Mounting your battery, Center of Gravity.

[dirtdad]

That red chopper... I think it needs to be a licensed vehicle now. It has no chain or gears. That's really pushing the limit.

I tried. CA DMV would not let me, they said it did not need registration or license and sent me home, they said it was a bicycle. CA DMV code has provision for electric bikes with our without pedals that can propel the bike. Gotta love California. I have ridden hundreds of miles on it, right past, alongside, in front of sheriff, CHP, local police, etc. No problem. Thank goodness they are focused on real crime issues.

 

[Patriot]

Whoa. I didn't know that. You're good to go then.

 

[mikereidis]

I think getting the battery, and all weight, as low as possible is a good thing for cornering and general stability.

OTOH, how much do you weigh and how high is your body CG on the bike ? Except for low recumbents, the rider affects the overall package CG more than anything else IMO. So would having an extra 20 or whatever pounds of battery at or below the CG of your body really matter much if you weigh 160-200 pounds or 8-10 times the battery weight ?

I'd be more concerned about securing the battery so the CG doesn't shift unexpectedly in corners.

 

[dogman dan]

I NM, i don't believe the law says anthing about the peadles being able to function. But over 30mph and its not a moped anymore. If I build a chopper it would be a moped so It could go faster than 20.

 

[swbluto]

Basically, the lower you can go, the better. Instead of leaving this oft-repeated advice without an explanation, I'll provide one!

When wobbling back and forth when standing-up or pedaling while standing, the pivot is where the tires come in contact with the road and the greater the distance of any mass away from that pivot(I.e., the higher up it is), the more torque it'll exert on that pivot. So, with higher up masses, you'll get more gravitational torque around the pivot stemming from whatever vibration(wobbly wheels or pedaling) and you'll have lessened ability to "control"/dampen that torque/wobble. The reason why it seems so much greater when you're standing up, in particular, is that your body's mass is now being applied to the pedals which are fairly close to the ground instead of your seat, which is typically further away, so there's less torque coming from your body to the bike when standing. 8)

 

[D-Man]

Removed from useless trashed thread.

 

[jmygann]

If going to Lifepo4 can I split the pack with longer wires and use 1 BMS and 1 charger... ?

curently have 48 volts of 12 ahr SLA

 

[Tiberius]

Bicycle dynamics and stability is quite complex, so while there may be advantages to getting weight down low, I'm not convinced that it is as important as on a 4 wheeled vehicle. As has been pointed out, making sure any load doesn't move is much more important. One of the problems I've seen with rack mounted loads is flexing of the rack and/or frame, which can really affect the steering.

On this build, I thought getting the battery weight central was more important than getting it low. There are 24 Headway cells in there. The battery pack can unbolt so the bike can be folded. Handling is amazingly good - much better than it has any right to be, seeing as how I started with a pretty poor bike.



Sorry, photo is not that good. I didn't realise how much glare there was from the battery box.

Nick

 

[Jeremy Harris]

Neat mounting solution, Nick.

I agree that putting weight low is not always good for stability. Old British motorcycles had a low C of G and didn't handle too well, in my experience (I owned a BSA Bantam and a Triumph T100). The Japanese came along with bikes that had a much higher C of G and which felt much more responsive.

Also, my 'bent has a low C of G and is definitely less stable at low speed than a conventional upright bike.

Whether this is the whole story with regard to stability and handling I don't know, but it does seem to me that having weight low down isn't automatically a good thing.

Jeremy

 

[Tiberius]

Neat mounting solution, Nick.

Thanks Jeremy,

The box is a glass fibre cover on a baseplate machined out of PVC. The idea is that I can machine the PVC out further to mount the BMS in there too. The mounting system is glass fibre moulded in situ around a former built of wood and my daughter's play-do. After the resin has set, you can dig the former out. Its all finished with aluminium paint - I was careful to only get it on the outside, but it doesn't conduct.

The final effect is pretty striking in a side view like that, but with a rider on its much less obvious.

I too am not convinced by the low CoG argument; I think getting the extra weight close to the rider may be just as good.

Nick

 

[docnjoj]

My only concern would be anatomical! Can U put both feet down at the same time????
otherDoc

 

[Tiberius]

My only concern would be anatomical! Can U put both feet down at the same time????
otherDoc

A very valid concern. Yes, I can. The design criteria for the battery box included rounded edges and no fixings along the top or sides. I reckon it would actually be marginally better than a traditional crossbar if I slipped off the saddle.

Nick

 

[docnjoj]

Hey Somebody got into my post! At least the comment was well written!
otherDoc

 

[Ypedal]

Woops.. sorry bout that Doc.. my fault.. ( see what happens when you have the fancy Moderator buttons and have not had your morning coffee yet.. hehe )
--------

Hehe.. yeah.. that sure looks like a testicular dizaster ! ...

