Specialized Big Hit FSR with midmount
- Thread starter Tench
- Start date
The motor has a 14t freewheel on it driving onto a 48t chain ring, the other front chain ring which drives the rear has a 44t driving a 13-34 7 speed cassette. In top gear, 14-48 and then 44-13 are virtually the same ratio so the motor is turning about the same speed as it would if it where in the wheel with the pedal cadence the same as it would be on any push bike with 24" wheels and this gearing, i would say it was just normal bike gearing. However the fun starts when the lower gears are used, at the other extreme in bottom gear 14-48 then 44-34 the motor is turning 3 times to one turn of the wheel, this is where the real advantage of the mid mount is found.
There are some pics of the series/parrallel changer plugs and an explanation of their construction somewhere in the middle of the build log, just been and had a look it is half way down page 5, read the text between the pics of the plugs for an explanation of how they are wired.
There are some pics of the series/parrallel changer plugs and an explanation of their construction somewhere in the middle of the build log, just been and had a look it is half way down page 5, read the text between the pics of the plugs for an explanation of how they are wired.
nice one tench 
cracking build,I no how you can save a shitload of weight and money,i built a mid drive with a golden motor 500w trike motor and ran it on that 72v stealth battery i bought off you stays cool even with me on it!I will post some pics when i can find my camera,seriously tho m8 you carnt go wrong with my setup ,72v 15 fet 4110 from zennid scooter parts uk £45 deliverd,500w golden trike motor £120 deliverd including import tax, you already no where to get your throttle you told me!petrol scooter uk about £15 quid deliverd,we can now get cheap lipo from robot birds in the uk also,same as zippy ect.i think these motors have been overlooked their about half the weight of that motor on your bike they also have a low rpm for easy direct drive or through the gears.i had mine way over geared 16t motor sprocket 52t on the wheel it did about 60 mph and im 15 stone and it still went up hills,it would not smoke tho even with that abuse,i think the controller was close tho!!quick question now sorry for going on!! Do you notice any enersha effects from the big spinning motor?? also sorry for my bad grammer 
cracking build,I no how you can save a shitload of weight and money,i built a mid drive with a golden motor 500w trike motor and ran it on that 72v stealth battery i bought off you stays cool even with me on it!I will post some pics when i can find my camera,seriously tho m8 you carnt go wrong with my setup ,72v 15 fet 4110 from zennid scooter parts uk £45 deliverd,500w golden trike motor £120 deliverd including import tax, you already no where to get your throttle you told me!petrol scooter uk about £15 quid deliverd,we can now get cheap lipo from robot birds in the uk also,same as zippy ect.i think these motors have been overlooked their about half the weight of that motor on your bike they also have a low rpm for easy direct drive or through the gears.i had mine way over geared 16t motor sprocket 52t on the wheel it did about 60 mph and im 15 stone and it still went up hills,it would not smoke tho even with that abuse,i think the controller was close tho!!quick question now sorry for going on!! Do you notice any enersha effects from the big spinning motor?? also sorry for my bad grammer Hi Splad, glad you put the battery to good use, you should start a new thread about your bike or add it to the thread dedicated to pics and info of mid mount projects;
http://endless-sphere.com/forums/viewtopic.php?f=6&t=38553
I am sure other uk builders would like to know more about it and where you sourced all you parts etc.
Simon.
http://endless-sphere.com/forums/viewtopic.php?f=6&t=38553
I am sure other uk builders would like to know more about it and where you sourced all you parts etc.
Simon.
Green Machine
100 kW
Hey Simon,
I really love the way you set up your charger and batteries....sleekest charging system i have ever seen.
What is the procedure to charge your batteries after you plug in the charging cables,in other words how complicated is the process to start up your charger? Are you confident enough in your system to charge in the house unattended?
How long does it take you to charge all your packs?
Did you customize the charger in any way?
How are you getting those led read outs?
Great build.
I really love the way you set up your charger and batteries....sleekest charging system i have ever seen.
What is the procedure to charge your batteries after you plug in the charging cables,in other words how complicated is the process to start up your charger? Are you confident enough in your system to charge in the house unattended?
How long does it take you to charge all your packs?
Did you customize the charger in any way?
How are you getting those led read outs?
Great build.
