Help with Razor Trike Conversion

Bralexander

100 µW
Joined
Nov 25, 2021
Messages
8
Alright, I am trying to build a somewhat lightweight, balance not needed, sort of pedal assisted, vehicle for my 11yr old, with mild cerebral palsy.

Here's my idea-
I already have a pair of motor/wheels from a Gotrax Hoverfly xl, along with the 36v battery pack. I think I can buy a Razor DXT Drift trike (I know they make an electric version, but it is critical that she can pedal, and the electric Razor trike has a front hub motor) and replace the rear wheels with the two hoverboard ones. Then get a 36v controller to run everything, and I already have extra throttles, brake motor cutoffs, displays, etc. This would allow me to build something that is stable, somewhat lightweight, appropriately sized, and she should be able to pedal the front wheel normally while using the throttle to assist with rear wheel power.
g3H0lvP.jpg

What I need help with-
1) Both motors are 350w, what 36v controller can I get to run both at a reasonable (15mph+/-) speed? My daughter weighs 90lbs.
2) How do I connect both motors to the controller. The phase wires can be tied together to keep both motors in sync, right? But then what do I do with the Hall sensor wires coming from the motors? It looks like there are 5wires from each motor and a normal ebike has 6?
3) Anyone know what the single white wire is coming out of the motors?
xAooZv7.jpg


I am pretty mechanically inclined, but have limited experience with electronics. I've built a couple ebike conversions, but don't have any electrical training or anything.

Thanks in advance,
Bruce

Also, if anyone has a better idea/vehicle, that is reasonably priced and would work better in this application, please let me know.
 
Bralexander said:
1) Both motors are 350w, what 36v controller can I get to run both at a reasonable (15mph+/-) speed? My daughter weighs 90lbs.
Depends on the motor winding. What speed did the original scooter they came from go, at what battery voltage, under the same terrain/riding conditions you need the trike to go this speed at?

If it did not go that fast and it was 36v, you'll need a higher voltage battery to reach that speed with those motors.

2) How do I connect both motors to the controller. The phase wires can be tied together to keep both motors in sync, right? But then what do I do with the Hall sensor wires coming from the motors?
For brushless multiphase motors to be correctly driven, they each need their own controller. If the motors were physically linked so they can't turn separately, one controller could read the signals from one motor and drive both, but especially in the trike situation you're building, that won't work because you can't effectively turn as the motors would be "locked together", driven identically (even if they could reliably be driven by a single controller's single set of phase outputs). If the motors turn at different rates, then the phase currents from the controller can't drive them correctly, and the feedback currents from a motor not in phase with the controller will interfere with both the controller and the other motor. It might just rough roughly, or it might cause the controller to try to correct it's output and cause other problems, or it might actualy damage the controller--it depends on exactly what happens between the three devices and the specific situation at that moment.

Anyway, it is fairly certain it wont' work the way you would want it to, except in a perfectly straight line. :(

(it is possible to run two motors in "tandem", in a line with each other, on one controller, if the wheels are the same size and the motors are identical, at least until one motor goes out of sync with the other from variations in wheel rotation, at which point operation is less predictable--runnign them at the two sides of a trike is not going to stay synced at all outside of a straight line and will be "unpredictable" results at any particular moment)

Two controllers means each motor/controller pair keeps itself in sync, and does whatever it needs to regardless of the physical situation (straight, turn, etc) or whether the motors are even the same kind / winding of motor, etc.

If you want to try with just one controller, it shouldn't hurt the motors, but it might the controller under the wrong conditions (won't know what those are until it happens).


You can use the same throttle or other control input source to feed both controllers, by using just the 5v/ground from one controller, and the signal from the throttle to both controllers.


If they were brushed motors, you could just parallel (or series) them, and they'd just work, with each motor's internal commutator doing the work of syncing current flow to motor rotation. But a brushless motor uses the controller to do the commutating, so it needs one for each separately-operating motor.

It looks like there are 5wires from each motor and a normal ebike has 6?
3) Anyone know what the single white wire is coming out of the motors?
Hall sensor wires for motor phase position sensing in a typical ebike/scooter/etc controller are just five: Power, 3 (UVW) hall signals, ground.

A sixth wire is usually a speedometer sensor (if it reads pulses output between that wire and ground that vary with motor rotation speed) or a thermal sensor wire (if it varies resistance between that wire and ground with temperature).
 
Thanks for clearing up some things for me!

Ok, so if I only ran one motor on the rear, like many "regular" adult tricycles, that should work fine and be much simpler, right? I knew there would be some "scrubbing" around corners if both motors were powered to the same speed, but didn't think it would be that big of a deal at such a low speed and low weight.

