Like I said, larger motors do have an advantage. That's the reason for the 3kg limit. This is the non-hub motor forum
0.5kg to 3kg should be the range that most people want to work within?
liveforphysics wrote:For specific power, even some dirt cheap RC motors are in the 4.6kw/Kg range. This is with a KV of 130, which easily enables the reduction to be accomplished in a single stage reduction. My own bike is an example of this.
Your motor isn't made to direct drive a rear wheel, you must also incur the losses from power transmission to the rear wheel. The drive train loss between a single stage of 4:1 or a single stage of 10:1 is in the fractional percent area. This is way more than compensated by the broad range of >90% efficiency from the RC motor vs the much heavier and lower efficiency alternator motors.
Over 4Nm continuous torque per kg of motor weight.
Less than 3kg in weight.
No energy input other than that to the motor itself.
Capable of practical use on an electric bike.
amberwolf wrote:At 5Kg I could just use my brushed PMDC 4-pole wheelchair motor, which thru the gearbox (an additional 3 or 4 kg) has enough torque to rip itself off my bike, destroy chains, and yank wheels out of dropouts.
3Kg makes that kind of challenge a lot tougher, *and* it gives back 4.4 pounds that one can use for batteries, cargo, or stronger bike frames.
FWIW, I could probably lighten up an F&P BLDC motor to fit in 5KG, but I don't know what kind of torque it would have. 3Kg is more interesting--there's no way I could cut that much weight off of it so it means trying to think of something even more efficient.
More efficient means better use of the very limited power we can carry, and can mean having to carry less of it to do the same work. So I'm all for a lower limit to this challenge, as it makes for more usable results.
jscoot wrote: I suspose so but it also limits a cost effective easy way to get more efficient drive system motors on the road fast!
amberwolf wrote:jscoot wrote: I suspose so but it also limits a cost effective easy way to get more efficient drive system motors on the road fast!
No, it doesn't. It only limits this particular challenge to a more efficiently powerful lighter motor.
There's nothing wrong with spreading the news about PMA motors anywhere you like that's appropriate, and if you have a design that fits within the limits of this challenge, you can show how to build one here in this challenge thread, too.
So I'd say start a thread (or continue one if you already have one) and show how to build them all the way from several ways to acquire a core unit, to how to take several different kinds apart, to how to modify them as needed, rewinding them where needed, etc., all the way up to how to mount them to the bike and build a drivetrain for them for most efficient use.
Then *that* will get more of them on the road fast.
If you sell them premade, then make a thread for them on the for sale section and that will get them on the road even faster if they're cheap enough.
how or what should i do to the output shaft to best facilitate testing on your end thud ?
It certainly wouldn't be fair to allow any type of torque multiplication to be included in the testing, integral or not.....Thud wrote:No reductions will be tested unless they are integral to the design. (we will leave reductions to another challange thread of someones creation)
liveforphysics wrote:Jscoot- I really don't see how you think those converted alternators can compare. You've got thick lams with poor copper fill and big flux gaps, stator teeth done in a grouped series arrangement that gives loads of end losses and weird flux patterns, and it's all put together in a package designed around being bolted to a 400lbs engine where adding weight doesn't make much of a difference.
My motor will be matching the KV of these motors, likely around 1/5th the weight, and easily half the inefficiency of these alternator/motor conversions.
It's like if were all working on building fighter jets, and you keep bringing up an E-bay link to a semi-truck you're selling. Semi-trucks are neat I guess, and even poor efficiency heavy motors have a place in the world somewhere, but I don't see how it applies to this thread.
If you can put something together under 3Kg, it would be great to have another entry in the competition.
Miles wrote:It certainly wouldn't be fair to allow any type of torque multiplication to be included in the testing, integral or not.....Thud wrote:No reductions will be tested unless they are integral to the design. (we will leave reductions to another challange thread of someones creation)
If it's not possible to easily disconnect a reduction we could just divide the output torque by the reduction ratio....
jscoot wrote:I thought the rules only included the motor ? Why not 5 Kg motors if you allow gearboxes/motors? are the rules changing already?
Miles wrote:jscoot wrote:I thought the rules only included the motor ? Why not 5 Kg motors if you allow gearboxes/motors? are the rules changing already?
Randy, try to understand what I've written before you reply.
Thud wrote:Lets start a discusion regarding the actual test procedure.
I am thinking 36 or 48 volts (I have 56ah of SLA at 48v for testing)
1) start the test at no load & measure rpms & amp draw.
2) apply load to 90% of no load rpm & measure amp draw & foot pounds of tourque.
3+)progress down to 50% of no load rpm & see what tha amp & tourque are at.
X) final is to measure max tourque (up to controller amp ratings at least)
Q- is The max the max tourque measurment pertinant to this challenge?
Or- should we just load the motors to the tourqe level determined via weight of the unit & see if it:
A) achieves the goal & is inside the amp limitations of my test equipment
B) is capable of maintaining that level of output.
This is assuming that we are still inside amper ratings of my sisy speed controllers
I have the CC ICE100(30v max), the new turnigy 200 amp unit(50v max) both sensorless & I plan on ordering a 36 volt infineon & going all "methods" on it to get the voltage/amperage where I feel I need it.(sensored)
Do you let them fry (thud-why not?) or will there be a heat measuring device the tester will use to save anyones motor/controller ? (thud-I will let the builders determine if they want their motors tested to failure ie "smoked" trying to meet the challenge)
Even though Ebike motors are always getting a breeze while in use on a ebike(thud-speculitive),
will all the testing be done in still air or with a small fan a few feet away ?( I will have a small fan to create air movement. not nesisarily directed air over the motor, more to keep the eddy brake dyno in check) what will the room tempture be ?( ambient basment temp here in MI. between 50-70f)