Using RC motors on E-bikes [Archive]

[cinejeff]

I have a question about controllers. Is there a hardy ev controller that would work with these brushless rc motors? It seems that the esc is the weakest link in the puzzle.

I too am considering the HXT 130kv as many others are, but not at max amps... I have a bit of rc experience and know first hand how much these little motors can generate, the RC ESC's with servo controllers seem to be a bit of a compromise in durability. I understand the weight concerns (rc stuff is truly featherweight) but I am concerned about amperage spikes frying controllers like others have experienced. I am sure something must exist, although at what cost is to be seen.

Nice project Matt, many others are following your lead, me included.

 

[recumpence]

I wouldn't be concerned about the durability of the RC controllers. First off, mine was a freebie from Castle Creations. It may have been a reject to begin with. Second, I was overamping the snot out of the thing. Just make sure the ratings are observed.

Matt

 

[johnrobholmes]

RC controllers are rated conservatively if you buy a nice one. I would worry more about the batteries as long as you select the right ESC.

 

[recumpence]

Good call. :wink:

Matt

 

[Drunkskunk]

The only problem with the RC controllers is they have no current limiting, so at stall, they can have HUGE power spikes. A big enough controller can handle that, but often, only an RC battery can take that much currant dump.

 

[johnrobholmes]

If the batteries were fragile enough to need current limiting, you could install a fast blow fuse as a precautionary fail safe. I prefer to choose batteries that will see full load at only 1/4 to 1/2 of their continuous discharge rating. Even in a stall (which really doesn't happen with a sensorless ESC as they just lose synch instead) my packs won't get worked too hard.

 

[recumpence]

My Power Jazz arrived today. I have a very busy work week this week. But, I will try to get it up and running ASAP. I will post pics soon. It is about twice ther size of my Castle Creations HV110.

I am having alot of fun with this. But, at this point, I have $1,800 in my pack, motor, and controller!

Matt

 

[cinejeff]

The Power Jazz 63V looks awesome, I cant wait to see how it performs.

Jeff

 

[johnrobholmes]

$1800 is still about what you would have sunk into a "full size" system, but yours is what- 5 pounds total?

 

[scottclarke]

Mine does nearly 3KW - motor weighs 700g - pound and a bit - the controller weighs 170g I think - less than half a pound.

Motor cost £80 and the new controller cost £170 - throttle was free of a motorbike - the servo tester was £5 and the linear pot a few pence. But of course it required fabrication of metal to make it fit togther! Oh - forgot chain and sprockets - another £100 but I have a wide selection now!

 

[recumpence]

My entire system weighs 13 pounds. That is motor, controller, lipo packs, and all mechanical components, chain, etc.

The pack is 80 ounces (5 pounds roughly). So, without the pack, my system weight is 8 pounds.

My motor is, admittedly, way more money than would be required. But, I have a solid 6KW of power available or about 10KW for 15 seconds (If I could get the drive line to handle that much). So, all things considered, my system is about peak for what can be expected from a 13 pound compact system with decent efficiency and high power. It is not perfect, though. I would love to go down to a single stage to teh rear chain (two stage from motor to wheel). Maybe this winter?

Is it wrong to still want more?

Matt

 

[johnrobholmes]

Is it wrong to still want more?

Matt

That is never wrong. I feel the same way. More voltage for me

 

[eP]

My motor is, admittedly, way more money than would be required. But, I have a solid 6KW of power available or about 10KW for 15 seconds (If I could get the drive line to handle that much). So, all things considered, my system is about peak for what can be expected from a 13 pound compact system with decent efficiency and high power.

Your system is not well balanced for now. Your battery pack is still too weak for 6kW output, and your voltage or Kv is too low to get decent efficiency at 6kW battery load level.
4-6 LiPo cells more is what your system need IMHO for decent efficiency at 6kW battery load (P_in) instead 12 cells only (presently).

