Motor controller for smooth starting of outrunner?

[joec]

Hi all, I've been reading this board for a few months, and this is my first post. It looks like a great community, and I hope this post isn't too far off topic.

I have been following some of the non-hub motor e-bikes, specifically the 1kg friction drive and some of the others that use small lightweight outrunner motors. My goal is to build a pair of these friction drives and mount them onto an ultralight manual wheelchair. I will then use an RC two channel mixer to get differential steering and a pair of speed controllers to drive the motors. I am looking at hobby RC speed controllers, but it seems that my needs are somewhat different from most of the RC and E-bike people.

I plan on gearing the vehicle to run about 6 to 7 mph at full battery voltage, and need to be able to smoothly start from a dead stop, either in forward or reverse, and to be able to apply enough current to generate some really serious torque for up to thirty seconds at a time, allowing me to drive the thing up a steep hill or over an obstacle, without starting a fire or going immediately into thermal rollback.

I haven't settled on a battery pack yet, but I have a Hyperion 1420i to charge whatever lithium is most appropriate for the motor and controller. I have my eye on the following motor: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=7870 . I have access to a CNC machine and oscilloscope, so I'm not too intimidated by adding sensors if it will help.

So my question is- does anybody on the forum have any suggestion for a speed controller that has well behaved current limiting, the ability to start such a motor smoothly from a standstill, and the ability to give both forward and reverse speed control without having to hit a "reverse" button? (control is through a joystick, and it's not feasible to manually control forward and reverse for each motor independently as I drive around in a cluttered environment).

Thanks in advance if anybody can suggest a controller that might meet my needs. I'll be happy to post the results here if there's interest.

 

[Thud]

Welcome Joe,
Going by what is currently available I would recomend a 9 or 12 fet controller from the e-crazyman (e-bay) or member Lyen on this board. Definatly pm Lyen & have a chat about your requirments. He has proven himself here many times & has helped me on more than 1 occasion.
I am certain Lyen has the tech know how & equipment to get you a pr of controllers with revers capability....I have no idea on how may options there are for the mixing interface for your stearing requirments. But there are many bright fellows about who will chime in shortly.
you will need to add the Hall sensors to those motors, but that is an easy project to address & it sounds like you have more than enough know-how to succeed.

a pr of those motor geared to 7 mph should have no issue climbing a wall. I can't think of a single RC type controller that would come near your stated parameters.
Good Luck & keep us posted. T

 

[joec]

Thanks for the warm welcome- I did indeed email with Lyen a while ago, and it does sound like his controllers are very close to exactly what I want. The main problem is that they require a button to switch between forward and reverse. I can tell he's a busy guy, but he did say he'd get back to me if he finds a way around that one.

The best mixer I've found, as far as I can tell, is called a V-tail mixer: http://www.hobbyking.com/hobbycity/store/uh_viewItem.asp?idProduct=6321

It takes two RC pulse streams from the X and Y axes of a joystick (after the joystick voltage is sent through a servo tester to turn into an appropriate RC signal), and mixes them to two channels of proportional control for something resembling differential drive steering. I don't know for sure that this will work, but it's cheap and small and light, and other people have explained to me that they've seen it used for this kind of thing before, mostly for combat robots.

I'm a mechanical engineer with only limited electronic knowledge, so coming up with a circuit from scratch to reliably toggle the forward/reverse button on a controller while driving on the fly is a little intimidating to me. If an experienced electronics person came up with a circuit I could source the parts and solder it up. I would definitely prefer if there was something out there that could just take an RC signal or 0-5v signal and give proportional forward/reverse control. Doesn't hurt to ask, right?

 

[oldpiper]

Would putting a button on the top of the joystick work? That would probably be the easiest solution. Otherwise, you could set up a double-throw relay on microswitches, which would interface with the joystick just past the center point to complete one circuit and break the other, like a model railroad track switch circuit. Shouldn't be difficult to do if you can fit it in the space you have to work with.

Cameron

 

[gwhy!]

