Freewheeling crank drive (was: Stepper motor as ebike drive)

Malcolm

Malcolm

10 kW
Joined
Jan 26, 2007
Messages
755
Location
Newcastle upon Tyne, UK
I've been looking around at various motor options for ages, trying to decide whether to go for a hub motor or bottom bracket drive. I like the idea of a bottom bracket drive for efficiency and versatility, but the difficulty is finding the right gearing solution. I keep coming across planetary gear drives that are designed for stepper motors and servo drives. I'm just curious to know if could you run a motor like this with a standard brushless controller http://cgi.ebay.co.uk/8-5Nm-Stepper...1281467QQihZ003QQcategoryZ26209QQcmdZViewItem or would it need a dedicated controller?
 
Hi Malc

Nice to hear from you again, If you are planning on going down the geared route the Randy Draper system is a very efficient way of doing an assist, have seen stepper motor systems but you should be able to knock up a system ALA Randys design as you certainly have the machine skills to do it, that would be the way I would do a custom build, the Hub motor of course is a nice off the shelf unit but If I were making my own rig it would be direct drive from the motor to a 3 speed rear gear like Randy did, sure he didnt make many friends on the forums but his Idea for a custom built drive is very efficient and you should be able to get a good range of speed with a 1KW or so motor, I can even supply you a motor if you need one, the advantage of doing this is that you can always keep the motor in its most efficient range by altering the gearing which in turn means the motor wont heat up as much and magnets fly off and crack etc etc. I have a box load of Kolmorgen motors should you wish to have a go yourself, they would need an external controller to get the best performance however you could run it fine at lower speeds with the built in unit.

Good Luck

Knoxie
 
stepper motors are a totaly different animal.they are designed for motion control in machinery. each time the drive "Steps", the motor will step a designed number of degrees and then the motor and drive will lock the shaft into the new position. 1.8deg. per step is a common value. that would make for a motor than can "Step" 200 times per revolution and the motor shaft is magnetically "locked" between steps.

this makes it good for machines. if i know that it takes 48 steps for my machine to move from point "A" to point"B" my control electronics meters out 48 pulses to the motor. stepper motors are designed to make these "Steps" reliably and accurately and not to spin a wheel at speed. the controller you would need to do this would definitely be a custom built item.

the motors will also only do a certain number of steps per second. so the motor at the shaft may only be capable of 50 or 100 rpm which is too slow for a BB drive. the reason for the gear drives here is for torque multiplication and to increase the number of steps per revolution. these motors do not produce the greatest amount of torque.

a similarly sized BLDC motor will produce more torque and much higher RPM. you can buy them, but they will cost some serious bucks. the motors and gearboxes come in standard sizes. thee common ones being NEMA17, NEMA23 and NEMA42. NEMA23 is the most popular. these standards define the size of the mounting flange for the motor and gearbox.

rick
 
Many thanks for the explanation Rick. The torque rating for the motor I linked to seemed pretty good, but if it only runs at low rpm then it's not much use. I thought it looked too easy. 8)

Hiya Paul! Hear you've been busy with a new job. Hope they're paying you enough to make it worth giving up your ebiking time. The Kollmorgen sounds interesting. I've heard them mentioned many times here, but not seen them for sale anywhere over this side of the water. You wouldn't by any chance have a USPD planetary drive that would fit it, or know where i can get hold one, would you? I know Fechter's mentioned in the past that it will fit the Kollmorgen too. The stock controller would do fine to start with.
 
Malcolm said:
Many thanks for the explanation Rick. The torque rating for the motor I linked to seemed pretty good, but if it only runs at low rpm then it's not much use. I thought it looked too easy. 8)

Hiya Paul! Hear you've been busy with a new job. Hope they're paying you enough to make it worth giving up your ebiking time. The Kollmorgen sounds interesting. I've heard them mentioned many times here, but not seen them for sale anywhere over this side of the water. You wouldn't by any chance have a USPD planetary drive that would fit it, or know where i can get hold one, would you? I know Fechter's mentioned in the past that it will fit the Kollmorgen too. The stock controller would do fine to start with.
Click to expand...

Hello Malc

Yes new job is going well should get some time for some e-bikery now as well, the Kollmorgen stock controller is 24V 32A and do work well, there have been a few people use them for mid drives, there was a user on here that has done so, however I would like to see a stock motor running ala Randys bike that would be cool! I have the motors here and would gladly send you one up to play with if you think you could lash something up? I just dont have the tools to do it or the time! but would love to see it done! If you want to connect the external controller I can give you the details on how to do that as well.

As far as the gearbox goes you could try tony at electrodrive or thesuperkids.com as they certainly have the innards of the planetary drives on for 50 dollars, however if ran it like Randys conversion you would not need it, I can dig out the motor speeds from somewhere, you could look on evdeals.com as they have the motor details on all the different types.

I should get around to making one myself this year, drop me a line if you want to play with one.

Cheers

Knoxie
 
Since you've brought up steppers, there's a trick I found in an OLD book on electric motor's I've been meaning to try. It was a simple method to get a 2-phase motor to run on 3-phase power.

referring to the .pdf spec sheet from the e-bay auction http://www.motioncontrolproducts.co.uk/pdf/FL86STH118-4208A-H.pdf
I'd connect the yellow and blue wires, then the black orange and brown wires. This would form a crude 'Y' winding. Now a sensor less BLDC controller should make it run when the red white and green wires are connected to the controller. (ofc. a full re-wind to a 3-phase winding would be better. Hopefully the motor would have a 12 finger stator, a lot of steppers have 8 finger stators)

Personally, I think ~300rpm is about a perfect motor/gearbox output speed for BB drive. At that speed it's an easy 3:1 chain reduction to get to my 105rpm max cadence. And the 3:1 reduction puts a nice comfortable 60rpm cadence on the high side of the peak power point.

