Which Controller (edit: hub motor) for my daughter's wheelchair?

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Buk___
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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Buk___ » Dec 20, 2017 4:42 pm

Glyn wrote:
Dec 20, 2017 2:56 pm
Buk___ wrote:
Dec 20, 2017 2:21 pm
If you apply the full voltage to any motor, it will draw as much amperage as the controller can supply. The power consumed will be V * I drawn.
I don't think I understand what you're saying here sorry Buk.
Using the motors I've purchased as an example, they're rated at 48v, 20a continuous, 45a peak.
Are you saying that if I connected them to a 48v controller capable of supplying 100,000a, then they would indeed draw 100,000a?
No. The windings would melt long before then.

My point was that a motor is not inherently "48V" by construction. For example, the "36V 201rpm" Q motors are widely rumored to be identical to the "48V 260rpm" versions.

A motor's speed is defined by its windings and magnetic constuction and is captured by its kV. The 36V 201rpm is 201/36 = 5.583 kV (rpm/volt). Feed it 48V, and 48 * 5.583 = 268. Close enough to the 260rpm rating, with the discrepancy explained by the fact that the windings, cores, & back iron have limits to how much magnetic field they can produce or contain -- saturation.

Feed that same motor 24V and you have a 134rpm motor, though it may well empirically measure as closer to 150rpm because nothing is close to saturation. Provided that the controller can deliver enough amps; and the windings (and intermediate cables) can withstand those amps.

Conversely, feed it 72 volts, you probably won't get a 401rpm motor because of saturation.


But, and this is really important for your application, you cannot simply take a motor that is rated as 48V and feed ever lower voltage at higher amperage in order to to achieve greater torque at lower speed. If your motors are designed to run at 48V 20A, and you attempt to feed them 12V at 80A, you will likely melt the windings or cables before you get the motor to a speed where it can use the amps supplied to do work; so much of the power you supply will be converted to heat which it is not designed to handle.

The benefits of a geared motors for low speed applications are:
a) the speed is mechanically divided by the gear ratio, so the motor can turn faster and get closer to its optimum efficiency band whilst the wheels turn slowly.
b) The torque produced by the motor is multiplied by the gear ratio, allowing more efficient delivery of the torque required at the wheel. At the expense -- or actually benefit in your case -- of lower speed.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by amberwolf » Dec 21, 2017 1:33 am

Glyn wrote:
Dec 20, 2017 2:15 pm
I'm not sure I know how to interpret the outcomes correctly but if you're suggesting that I can answer my question by looking a the graphs then...
To use a system with a voltage half that of another, but still get the same power out, you'd have to use a controller with twice the current limit. (use "custom controller" to create both the simulated controllers).

You'd also want to compare them on a simulated slope similar to what you expect them to run on, to see what will be happening under the conditions you will use them at. If you are runnign them on the flat ground, (zero slope) then the power draws will drop as the speed rises (up to a point where power to maintain the speed begins to rise again).

You'd also want to compare them at the speed you expect to run at, on that slope.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by dogman dan » Dec 21, 2017 7:26 am

See what you mean about 6 motors now. Great design.

Yer overthinking this, one test is worth a million words. some simple remote thermometers can tell you how much your motors overheat. Overheating is basically a race against thermal mass. You might have so much mass on those motors you can get away with a LOT. 20" wheel will help with the rpm.

Its going to do everything you need easily, except for a long enough, steep enough hill. If the thermometers say stop and enjoy the view awhile half way up, then do so. A colder day than the hottest day of summer will also help a lot. And, you can drill cooling holes in the covers to make that cooling stop do its job much quicker. Holes also allow you to judge motor overheating just by the smell. You can also cool a motor quicker with a spray bottle. So what if it does not do the thing in one continuous go. Great view, stop and cool and enjoy the view. Only the most serious shit is going to phase that thing. It is going to zip up anything less than real rock staircase no sweat.

You have a great method for limiting voltage, its called the throttle. Run your rig on a convenient voltage, such as 36 or 48v. No need for running them on 12v, to limit speed. Just limit speed as needed by throttle, or three speed switch.

Version II, other lower speed wind motors can be found. IMO, 500w rated ones will do x6. each one can handle up to 1500w, so still no problem to run 6000w total.

Just because your motors are rated to 1500w, does not mean they like, or need to run at 1500w. My best estimate of your needs is that climbing that hill, provided you don't flip end over end, will take about 4000w, call it 6000w for some extra in case you need it. ( might take more because of wasted watts at too low rpm)

Ok, thats easy peasy. 36/48v controllers that have reverse are easy to find and cheap in 20 amps size. 6 of those will get you 4500w if you run 36v, and 6000w if you run 48v. three motors on each throttle, for the skid steering. Try for regen braking too.

