Electric trail bike

I recall around 40 something amps just cruising behind the shop at maybe half speed. At that rate it should run for around 30 minutes. Something's up.

Load.... try it with my fat ass on it.... 80 amps and 15 minutes...

Do those meters have a hold function? What was the peak draw during your tests?

At half throttle what rate is the controller operating at?

It would be pretty informative to put it on a dyno and run some tests under load. I bet it would be very enlightening....

So really then, generally, the available amp hours needs increasing, right?

I know its is a bit late in the game, but sine I guess you have the engine still....

one of the ebike designs I wanted to play with used the existing bottom end of a bike to get the advantages of gears. You gain weight, but get back some controlling in your power output to the dirt.

So, could you get a thicker crankshaft chain going and get that tranny back in there?

or invent a motorcycle rear derailleur

This is awesome.

I am curious why no gearbox? Is the weight penalty too great or do you feel that it is not needed? How much more/less current does the motor draw at full speed than at half speed if the power delivery at the rear wheel is the same?

I have no experience building with lithium Ion batteries but what I did read is that you have a good chance of creating a grenade if you don't know what you are doing. What do you have to do to keep the batteries from being dangerous while they are between your legs?

Best of luck to you. If someone with money wants to take your ideas, don't think of it as selling out, think of it as filling your pockets for the next experiment while giving the rest of us a shot at stealthy trespassing. I know belt drives are not ideal on dirt but you should throw one on that thing just to see how quiet you can make it.

At this point, I estimate the bike to be worth at least 15 million dollars if sold to the government.


http://www.wired.com/dangerroom/2011/08/pentagons-lightning-gun/

Regarding the gearbox, I didn't put one in because there isn't much room. It would be very nice on a multipurpose bike to give better top speed while keeping low speed torque, but one gear seems to be enough for now.

The motor has a fairly constant efficiency at medium to heavy loads. It wastes a bit of power at high speed and low load, but that's about it. The Agni website has the charts for the motor performance.

Battery safety isn't really an issue, they aren't lithium-ion.

Supposedly lithium batteries generally don't have much of a problem with this, but it's definitely something to look in to further.


I've been reading that LiFe batteries generally don't work well until they've had quite a few charge/discharge cycles to break in, so I'm trying that now.

Is there a way to make the impulse curve progressive? meaning to make the impulses short interval at small throttle inputs for torque, and then space them out accordingly the faster you go? This is to stretch battery life, that is..

Nope, the controller frequency is fixed. The throttle sets the ratio of on and off time.

I just noticed that this new build subforum is subtitled "Batteries Not Included".

I rode a very similar bike yesterday afternoon....

This dude at the mx track had built one from a ktm 125sx. It was working and he rode it around a handful of times. I took a little spin in the parking lot and was really impressed with the amount of power.

He seemed to be having power issues as well. His bike was only good for 10-15 min on a motocross track and it sorta struggled uphills he said.

Very awesome Idea and Im thinking with enough tweaking you will have quite the entertaining trail bike.
At this point I believe electric vehicles are the wave of the future.

Yeah, about batteries. One of the parallel sets of cells has gone bad, so I pulled them out. The batteries take forever to charge when I run the balancer, so I need to re-do it.

Cool. It seems like there are a bunch of these projects running around.

I have no lack of power, but wish I could get 10-15 minutes of real run time. Yesterday I ran the bike around in circles in my driveway just as a sort of break-in. It ran for about an hour and a half which was nice, but that was at bicycle speeds.

Aren't these cells handier to assemble a pack?
http://www.ev-power.eu/index.php?p=p_46&sName=lifeypo4-cells-(3.2v)

I used the 200Ah cells in a project and they seem to hold up fine. Cells are from Thundersky.

http://www.diyelectriccar.com/forums/
Youtube


To the OP, A123 is now selling 20ah pouch cells to the public. www.mavizen.com who also sells conversion kits, There are plenty of other battery options as well.

I'm sure they're much easier to work with and they are definitely a lot cheaper, but I thought they'd be a little lacking as far as power output.

Nice. They don't seem to like small-scale sales. Do you know of any distributers that are US based? As an Oregonian I am allergic to any sort of sales tax, but especially at UK rates.

There are a lot of batteries out there, all with about the same energy/weight ratio but few that can deliver enough power.

There's not much news recently, but I've been working on getting the battery management right. I was running without it which ruined a couple of cells. The BMS boards that I built didn't working quite right, so I'm fixing them (with a knife and a lot of extra resistors) and integrating them into the battery packs.

In my experience there are a few ways to significantly shorten the life of lithium cells, including the 'power' LiFePO4's:
- Overcharge (Vcell>3.65V) or underdischarge (Vcell < 2.5V) it.
- Charge them at low temperatures. Below 0C/32F is a a no-go area.
- Run them down more than 80-85% DOD. Lithium cells like microcycles.
- Draw excessive currents out of them. Much more than 1-2C continuous and 10C bursts will significantly shorten cycle life.
- Let them get hot.
- High discharge currents when cold. They should be threated the same as a petrole engine: medium loads only when cold, let it rip once warmed up.

Yes, they can provide 30C worth of current. Yes, you can charge them with several C's. Yes, they will work at 70 degrees C.
But that doesn't mean one can expect a long useful life for all cells, as you already experienced. Lies, damn lies, datasheets.

You're far better off purchasing a higher capacity pack and loading it less (1-2C cruising, 10C peak maximum). Much more kWh's per $ out of the pack during it's useful life. And a much more acceptable runtime.

Also: a voltage clamp is not a BMS.... for a certain application I have been using active charge redistribution to prevent the weaker brothers in the chain from overcharging/underdischarging. Charge inductor from the strongest cell, discharge in the weakest. Works extremely well in exctracting the last useable mAh out of cell string and keeping the cells healthy.

This is cool!