change ratio to avoid overheating?

[guido]

well after some initial problems and questions posed on the forum I can now post some pics, however it remains an open project and a truly finished bike is for somewhere in the future. for now 2 things are to be solved, the first is integrating the charger this is relatively simpel. But the real issue is that the system tends to heat up significantly leading to a stall, waiting 5 minutes or so and I can go again. The motor gets hot to the touch and so does the controller and all that at not even full speed but say 70 % over 5 km or so. I am thinking that I am driving the motor at to low revs and should put in an extra downgear. however this set was sold to me as a kit so I am thinking that every part is more or less made for each other exept for the battery. In defense of the material I do have to climb quite steep hills for kilometers and it was a hot day. now for the specs, motor 1200 Watts cyclone, Battery 48 volts 32 Ah LiFePo4, gears shimano nexus 7 speed, rims 28 inch tyres 28x2.00 roaduse




So should I put in an extra standard downgear between the motor and the crank and/or does anyone have an idea on how to make a cooling device for this type of motor, thinking of liquid cooling with small radiator myself but this means extra weight and extra tinkering. does anyone have some pics of a cooling system, for I am quite visually directed and one pic says more than a thousand words
ok thanks for any replies and if I decide to make a watercooling devise I`ll upload the pics

 

[NeilP]

Well after looking at the cyclone site the other day I was going to say it ws overheating because the Cyclone FAQ says not to run above 24 volts..but the website only seems to mention 350 and 500 W kits, and no 1200 or 900 watt kits for sale.
But I have seen articles and other questions about them, so that first response is out.

Trouble with changing gearing for the hills is that you then loose the top speed on the flats.

Is it possible to fit a 2 or 3 chain ring front sprocket ..and then fit the drive on the LHS of the bike, so you can have much lower ration for the hill climb.

Possible fit some fins to the outside of the motor to give greater surface area, like the fins on an air-cooled petrol engine

 

[guido]

well yes that would cost me in top speed but the sticker on the motor itself says maximum 4500 rpm, and at the ratios I use right now I am not even getting close to that,
also my wheel cirumference is quite large 228 cm and i think the system was designed for a 26 inch wheel with more gears, I`ll look into cutting the ratio in half between the motor and the crank, after the crank is no good, for then my own input will become useless because my rpms are rather limited. I will be trying fans on the motor and the controller though, a lot less work than a liquid cooling system
thanks for the reply

 

[NeilP]

How many chain rings do you have on the crank? just the single one and at the rear a Nexus 7 speed?

How many teeth are there on the big chain ring and the drive on the motor?

Count up all the numbers of teeth and tell us the ratios of the hub and work out the correct gearing.

I am sure i have seen these kits pictured with the chain driving the crank on the left hand side of the bike, so enabling you to have a gear change derailleur ont eh pedal chain ring with the nexus, so you have two or three ratios up front as well as the 7 at the rear hub.

Getting the ratio correct to keep your motor in the correct speed range is going to be far better than just trying to get rid of the XS heat produced by runnin git at the wrong speed.
Even the controller will run cooler at full throttle than it does at half throttle, it is how it is designed, due to the switiching of the FETS, that is as much as I can tell yo about that.

 

[guido]

on the motor is a 14 teeth sprocket on the rear wheel 18 teeth the crank has 3 blades one 32 teeth and two 48 teeth blades
right now the motor drives a 48 teeth blade and the other 48 teeth blade drives the rear wheel so that is 1:1 and doesnt come in to the equation the ratio therefore is 14:18

the easiest way of letting the motor run at higher rpms is to use the 32 teeth blade to drive the rear wheel, however that does mean that any pedalling from my side becomes completely useles because I just cant get that frequency myself. I will try this during the week to see how it goes

the nexus has several gears but these are neccesary to change between running on the flat or hills the middle gear is more or less 1:1

any ideas are welcome, at this moment I still think that reducing the ratio between the motor and the crank is the most effective because this way I can still pedal, although this is also the most complicated, I`ll have to get some parts from a scrapyard.