Best regards

 

[recumpence]

I don't know why you think my pack is too weak for my application. This pack only drops 3 volts maximum at 100 amp discharge. How much better do you want? I do not mind doubling up my AH, though. Longer range would be nice. :wink:

I would love to go up to 15S (my controller maxes out at 63 volts). But, I have been told by many people through an RC forum I frequent that the motor will build up with too much heat if I go with that much voltage.

Remember, the system only draws huge wattage for a few seconds at a time. So, efficiency at those loads isn't as critical as it is at lower loading where the system normally runs.

Matt

 

[safe]

But, I have been told by many people through an RC forum I frequent that the motor will build up with too much heat if I go with that much voltage.

Whatever became of your Armature Current Limiting circuit efforts?

If you want to continue to push the limits of power you can knock out a lot of the torque and heat problems if you can get ACL to work. By placing a limit on the torque your driveline issues would be resolved and you might be able to go without a slipper clutch entirely. After trying out ACL on my old bike I did find that the linear ramping of the power makes for a very predictable system. Less stress on the drivetrain that's for sure and less heat, but you really start to need multiple speed gearing to exploit the idea fully. (and you need really low gears) It's kind of an "all or nothing" decision... either you continue down the standard controller scheme and wrestle with heating and torque problems (which are serious problems) OR you switch everything over to a finely tuned multiple speed gearing (integrated with the pedals) and ACL. Once you switch design paths the decisions that follow it are inevitable and inescapable.

Restated:

You are stuck in somewhat of a "design paradox" because the RC motor is sort of the "finesse" solution to creating power and yet the one speed is the "brute force" way of delivering it. To get to the "Holy Grail" of sophistication it makes more sense to go with the RC motor, multiple gears, motor-pedal integration and ACL. Philosophically all the "finesse" solutions could be combined on one bike. (no one has gotten anywhere near doing it yet)

 

[recumpence]

Our current limiter project has morphed into a full power management system. We hvae the micro controller running various simulations right now. It will probably take the rest of the season to get it running, though.

Matt

 

[dirty_d]

how will that system work by the way? does it monitor current and send the servo signal to the controller to change the throttle? if it does id be worried about the response time, the servo signal is a pulse every 20ms right, it seems like the current could change a lot during 20ms and you'd have a lot of oscillation and crap, i dunno i think im just paranoid.

 

[recumpence]

Yes, there will be a current sensor that will reduce throttle as the processor dictates. The software will have a dampening factor programmed in to (hopefully) dampen out spikes.

As it is now, we plan on setting up an LCD display to show various parameters. The current limit will be adjustable on the fly as will the rate of slope of throttle roll-off. We will also have a throttle expo we can program in. Many variables will be measured and accounted for by the processor.

I am at the mercy of the hardware and software engineers that are doing all the work.

I will come together eventually, though.

Matt

 

[eP]

I don't know why you think my pack is too weak for my application. This pack only drops 3 volts maximum at 100 amp discharge. How much better do you want? I

So lets look again what you sid before:

I have a solid 6KW of power available or about 10KW for 15 seconds

Your 42 volts pack is just to weak to deliver solid 6kW of power.

Try to calculate your motor efficiency at that power in level for your 12S pack.

I would love to go up to 15S (my controller maxes out at 63 volts). But, I have been told by many people through an RC forum I frequent that the motor will build up with too much heat if I go with that much voltage.

It depend on Rm and Io values. RC guys most of time go at WO, so more voltage means more available power and more heat for them.
But your case is quite different. As long as you dont need more than 6 kW power_in - more voltage means better efficiency and as a result less heat at heavy load for you and your motor.
Hovewer it means worse efficiency and more heat for light load at the same case. But if you need more than 30 mph average speed so motor load is heavy enough for higher battery voltage and higher gear ratio i'm sure.

Remember, the system only draws huge wattage for a few seconds at a time. So, efficiency at those loads isn't as critical as it is at lower loading where the system normally runs.