I have programmed the charge parameters for the main pack into one of the ichargers memories and saved it as "bike", When it is connected i select "bike" in the menu and press go, it balance charges and stops when all the cells reach 4.2v. The 2 meters in the charger housing are displaying the volt and amp output from the power supply to the icharger, the icharger can display these numbers but i have them visible all the time. the 2 meters are powered from a phone charger fed from the 240v input and i have a 50 amp shunt between the power supply and charger so i can measure the amps. The i charger is not modified at all. I am in the process of removing the dc/dc dropper off the bike and putting the lights onto a seperate battery, i will create another set of charge parameters in the charger saved in another memory as "lights" to charge this small pack seperately, i like to keep things very simple to ensure no mistakes are made, i am not fond of magic smoke! I have only done a few charge cycles on this pack, it has run without a hitch and as i am only charging at 12 amps with the pack for charging configured by my series/parralel changer as a 6s 48ah that equates to 1/4c so i dont see why i cant leave it unattended, i have not done so yet but my confidense is rising, nothing is getting warm other than the power supply. It is a 350w one, i have pushed it as far as 440w, it handled this for half an hour, it is back down to 350w now, i pushed it to see if it had power in reserve to ensure i was not thrashing it running it at 350w continuously. All my individual packs where charged seperately before the bike was assembled, none of the packs showed any anomilies and the balance has always remained perfect. The setup is basically as simple as the Lifepo4 battery and charger i have on the wifes bike. A full charge from bone empty would take around 4 hours.
I do need to rebuild the charger as the heat from the power supply is being pulled through the icharger by its internal fans, i need to partition the box so each has their own air flow and vents to prevent this.
Simon.
I do need to rebuild the charger as the heat from the power supply is being pulled through the icharger by its internal fans, i need to partition the box so each has their own air flow and vents to prevent this.
Simon.
hjns
100 kW
I read the whole thread and I continue to be amazed. Very professional work. Well done!
If you push the motor hard, does it get warm?
If you push the motor hard, does it get warm?
Yes a little, but all motors will produce some heat, i have held it flat out for about a mile and it was barely warm, not hot. A long session in the woods climbing banks is called for, this would really test the cooling, if it does ever become a problem which i dont think with my sympathetic riding style it will be i would opt for the oil bath cooling that a few others have had good results with.hjns said:
hjns
100 kW
Ah, my line of thinking. There are some quite nice threads about oil cooling. However, with your experience, how would you do it? The oil bath I mean.
Most people seem to have gone for an ATF but i would look into using the low weight fork oils used in motorcycles, they are formulated to not froff as they are designed for dampers so could be a good choice and are available down to an SAE of 2.5, thats like water! (less windage losses?) I had thought of venting it down the centre of the axle on the opposite side to the wires so a breather pipe can be attatched and placed so it can breath but not allow water in or oil to escape.
hjns
100 kW
Thanks man! Very helpful.
pchen92
100 W
Wow ! Awesome job 
I have seen your post quite a while and I am always on admiration when I see your photos
I was thinking of doing the same setup on my Giant DH Team. How are the chains holding up this kind of power ? Do you have shifting problems ?
How did you manage to fit the two chainrings ?
Sorry I am french and I don't understand everything
I have seen your post quite a while and I am always on admiration when I see your photos
I was thinking of doing the same setup on my Giant DH Team. How are the chains holding up this kind of power ? Do you have shifting problems ?
How did you manage to fit the two chainrings ?
Sorry I am french and I don't understand everything
No need to apologise for being French, your english is better than my French! and this is a global forum.pchen92 said:Wow ! Awesome job
I have seen your post quite a while and I am always on admiration when I see your photos
I was thinking of doing the same setup on my Giant DH Team. How are the chains holding up this kind of power ? Do you have shifting problems ?
How did you manage to fit the two chainrings ?
Sorry I am french and I don't understand everything
I am glad you like my bike, thanks for the compliments
The chains dont seem to be complaining, i am carefull not to shift gears when under power. The chainwheel setup is an off the shelf item from Eclipse bikes,
http://eclipsebikes.com/chainwheel-cranks-p-1008.html
I allready had a similar setup on another bike which had 2 x 44t chainwheels, they both now have 1 x 48t and 1 x 44t with the 3rd small chain wheel removed. doing it this way slows down the pedals in relation to the motor which makes the bike more relaxed to pedal assist at higher speeds.
pchen92
100 W
Thanks you.