Marty
 
FrankG said:
Steppers are ... such a valuable resouce to put them on an Ebike or E anything other than a CNC machine is a shame...
Click to expand...
Good point, it's better to make things out of scrap than to turn them into scrap :)

Marty:
Thanks for that. I'm almost tempted to try it and you're right of course, a few hundred rpm is ideal for a bottom bracket drive. We need someone to start building custom brushless motors for ebikes.

Knoxie:
I don't know the details of Randy Draper's system, but from the photos I've seen he seems to use a parallel drive with two chains and an oversize sprocket on the rear. Looks a bit messy to me. I was thinking of an inline system: motor driving through a freewheel on the right crank – a bit like the Elation system. Have you seen the freewheel cranks that the trials riders are using? They've added a freewheel to the right crank so that the entire chain freewheels with the back wheel. It looks just about perfect for the job (aside from the price that is): http://www.onza.com/site_files_flash/spares_tensile_uci_freewheel_cranks_flash.htm

Hopefully there should be room to weld a second, larger sprocket to the freewheel, alongside the existing sprocket. Then you can drive the small freewheel sprocket from a motor mounted next to the bottom bracket. The larger freewheel sprocket is linked by chain to the rear wheel through your normal gears. Thanks to the freewheel you don't have to pedal while the motor is spinning. This is why I want a geared motor, so I can drive straight to the freewheel. Sound feasible?
 
Malcolm said:
Have you seen the freewheel cranks that the trials riders are using? They've added a freewheel to the right crank so that the entire chain freewheels with the back wheel. It looks just about perfect for the job (aside from the price that is)
Click to expand...

Hi Malcolm,

I created my own freewheeling cranks using the same idea. The ENO 22t freewheel has weight-saving slots milled circumferentially that you can bolt through. I had a chainring made by Highpath Engineering but you could probably find one that you could adapt.
 
a bit cheaper would be the cranks from Cyclone (like in the Cyclone BB drive). the right hand one is also threaded for 1.375 X 24TPI for free wheels. but it is a square drive instead of an ISIS. they do sell them separately as spare parts.

rick
 
Miles said:
I created my own freewheeling cranks using the same idea. The ENO 22t freewheel has weight-saving slots milled circumferentially that you can bolt through. I had a chainring made by Highpath Engineering but you could probably find one that you could adapt.
Click to expand...
Excellent! Photos please...

Thanks for tip about the freewheel. They also make a double freewheel, but gosh you American chappies do charge handsomely for your handiwork :shock:
http://sheldonbrown.com/harris/white-freewheels.html

No disrespect meant to Sheldon Brown of course.
 
The ENO freewheels are by far the best. You really need a decent freewheel if you're using it at crank torque levels.

These guys are a good source for trials stuff in UK: http://www.tartybikes.co.uk/about.php They were really helpful to me.
 
That's neat. I see you got the Echo cranks, which are a good deal cheaper and have a square taper fit. I just realised that the problem with standard cranks as opposed to the dogleg Cyclone cranks, is that there's very little space between the cranks for a bottom bracket drive. Looks like you've mounted the motor near the rear axle. Any chance of seeing the rest of it? I know you're reluctant to show the rest of the bike until you've tidied things up, but I'm curious as hell :lol:
 
Malcolm said:
That's neat. I see you got the Echo cranks, which are a good deal cheaper and have a square taper fit. I just realised that the problem with standard cranks as opposed to the dogleg Cyclone cranks, is that there's very little space between the cranks for a bottom bracket drive.
Click to expand...

Yes, I measured 120mm between the cranks at mid-length. You can get longer BB axles, though. I don't feel comfortable with widely spaced pedals, myself.

You could use the Cyclone cranks with a better freewheel, I guess.
 
Ah well, guess I'll just have to curb my impatience :)
No, I don't like the idea of the splayed cranks either. 120 mm between the cranks may not be big enough. Back to the drawing board.
 
Yes, something like a Tongxin or Tarn motor could work well. I'm partly put off by the thought of the whole motor spinning away – seems a little wasteful. Definitely worth considering though.
 
Shimano had a Front Freewheel System (FFS) in the 80s where the freewheel was in the bottom bracket. I got one on ebay a couple of years ago but I've never installed it. I think Schwinn and Panasonic road bikes had them. They're still out there on ebay from time to time for not too much $.
 
Hello Miles

Thats a neat looking crank!! hmm need to get my head around your system any chance of some more photos? looks neat enough to me? I am going to send Malcolm a motor so he can have a play and see what he comes up with, I still think its far simpler to drive the rear wheek directly and use either a freehweeling crank or 2 x freewheeling rears, Randys system is not too tricky to replicate if you have the tools, the only pricey thing is the multispeed geared hub, there are other options for the geared hub but I doubt that they are strong enough, Randys system does seem well proven.

I have been toying with doing a Draper style conversion as I have so many motors lying about, OK its not as stealthy or slick looking as a hub motor but it does make for a very efficient drive system and of course you get the satisfaction of making it yourself!! if you have the tools!!

Thanks for the picture miles really neat looking and Malcolm I will try and get that motor off to you before the weekend.

Happy days

Knoxie
 
Hi Paul,

Thanks! My system is evolved from Randy's. I've used a Gates belt from the motor (same motor as Randy) to a pulley on the Dual Drive which has its own isolating freewheel. Rather than a second freewheel on the Dual Drive, for the chain, I have retained 4 sprockets and the derailleur mech - this is the reason that I needed the freewheeling cranks.

What is the length of the Kollmorgen motor?
 
Good Morning Miles
What motor is it? I thought Draper’s motor was shrouded in secrecy. –grant
 
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