Wanting to have the motor use the gear train I decided to make a low tech mid-drive. Using a crystalyte hub motor through a jack shaft to the drive train. This allowed me to gear down the motor for the top gear and of course the lower gears and provide an overdrive from the crank. This allows the use of higher voltage to the motor and operation within a higher efficiency overall. Well how did it work, as I have not increase the battery voltage the planned 40% yet my 19 miles of test riding today was not that inspirational. Top cruising speed dropped from 27mph to 25mph due to the 33% top gear reduction. Testing up hills worked out well in low gears, although the speed was quite slow. I am running a 50% overdrive from the crank to wheel so cadence speeds are nice and low at speed, this was nice. Noise level was not an issue as it is really no louder than a freewheel clicking, wind noise is dominant. Overall I am not sure it was worth going to all this effort to make this change as the simplicity of a hub drive is hard to beat. It is nice to pull off a light weight rear wheel without a 12# hub though. Starting from a dead stop of course is much better, I think once the battery voltage is increased I maybe more pleased with the results.
Mid Drive LWB Recumbent using Hub motor
- Thread starter linear
- Start date
John in CR
100 TW
Linear,
I'd love to see some pics. Soon I'll start construction using the same approach, so I'd like to see where you put the motor.
John
I'd love to see some pics. Soon I'll start construction using the same approach, so I'd like to see where you put the motor.
John
John,
I can post some pics as soon as I figure out how to do that. I might add that this is a sort of proto type as I was changing plans as I went along. I did make CAD drawings on what I was planning on doing as I went through the process. Some of my concerns were chain tension as I made this a bolt on system, 2 bolts for motor mount and 1 bolt for jack shaft. The motor mounts quite low to ground and within a few inches from front of back tire, low CG but you cannot go up a street curb with this mounting. The motor mount is very strong and provides a mount for heavy battery packs again low CG which are basicly below the seat. The whole drive train is built from parts on hand using disassembled free wheel components, and welding up spockets to shafts and such. It is easy to configure a selection of crank drive overdrives within a given build, I have 5% and 50% on the current build, but the 5% sprocket is just a spacer on the freewheel stack, but could be used. Maybe this is too much detail on my approach as you just want pics, keep in mind this is just a first cut at a design that I feel meets my needs better than any thing that I say as a bolt on package for $1000 or more. As my design is application specific some of the details are of limited interest. I was very concerned with positioning as chain tension is pretty high. Let me see what I can so on a couple pics showing motor position. With the battery packs mounted the view of motor mount is blocked.
I can post some pics as soon as I figure out how to do that. I might add that this is a sort of proto type as I was changing plans as I went along. I did make CAD drawings on what I was planning on doing as I went through the process. Some of my concerns were chain tension as I made this a bolt on system, 2 bolts for motor mount and 1 bolt for jack shaft. The motor mounts quite low to ground and within a few inches from front of back tire, low CG but you cannot go up a street curb with this mounting. The motor mount is very strong and provides a mount for heavy battery packs again low CG which are basicly below the seat. The whole drive train is built from parts on hand using disassembled free wheel components, and welding up spockets to shafts and such. It is easy to configure a selection of crank drive overdrives within a given build, I have 5% and 50% on the current build, but the 5% sprocket is just a spacer on the freewheel stack, but could be used. Maybe this is too much detail on my approach as you just want pics, keep in mind this is just a first cut at a design that I feel meets my needs better than any thing that I say as a bolt on package for $1000 or more. As my design is application specific some of the details are of limited interest. I was very concerned with positioning as chain tension is pretty high. Let me see what I can so on a couple pics showing motor position. With the battery packs mounted the view of motor mount is blocked.
John in CR
100 TW
linear said:
That's because it is really low. I envy the good roads you must have to ride on. I plan to go directly from the motor to the wheel, and use the motor as the jackshaft. My bikes though, are electric first with human assist instead of the more typical electric assist on an HPV.
John
Ok its really low, even if I raised it from the 2" the most I could go in the present location with a different mount is about 3.5", I'll try that on the next bulild if I decide the mid drive is the way to go. The roads around here have pot holes, I just try to avoid them for now. Using the motor as the jackshaft would require the use of small <11 tooth sprocket for the gear down, didn't have any of those, and even smaller for the crank overdrive. What are you gaining by moving the hub out of the wheel gear ratio wise in your design.John in CR said:
Looking at this mounting issue a little furthar it is a no win situation trying to improve the clearance, it is easier just to build up a 3rd LWB frame that allows a motor of this diameter to fit within the frame below the seat. It would be nice to go over a speed bump without having the motor hit it that would get old real quick. Thanks for you input, maybe the electric assist isn't worth the hassel anyways. I just rode the thing for the first time yesterday and am now ready to abandon the bolt on approach less than 24 hours later. You have helped me to not tread any further down this path. Have a good day. I think I'll head out and give it another ride before I mothball this one as the winter cold is setting back in shortly.