 

[NeilP]

I am interested in the wheel size you mention..never heard of a 28 inch bike wheel before,,I know of 26 and the new 29 inch wheels on mountain bikes.but 28 inch? Is that maybe a 700?

You are calling them 'blades' ..I can only assume that you are meaning the front sprocket/ chainrings. I just want to check to be doubly sure that we are talking about the same thing..sure we are but want to check

If you are pulling up steep hills with the 48 tooth front ring, when you have a 32 available, then that is your reason why you are overheating the motor.

if you find that the 32 is too small, then change it for something else, a 39 or a 42.

Another question..I have never seen in the flesh, let alone used,a cyclone kit..How many chains does your kit have?
two chains..motor driving the crank, or a single chain setup, the motor driving the chain that goes to the back wheell. I am guessing from what you have said is that you have the two chain setup, allowing you to change between the 48 and 32.

I suggest changing the 32 to something slightly bigger..39 or 42..it will reduce the load on the motor, so it wont heat as much, but you will have to try spinning your legs as fast as using the 32

 

[guido]

here a pic of the drive train, its a 2 chain system with the 3rd blade on the inside of the 2 you can see on this pic, i know it is the easiest solution to solve the ratio problem from the motor point of view to use the smaller blade as the secondairy drivetrain, i`ll give it a go. but if I can find me a larger blade on the outside than I prefer that, dont know if that is available though, all other solutions to change the ratio between crank and motor is far more labour intensive (multiple sprockets/gearbox material from a moped.............
oh yes I call the small sprockets on the motor and rear wheel sprockets and on the crank blades, sort of a direct translation from dutch, but I guess they are all called sprockets then?

 

[guido]

ps 28 inch rims are the standard size for a bike in holland, and the 700 is basically the same, I was told that 29 inchers dont really exist but that these are 28 inchers with extra thick tires.
to change the gear from the larger to the smaller `sprocket` I have to change the chain, with a nexus there is no chain tensioner like with multiple sprockets at the rear

 

[spinningmagnets]

Even if you end up deciding that a different system is what you need to handle the loads you are seeing, you can't sell the old system if it gets fried, so..

I would recommend attaching a temp probe to the shell of the motor, there are several available for under $20.
http://endless-sphere.com/forums/viewtopic.php?f=1&t=25502

also add the optional cyclone shell-fins. Like this:

I'm surprised that the motor is getting as hot as you describe. When it is getting hot enough to start cutting out, I would assume you would down-shift to a slower gear. There are rear-wheel gear clusters available with a higher tooth-count than stock clusters. Perhaps a lower bottom gear would help?

 

[NeilP]

oh yes I call the small sprockets on the motor and rear wheel sprockets and on the crank blades, sort of a direct translation from dutch, but I guess they are all called sprockets then?

I think the big ones are generally called ' chainrings' in the bicycle community, and the rear,sprockets . In a mechanical / farm engineering scenario, they would all be called sprockets, chain wheels or probably others too, but blade is one Inhad not heard before.

Ah, now you have given us that one extra bit of info that there is no sprung chain tensioner and you have to change to a smaller chain makes the situation far clearer. I could not understand why you were not just changing down to the 32 when you needed it. I understand about Nexus hubs and no rear dérailleur, but since there is two usable front chainrings, I automatically assumed the rest of the gear change system for that front pair of rings had been fitted also.
So to me, the solution is to fit a rear dérailleur tensioner unit if the bike has a mounting bracket for it, and fit a front gear change unit, to enable changing from a 39 to 48 while riding.
If there is no mounting bracket, then I am sure some other chain tensioning system is available

And as I said earlier, and spinningmagnets repeated with a picture of the device, fit the cooling fins to the motor. If cyclone manufacturer them ready to go then that makes job even easier.

Temp probe great idea, then you can compare your motor temps to that on the yclone website; I am sure I gave seen reference to temps on their FAQ page.

Another fixed gear alternative may be to change the rear sprocket on the Nexus hub, a quick google for them shows them available in 16, 18,19, 20 or 22 teeth. Or at the front, change the 48 tooth secondary drive primary gear for a smaller one

 

[NeilP]

http://www.cyclestore.co.uk/productDetails.asp?productID=16315&categoryID=867

 

[amberwolf]

well yes that would cost me in top speed but the sticker on the motor itself says maximum 4500 rpm, and at the ratios I use right now I am not even getting close to that,

THat might be why it is getting hot, if you are running at the rated voltage for the motor, and running at full throttle (so the motor is actually getting near that full voltage).