Another thing< not so much of a problem once you get on the bike ) is stepping over the bike, i'm flexible enough i can lift my leg over the frame but from letting various people test my bikes i've noticed the tendency to lean the bike over to step into it.. high battery weight = bike ends up on it's side on the ground... :|

 

[docnjoj]

Thanks ypedal! I thought I needed more coffee!
otherDoc

 

[Lenk42602]

 

[pizark]

i used to run 48V 10AH of SLA inside my triangle frame. And an X5 motor too. To be honest, it didnt feel bad at all,.. def. better than being on the rear rack. Since then.. I tried using 2-24v 12Ah NiMH's on rear rack, mounted low in separate panniers. yeah the batt pack went from 30lbs to 20lbs,.. but the heavier SLA's mounted in the frame still felt better than the lighter NiMH's on the rear rack.

My latest setup uses the NiMH batts in the same side/rear panniers, but on a 408 motor. X5 is sitting in garage. Feels a lot better. I'm debating whether to move the NiMH batts back into the frame, but can't find a nice bag to put them in. Old SLA's weren't as tall.

If you do a search under pizark, you'll see pics of my SLA setup. i think it looked pretty good. most ppl couldnt tell my bike was electric. They thought the bag in the frame was just for extra storage room. I got it at REI. Novara-brand.

 

[pwbset]

X5 is sitting in garage.

Which X5 is it? How much you want for it? :wink:

EDIT: Whups.. nevermind... found it...http://endless-sphere.com/forums/viewtopic.php?f=3&t=5858. Wish it was a 5305... :|

 

[Tiberius]

View attachment 1

Hi Lenk,

What's the width of your battery and tray? Do you ever catch your clothing on the tray?
I wanted to keep my battery pack below 100 mm (4") width so I could still pedal. It ended up at 84 mm and I think a better design could have got it down to 80. This is with 38120 LiFePO4 cells.

Nick

 

[safe]

On this build, I thought getting the battery weight central was more important than getting it low.

"Center of Mass" is in the center of the bike and not really low. When you are on a mountainbike the "center of mass" is high because the overall body is high.

So for a mountainbike this bike seems very close to being totally right. Ideally the top tube of the frame would integrate the batteries... that's about as good as you will get.

People that mount their batteries on the back or down really low are doing it wrong.

 

[Tiberius]

Ideally the top tube of the frame would integrate the batteries... that's about as good as you will get.

Hi safe,

I did think about that. But on this bike it would be difficult - for one thing its a folder!
Its also a thick aluminium frame.

I may well do that on another build, if I start with a conventional frame, made out of steel so I can weld or braze it. My idea would be to replace the top tube completely, either with a large hollow rectangular section, or with two/three/four small tubes with the battery pack inside.

Nick

 

[Fumesucker]

Neat mounting solution, Nick.

I agree that putting weight low is not always good for stability. Old British motorcycles had a low C of G and didn't handle too well, in my experience (I owned a BSA Bantam and a Triumph T100). The Japanese came along with bikes that had a much higher C of G and which felt much more responsive.

Also, my 'bent has a low C of G and is definitely less stable at low speed than a conventional upright bike.

Whether this is the whole story with regard to stability and handling I don't know, but it does seem to me that having weight low down isn't automatically a good thing.

Jeremy

I tend to agree, think of balancing a dowel on the end of your finger, when the dowel is long it's much easier to balance than when it is short.

I too have noticed that I have a hard time riding my bikeE 'bent slowly, I'm all over the place trying to climb steep hills..

 

[gogo]

^BMW has long touted the horizontal twin (boxer) layout on their motorcycles as a superior weight distribution.

Sorry, I couldn't find a still photo to post, but check out this concept bike video for an implementation of weight distribution:
http://www.youtube.com/watch?v=XAlWJx7gtbY&feature=related

It has a square space in the frame between your legs for cargo space. You could fit a lot of batteries in there!

 

[SamSpeed]

One aspect of CG is "ground handling" -- that is pushing the thing in and out of the garage. I rode an e-go scooter recently and was impressed at how easy it was to handle. It's heavy, but the batteries and motor are all under your feet. Better than my bike with 36v SLA's on the rack. This could be an issue depending on the size of the rider. My daughter is about 120 lbs. and finds my bike a bit "tippy" until she's on the road.

I agree about the virtues of a high CG though. Also have a bike-e ...

 

[safe]

One aspect of CG is "ground handling"...

It is definitely a choice... either you build for "comfort" and "ease" or you build for "performance". From the performance perspective the weight needs to be pretty high. Mountain bikes definitely need the weight up because you start off so high up to begin with.

Street bikes (like road racer types) try to use as low of a center of mass as possible, but they've increased their suspension and ride height to higher levels than once thought useful. At one time it was believed that 2-3" was all the travel you wanted, but now I guess it's risen up to more like 5-6". That's still short compared to the 12" on motocross bikes.