John in CR
100 TW
linear said:
Multiple speeds, of course. I have mountains to cross, that would kill a direct drive hub motor. I want a straight chain in high gear and in low gear, so I plan to do a 3 speed, but in a fashion similar to the Phaser gearbox. It will look similar to a regular cassette on the wheel, and invert the cassette on the motor. The same linear increase in tooth number of each sprocket (all odd numbers for even chain wear), will give a non-changing chain length, so I may even be able to get away without the "S" in the rear derailleur. That is if I can tie the front and rear derailleur cables into a single common shifter. If a standard front derailleur can do more than 3 gears using the narrow rear cassette spacing of the front sprockets, then I'll have more gears, but 3 is sufficient to get the range of gearing I want. If I can't get rid of the S in the chain, then the front and rear sprockets don't have to be mirror images, but odd numbers for at least the highest and lowest speeds (the mountain goat, and the flatlander).
Why go to the extra effort? you might ask. Chain durability, reduced sound, and efficiency, in that order.
Here's an idea for you. Put a small tire directly on your hub motor. Then curbs and stuff wont' be an issue, other that the difference in speed, and it will at least offer some protection.
John
John in CR said:
Just got back in from a short 4 mile ride in rain gear, not a real nice day, its still winter in Michigan here, 50 degrees and rain. I did go over some wooden ramps on bike paths willing to take a motor stike just to see what I can cross on a typical ride, no hits. Putting a small tire directly on the hub would eliminate the need for the rear wheel altogether, good tip!
Now that you described your design it sounds like an elegant system, should be very nice when you get it built up. I would imagine crossing a couple mountain ranges would require an pretty large capacity energy source, maybe a small nuclear reactor would complement the system well. The electric bike thing is really all about the battery IMO, without that done well many things are a non issue. Until I find a low cost battery solution a sub 30 mile range toy is all were going to have on this end. My options on this are use it as is or just through out in mondays trash, as this home built frame was already phased out by my 2nd build the loss is minimal. If i get the energy I will just built a 3rd frame specific to this approach as I have pretty much everything on hand already, just need to get the battery solution figured out as I would like a reliable 60mile round trip range so a 100mile max range using lipo is most likely the ticket.
Edit: 2/14/09
I looks like another option to scraping the frame when this gear testing is done is to cut out long chain stays from BB to rear triangle, lengthing the down tube, and rebuild the frame opening to accomidate the motor size. Sometimes a little rework is in order.
Best Regards,
Joel
I know this approach will not appeal to hardly anyone but I thought I would include a little more info on what I was planning on getting out of this. As we all know brushed motors have poor efficiency when you start bumping up the voltage in a large wheel. But through some gearing this is improved greatly IMO. I found when riding with vehicle traffic more power is required on even slight up grades or the cars want to run you of the road, so the brushed was not doing it for me.