If you run a motor under load below the speed it would spin at without a load at the same input voltage, the BEMF of the motor will be lower than the input voltage, and it will cause current to flow. The greater the difference in speed between loaded and unloaded at the same voltage, the greater the current flow in the motor. Some of that power is being used as rotary energy to spin the motor and load, but more and more of it will be waste heat the higher the current flow is. At some point this will be more total wattage than the motor can safely dissipate as heat, and it will begin being damaged by heat buildup inside it.

So making sure you setup your gearing so that the motor doesn't spin under load too slowly vs it's rated unloaded speed for the same voltage, is essential to get it to be more efficient and not kill the motor. If setting up the gearing optimally for hte motor to let it spin fast enough results in too slow an output speed at the wheel, then you probably don't have a big enough motor.

 

[NeilP]

Yes, exactly, that is what I alluded to earlier when I asked for the number of teeth on all gears
I was going to calculate the motor RPM at various speeds, but the 28 inch wheel comment knocked me off track. Also Guido did not post the internal ratios of the Nexus, and I never got around to looking them up.

Anyone else heard of a 28 inch wheel?

 

[NeilP]

Smaller 7 tooth motor sprocket and cooling fins available on theCyclone Taiwan site..but not the US site

http://www.cyclone-tw.com/order-parts.htm

What sort of speeds do you ride at in KPH?

Try using the Sheldon Brown gear calculator page

http://sheldonbrown.com/gears/


From the figures you have given so far, and from what you have said about the 32 tooth front ring causing you to have to pedal too fast, I do think that just changing the motor sprocket for a 7 tooth, and maybe getting a chain tensioner
http://www.bikebling.com/Bicycle-Chain-Guides-Tensioners-s/201.htm

front derailleur
and 39 tooth front ring,
then you can have higher motor rpm's, keep your 48 front for the flats and down hills and then change to the 39 for the up hill sections

I am going to play with the calculator now and see what sort of motor RPM you currently get, assuming cruise speeds of about ...what 40 to 50 kph? max sort of speed, average of around 30-40 and hill climbing a bit less?

 

[NeilP]

This is your current setup
Hub ratios across the top
This is with the chain on 48 at the front
18 being the rear sprocket size on the hub
The rpm figure is the rpm of your pedals. I went with 60 rpm to give speeds (along bottom in white), of what I considered you may be riding at.
That gives motor sprocket rpm of 206rpm at constant pedal speed of 60 rpm (EDIT with data from later on about 5:1 motor g/box, this gives motor rpm of about 1030)



You say that using the 32 ring on the front is too fast pedal speed..but if you did that gives motor sprocket rpm of 308rpm at constant pedal speed of 90 rpm
EDIT with data from later on about 5:1 motor g/box, this gives motor rpm of about 1540

That would be this


Not sure what the best speed to run these motors at is? Anyone? OK so max is 4500. To get anywhere near that is going to require a big leap in gear ratios from motor to crank, but motor to crank chain sets to do that are not available in these sort of ratios from Cyclone, so one can only assume that Cyclone are not expecting the motors to be run often at those max RPM figures.

Putting a 7 tooth on the motor, is going to give an instant increase in motor rpm, which sounds like the easiest way to go


Just foudn the cooling fins for the motor on UK site..closer than Tawian

http://eclipsebikes.com/motor-cooling-fins-p-982.html

 

[NeilP]

here is another set of calcs, at 60 rpm, pedal speed (cadence) that would show the speeds you would get if you changed the rear sprocket, and also included is the speeds you would get if you put a 39 tooth ring in in place of the 32.

The calculator does not work the other way so you an put in speeds and see what pedal RPM you get, so you will have to do a load of calcs yourself to get pedal rpms you feel comfortable with.