Last questions : How do you change the thread of the right side of the motor ? Can I just put a lefthand bmx freewheel on the standard thread ? Or it won't fit ?
Thanks
Last questions : How do you change the thread of the right side of the motor ? Can I just put a lefthand bmx freewheel on the standard thread ? Or it won't fit ?
Thanks
Kepler
10 MW
I keep going back to this thread to check out details more closely. The motor modifications on their own must have been quite a job. Did you fabricate a new motor shaft or modify the existing shaft? Also the fact that you removed the stock freewheel threaded section and machined a new lefthand 30mm thread is the perfect solution and a task probably beyond the average hobby machinist. Inspiring stuff.
A question. Could you use 2 x 48 tooth chain rings? I would imaging with the speed this bike is capable of, the 44 tooth would be still end up being too quick in relation to cadence.
A question. Could you use 2 x 48 tooth chain rings? I would imaging with the speed this bike is capable of, the 44 tooth would be still end up being too quick in relation to cadence.
Pchen92, it think the answer to your post was in the following one from Kepler,
Kepler, yes i made a new shaft, (the original is now residing in Aus) the bearings in the motor where changed to 3/4" bore ones allowing me to use thicker journals, i also increased the size of the oil seal to 24mm i/d to run on a spacer which protects the wires. The spindle is in fact made of 2011t3 alluminium with having large square ends and not having a thread with a small core dia and 2 flats i could do this. This alloy machines very nicely which allows the accurate dimensions needed for good bearing fits and has good mechanical strength.
Data sheet;
http://www.aalco.co.uk/datasheets/Aluminium-Alloy_2011-T3_3.ashx
The machining of the lefthand 30x1mm thread is really easy as you work left to right with the tool running away from the work piece, far easier than doing a right hand thread where you have to work towards the work piece with stopping in time being critical! place the tool in an undercut then engage the feed, the tool travels off the end of the thread, easy! well it would have been, my small metric lathe didnt have enough swing, i made the brass adaptor on it but had to go and do the side cover on a bigger DSG 13x42, a much bigger machine, this had the complication of an imperial lead screw which makes you scratch your head a little!!
I also changed the woodruf key to full length (and made it fit properly) (the only job on the whole bike that a cnc was used for)There is also another bearing inside the brass sprocket mounting directly in line with the chain to support the sprocket carrier and take the load off the threads. It seems to be a solid design.
The pedal cadence i learnt from having built the previous bike, we learnt that having the driven sprocket slightly larger than the driving one makes for a much more suited pedal speed. i could have used 2 48t rings but i would sooner have better ratios at lower speeds, flat out i am just hanging on not pedaling!! 8)
Kepler, yes i made a new shaft, (the original is now residing in Aus) the bearings in the motor where changed to 3/4" bore ones allowing me to use thicker journals, i also increased the size of the oil seal to 24mm i/d to run on a spacer which protects the wires. The spindle is in fact made of 2011t3 alluminium
with having large square ends and not having a thread with a small core dia and 2 flats i could do this. This alloy machines very nicely which allows the accurate dimensions needed for good bearing fits and has good mechanical strength.Data sheet;
http://www.aalco.co.uk/datasheets/Aluminium-Alloy_2011-T3_3.ashx
The machining of the lefthand 30x1mm thread is really easy as you work left to right with the tool running away from the work piece, far easier than doing a right hand thread where you have to work towards the work piece with stopping in time being critical! place the tool in an undercut then engage the feed, the tool travels off the end of the thread, easy! well it would have been, my small metric lathe didnt have enough swing, i made the brass adaptor on it but had to go and do the side cover on a bigger DSG 13x42, a much bigger machine, this had the complication of an imperial lead screw which makes you scratch your head a little!!
I also changed the woodruf key to full length (and made it fit properly) (the only job on the whole bike that a cnc was used for)There is also another bearing inside the brass sprocket mounting directly in line with the chain to support the sprocket carrier and take the load off the threads. It seems to be a solid design.
The pedal cadence i learnt from having built the previous bike, we learnt that having the driven sprocket slightly larger than the driving one makes for a much more suited pedal speed. i could have used 2 48t rings but i would sooner have better ratios at lower speeds, flat out i am just hanging on not pedaling!! 8)
Kepler
10 MW
Wow, that is some serious modification. Thanks for the detailed explanation.
