TongXin (a.k.a. Nano) motor project

[Jeremy]

As some will know, I fitted a Crystalyte 405 to the 20" front wheel of my recumbent a few weeks ago. This works OK, but delivers way more power than is either needed or legal (unless restricted, which is what I've tried to do).

I spotted that Rennaisance Bikes in Vancouver had some TongXin motors on sale, so decided to risk buying one to fit to a spare folding bike. I ordered the motor and 36V controller last Friday evening, it was despatched from Vancouver on Monday and arrived here (near Salisbury) yesterday (via economy rate TNT!). Best bit was the price, just $200 for the hub and controller.

First impressions are that it looks an amazing little thing, very, very light and if anything it looks to be better finished than the Crystalyte. The hub is a sensorless (3 wire) one and the 36V 15A controller is also tiny, little larger than a cigarette packet and is completely sealed. The hub freewheel seems very low drag too, which is a major difference to the Crystalyte.

It initially looks to be a good option for a budget ebike, provided that all that's needed is a bit of power assistance. Being so small, I doubt that it's going to be very powerful or be much help on steep hills, but only a test will tell!

Hopefully I will get this laced up into a wheel this weekend so that I can try it and report back on performance.

Jeremy

 

[HarryB]

Two questions:

What is speed of the motor? 190rpm?

What size wheel are you going to put it in?

 

[Jeremy]

The motor is a 260 rpm one, according to the label, model number 120SWX24, although the curves I have seem to show that max hub rpm is about 215 at no load, 36V. TongXin only publish one set of motor curves, so I have no idea how these relate to the motor I have. I suspect the curves are really for the "190rpm" motor.

The motor is going into a 20" rim and I'll probably run it at 36V. This should give reasonable hill climbing performance, I hope, and not provide any real assistance on the level at speeds over about 15mph. If this is how it seems to work, then I may put it on the recumbent as a replacement for the Crystalyte 405, as all I really need on that is hill climbing assistance

I wish we had some really solid data on these motors - trying to make sense of the garbled Chinese information is really challenging at times!

Jeremy

 

[frank9755]

Jeremy,
Good luck with your Tongxin. I've got one too, which is currently being made up into a wheel, for my Christmas project bike. They do look pretty!
I'll post details when I've got mine working, and look forward to hearing how you get on with yours.
Regards
Frank

 

[frank9755]

...TongXin motors on sale, so decided to risk buying one to fit to a spare folding bike. Jeremy

Jeremy,

If you fit a Tongxin to a folding bike, you could send it to AtoB magazine to get a 5-star rating and try to break their range record!

Frank

 

[Jeremy]

I have to own up (shamefully, perhaps......) to not being an A to B subscriber. What's the nature of the range competition and why is it about folders?

The TongXin is indeed a pretty little motor. I dropped it into my LBS this morning for them to lace it into a nice Velocity Razor 406 rim, with 2mm stainless spokes. I should get it back next week, just in time for it to be my Christmas project too!

Jeremy

 

[giguana]

if you want the 405 motor to have half the power(torq and speed) you can put a 100kohm resistor onto the throttle sensor...

the motor responds to throttle resistance of between 350Kohm 30Kohm.

350k the motor will make a tiny sound and not turn,
270k, the motor will do about 3kph on flat but not start from standstill
100k is about 50% power
50k is about 75% power
30k is the motor on full power

if you look at the throttle connection coming from the controller, on the back there are 3 metal strips. the one on the left is voltage sensor(!), in the middle is neutral, and on the right is 5V.

you can put some kind of potentiometer, it has to be very safe or you will be crashing at full speed, basically it's probably a good idea to have 100% resistance at standby, jumping straight onto 270k as a minimum setting, and 30k max. I'm going to make myself something that I can use with gloves in the winter because it's freezing!...

to be honest I read something that said that the tongxin might just be just as powerful as the crystalyte but goes about 20% further. apparently these two guys did a race and the crystalite was struggling in the last 5 miles although it might be another model.