Bike gear inches and expected motor efficiency vs. speed
Assume cassette of 14-28T
motor sprocket 14T
jack shaft motor 28T 0.75:1 wheel diameter equivalent 19.5" high gear 9.75" low gear
jack shaft drive 21T 1.33:1 gear reduction from motor
jack shaft crank1 14T 1.50:1 cadence reduction
jack shaft crank2 20T 1.05:1 cadence reduction
Cog teeth == effective wheel diameter for motor simulator: thrust/efficiency Cystalyte brushed DC @ 60 volts
Chain Rings 48-38-28
34T == 8.03" cadence = 80 @ 7.64MPH in small ring w/ 1.5:1 OD gear inches 32.0 thrust 70# EFF 50%
34T == 8.03" cadence = 80 @ 10.4MPH in mid ring with 1.5:1 OD gear inches 43.4 thrust 63# EFF 62%
34T == 8.03" cadence = 80 @ 13.1MPH in big ring with 1.5:1 OD gear inches 54.8 thrust 42# EFF 75%
34T == 8.03" cadence =104 @ 17.0MPH in big ring with 1.5:1 OD gear inches 54.8 thrust 10# EFF 80%
28T == 9.75" cadence = 80 @ 12.6MPH in mid ring with 1.5:1 OD gear inches 52.9 thrust 52#
28T == 9.75" cadence = 80 @ 15.9MPH in big ring with 1.5:1 OD gear inches 66.9 thrust 37#
28T == 9.75" cadence =101 @ 20.0MPH in big ring with 1.5:1 OD gear inches 66.9 thrust 10# EFF 80%
24T == 11.4" cadence = 80 @ 18.6MPH in big ring with 1.5:1 OD gear inches 78 thrust 30# EFF 75%
24T == 11.4" cadence = 99 @ 23.0MPH in big ring with 1.5:1 OD gear inches 78 thrust 10# EFF 80%
22T == 12.4" cadence = 80 @ 20.3MPH in big ring with 1.5:1 OD gear inches 103 thrust 28#
22T == 12.4" cadence = 89 @ 24.7MPH in big ring with 1.5:1 OD gear inches 103 thrust 10# EFF 80%
20T == 13.65" cadence = 80 @ 22.3MPH in big ring with 1.5:1 OD gear inches 93.6 thrust 25#
20T == 13.65" cadence = 97 @ 27.0MPH in big ring with 1.5:1 OD gear inches 93.6 thrust 10# EFF 80%
18T == 15.16 cadence = 80 @ 24.7MPH in big ring with 1.5:1 OD gear inches 103 thrust 23# EFF 74%
18T == 15.16 cadence = 96 @ 29.5MPH in big ring with 1.5:1 OD gear inches 103 thrust 10# EFF 80%
16T == 17.06 cadence = 80 @ 27.8MPH in big ring with 1.5:1 OD gear inches 116 thrust 21#
16T == 17.06 cadence = 94 @ 32.7MPH in big ring with 1.5:1 OD gear inches 116 thrust 10# EFF 80%
14T == 19.5" cadence = 80 @ 31.8MPH in big ring with 1.5:1 OD gear inches 133 thrust 18#
14T == 19.5" cadence = 94 @ 37.5MPH in big ring with 1.5:1 OD gear inches 133 thrust 9# EFF 80%
jackshaft rpm 1/2 motor rpm 28T/14T
jackshaft rpm cadence X 3.43 == 48T/14T BIG Ring
jackshaft rpm cadence X 2.43 == 38T/14T MID
jackshaft rpm cadence X 2.0 == 28T/14T SMALL
Bike gear inches and expected motor efficiency vs. speed
Assume cassette of 14-28T
motor sprocket 14T
jack shaft motor 28T 0.75:1 wheel diameter equivalent 19.5" high gear 9.75" low gear
jack shaft drive 21T 1.33:1 gear reduction from motor
jack shaft crank1 14T 1.50:1 cadence reduction
jack shaft crank2 20T 1.05:1 cadence reduction
Cog teeth == effective wheel diameter for motor simulator: thrust/efficiency Cystalyte brushed DC @ 60 volts
Chain Rings 48-38-28
34T == 8.03" cadence = 80 @ 7.64MPH in small ring w/ 1.5:1 OD gear inches 32.0 thrust 70# EFF 50%
34T == 8.03" cadence = 80 @ 10.4MPH in mid ring with 1.5:1 OD gear inches 43.4 thrust 63# EFF 62%
34T == 8.03" cadence = 80 @ 13.1MPH in big ring with 1.5:1 OD gear inches 54.8 thrust 42# EFF 75%
34T == 8.03" cadence =104 @ 17.0MPH in big ring with 1.5:1 OD gear inches 54.8 thrust 10# EFF 80%
28T == 9.75" cadence = 80 @ 12.6MPH in mid ring with 1.5:1 OD gear inches 52.9 thrust 52#
28T == 9.75" cadence = 80 @ 15.9MPH in big ring with 1.5:1 OD gear inches 66.9 thrust 37#
28T == 9.75" cadence =101 @ 20.0MPH in big ring with 1.5:1 OD gear inches 66.9 thrust 10# EFF 80%
24T == 11.4" cadence = 80 @ 18.6MPH in big ring with 1.5:1 OD gear inches 78 thrust 30# EFF 75%
24T == 11.4" cadence = 99 @ 23.0MPH in big ring with 1.5:1 OD gear inches 78 thrust 10# EFF 80%
22T == 12.4" cadence = 80 @ 20.3MPH in big ring with 1.5:1 OD gear inches 103 thrust 28#
22T == 12.4" cadence = 89 @ 24.7MPH in big ring with 1.5:1 OD gear inches 103 thrust 10# EFF 80%
20T == 13.65" cadence = 80 @ 22.3MPH in big ring with 1.5:1 OD gear inches 93.6 thrust 25#
20T == 13.65" cadence = 97 @ 27.0MPH in big ring with 1.5:1 OD gear inches 93.6 thrust 10# EFF 80%
18T == 15.16 cadence = 80 @ 24.7MPH in big ring with 1.5:1 OD gear inches 103 thrust 23# EFF 74%
18T == 15.16 cadence = 96 @ 29.5MPH in big ring with 1.5:1 OD gear inches 103 thrust 10# EFF 80%
