Macquarie College Endurance Comp Build

[jman231994]

Hey guys, as part of a competition me and a couple of my friends at school are entered in an endurance competition organised by our local university. We entered it last year and came 4th, this year we want to win. Basically the rules say we must have batteries under $220AUD, less than 5kg and of a "safe" chemistry. Last bike standing wins, if some are still going at 90 mins the one in front wins. Theres more rules than that but I'd be here for hours typing them up, if you want to have a look it's the Hunter Valley Electric Vehicle Prize.

So, our bike is built on a completely custom aluminium frame designed by myself and tweaked with testing, the motor is a cyclone/headway 960w 36v, and the batteries are headway lifepo4's, 10ah all up. We've been cutting it tight with time as the race is this sunday and we only got the batteries today, but it was worth it. By waiting longer than the other teams we were able to get headway cells rather than a complete aluminium rack pack. So we can charge faster and discharge faster.

We assembled the battery today and hooked it up for a test ride.....8th gear in the vice, 86km/h. 9th gear is there but the chain rubs on the frame so we've tuned it out. In the race we only need to average 30km/h so were comfy there, I took it up to 43km/h in 6th gear around our school oval and it was still accelerating. So 4th or 5th is probably ideal for us.

Annoyingly I cant put some photos of it up right now, but I'll try to later this afternoon.

The one issue we have with it is that it gets a bit wobbly at speed, sort of around 35-40km/h and up. What would be our best option to reduce this, the weight is mostly on the back wheel end of the bike and some could be moved forward, also the batteries are up pretty high so we could drop them below the frame to get the cog lower....Am I on the right track with those changes to rectify the issue?

Any ideas would be great to reduce our rolling resistance or extend our battery life and all of that, so yep, I'll get some photos up later, and take some good ones tomorrow with maybe a video

Thanks

[Xanda2260]

Wobbling is likely frame flex. Shifting the cog forward and down will likely help, but you may find the frame needs stiffening some.
Really looking forward to pics of this event (if you have time of course).

[jman231994]

Wobbling is likely frame flex. Shifting the cog forward and down will likely help, but you may find the frame needs stiffening some.
Really looking forward to pics of this event (if you have time of course).

Yea It could be, the way we designed it means there will be very little flex through the frame, except possibly in the rear arms which were meant to have an extra strut each but ended up not needing it.

I also wanted to know if anyone has a smart way to mount headway cells in their orange holder things, I was thinking of just drilling holes in the plastic and bolting the pack through them

I found a pic of the frame just after we got it made, the bike in the foreground is last years model haha

[amberwolf]

Wobbly at speed sounds more like headtube angle to me, based on results I've had with CrazyBike2.

Does the wobble go away if you stop pedalling? If so then what he suggested above would probably help.

If not, then try a different fork length/tire size, which will change your headtube angle. At a guess you will need shorter fork or smaller tire, probably not by very much, but longer/larger might fix it too (though might introduce wobble at slower speeds).

Larger rear tire will also do the same thing that smaller front will, and vice/versa, so if you can't get enough correction with the one, you can also do the other at the same time.

[heathyoung]

Nice - the battery limitations were severe this year weren't they?! No fun chemistry.

I was prepping a bike for it this year, but had a bad accident that stopped me from completing it (and competing). I got around the battery limitations using those 20AH A123's and a DC:DC converter in the home-made controller to get maximum energy density out of them - it just fit the price and weight limit. But I never got to try it out

Couldn't even take the Vectrix VX1 for display either this year (sulk).

[John in CR]

Jman,

It looks when you stretched the wheelbase that it may have decreased the trail a bit on a bike with not a lot of trail to begin with. I had exactly the same problem with my cargo bike, and it got worse as I tucked down for better aerodynamics. You need to increase the trail to get more stability at speed. From you pic, I looks to me like you have only about 1-1.5" of trail. How to change that at this late stage is the problem. I hacked my headset off and welded it back with more slack head tube angle. If yours is AL, that's not an option, so you have to get the tire's contact patch to trail the straight line looking down the head tube by more than it does now by some other method. It's a smaller wheel on the back that would help, though I don't think that's really enough without going too small due to the fairly long wheelbase.