 

[frank9755]

The AtoB reference is joke about their slightly over-the-top praise of the Brompton-Nano, which puts a Tongxin motor, in a rack bag on a Brompton folder, with power from a 7Ah battery. The combination gives assistance up to speeds of c13 mph. They put a fit cyclist on it and discovered he got a range of c50 miles - presumably because he spent most of the time pedalling above the cut-off speed.

Based on this test, they rated the Brompton-Nano as one of the two (now three) top electric bikes on the market

Frank

 

[Jeremy]

Giguana,

I've already done something similar with the 405 controller, but as it's a voltage signal from the throttle (the controller isn't current driven) I used a potential divider to change the throttle range. I also biased the zero up slightly to make the controller response a little more linear.

My throttle sensor, like most I think, isn't a potentiometer at all, it's a Hall effect sensor with a voltage output, ranging from about 1V for zero to about 4V for full throttle.

This works OK, but the motor still draws a lot of current and provides a fairly non-linear response, with more power than I need. It's also a heavy motor, much, much heavier than the TongXin.

Frank,

Thanks for putting me in the picture! If my installation provides good power below 15 mph and little or no drag above this speed, then it will be ideal for the recumbent. I can pedal the 'bent fast on the level or up gentle hills, but really need a bit of help to keep some speed up on steep hills. The 'bent is less stable at low speeds, so changing down to the granny gear doesn't work too well, in fact the wobbles when trying to ride at very low speeds are a bit of a worry in traffic.

 

[flecc]

Jeremy

Reports on the Nano in smaller wheels with 24 volts have been of good climb ability, and I think that might be all you need for your 'bent. There's not only the saving in battery weight, but also the longevity of the roller drive. It's usage with 36 volt power which is most likely to shown up this innate problem.
.

 

[Jeremy]

Thanks for that tip, Flecc. I was wondering if it would be OK at 24V, but the very small size of the motor made me wonder. I will try it on a couple of my test 12V SLAs to see how it goes, then look at getting some decent NiMH packs for it, perhaps.

Interestingly the LBS (who are Powabyke dealers) thought that the hub was a dynamo when I took it in! They were surprised that it was so small and light for a hub motor.

Jeremy

 

[flecc]

Definitely worth trying at that. Reading between the lines in feedback, you could be pleasantly surprised at the torque around 10 mph in a 20" wheel.

That Powabyke motor is so far behind the times now, not surprising the Nano would give them a surprise.
.

 

[giguana]

the hall effect sensor is a kind of potentiometer, you can replace it independently with .5Mohm variable resistor of some kind, which means you will much more control than a hall effect. with a hall effect sensor there is about 2 mm of difference in between slow pace and jogging pace, so if you just want to admire a roadside you have to really concentrate on it, but with a potentiometer you have gradual and complete control of all the power levels. A massive improvement!

YouTube - nano motor electric bike kit: freewheel demonstration

 

[Jeremy]

As I said before, the Hall effect sensor is a voltage output device, it has a low apparent source resistance (near zero in fact, albeit with a max source current limit) and therefore behaves slightly differently to a resistive potentiometer.

A resistive potentiometer will simulate a voltage source, but will be non-linear if required to source any current, due to the difference in current between the two parts of the track (obviously the part "above" the wiper is sourcing the standing current plus the current to the controller, the "lower" part is only sinking the standing current).

Provided that the total potentiometer resistance is low in comparison to the input resistance of the controller, say around the 5k ohms to 10k ohm source resistance that is recommended for these controllers, then this non-linear effect is negligible. If the potentiometer resistance increases though, the non-linearity gets progressively worse with increasing source resistance.

Here is a worked example to demonstrate this, with a 100k ohm controller input resistance (mine seems to be about 80k ohms as far as I can tell) and your suggestion of a 500k ohm potentiometer.

The resistive potentiometer will deliver the following percentage voltages for the stated percentage rotation:

0% rotation = 0% voltage

25% rotation = 13% voltage

50% rotation = 22.2% voltage

75% rotation = 38% voltage

100% rotation = 100% voltage

Can you see how the loading effect of the controller input resistance makes a high resistance potentiometer highly non-linear?

The Hall device will happily source the current needed to provide a linear output, due to it's low output resistance, although the mechanical design of the Chinese ones I have does introduce some non-linearity due to the mechanical arrangement. I've partially compensated for this by summing a small zero throttle voltage to the output.

