How to find peak power + best final drive for HXT 80-100-B?

[northernmike]

Hey guys.

So, having been 2.5kms or so on my HXT 80-100-B moped conversion geared probably way too high, I'm curious as to how I should calculate a proper gear.

Top end I will estimate at 50-55kph running 48V of marginal SLA.

From math I don't grasp, at 48V x 130rpm/V, I should be doing 70kph flat out. Approximately.

I'm coming to suspect that peak power is at 1/2 no load speed, something Miles posted on one of liveforphysics' threads.

If I'm looking for 50kph, should my gearing stay the same, or change?

Or am I even asking the right questions?

I love this stuff.

Here's a pic 'cause I can't help myself.

 

[Miles]

Mike,

That's the calculation for the no load speed.

At the no load speed the torque output from the motor is zero.

The peak efficiency is around 85% of no load speed. That's the figure I use to work out gearing. That still doesn't necessarily mean that you'll have the torque to reach that speed, though.....

 

[HAL9000v2.0]

I make calculations like this: Measure stall torque, then take torque number from some ICE bike that I know acceleration and gearing , then calculate wheel torque /rpm on ICE bike and take 3/4 of value. From that number I calculate gearing and then use kV/V and V of batt to see where top speed migh be...
I'll say you need 70-80Nm on the wheel for normal acceleration.

Of course you can calculate all that numbers...

 

[Miles]

You can use this spreadsheet to give you an idea of the power requirements:
http://www.endless-sphere.com/forums/viewtopic.php?f=11&t=538&start=2

 

[liveforphysics]

I'm using your same motor, except 2 of them. I'm running a 24" rear wheel. I use 8:1 gearing, and it seems to be a decent balance between top-speed and low-end torque. The controller has been the weak-link though. What are you running for a controller?

 

[northernmike]

Luke I used a Castle HV 110 - til I put 54V to it mistakenly and blew it up.

I'm hesitant to try anything too demanding with it until I have the capacity to generate some metrics.

I do have an array of pulleys and sprockets to let me re-gear, though, and will probably end up fine tuning for an "off-the-line" biased ratio. This bike is going to be used in the city primarily - in traffic - and squirting through intersections and around trucks will be the priority.

What voltage @ 8/1 ?

 

[liveforphysics]

42v with 8:1 on a 24" wheel seems to work pretty well for me, but again, it's two motors pulling together, so I guess for your situtation you would need 16:1 for the same off the line torque.