 

[Tench]

I built one of these Cyclone kits using the 900w motor onto a 26" mountain bike, there are pics of the build in the project one link in my sig. It has had the gearing changed slightly since we first built it, it now runs a 14t on the motor driving a 48t on the crank with a 44t driving the rear wheel through a 7 speed cassette. This bike runs a 36v 20ah ping, 0ver 40v off the charger with a 35a limit set in the CA and will quite happily pull w.o.t for 15 miles in top gear (11t at the rear) at 30+ mph with no pedaling without any heat issues.
Looking at your pics you do apear to be using the motor with built in reduction gearbox like ours, i believe the planetary gearbox built onto the cyclone motor has a 5:1 reduction so you should be looking at a maximum motor drive sprocket rpm's of 900.
Sorry i dont have any solution to your over heating issues but i would suggest it is not related to the gearing?
It may be worth stripping the gearbox off it to make sure it is not tight inside, this would create heat and the additional friction loads may heat the controller up? Take the chain off and measure the no load current draw at full throttle.

 

[NeilP]

Ah, more info, I had seen that there was a gearbox on these motors but had forgotten about that

 

[darkangel]

it is not your gearing man, it is your controller and motor

ride it till you kill it and then buy the same thing again, if you have money

 

[NeilP]

Yes, of course, could be something up with motor or gearbox being a bit tight that is causing the overheat issues too, but
Until the OP gets back to us, and while I have some time to kill, I will waste a bit more of yours with some more ramblings and ideas I have going round in my head about this, related to the OP's original question about changing the ratio to get the motor speed up a bit.


Edit....bugger, I worked these figures thinking you had a 14 rear, not an 18, and did not notice that the 7 tooth motor sprocket was only for the bigger motors...... Shit ....so i deleted most of this post as I made lots of mistakes..

If Guido come back with the speed and gears he is using on his up hill sections, when he feels the motor is overheating, we can work out the actual speed that the motor is running at, and see if it is really way too low and a gearing change is in order

 

[Tench]

Neil your getting a bit confused mate, the 7 tooth sprocket available from Cyclone is for the 1500w motor that does not use a reduction gearbox, they only supply this type of adaptor for the upto 1200w motors;

http://eclipsebikes.com/tooth-cyclone-dicta-motor-freewheel-p-1001.html

 

[NeilP]

Ah well that frocks that theory up eh:

I went back up and deleted the crap in the above post to take in to account `the info Tench just supplied

the 7 tooth I saw was here:
http://www.cyclone-tw.com/order-parts.htm

 

[Chalo]

If there is room for it, use a larger driven sprocket on the crank. Up to 56t should be relatively easy to find. That alone would increase your motor speed by the ratio of 56:48 for any given pedal speed, or about 17% more motor rpm than you have now, without affecting the bike's speed relative to the pedals.

If you can pedal a bit faster, then you could also use a smaller drive sprocket on the crank, like 44t or 42t. (With a 56t driven sprocket, those would be respectively 27% and 33% increases in motor speed for the same pedal speed.) Or you can use a rear hub with a wider gearing range like the Alfine 11 speed, and the wider gears can offset your need to pedal faster.

Also, if the freewheel at the motor's gearbox shaft is not already the minimum size for that freewheel thread, you should change it to the minimum. M30x1 metric freewheels are usually 14t or 15t, but you can get 13t versions. 1.37"x24 freewheels usually bottom out at 16t, but there are a few 15t units out there.

The moral of the story is that if you need to run the motor at higher rpm without pedaling at higher rpm, then the ratio at the motor input stage must increase.

Chalo

 

[NeilP]

do you know if the motor to crank chain, is the same pitch as the standard bicycle chain ? or is it a different type?

 

[Tench]

Yes the motor to crank chain is the std bicycle pitch chain, not sure which thread is used, i suspect without going to measure it that it is the m30x1mm which would allow the fitment of a 13t sprocket but what i find hard to understand is how ours happily pulls an 11t rear once upto speed without complaining which would lead me to believe it is not the gearing that is causing the heating of the motor and controller as our motor never gets above mildly warm and the controller stays at ambient temp. We have relubed the gears a couple of times during its life though, it runs very quiet now compared to when it was new.