Hi Joe and welcome,
I think ( from the limited experience that I have gained using RC esc with using very low gearing ) that you maybe able to use a rc controller for this application as the gearing would be really low indeed. You could use car or boat esc which have a proportional reverse function Im pretty confident that startup sync will not be a problem because of the gearing. You can use something like a add on current limit circuit ( there are a couple of options for this ) if the controller don't have current limiting built in. I really think it would be worth giving this setup ago with some of the cheaper boat/car controllers as I think they will be fine. As Thud have already have said the motors when geared that low will climb anything, one thing that may be a problem is being able to pull away without flipping the chair over ( this will not be good ) you may have to incorporate a slow ramp up and down within the throttle to make it usable no matter what controller you opt for.

 

[joec]

Thanks for the suggestion, oldpiper but I'm afraid that the switch on top would take too much coordination. You'd really need two switches, one for each motor, since you often turn in place by having the two wheels rotate in opposite directions. It's quite intuitive once you drive it for a while, but having a joystick and two buttons would take an awful lot of coordination.

I think what you're suggesting with the relays and microswitches is what I'd have to do in order to toggle the forward/reverse switch, but I'd have to do it all solid-state for reliability. I would also need to figure out how to pick the triggering points for the left or right motor to switch into reverse mode. Obviously the joystick pulled straight back should have both motors in reverse, and the joystick deflected straight to one side should have one motor going forward and the other backward... but it's the other situations that I need to think about in order for control to make sense.

If it seems like I'm being picky, think about your car. Imagine for a minute that you drive cars all of your life, and then one day you need to drive a rental car where NONE of the controls work the way you think they should. Unless it's a change for the better that gives a tangible benefit after you get used to it, the sudden change to something less familiar (and potentially much less convenient) is definitely not preferred.

 

[joec]

Hi Joe and welcome,
I think ( from the limited experience that I have gained using RC esc with using very low gearing ) that you maybe able to use a rc controller for this application as the gearing would be really low indeed. You could use car or boat esc which have a proportional reverse function Im pretty confident that startup sync will not be a problem because of the gearing. You can use something like a add on current limit circuit ( there are a couple of options for this ) if the controller don't have current limiting built in. I really think it would be worth giving this setup ago with some of the cheaper boat/car controllers as I think they will be fine. As Thud have already have said the motors when geared that low will climb anything, one thing that may be a problem is being able to pull away without flipping the chair over ( this will not be good ) you may have to incorporate a slow ramp up and down within the throttle to make it usable no matter what controller you opt for.

Thanks, gwhy, do you know if these controllers can go into reverse without a "go into reverse now" signal? I read a few spec sheets (the ones I could find) and it wasn't very clear how that works.

If they need that signal, then I'm in the same predicament as with Lyen's controllers. What would be ideal is if they can take an RC signal that goes from (for example) 0-100 with "50" equal to no speed, "0" equal to full reverse, and "100" equal to full forward. If I could have this, then I'd be able to accomplish the rest with the RC mixer and the RC ESC settings (including the ramp rate).

I am looking at roller approximately 1" diameter pressing on a 24" wheel, probably with a small belt reduction to improve motor life and maybe give some more reduction. (looking at the math, wheel diameter is actually irrelevant for top speed on a friction drive, so maybe another size wheel for convenience)

 

[gwhy!]

Thanks, gwhy, do you know if these controllers can go into reverse without a "go into reverse now" signal? I read a few spec sheets (the ones I could find) and it wasn't very clear how that works.

If they need that signal, then I'm in the same predicament as with Lyen's controllers. What would be ideal is if they can take an RC signal that goes from (for example) 0-100 with "50" equal to no speed, "0" equal to full reverse, and "100" equal to full forward. If I could have this, then I'd be able to accomplish the rest with the RC mixer and the RC ESC settings (including the ramp rate).

The 120A boat controller I had a play with you trim the servo signal so center is off, so yes stick forward goes forward and stick backwards the motor runs backwards, this was the same with the car controllers is used to use many years ago. I cant say 100% that all car/boat controllers work this way though, maybe some one else could chip in with a little more knowledge on this type of controller.