The hoverboard these motors came from only went like 7.5mph or something, but I am not sure if that was them running maxed out, or if there was a speed limiter built into the hoverboard. I have no idea what the KV of these motors is, and don't know how to find out.
 
Bralexander said:
Ok, so if I only ran one motor on the rear, like many "regular" adult tricycles, that should work fine and be much simpler, right?
You can, and the rider should be able to get used to the assymetrical push of a motor only on one side; I've ridden two different delta trikes powered with a motor on only one side, and they ride fine that way once used to it.

I prefer motors on both sides...but it isn't strictly necessary.


I knew there would be some "scrubbing" around corners if both motors were powered to the same speed, but didn't think it would be that big of a deal at such a low speed and low weight.
Scrubbing would be fine, which may happen with a dual-motor-dual-controller setup (depending on weight on the tire, and the tire's actual traction on that surface) but that's not necessarily what will happen with a dual-motor-single-controller setup, because the motors could become unsynced if they don't scrub but both have full traction. That's when one could become unsynced from the controller and problems could occur.

Actual results for your setup would have to be tested experimentally to see if it's a problem or not.



The hoverboard these motors came from only went like 7.5mph or something, but I am not sure if that was them running maxed out, or if there was a speed limiter built into the hoverboard. I have no idea what the KV of these motors is, and don't know how to find out.
If the board was 36v, it is unlikely the motors would be wound for anywhere near twice the speed they were used at for the voltage supplied. Might be a little more, but probably not much (less than 10mph, I would guess).

It is possible that there is a speed limiter as well, but it's probably not much lower than the max speed the motors could spin, no load, at lowest possible battery voltage before BMS shuts it off.

If you can connect the motors back to the original controller setup, you may be able to test it offground (manually triggering the go-forward type of input) to see if the max wheelspeed shows up as higher than the max it does when riding it, at a full charge. If it does, then it's not speed-limited by the controller, just by battery voltage vs motor winding. In that case, the speed they go off-ground can be computed down to RPM (various calculators on the web for wheelspeed vs RPM), then that divided by the system voltage gives you the kV (RPM/Volt).

You can then use that to figure out how many volts you have to have to get a certain RPM, and thus a certain speed. If you leave out the conversion to RPM, then you end up with MPH/Volt, and get a more direct result.


Otherwise, you can test the motor speed when you get a new controller. There are phone apps to measure RPM of a spinning object so you can guesstimate speed (which under load will probably be 80%-ish of the unloaded speed, depending on the load).

Note that If you get one that's only capable of 36v, then you'll need a new one to use a higher voltage if that's what's required to get 15MPH. (most likely would need 72v for that if the original system was 36v and really had a max real speed of 7.5MPH limited by voltage vs winding).



BTW, if you can figure out the control sensor's output voltage range vs the controller's response to it, you can probably use the original board's controller to run both motors (because it's designed for two separate motors already, and really has two controllers in it linked by a brain / logic).

You'd just need to make a throttle "adapter" that will convert the throttle's output range (usually around 0.8-1v at "off" to around 3-4v at "full") to whatever the voltage range the controller needs to go from stop to full forward motion.

If the board's controller has two separate control-voltage inputs, you'd just parallel them to run to the new throttle.
 
Just for my 2 cents, I've done a ton of playing around with those hoverboard motors. They're fun. They can usually be ran at up to 48v without worrying about the motor surviving. Depending on manufacturer, they could be would a couple of different ways, with either aluminum or copper, and if it's copper, you can bet it'll take a decent amount higher volts and amps than what it's rated for. They're also almost always wound in Y configuration; you can rewind it to Delta if you want different performance. Have you opened the motors yet to see what you have?
 
harrisonpatm said:
Just for my 2 cents, I've done a ton of playing around with those hoverboard motors. They're fun. They can usually be ran at up to 48v without worrying about the motor surviving. Depending on manufacturer, they could be would a couple of different ways, with either aluminum or copper, and if it's copper, you can bet it'll take a decent amount higher volts and amps than what it's rated for. They're also almost always wound in Y configuration; you can rewind it to Delta if you want different performance. Have you opened the motors yet to see what you have?

No, that's one of my next steps, is to open one up!
 
harrisonpatm said:
They can usually be ran at up to 48v without worrying about the motor surviving.
The motor itself can almost certainly handle a couple hundred volts or more--it would just be spinning so fast at full throttle it'd be ridiculous unless it were being used as a gear-driver for a non-in-wheel-motor application. :lol:

The current it can take...that is probably a lot more limited, but probably at least twice it's "rating" for a few seconds at a time, at least--would be a good idea to use thermal monitoring to prevent overheating beyond that.

