Next step is to build the support bearing for the freewheel in the cranks so they can handle the 2.5kW of power.
Image courtesy of Endless Sphere member Miles quoted http://endless-sphere.com/forums/viewtopic.php?f=28&t=47618
Image courtesy of Endless Sphere member Miles quoted http://endless-sphere.com/forums/viewtopic.php?f=28&t=47618
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Getting there… The flex in the motor bracket has now been removed and I have installed the freewheeling cranks.
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So I’ve done a bit of riding now and have some basic figures.
I wanted to calculate my efficiency in Wh/km, but I cant count the current during discharge at the moment so I have decided to using charging current (CC) to calculate the numbers. Also I was pedalling during this so the numbers are just motor input and not accurate in overall Wh/km unless I make some calculations for my input too.
Coulombic Efficiency = 98%
Distance travelled 31km
Average speed 25km/h
Current in during charge 9Ah (100mins at 5.4A)
Nominal Voltage = 51.2V
Average Efficiency ( 51.2 x 9 x 0.98) / 31 = 15Wh/km
So top speed was another number I was interested in, previously the bike reached 54km/h which was already fast enough, but I recently swapped a chain to reduce drag in the drive chain and with a fresh charge reached a new top speed of 63km/h. I think that speed recording may have been slightly out or slightly downhill and I would say the bike has a max speed of 60km/h on flat road. Obviously at this speed a crash can be fatal so I will not be increasing the power, instead I will try and get the bike looking more presentable and improving reliability.
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60kmh, may I point out that you just took the cake for fastest DIY electric vehicle in HSBNE?
@rut4ger @victorv
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And I need to hurry and finish my skateboard…
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It has been over a month since posting here are some updates:
Cranks…cranky, most of the time at HSBNE working on the bike has been spent getting the freewheeling cranks to the point I am happy with. After initially testing the bike I realised that the bearing in the freewheel was not strong enough for the job so I needed to machine a support bearing carrier to help it out. The job was a bit tricky because I had to work with tight press fit tolerances and in the process had to rethink what I was doing a couple of times. I finally got this finished last week so the bike is a goer!
Battery…, after the initial test I realised the battery works and I thought I’d better have a way of measuring individual cell voltage in case I run it too low and kill a cell. I added some sense wires to each of the cells and bought some Hobbyking 8s cell voltage checkers. This way I can ride until I hear the beeping and I can adjust the voltage alarm settings too. At the moment I have it set at 2.9V per cell for LiFePO4 if I have it any higher the buzzer goes off from the voltage sag of hard acceleration.
Next to do is to get some more kms on the bike and I am seriously considering getting the VESC 4.8
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Another update:
I’ve travelled about 300km on the bike since the conversion and so far so good. The reliability has been quite good, with only a couple troubles so far. The first is that the chain will occasionally drop while changing to first gear, though I think I’ll just need to adjust the cable. The second is that one of the cells is in a sad state, down to about 6Ah of the original 12Ah. I removed it from the pack so now have a 15s setup, the good new is that this brings me down to comfortably under 60V so I can use the VESC which now has FOC!
The sine wave controller will definitely match the motors back EMF better.
Also here is how the cranks turn out with the support bearing etc.
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