 

[liveforphysics]

Reversing on the fly is critical with this setup.
Sensors are critical as well to ensure smooth 0rpm torque control.


You want a pair of this controller:

http://www.hobbypartz.com/ezbrescfor18.html


And a pair of 1/5th scale bldc sensored RC car motors.

All together that will be about $400-500. Should give about 5hp output, weigh very little, and geared for 10-15mph peak, it would climb trees.

 

[joec]

Excellent!

I will most likely turn down the current limit quite a bit, and just bump it up until it can get up typical hills and thresholds, then maybe a bit more to have some reserve.

You have no idea how pitifully pathetic most "lightweight travel" powerchairs are. They will barely climb up a legal ramp, and get stuck on ridiculously small thresholds unless you take a running start. They start at about $1500 also, and weigh about a hundred pounds. If I can add a mere 25 pounds to a 25 pound manual chair, it will be a real game changer. I'll definitely post updates and pictures as I go.

Thanks!

 

[liveforphysics]

Excellent!

I will most likely turn down the current limit quite a bit, and just bump it up until it can get up typical hills and thresholds, then maybe a bit more to have some reserve.

You have no idea how pitifully pathetic most "lightweight travel" powerchairs are. They will barely climb up a legal ramp, and get stuck on ridiculously small thresholds unless you take a running start. They start at about $1500 also, and weigh about a hundred pounds. If I can add a mere 25 pounds to a 25 pound manual chair, it will be a real game changer. I'll definitely post updates and pictures as I go.

Thanks!

A pair of 1/5th scale RC motors with an appropriate planetary reduction (likely a 4-stage box to get the reduction you need) will be a no-joke power source.

But, these ESC's don't have the option for current limiting or current control, and it's actually not what you want. They are setup to do speed-control only, and IMHO, this is the perfect control method to keep a power-chair tracking straight. Remember, with an RC ESC, it doesn't matter if it says 150amps or 1,000,000amps, it can only pull the current that the motor and battery voltage combo permit it to pull, and the number they put on the pack is just the number you should avoid exceeding making it pull or it fails. So, this 150amp ESC connected to the right motor may only ever draw 60amps (just picking a number here), and the same battery and motor would draw that same 60amps at that RPM point if the ESC had the number 15a, 150a, or 15,000a printed on it.

 

[joec]

Thanks, Liveforphysics. I have been playing with the e-bike simulator for quite a while now, and I think I'm starting to get a good handle on it. I feel like I have a decent understanding of brushed motors with current feedback PWM controllers (the norm for powerchairs), but the RC motors are new to me.

Another resource I've found for looking at gearing and current draw is here: http://members.toast.net/joerger/squid/newtorquecalc.htm

I typically build full sized powerchairs for sport use, typically with two 70 amp hour AGM batteries in series and a motor like this one- http://www.robotmarketplace.com/products/NPC-T74.html . The typical powerchair controller will only deliver about 80 amps to each motor, and with the PWM current limiting, there is only a very brief instant where the battery current is much over 80 amp. The current limiting really comes in handy for saving the batteries, wires, and motors during shoving matches against other chairs. The chairs are geared for at about 7mph, and have enough torque to spin the wheels unless you have a lot of weight and a very grippy surface.

I'm playing with the idea of using the RC motors for sport use, but pushing them that hard (compared to just driving down the sidewalk) will take a lot more effort to prevent smoke. See video here: http://www.youtube.com/watch?v=nHQ-POSC4eM

 

[deVries]

But, these ESC's don't have the option for current limiting or current control, and it's actually not what you want. They are setup to do speed-control only, and IMHO, this is the perfect control method to keep a power-chair tracking straight. Remember, with an RC ESC, it doesn't matter if it says 150amps or 1,000,000amps, it can only pull the current that the motor and battery voltage combo permit it to pull, and the number they put on the pack is just the number you should avoid exceeding making it pull or it fails. So, this 150amp ESC connected to the right motor may only ever draw 60amps (just picking a number here), and the same battery and motor would draw that same 60amps at that RPM point if the ESC had the number 15a, 150a, or 15,000a printed on it.

