change ratio to avoid overheating?

[guido]

wow lots of feedback
cruising at 40 kph on the flat, uphill I choose the lowest gear and manage 20 kph
the axle is 20 mm and the 7 teeth sprockets are for 12 mm axles so I dont think I can manage that but yes a reduction before the crank would be optimal. I am thinking on scrapping an old 2500 Watt angle grinder for a reduction
tomorrow is a second real test day and I will also get me a second chain to try the smaller chainwheel

yes I see the added downside of heatproduction, this is just energy I should be using to get from a2b, and heatproduction can be an excessive drain on the battery, all the more reason for me to build me an extra reduction

 

[guido]

I will be getting myself that 56 teeth sprocket, thats an instant improvement, and maybe with the smaller sprocket on the crank for the secondary drivetrain, I might be fine

 

[NeilP]

wow lots of feedback

Yes, sorry about that, a lot of that is me waffling and trying calculations out....Edit..now deleted as it was all just SOOO wrong

Tench did mention that maybe a 13 was available for the motor in 20 mm

But I would take the advice also given to strip and check the gearbox
While you were at it, it may be an option to machine it to make it fit the 12 mm 7 tooth sprocket, or see if you can slide the motor to the left slightly, and get a 7 tooth welded to a 14 tooth, or make up a carrier to fit the 7 on the 20mm shaft

Near the top of this page, Tench posted his speed figures
Working that back,
30 mph = 48kph
48kph=800 meter /minute
26 inch wheel rolling radius = 2.075m
Rear wheel RPM = 385 with 11 tooth sprocket driven from 44 t crank
gives crank cadence of 96
crank turned by 48 tooth with 14 on mootor...

So motor sprocket is turning at 330
therefroe with 5:1 g/box ratio
motor turns at 1650 RPM

EDIT figures in RED are corrected RPM figures changed due to info later in the thread, it appears the ratio is in fact 9.33:1 not 5:1

So his smaller motor is running at WOT for 15 minutes at 1660 rpm (3079) taking the bike to 48 kph and not overheating

Your figures give motor speeds of 1492rpm (2784)in Nexus low gear at 20 kph and 1252 rpm (2336)in Nexus high gear at 40 kph

So your motor is running at slower speeds for sure, but is it that much slower to make that amount of heat difference?

As others ( that have experience with these units) have said, the heating may well have other causes.

Going to a 14 motor , 56 crank setup would give motor rpm of 1740 (3247)in low at 20 kph and 1415 rpm (2640)in high at 40 kph

 

[guido]

ok a test further and this is the outcome
I left and started climbing at once in the standard setup, 14 motorsprocket 48/48 cranck with nexus in first, climbing speed reached 32 kph without paddeling for lack of superhuman paddeling capabilities ,then on the flat max speed with paddeling in 7 gear 60 kph this was fun, until the chain broke. I was 10 km from home luckily 4 km of which downhill.
Fixed the chain and did a second run and yes I managed to overheat the motor in about 3 km, the first 2 steadily uphill. waited 5 minutes and went back.

I ordered a 56 teeth sprocket and wil get this end of the week, further more i`ll try to get a 13 teeth sprocket, all in all that wil help me get the ratios down

I was a bit unwilling to open the gearbox but I will do so tomorrow, I`ve been reading up and the internal resistance can be significant I am always avoiding this in case I wreck something

just as extra info: bike weight with rider is about 130 kg that is 286 pounds

well a few things to change and check but I`ll keep posting new results

ps something else, I was told to disconnect the processor from the battery before charging, Im not real happy with the spark when reconnecting, is that really a must? what can go wrong if I dont, reason: I want to incorporate the charger in the frame, its easier if disconnecting the processor is unnessecary

 

[boostjuice]

The cyclone/headline planetary gearboxes feature 9.33:1 reduction, not 5:1

The motor has a Kv of ~150

 

[NeilP]

The cyclone/headline planetary gearboxes feature 9.33:1 reduction, not 5:1

The motor has a Kv of ~150

Ahhh bollocks...you could have said that earlier :wink:

 

[NeilP]

ps something else, I was told to disconnect the processor from the battery before charging, Im not real happy with the spark when reconnecting, is that really a must? what can go wrong if I dont, reason: I want to incorporate the charger in the frame, its easier if disconnecting the processor is unnessecary

By processor, i am assuming you mean the controller. The processor or MCU is an integral part of the Controller..it is the brain inside

Spark caused by the capacitors in the controller re charging when pluggin battery back in. cAN BE ok, BUT IT DOES CHARGE THE CONNECTORS AND CAN cause damage to components inside

Look up pre charge resistor ont eh forum here... use Google Advace earch and searcht eh ES site.

basically you connect the battery first via a resistor, to allow a slow tricklle of current to charge t he controller capacitors then after they charge you quickly remove resistor and plug iin direct...rushing now as shoule be at work

Good lucvk

 

[guido]

here some figures of my own

Rolling radius 228 cm
14t motor sprocket/18 t rear wheel sprocket = 0,77 (cranck sprockets 48t/48t does not come in equation)
Gearbox on motor 1/9,33

Speed 38 kph uphill in first gear
first gear hubratio: 0,63
0,63x0,77/9,33 = 0,0525 = downratio from motorsprocket to the wheel in low gear
38 kph/60=633 mtr/min
633/2,28=278rpm/min rear wheel
278/0,0525=5295 motor rpm ? seems fast enough when max rpms for the motor are 4500
Now at another speed in high gear slightly downhill …………………………..
Speed 70 kph
Seventh gear hubratio: 1,55
1,55x0,77/9,33 = 0,1279= downratio from motorsprocket to the wheel in high gear
70 kph/60 = 1167 mtr/min
1167/2,28 = 512 rpm/min rear wheel
512/0,1279 = 4003 motor rpm; seems fast enough as well
Done the calcs and now I also don’t see why I need to downgear between motor and crank other than to provide a better peddalingspeed for myself, I now also think that there is another reason for the heating problem that keeps occurring. The gearbox has been checked and is not too tight, I took out a bit of grease that seemed overdone but not so much as to make a real difference.
I will put in a 56 teeth gear for my own pedaling, should arrive end of next week. I do run a 48V 32 Ah battery, I am now thinking that I am just pushing to many amps…………… Will be trying not to run full throttle all the time, see how that goes, it’s the engine running hot not the controller as much.

 

[NeilP]

Yes, those rpm figures, that you calculated, at these speeds, scale up from the rpm figures I worked a few posts back with the speeds yo gave earlier, so it does look the the RPM for the motor is OK.

Do you have a CA or a Watt meter you can put in line with the battery to the controller and measure the load and wattage the motor is pulling...under load and no load.

That will be a way at least to see if you are getting excessive no load currents, and therefore a problem, or if it is just that you are working the motor hard and it is just getting hot because of hard work

 

[guido]

placed a 56 teeth sprocket on the cranck, et voila, instant improvement. Just not as much as i hoped for, I still overheated, but its hopefull cause I could get a lot further and pedalling is way more comfortable and effective especially in the higher gears. Now a 12 teeth freewheel sprocket on the motor and its fine by me, this in combination with cooling fins should solve the entire problem.

does anyone know of a 12 teeth freewheel sprocket for a 1200 W cyclone?

ps now I have an other way of keeping the optimal rpms
using the same way of calculations as in the previous post I have calculated the speed for every hub position corresponding with 4500 rpm for the motor, this way I have to keep in mind that for a certain speed I should be in a specific gear, but its worth it, its only 7 gears anyway. the note with the speeds is stuck on the bike but I believe its something like 27 kph in first and 68 in seventh.