To verify that more trail would make a difference, loosen the headset and turn that front wheel backward if there's clearance with the frame. That will give you more trail than you need, but taking it for a spin that way would demonstrate the difference in stablitiy at speed. It would just be very sluggish at slow speed with that much trail. You could easily find another fork in time that has less offset, which will give you more trail. If the one you have is steel, you may even be able to bend it straighter.

You definitely want stability at speed, so then you can shorten the handlebars for better aerodynamics, and wobbling will hurt efficiency. Are you allowed to pedal? If not then get rid of anything you can, chain derailleur, etc.

[jman231994]

Nice - the battery limitations were severe this year weren't they?! No fun chemistry.

I was prepping a bike for it this year, but had a bad accident that stopped me from completing it (and competing). I got around the battery limitations using those 20AH A123's and a DC:DC converter in the home-made controller to get maximum energy density out of them - it just fit the price and weight limit. But I never got to try it out

Couldn't even take the Vectrix VX1 for display either this year (sulk).

Yea as soon as we saw this years restrictions we knew it was likely because of us hahahaha. We had 26kg of batteries on the old bike, it's a shocker to move around and the weight was definitely our losing factor

Does using a DC:DC cause an increase in current the same way you would by changing voltage? Plus a bit for efficiency I guess. I honestly didnt know DC:DC's existed til the other day and now i'm continuously checking them out in the jaycar catalogue lol. Will you be there this weekend to watch the race, I'm sure they wouldnt mind you bringing what you did get done to show off part of the construction stage of bikes?

Jman,

It looks when you stretched the wheelbase that it may have decreased the trail a bit on a bike with not a lot of trail to begin with. I had exactly the same problem with my cargo bike, and it got worse as I tucked down for better aerodynamics. You need to increase the trail to get more stability at speed. From you pic, I looks to me like you have only about 1-1.5" of trail. How to change that at this late stage is the problem. I hacked my headset off and welded it back with more slack head tube angle. If yours is AL, that's not an option, so you have to get the tire's contact patch to trail the straight line looking down the head tube by more than it does now by some other method. It's a smaller wheel on the back that would help, though I don't think that's really enough without going too small due to the fairly long wheelbase.

To verify that more trail would make a difference, loosen the headset and turn that front wheel backward if there's clearance with the frame. That will give you more trail than you need, but taking it for a spin that way would demonstrate the difference in stablitiy at speed. It would just be very sluggish at slow speed with that much trail. You could easily find another fork in time that has less offset, which will give you more trail. If the one you have is steel, you may even be able to bend it straighter.

You definitely want stability at speed, so then you can shorten the handlebars for better aerodynamics, and wobbling will hurt efficiency. Are you allowed to pedal? If not then get rid of anything you can, chain derailleur, etc.

I think you might have missed what I said haha, this years bike is the frame in the background, the complete bike is last years: now it was one of the most stable bikes I have ever ridden, weighed a ton but you just couldnt tip the thing, I crashed it once by leaning it too far and scraping the foot tray, all it did was bounce back up and keep going hahaha

But you are right about the headset angle, it needs more angle on the fork to take out some wobble, however as you said, its pretty much too late. I have another fork I'm going to try out with it incase its different but I'm pretty sure theyre the same. I will look into bending it though but I'd really prefer not to unless I added some extra strengthening. One upside though is that it starts getting wobbly over our minimum required speed of 30kph, so it should be manageable for the race

But yea, no pedalling whatsoever, we dont even have a bottom bracket haha, but we do need the derailleur to let us shift for more oomph up the hills.



Heres a couple more pics I found floating around on my phone, nothing too recent though sadly

[John in CR]

Yeah, I missed that was last year's bike. This one is looking much more slippery through the air, so I hope you cure your wobble. You don't want it to turn into a tank slapper.
Good luck with the competition!
John

[jman231994]

Yeah, I missed that was last year's bike. This one is looking much more slippery through the air, so I hope you cure your wobble. You don't want it to turn into a tank slapper.
Good luck with the competition!
John

The wobble is pretty much gone now supposedly, we moved the batteries forward and it seems to have fixed it. So yea, hopefully it will stay upright haha. Thanks, only 2 days now, just haha.


I have some more photos too, the fairings arent on it yet, we'll do that the morning of the race. I'm absolutely knackered now, so photos will be up tomorrow morning....promise haha