Depending on manufacturer, they could be would a couple of different ways, with either aluminum or copper, and if it's copper, you can bet it'll take a decent amount higher volts and amps than what it's rated for.

Interesting. I've never seen a hubmotor wound with aluminum wire; I suppose someone could do it but there's no reason to--it's not really cheaper than copper and it doesn't do the same job nearly as well, and it is harder to work with, easier to break, etc. Would cost them more in labor to deal with than just do the regular way.

I'd be curious to see pics of a "typical" bike/scooter/board/etc motor wound with something else than copper, though, if you happen to have one open.

They're also almost always wound in Y configuration; you can rewind it to Delta if you want different performance.
Doesnt' really have to be "rewound" for that, if it's wired up like most, just reterminated/rewired. Wye (Y, star) terminated motors have one end of all the phases tied together (in the center of the Y) and the three other ends loose (the ends of the Y). Delta you just undo that central termination, and then (after determining which of those three goes to which of the open phase ends by continuity) tie pairs of ends together to make the "triangle" of phases (that make a delta symbol). It may require experimentation to find which direction to connect them to each other, so that everything is in the right phase with each other (I've never done that part).

Phase resistance and inductance are lower in Delta, thoughand some controllers aren't as happy about that as others, in various ways, as it increases the phase currents it has to supply (about half the amount of winding length is now applied across each phase to phase connection than in Wye) and changes "how they're applied" (to keep from getting long and drawn out technical). There can be other issues, too, depending on system. Also, IIRC continuous torque (all other things the same) is lower at the same speed on Delta; it's less efficient than the same motor in Wye because of recirculating currents that don't happen in Wye.

But it does make the motor faster, by about 1.4x, IIRC. (don't recall the exact number) EDIT: this posts says 1.73x
https://endless-sphere.com/forums/viewtopic.php?t=82545#p1211547

Here's a good post about pluses and minuses when switching between the two on the fly:
https://endless-sphere.com/forums/viewtopic.php?t=25136#p362955
and another with test data, etc
https://endless-sphere.com/forums/viewtopic.php?f=2&t=9215
 
amberwolf said:
Depending on manufacturer, they could be would a couple of different ways, with either aluminum or copper, and if it's copper, you can bet it'll take a decent amount higher volts and amps than what it's rated for.

Interesting. I've never seen a hubmotor wound with aluminum wire; I suppose someone could do it but there's no reason to--it's not really cheaper than copper and it doesn't do the same job nearly as well, and it is harder to work with, easier to break, etc. Would cost them more in labor to deal with than just do the regular way.

I'd be curious to see pics of a "typical" bike/scooter/board/etc motor wound with something else than copper, though, if you happen to have one open.
They're also almost always wound in Y configuration; you can rewind it to Delta if you want different performance.
Doesnt' really have to be "rewound" for that, if it's wired up like most, just reterminated/rewired. Wye (Y, star) terminated motors have one end of all the phases tied together (in the center of the Y) and the three other ends loose (the ends of the Y). Delta you just undo that central termination, and then (after determining which of those three goes to which of the open phase ends by continuity) tie pairs of ends together to make the "triangle" of phases (that make a delta symbol). It may require experimentation to find which direction to connect them to each other, so that everything is in the right phase with each other (I've never done that part).
e.com/forums/viewtopic.php?t=82545#p1211547
This is what I meant by rewind, yes, I guess I just meant reterminate. Though if you're feeling adventurous, actual rewinding, with thinner or thicker gauge wire depending on what you want it to do, is also rather easy with these motors. Though very time consuming. For example, you can redo it with thinner wire, for more turns, higher kV rating, giving you higher speeds at a given voltage, at the cost of less amps you would be able to handle. I'm sure that's not necessary in this project, though, factory gauge at either star or delta would be fine.

As for a pic of aluminum windings, I can't help currently, because what I actually did with most of them is go through them for scrap, for the magnets and the copper, then to rewind for wind generation experiments, then sold the material when I was done, to the scrapyard to fund projects. I probably went through 2-3 dozen of these hoverboard motors, all different brands, and I'd say about 1/4 to 1/3 of them were aluminum windings. The enamel coating would be copper colored to "trick" you. These were all cheap mass produced hoverboards, a dumb fad toy to begin with, and the knockoffs were cutting pennies by using aluminum. My guess anyway.
 
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