16T == 17.06 cadence = 80 @ 27.8MPH in big ring with 1.5:1 OD gear inches 116 thrust 21#
16T == 17.06 cadence = 94 @ 32.7MPH in big ring with 1.5:1 OD gear inches 116 thrust 10# EFF 80%
14T == 19.5" cadence = 80 @ 31.8MPH in big ring with 1.5:1 OD gear inches 133 thrust 18#
14T == 19.5" cadence = 94 @ 37.5MPH in big ring with 1.5:1 OD gear inches 133 thrust 9# EFF 80%
jackshaft rpm 1/2 motor rpm 28T/14T
jackshaft rpm cadence X 3.43 == 48T/14T BIG Ring
jackshaft rpm cadence X 2.43 == 38T/14T MID
jackshaft rpm cadence X 2.0 == 28T/14T SMALL
John in CR
100 TW
Joel,
I got a bit lost in the technical. What was the result of your learning exercise? Was it that the motor mount needs a triangle for proper support, since that's my plan (a triangle motor mount that can slide in the bolt attachments for proper chain tensioning) if I can't attach the mid motor to the frame near the motor's axle?
John
I got a bit lost in the technical. What was the result of your learning exercise? Was it that the motor mount needs a triangle for proper support, since that's my plan (a triangle motor mount that can slide in the bolt attachments for proper chain tensioning) if I can't attach the mid motor to the frame near the motor's axle?
John
John in CR said:
My learning exercise was in the area was more in the fabrication area as I do not have a machine shop and I had to make due with what I had down stairs in the wood shop. I found that it is a must to make sure gears are concentric on the jack shaft motor side, it is critical to good operation, as I kind just wiped out the first one on a 5/8 shaft 18 inches away from the drill chuck, just using a marker to draw a circle on the steel sheet welded to the tube sliding over the shaft. Made a 2nd with a bit more care on that.
Of course the major deal was the ground clearance thinking I could get away with a bolt-on below he long chain stays, as it was easy, but you caught that pretty quick, good eye. The front end of my vette is almost that low and its a 170+ mph machine, so the low motor mount seemed a non issue to me.
I very much under estimated the time it takes to fabricate this stuff, I spent a few days on this not sure how many I think maybe 4 or more. I almost quick after 2 and then hearing of the warm up here built it just to get it out of the shop.
Frame flex, with this thing build up and hanging from the ceiling down in the shop, I notice the chain would develop slack under full power stall conditions, using the back brake, after furthar review it became apparent that it was twisting the whole frame just a little bit. Again another reason to move the motor within the frame, if the road clearance wasn't enough. Originally I planned on a compression strut with bearing on from the motor mount to the jackshaft to control that force, but have since shortened the shaft as the flex was not that bad.
So you are right about being concerned with that motor mount issue. A provision for a compression strut may return to my design if the jackshaft stays below the chain stays as a seperate assembly. As I have already tested at stall levels with a 35Amp limit, I just need to get moving on to 60volt testing on the road later when the weather warms up and put together a suitable battery pack.
If I like it I may go through with the frame mod, what ever I do I want a clean chain line. I figure that I can carry either 2 or 4 18# nicad packs on the bike now, so if I ever move to real batteries I may have some range in the future. My interest is to move toward short range light weight designs.
Although this is a little off topic but for my application a big 5 series crystalyte in the wheel would have done just fine, but my goal was to see what I could get out of a cheap brushed X-lyte at 1/5 the price of motor and 1/3 or less the price of the controller. I could make my own DC controller, but as cheap as they are its easier just to mod an existing unit.
Not sure what else to say, I'll keep an eye on your progress.
edit 2/16:
Other things I forgot to mention
Rims heat up pretty fast when using the brake as a load
The gear cogs in the freewheel/cassette have to in good shape, as I started with a lightly used mega-range at first it had skipping on the 16T and 18T, so had to swap that out prior to riding it. I have a feeling that the freewheel/cassette cogs and wheel drive chain will have short life spans.