Build that, and try it. Just ride it yourself some, adding radio control later once you refine things a bit. Betcha you don't need full throttle to get up some crazy steep hills with half throttle on it. You can easily limit the throttle signal if you need less power. If its not enough power, then just buy some bigger amps controllers. 40 amps is still not super pricy.

Radio control tests wont be same as she is on the throttle. So I still urge you strongly to have her on tethers on the actual climb. She's on her own still if you don't pull her up. I'm just saying, both up and down, having something like two strong men on the leashes can prevent a flip, belaying her if needed. There is NO SHAME in this.. Its just basic mountianeering. Sensible people climb on belay.

Start testing with six controllers like this. Has reverse, and the three speed switch is another good way to limit power if you find you don't need 4000w. https://www.ebay.com/itm/36v48v60v64v72 ... SweQBZmVGH

Better still though, one like this that also has regen braking. It might be quite possible to add regen to it though, simply adding wires to the right terminals inside.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Glyn » Dec 21, 2017 9:44 am

Thanks all for the continued support. Will reply to each in due course but I just wanted to quickly share an idea I had for hub cooling.
In this Youtube video, the guy drills holes in the hub to allow air through.
In this video, the guy installs 4 electric fans inside the hub.

I came up with another idea which is a combination of the two and in my opinion a more elegant solution:

You could take the fin design from one of these blower fans:
Image

And add something similar to the inside of the hub, forcing air through without running additional cables:
Image
Image

What do you think?
Check out my mountain wheelchair project.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Buk___ » Dec 21, 2017 10:33 am

Glyn wrote:
Dec 21, 2017 9:44 am
Thanks all for the continued support. Will reply to each in due course but I just wanted to quickly share an idea I had for hub cooling.
In this Youtube video, the guy drills holes in the hub to allow air through.
In this video, the guy installs 4 electric fans inside the hub.

I came up with another idea which is a combination of the two and in my opinion a more elegant solution:

You could take the fin design from one of these blower fans:
Image

And add something similar to the inside of the hub, forcing air through without running additional cables:
Image
Image

What do you think?
If you need to add cooling it means you are generating lots of heat, which means you are wasting energy, which means bigger batteries, which means more weight, which means more torque needed, which means more amps, which means more heat.

At this stage you better design to be efficient, thus lighter.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by amberwolf » Dec 21, 2017 2:27 pm

If you need ideas that have already been tested and documented, there's an entire thread on Definitive Testing of hubmotor heating and cooling,
https://endless-sphere.com/forums/viewt ... =2&t=48753
along with lots of other threads (many linked in that one) about cooling hubmotors.



FWIW, almost anything you can think of regarding bikes and motors and stuff has been covered in a thread here somewhere. ;) Often, using the idea word as a keyword with * in front of and behind it, and looking just in topic titles and displaying as topics, will find the threads (though there may be a lot of irrelevant results too, it is often obvious which threads you need by their titles). So if you need info or clarification you aren't getting as replies here, the info is probably somewhere else on ES.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by dogman dan » Dec 22, 2017 7:37 am

Yes, its all here. I did not delve deeply into hub cooling, even though I've melted a few motors. One motor I did eventually melt down in a race had some smaller cooling holes in the hub. The main benefit I found from them was you could stop to cool. In most hub overheats, the rider is going 40 mph or so, creating some great cooling of the motor shell at least. But stop, and that cooling stops, and a thermometer in the hub shows a dramatic spike in heat after you stop. With the holes, even fairly modest ones, you see a lot less heat spike when the motor is stopped.

This is why I suggested cooling holes, even modest ones, that allow convection to pull the hottest air out of the hub when you stop, or, in your case, you are riding very slow. And as I said, you can actually judge when to stop by the smell of the varnish on the stator wire. Just like knowing a pie is done by the smell.

Once you have stopped, nothing beats some water to cool the shell, which then can absorb more of the heat coming from the stator. If it were not for the effect on traction, I'd suggest misters on each motor. With cooling holes, and some spray bottles, you can make stops to cool down fairly short.

You might look into a grin product that helps stators move the heat to the shell, Statorade. It can be used if you do not open up cooling holes. But since you most likely will end up replacing these motors anyway for lower rpm wind, I'd start with running them stock, then if overheating does seem to be imminent, try the cooling holes. You can do a decent test with only a small but extreme steep hill, repeated over and over. Like a set of stairs.