I see what you mean with the chain ring sizing. I suppose if you really wanted the improve high-speed cadence you could go with a 56/48 combo and perhaps a 15 or 16 tooth free wheel on the motor. A lot mucking around though especially if your not that fussed with pedaling at high speed. Personally a hate not being able to pedal with some load no matter what speed I am doing.
I see what you mean with the chain ring sizing. I suppose if you really wanted the improve high-speed cadence you could go with a 56/48 combo and perhaps a 15 or 16 tooth free wheel on the motor. A lot mucking around though especially if your not that fussed with pedaling at high speed. Personally a hate not being able to pedal with some load no matter what speed I am doing.
Another consideration with a full suspension DH bike is the sprocket dia, the larger you go the higher above the swing arm pivot the chain becomes, this then has a tendency to pull the swing arm upwards when under power creating a squating effect on the rear of the bike, not good for traction and it tends to make the bike want to wheelie, it also hinders the shocks control of the suspension when under power, smaller is better to prevent this, too small and it is not fast enough, its all a compromise. maybe an XC bike with less travel would be better suited rather than a DH one 
or ideally have the chain line pass across the swing arm pivot to eliminate its influence but its nice to have the plush long travel of a DH bike
This a major consideration when designing motorcycle chassis, the position of the sprockets and their dia need to be established before the engine can be positioned in relation to the swingarm pivot and wheel centre or the driving power can lift the back wheel off the road and you will just wheel spin everywhere, with care a little downward force can be created adding to the available traction.
The concentric setup that Stealth use is not quite perfect regarding influence on the suspension but the small sprockets and heavier shock they use minimise it allmost to the point of insignificance, it is as near perfect as you can get regarding constant chain tension aswell.
A powerfull full sus e-bike really does need a purpose made frame to work really well, Watch this space!
or ideally have the chain line pass across the swing arm pivot to eliminate its influence but its nice to have the plush long travel of a DH bike This a major consideration when designing motorcycle chassis, the position of the sprockets and their dia need to be established before the engine can be positioned in relation to the swingarm pivot and wheel centre or the driving power can lift the back wheel off the road and you will just wheel spin everywhere, with care a little downward force can be created adding to the available traction.
The concentric setup that Stealth use is not quite perfect regarding influence on the suspension but the small sprockets and heavier shock they use minimise it allmost to the point of insignificance, it is as near perfect as you can get regarding constant chain tension aswell.
A powerfull full sus e-bike really does need a purpose made frame to work really well, Watch this space!
Completly agree about the suspension,i have rode a lot of the xc and dh bikes ,the giant nrs system would work well but then you would lose space in the frame,have u seen the ddg slammer?not as good for peddaling but i think it will be great as a powerd chassis, its got the pivot on the bottom bracket so no chain issues ive got one and it works well,its about 6 in travel ,you can borrow it if you like but its just the frame now,i suppose you want to build in as much ajustabilty as you can so you can have it exactly how you like it .how about an ecentric suspension mount?
Thanks guys, i have not been twiddling my thumbs these past weeks, i have made a stronger support for the drive side of the motor as i was not happy it would have been long term dependable which also has a shield to stop the front tyre chucking muck onto the chain and also removed the dc dropper, the lights are now on their own batteries which gives me a constant brightness on the rear light, before when i switched from high beam to low beam the rear light got brighter because the low beam draws less current, it was like a brake light coming on, oh and the low beam light was not on it in any of the previous pics. All i have to do now is fit a low voltage alarm to the lighting circuit to let me know when those batts need charging and i will consider it 100% FINISHED!!
I will get some pics up of the few mods i have done.
The major decisions for the next one have been made, frame and motor choice, voltage etc, i am in the process of sorting out all the smaller details to ensure i dont hit any snags once i start building it, not come across any issues that will prevent me from doing what i want yet, when i have completed all the details i will spend some money and get stuck in, the new one will be a Tiger compared to this pussycat!!
I will get some pics up of the few mods i have done.
The major decisions for the next one have been made, frame and motor choice, voltage etc, i am in the process of sorting out all the smaller details to ensure i dont hit any snags once i start building it, not come across any issues that will prevent me from doing what i want yet, when i have completed all the details i will spend some money and get stuck in, the new one will be a Tiger compared to this pussycat!!