One point I read about avoiding ESC frying & burning the magic smoke is matching the right battery to the ESC too. From the HobbyKing Blog:
"Some of our customers may be unaware of the damage caused to an ESC by a poorly functioning LiPo. If your LiPo is worn out, of poor quality or damaged, do not connect it to an ESC/Motor combination that will push the battery to it's limit. ESC's require a power source that can constantly supply the power needed to open/close the mosFET's in the ESC. A poorly performing battery will cause the FET's to stay open causing the ESC to burn or overheat. Yes, a low voltage or low C battery can damage your ESC!"

 

[joec]

Ok, so I'm hearing that the model car controllers have real forward/reverse control like I need, and encoders for smooth torque control around 0 rpm. What I forgot to mention was the original reason why I wanted to use outrunners- low motor RPM for less acoustic noise. There's no doubt that a 30,000 RPM RC motor would get the job done, but I don't want to lose 15% of my power in the gearbox, and I don't want to sound like a blender.

I'll look a bit more at what happens with no active current limit for various gearings of outrunner motors.

 

[AussieJester]

You could simply run two throttle controls one per motor, situate them near your wheelchairs
brake levers, 'skid' steer the chair like you do a Bobcat
would negate alot of the complexity. Best of luck with it either way, if i am still alive when im
old and weak i might think about converting my own wheelchair to electric, hopefully though
that day won't come.

KiM

 

[joec]

I've just read that the Kelly KBS controllers are available with a center-point throttle, exactly what I wanted for the wheelchair project:

http://kellycontroller.com/stick-shift-throttle-firmware-p-625.html

Does anybody know any reason why the Kelly controller would be unhappy with a Turnigy SK 63-74 170KV or the big 80-100 130KV if I added hall sensors? I am considering rewiring from delta to star just the sake of gearing for a reduction other than friction drive. If that makes the Kelly controller happier, I'd do it for that reason as well.

The RC controllers look great, but the highest voltage I've seen for an cheap controller that looks usable is 21 volts. I'd prefer to be able to run as high as 28 volts for compatibility with existing wheelchair battery systems so that I can build and test this in sections to spread out the cost and risk. I'm also less convinced that the RC controllers will be as reliable and predictable as a controller that's normally used for human transport, the Kelly controller.

 

[AussieJester]

Does anybody know any reason why the Kelly controller would be unhappy with a Turnigy SK 63-74 170KV or the big 80-100 130KV if I added hall sensors?

Im far from qualified...hopefully will be corrected if wrong....but the Kelly controllers are not capable of
running the motor in question due to their high electrical rpms... Your best bet is contacting forum member 'Lyen'
and getting him to hook you up with a suitable Infineon controller... If you ask forum member 'Thud' nicely he may
have a hall sensor bracket that fits straight in the Turnigy too ... IMHO although i use a Castle Controler HV160 on my Turnigy motor, it wont due what you need in a wheelchair, the start up will not be good, really needs load taken off before applying power i.e a kick off to get rolling or a pedal assist..Out of interest, being a paraplegic myself, what chair are you
fitting this too? I have built a couple of wheelchair friendly trikes that might interest you? aussiejester69 on youtube to view vids

Best of luck..

KiM

 

[texaspyro]

It would be very easy to rig a small microprocessor to read the joystick position and output a 0-5V throttle signal and a direction signal that could drive standard ebike controllers. No need for a direction button, the micro takes the 0-5V joystick signal, if over 2.5V set the forward bit, else set the reverse bit. output abs((Vjoy-2.5V) * 2.0) to the controller throttle signal.

You would need to use either sensored outrunner motors, sensors added to an sensorless motor, or a possibly a vector controller like the one that Ricky is working on.

One area of concern might be the electrical and mechanical chaos and stress that can occur when slamming from forward to reverse.

 

[John in CR]

There are already brushless motored wheelchairs, so everything is already done for you by someone somewhere with the only question being the currents you need. Full control of both motors will be via a single joystick.