Jeremy

 

[jha07]

Hey Jeremy

I too find that the throttle on my crystalyte controller to be not very linear. How would I go about making it more linear?

 

[Jeremy]

I'll post the final details once I've got mine tweaked to be a bit better than it is now. The key to this apparent non-linearity is really the way the controller works, I think. Looking at the brushless controller circuit used in the Crystalyte it seems that the throttle input is really giving a motor speed control, rather than a motor power control (or more accurately a motor torque control). I'm reasonably sure this is why they seem non-linear, as the way to produce best throttle response might be to arrange for the controller to provide increasing motor torque with change in throttle position.

This would overcome the problem I had of needing to move the throttle a long way to get enough torque to move off, only to find that the motor then gave more power than was needed.

For interest, here are the voltages measured from the Hall throttle (with a 5V supply), relative to percentage throttle position:

0% = 0.89V
25% = 1.45V
50% = 2.42V
75% = 3.55V
100% = 4.24V

Ideally, the voltages from the throttle should be 1V, 1.75V, 2.5V 3.25v and 4v, as the controller is expecting to see a 1V to 4V input. What I've done initially is attenuate the range, so that the controller only sees a maximum voltage of 2.5V and sum a voltage at the lower end to bring the minimum up to about 1V. This isn't perfect by any means, which is the reason I'm going to do some more experimentation before recommending a good mod.

Jeremy

 

[giguana]

that is interesting about the non linear behaviour of the voltage controllers, you are right I have my figures are little bit wrong, I have to press a very hard on the wires on the electronics kit I have because otherwise the figures are skewed...so I have done some measurements with my 406 with the standard 20A xlyte controller...this is using an assortment of ceramic resistors.

kohm = estimated rotations every second / kph drainbrain reading
690=0.8 / 6
570=0.9 / 13
503=1.0 / 14
470=1.2 / 14
320=2.0 / 18
270=3.0 / 22
220=4.0 /26
147=5.0 /27
100=6.0 /30
80=8.0 /38
47=12.0 /44
33=12.0 /44

I think resistor values above 600k would be too weak to be useful, the plan is to make the potentiometer fall to zero after about 600 by cutting the resistance thread...I am thinking of using a slide potentiometer mounted with a spring, with some safety cut-off breaks.

you can make a graph of the values, I'm about to do so, but that's a pretty fair estimate of a linear taper. that said I want a nano!

 

[Ian]

Apart from any concerns about linearity I wouldn't fancy using a pot because of concerns about reliability. Only the highest quality industrial spec. rotary pots would be suitable in a wet dusty environment, and such pots usually require a high operating force. A slide potentiometer would be virtually impossible to seal against dirt and moisture.

By contrast a hall effect sensor is inherently waterproof and if the external connections are sealed will work perfectly even when immersed, which given Fleccs testing methods may be important

 

[Tiberius]

Actually a linear response might not be what you need. It may be better to have more throttle movement for a smaller speed change near the lower end, if starting off and controlled slow motion is important. But then I know another application (hovercraft) where you only use the top third of the range. My point is that the ideal mapping between the throttle position and the controller input voltage is unlikely to be exactly linear. All you want to start with is to make sure that it does cover the full range and is reasonably well behaved.

More important might be what the controller is setting? Is it rpm, torque or power? A quick check with a scope on my Torq shows that the throttle control varies the width of the pulses sent to the motor. The repetition rate is fixed at about 16 kHz, and the current drawn within the pulse is set by the motor and the rpm. I don't know if the controller does then adjust the pulse width according to rpm or current but I haven't seen it doing it.

Jeremy, is it possible that your observation of it running away after getting in motion is a battery effect? Once the motor is turning the current drawn drops; if the battery voltage then goes up significantly it might give the effect of more motor power instead of less.

HTH

Nick

 

[Tiberius]

Hopefully I will get this laced up into a wheel this weekend

Hi Jeremy,

Interesting project. I take it you bought the motor only, not built into a wheel. Are you doing this yourself, or is there a local shop that does it?

Nick