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Re: ES DIY Motor Challenge

Posted: Nov 09 2012 1:06am
by liveforphysics
We need to have a time constant to hold the torque for on video.

I think 5mins would be fair. Anyone have objections to 5mins showing the given torque output on a dyno?

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 4:02am
by Miles
I guess it depends on the thermal time constant of the motor. I'd say 15 minutes. :)

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 4:16am
by Miles
I'd rather lower the torque target but ensure that we have something that could be described as a practical continuous rating. Just my thoughts, though.

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 4:24am
by liveforphysics
Miles wrote:I'd rather lower the torque target but ensure that we have something that could be described as a practical continuous rating. Just my thoughts, though.
Thays perfectly fine my man. I have 250amp 120vdc chargers next to my dyno. I was just thinking about Farfel trying to sustain say 16kW out of his battery for a period of time without running his battery out. But, if he is keeping the speed low, he could be making max torque at a low rpm amd only drawing a few kw, in which case 15mins would be fine for a couple kwhr pack.

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 4:32am
by Miles
liveforphysics wrote:I was just thinking about Farfel trying to sustain say 16kW out of his battery for a period of time without running his battery out. But, if he is keeping the speed low, he could be making max torque at a low rpm amd only drawing a few kw, in which case 15mins would be fine for a couple kwhr pack.
Good point. What would the efficiency hit in the motor be, from running it at a low duty cycle, though? I guess that's all part of the "practical" :)

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 4:36am
by Miles
What do you think of the idea of increasing the target by 10% each time it's reached?

How about lowering the targets to these to get things under way?

Under 3kg.........3Nm/kg
3kg - 10kg.........4Nm/kg
10kg - 20kg........5Nm/kg

Is the weight differential fair?

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 10:56am
by Farfle
I got another 8 nano packs I was planning on adding this winter that I can toss in on a heavy gauge extension cord. Hopefully should be enough for 15mins. The thermal rise time is gonna be slow, 24 pounds of this motor is in the stator. Plus when I replaced the sidecover, I didn't drill any cooling vents in it :oops: .we will see what It will do.

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 11:02am
by Miles
You're allowed to actively cool the controller :wink:

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 11:05am
by Farfle
Hmmm, freezing ass cold garden hose water sprayed on the heatsink should do the trick. What is the cont phase amps on the baby controller Luke?

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 11:38am
by Miles
I guess, according to the rules, you could also bolt a 7kg heatsink to the motor :mrgreen:

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 11:45am
by Miles
As long as you created the additional torque :)

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 11:54am
by Farfle
hah, maybe an equation for torque, like y=.2x+3 where Y it's max continuous torque and x is the weight in kg. When that's achieved, then you could do .3 then .4 etc...

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 12:00pm
by Miles
That's quite a thought..... We'd need to research what the "weight factor" should be, though, unless it was realistic, it would be less fair than having separate categories...

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 12:07pm
by Farfle
Yeah, I like the 3nm starting point, that puts it in the ebike realistic realm, puts your motor at 3.16 nm, and mine at 5.72nm both realistic goals. I think flux gap area and radius may come into play, but then we end up in a formula nightmare. How about a formula where you plug in the stats of the motor and it spits out a score number, than all entries are ranked?

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 12:42pm
by liveforphysics
Farfle wrote:Hmmm, freezing ass cold garden hose water sprayed on the heatsink should do the trick. What is the cont phase amps on the baby controller Luke?
If you can control temps on that controller (which isnt always easy), I believe you can do 240 or 260 phase amps continously. If you can control temps, it automagically dials back current to protect itself.

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 1:17pm
by Miles
Farfle wrote:Yeah, I like the 3nm starting point, that puts it in the ebike realistic realm, puts your motor at 3.16 nm, and mine at 5.72nm both realistic goals. I think flux gap area and radius may come into play, but then we end up in a formula nightmare
Yeah, let's keep it simple. Can we devise an algorithm that's self-correcting for the weight differential :)

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 1:35pm
by Farfle
liveforphysics wrote:
Farfle wrote:Hmmm, freezing ass cold garden hose water sprayed on the heatsink should do the trick. What is the cont phase amps on the baby controller Luke?
If you can control temps on that controller (which isnt always easy), I believe you can do 240 or 260 phase amps continuously. If you can control temps, it automagically dials back current to protect itself.
thanks, that might be enough to find the upper limits of this motor at a near stall rpm. Lets say with shoddy thermal paste and a fan blowing on it it could to 220A for the duration.

Using the calc on this page it is giving me .341 ohms per 10m for one strand of 18awg at 180C
.341 ohm / 15 strands is .0227 ohms lead to lead.
p=i^2R 220^2 x .0227 is 1098W of heat.

On second thought, might not be able to push this motor to its limit with the little guy Luke :twisted: :twisted:
Miles wrote:
Farfle wrote:Yeah, I like the 3nm starting point, that puts it in the ebike realistic realm, puts your motor at 3.16 nm, and mine at 5.72nm both realistic goals. I think flux gap area and radius may come into play, but then we end up in a formula nightmare
Yeah, let's keep it simple. Can we devise an algorithm that's self-correcting for the weight differential :)
doh, I meant 3.16 nm/kg and 5.7nm/kg , not just nm lol

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 1:44pm
by Miles
Yes, I read that. 5.72Nm is probably not much more than the parasitic torque on your motor LOL

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 7:27pm
by Miles
I propose that we use your formula in conjunction with my 3 categories. That way we can keep a better handle on the weight differential and adjust it separately for each category as the target is reached. What do you think? It would give more of a sense of competing with similar motors.

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 7:30pm
by Farfle
Miles wrote:I propose that we use your formula in conjunction with my 3 categories. That way we can keep a better handle on the weight differential and adjust it separately for each category as the target is reached. What do you think?
works for me, now we need more than two entries lol.

Re: ES DIY Motor Challenge

Posted: Nov 09 2012 7:32pm
by Miles
farfle wrote:works for me, now we need more than two entries lol.
:mrgreen:

Re: ES DIY Motor Challenge

Posted: Nov 10 2012 3:49am
by Miles
Ok, we have a more equitable system, thanks to Farfle.

Three weight categories:
3kg or less
Over 3kg to 10kg
Over 10kg to 20kg

The initial formula for the continuously sustainable specific torque target, in each category, is:
Specific torque (Nm/kg) = 0.2 * motor weight (kg) + 3

This will be adjusted by category (raising the bar), as it's achieved.

Anyone unhappy with this?

Re: ES DIY Motor Challenge

Posted: Nov 10 2012 5:40am
by Thud
that is just fine Miles.

but to stimulate activity, perhaps we should bump the prize up to 2 kudo's
:lol:

Re: ES DIY Motor Challenge

Posted: Nov 10 2012 5:47am
by Miles
:lol:

Re: ES DIY Motor Challenge

Posted: Nov 10 2012 11:52am
by pkirkll
Maybe we could get one kudo just for entering??????
:D