 

[joec]

Does anybody know any reason why the Kelly controller would be unhappy with a Turnigy SK 63-74 170KV or the big 80-100 130KV if I added hall sensors?

Im far from qualified...hopefully will be corrected if wrong....but the Kelly controllers are not capable of
running the motor in question due to their high electrical rpms... Your best bet is contacting forum member 'Lyen'
and getting him to hook you up with a suitable Infineon controller... If you ask forum member 'Thud' nicely he may
have a hall sensor bracket that fits straight in the Turnigy too ... IMHO although i use a Castle Controler HV160 on my Turnigy motor, it wont due what you need in a wheelchair, the start up will not be good, really needs load taken off before applying power i.e a kick off to get rolling or a pedal assist..Out of interest, being a paraplegic myself, what chair are you
fitting this too? I have built a couple of wheelchair friendly trikes that might interest you? aussiejester69 on youtube to view vids

Best of luck..

KiM

Thanks, I will look into electrical RPM capability of the Kellys, and I'll figure out what electrical RPM the outrunners will show at my proposed speeds. Regarding the chair I'm using- right now we have a Quickie folding LXI that I'd probably put this on. We live in a one bedroom apartment, so we have no place to store a trike unless it folds up to similar size. Speaking of wheelchair cycles, have you seen the stuff at http://riomobility.com/ ? I was one of the engineers on the Pivot, and had some minor involvement with some aspects of the Dragonfly. They were selling a version of the Dragonfly with a hub motor for a while, but I don't see it now. That was two companies ago for me.

I've already been in touch with Lyen, but the last we emailed he didn't have a solution for center-point throttle.

 

[joec]

I know of three existing brushless motor controllers for wheelchairs. The first is made by Invacare (Dynamic controls is the subsidiary that makes it), it handles a pair of big direct-drive brushless motors which weigh at least pounds each, and the full drive system costs close to $3k if you buy it as parts. In addition to whatever field sensors it uses, it also has an EEPROM and thermistor that need to be present and reporting normal values in order to work. Hacking this system seems like too much work and too little reward.

The second system I know is made by Penny and Giles, and existed in a Quickie P222 chair that's now discontinued. I have one specimen of this, but we stopped using it for its normal use because it developed a habit of shutting down unexpectedly and coming to a tire skidding stop for no reason. Not cool, and the manufacturer is absolutely not helpful in resolving it. They refuse to sell the programming interface to their motor controllers (just talking about parameter configuration, nothing deeper), and I had to get it through other means. I've played around with the idea of reviving this, but my electronics troubleshooting skills are somewhat limited. And with no feedback about what the intermittent error is, it makes it harder. Anyway, this system costs about $1k without motors.

The third system that I know of is made by Golden Motor. Trying to get technical information from them is like pulling hen's teeth. Their wheel motors weigh over 15 pounds each, and I have seen zero indication that they actually have the torque required for real-world use in an urban environment. Sure they're cheap, but if you get stuck at the first curb cut then what's the point? I have no confidence that Golden's stuff is up to the challenges of wheelchair use, and they haven't done anything to put me at ease.

Finally, I guess I should mention the Roboteq. They are introducing a dual brushless controller (already have a single channel if anyone's interested) that is capable of doing all of the channel mixing and wheelchair functions that I'd want, and it's capable of 50 volts and 75 amps per motor. Plenty of power, and I'd get great technical support, but it's $800 without the joystick.

Hopefully this gives some explanation of why I'm looking for a way to make a pair of Kelly or RC controllers work. This is a side project, only to be used occasionally, and if I can do it with $300 worth of control electronics instead of $800 or more, then I'm more likely to finish the project.

 

[AussieJester]

Regarding the chair I'm using- right now we have a Quickie folding LXI

I have a Quikie XTR myself, they make some killer chairs i have had this one 5 years and only broken the frame on it once
opposed to kiloing a handful of locally made chairs on nearly a daily basis...I wish you the best in your project
apologies i can't be of more help alas i'm not electrically inclined...just a dumb metal fabricator im afraid ...

KiM