These are the wrong motor for your needs. 550 rpm @ 48v.

https://fr.aliexpress.com/item/Free-shi ... 0.0.DIVMBq



Might be worth it to see what it might cost you to exchange them for a lower turn count motor, if the vendor has any.

The slow motors are hard to find. I only know one US vendor that sells them, for trikes.

This is a smaller motor, 500w rated. But much lower rpm @ 48v will help. But less mass to absorb heat than a bigger motor.

Brand: Electric Bike Technologies
Type: Direct-Drive (brushless, disc brake compatible)
Power: 500w nominal / >750w @36v / >1000 @48v
Max Torque: 39N-m @36v / 46N-m @48v
Max RPM: 194 @36v / 259 @48v
Cable: 8" axle exit, 3-phase / 5 hall effect
Connector: Round 8-pin 19/32" (10.4mm)
Weight: 12.8lbs (5.8kg)
Warranty: 1 Year (up to 48v - 600lb max load)

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Glyn
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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Glyn » Jan 09, 2018 4:53 am

Quick update - My daughter is doing brilliantly! She's been ill for 8 months then all of a sudden just before Christmas it was almost like a switch flicked and she was able to walk again. She's back in the hills, running around, and climbing again.

I've got this far with the wheelchair project that it seems a bit silly to give it up though. The aliexpress motors I purchased have arrived but they're the wrong dropout size for my needs. Return shipping to the vendor would cost me more than I paid for them in the first place. The fact that Chinese vendors can offer free shipping is incredible. They were never right for my needs anyway so I've decided to see if I can sell them on without using them.

I spent some time comparing motors on the simulator yesterday. Given a weight of 170kg, a gradient of 15%, and a speed of 5kph, these are the motors which had an efficiency above 35% (don't laugh :lol: )
Image
A couple of the results really surprised me. Firstly, the higher rpm Ezee motor had better effeciency and overheat time at this speed than the lower rpm model. I was also really surprised to see the Crystalite TC40100 which was at the lower end in terms of efficiency had the longest time to overheat at this speed. Would anybody care to share their thoughts on why this might be?

The motor I think I'm going with though is the MAC 536HF. It's a 48v, 500w, 32 magnet, 16 pair pole motor with a 1:5 reduction ratio. Importantly, they do a 20T version which has a top speed of 130rpm. Laced with 20'' wheel, the top speed is around 13kph. Although at 40Nm torque is lower than the other options, this still seems (to my very limited experience which extends little beyond this thread) to be the best candidate for my needs.

In addition to this, they also supply this part which allows the motor to be driven in reverse and saves welding the free-wheel:
Image
Check out my mountain wheelchair project.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Buk___ » Jan 09, 2018 10:15 pm

Glyn wrote:
Jan 09, 2018 4:53 am
...
Have you considered something like these.

Not hugely powerful, but geared for the job. With 6 of them it ought to climb mountains ok. Worth a look at least.

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Glyn
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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Glyn » Jan 10, 2018 3:51 am

Ye, wheels need to have a larger diameter though and would lose too much torque on those motors which are intended for smaller wheels.
Check out my mountain wheelchair project.

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by SlowCo » Jan 10, 2018 5:09 am

Very glad to read that your daughter is doing so well!

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Re: Which Controller (edit: hub motor) for my daughter's wheelchair?

Post by Glyn » Feb 12, 2018 7:17 am

Hi all,

I just wanted to say a huge thank you to everybody who has shared their time and advice.

My daughter's symptoms are now far more typical of ME. We've had some great days out climbing but it looks like she's still going to need this wheelchair so the project must go on.

6 Motors arrived last week; 48v 500w Mac 536hf. 32 magnet 16 pair poles. They have a 5:1 gear ratio and Mac have given them a 20T winding for me. Max RPM (At the wheel) is 130 which should give a top speed of 12kph on a 20" rim. They also pre-fitted a special shaft on the planetary gears which locked up the freewheel mechanism.

Of the six 1500w direct drive motors I purchased previously, three have been sold at the same price I purchased them for.

And to get back to the original post, I went with six Kelly KBS48101X controllers. There were many things which made me favour these controllers such as being able to drive the motors in reverse, regenerative breaking, and programmable voltage cutoff.

As I say, a big thank you to everybody who contributed to this thread. If you're interested, I've started a new thread for wiring the controllers: https://endless-sphere.com/forums/viewt ... =2&t=92802

"Over and out"
Check out my mountain wheelchair project.

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