a significant difference.