questions regarding my next mid drive build (astro 3220)

[bee]

I'm starting to reach the limits of my GNG kit and would like to start planning my next mid drive bike.

I'd like to use this 24" hardtail NS Holy 2: http://www.ns-bikes.com/holy-2,54,pl.htm
I want to upgrade it with some nice suspension forks, front disc break, and a fat rear tire.
I'm not 100% sure if I want to use a hardtail bike. With my current GNG, when I open up the throttle for wheelies, the bikes rear suspension compresses quite a bit, which seems to make it harder to control. I've read on downhill/freeride forums that a hardtail is better for beginners, but I'm not sure if that advice still holds true on a bike that's heavier because of the motor. This bike will also (possibly) be capable of pretty high speeds, I'm not sure how safe I'd feel going 50mph on the horrible roads here without a rear suspension.

I plan to attach the motor in direct drive on the left side using #219 chain and sprockets attached to the disc brake mounts of the rear wheel hub.

According to http://www.electricbike.com/astro/ the 3220 peaks at 7500 RPM and produces 8hp.

The largest #219 sprocket I can find for the rear is 105T, which gives me these options for the front sprocket:
10t: Speed at 7500RPM with ratio of 10.5:1 with 24inch wheel = 82.08kph (51.00mph)
11t: Speed at 7500RPM with ratio of 9.54:1 with 24inch wheel = 90.28kph (56.10mph)

With this gearing, will I still get a lot of torque in the 0-40km range for doing power wheelies and lower speed freeride/trials type riding, or do I need a larger gear reduction for that?

Can I safely go wide open throttle from a stopped position with this gearing and send 8hp into the disc rotor mounts? Anyone know the max torque I can put through the disc rotor mounts?

Is 7500RPM/8HP the limit for this motor or can I overvolt and increase the gearing to achieve better peak performance? I'm more interested in bursts of power rather than continuous power.

What kind of controller should I use? I was planning to attach hall sensors since I read that improves low speed control.

Would regen be possible with a big motor like this? My riding style is very inefficient so it would be great to harness all that constant braking power to prolong the ride.

I still haven't found a source for the smaller #219 sprockets that will fit the 3/8" or 1/2" astro motor shaft. Any suggestions?

Thanks

 

[MattyCiii]

My only experience in e-bikes is with Astro motors and left side drive. Here are my thoughts:
1. Regen? No way. Not with all that reduction. Use a freewheel. It never buys you much anyway, just use more battery instead.
2. Astro will custom wind the motor for different kv's, so you could specify a lower kv wind and use less reduction.
3. 10t and 11t will be harsh on the drive cog and the chain. I read somewhere here you want 16t or more in the driver.
4. I've put at least 6kw into disc brake mounts from a standstill. Brake mounts can handle it. But putting massive start and stop forces into the disc brake mounts can loosen the disc brake bolts... watch for that.
5. RE: Bursts of power. Recumpense has thrown 9KW through these motors without trouble. I can't find a hill big enough to peak higher than 6KW. I ride (commute style riding) my bike real hard, and it has not peaked 50*c ever.
6. I use Castle Creations HV-160s, and they're great. Never a problem starting from zero, and the HV-160 (sensorless) does just fine with it. I start from a standstill on hills all the time, never a problem.
7. I'd like to use #219 chain, but I have had the same problem with shaft sizes... so for now I use bicycle chain. Bur see #1 above, the bike chain has for me the advantage of working just fine with a bike freewheel.

 

[rodgah]

A 3220 or equivalent will not last long geared for such high speed used in the manner I think you want to use it in.

You will need a dual reduction to get the speed lower and the torque higher and keep the motor more happy.

You have to look at the rated constant power level closely. If you go beyond this (in peaks or short bursts) there is going to be excess heat to get rid of. Max Continuous means the maximum amount of heat that it can dissipate without increasing in temperature. Astro are very well manufactured motors and their ratings are very precise so simple answer is no you cannot just over volt or over amp this motor without consequences, you need to add additional cooling ie fan or extra thermal mass etc etc. If used with an RC controller you cant go full throttle from a stopped position you will need to add sensors and a sensored controller. Good quality hubs can take more abuse than a 3220 or 80/100 can produce. Regen is worthwhile but keeping in mind it is going to keep the motor hot and not give it a break to cool down.

look up recumpence drives or pm him if you want to know more.

 

[Thud]

Definatly gear softer...even if you need a 2nd stage.
do not get a lower kv motor & expect it to deliver its full potential on a lower voltage.
If you want full performance, you will need to spin the motor to its full speed. Approximately 8k rpm's.
Astro rates them at 4.5kw & that is a touch conservative....but you'll smoke it in 10 minuets loaded to 9kw.

Running it sensored will open the door for lower kv's pushed by higher voltage, Member burtie has an optical sensor kit for the astro's.

A single speed geared for 50 mph is going to be sluggish on acceleration. If your going off road, I recommend you gear for 20 ish mph. You will be enjoying the slam of acceleration & the true wheelie potential 5kw will deliver.

From experience, if you plan to pedal at all, you will need a freewheel in the drive.

As for hard tails, I like them.
There are no 219 sprockets that will bolt onto the shafts directly. You can get a .75" bore 12t from gokart supply. Its a simple job to make a reducer.

 

[gwhy!1]

I agree with everything Thud has said... I run a outrunner with a single reduction geared for a top speed of around 41mph, this is power limited to 7.5kw it gets hot and this is with a outrunner, a inrunner will get even hotter , also this is on a bike that is used on a flat track so the 7.5kw is on very short bursts ( a average of 6kw total ) so not lugging up hills or being used off road where the power limit will be held for longer periods . For reliable operation at lower speed a sensored setup is a must and to use a controller with active current limiting is also a must if gearing for higher top speeds as a single speed ratio.

 

[bee]

Thanks for the great advice, sounds like there's no way to do this without a 2 stage reduction so I'm going to spend some time designing something nice and compact. I am looking at various car/motorcycle parts to see if I can find some gears that I could put into a 2-3 speed planetary gearbox, since it would be great to take advantage of the astro motors power for low end torque and top speed.

 

[speedmd]

Hi Bee

I am planning a similar powered build. Thinking of using a good solid three speed hub for the jack shaft. If you find one, let us know.

cheers

 

[snoopshomme86]

i m running a alfine as second reduction after recumbence drive ,this time i test it and i think theres no need for a middrive.

its a little bit proto but it runns

 

[snoopshomme86]

did a little video but the quality is very bad becaus of the viedeo stabilizer at my phone .But you can hear the shifting.
http://youtu.be/cHn_O2hprLA