It strongly depend on terrain slope. Uphill you need pretty high power, downhill you need zero or you have to use brakes to keep the speed at safe level.

If you want high efficiency for light loads and heacvy loads too, so you need two gears or two motor system.

 

[Miles]

If you want high efficiency for light loads and heavy loads too, so you need two gears or two motor system.

Agreed.

That's why I started this thread:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=4930

 

[recumpence]

If you want high efficiency for light loads and heavy loads too, so you need two gears or two motor system.

Agreed.

That's why I started this thread:
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=4930

Agreed also.

I think a two motor system is best in this situation because a powerful motor spinning a high torque capable drive system has alot of drag and idel current. Running it at a lower gear will not eliminate that drag.

I have a very small efficient RC motor (400 watt) I plan on mounting using a third freewheel to run the bike at about 18mph or so (typical cruising speed for our streets). That should net (if I have it calculated right) about 12 to 13 WH per mile (maybe better). Then I can merely hit the throttle for my big motor and have alot of high powered fun up at 20WH per mile (or less if I am really on it).

Matt

 

[safe]

Our current limiter project has morphed into a full power management system. We hvae the micro controller running various simulations right now. It will probably take the rest of the season to get it running, though.

At least you are being realistic with your timelines. It's tricky to fiddle with the controller and get it to work right. You often come into contact with other peoples design decisions because no one seems to follow the spec exactly as you would expect them to. My cheap Chinese controller gave out a 5 volt power supply to the throttle and the throttle gave out a 4.4 volt peak voltage, but the controller sucked so much of it's own current back into itself that the actual voltage measured during full throttle with the system active was 3.3 volts. So you start off having to research the "quirks" of the controller if you want to get it right.

Since current is an average why not just do like I did and use a Hall Effect current sensor?

I know that it's brushless, but for an average of current it should be fine. The voltage is always DC even on a brushless right? Or is my lack of the differences of brushless compared to the simple brushed motor showing?

 

[safe]

I have a very small efficient RC motor (400 watt) I plan on mounting using a third freewheel to run the bike at about 18mph or so (typical cruising speed for our streets). That should net (if I have it calculated right) about 12 to 13 WH per mile (maybe better). Then I can merely hit the throttle for my big motor and have alot of high powered fun up at 20WH per mile (or less if I am really on it).

Ouch!

My brain hurts just hearing that you would consider such a "hack" of a solution.

Gears... it's like that movie long ago where the guy said something like: "Plastics, the future is plastics". The answer to your troubles is soooooo obvious I don't understand why you aren't getting it. If you took the 400 watt motor and had enough gears to cover everything and used ACL to limit heat you could scream the hell out of it and have all the power you ever wanted.

You already have the gears because you are riding a bike with gears. Bikes and gears have been together for a long time and they work great. I've pulled 1400 watts through a derailler for thousands of miles and no problems have developed.

Gears, gears, gears... you just have to see it...

I must add that your motor needs access to "granny gears" so that the motor revs itself out while only going 20 mph or less. You need really low gears and high rpms in the motor to get it to work right. But most standard bikes are geared with "granny gears" already and as long as you can get your RC motors output to the pedal crank down to about 100 rpms at peak you are set. 76 rpms is actually the standard for normal cyclists, only the pro's sustain 100 rpm for long, so I'd do all your calculations based on 76 rpms.

Once you've tried gears you will never go back... that's a guarantee! (100% guarantee from "safe")

Just throw in a front freewheel:

http://www.cyclone-usa.com/store.php?crn=203

 

[Miles]

I don't think it makes sense to gear Matt's motor down even more and put it through a relatively delicate pedal drive system, safe. Also, the Cyclone freewheeling system is a POS.

 

[TylerDurden]

If you took the 400 watt motor and had enough gears to cover everything and used ACL to limit heat you could scream the hell out of it and have all the power you ever wanted.

Unless you wanted more than 400W. :lol:

You could overvolt it, but then you'd have to cool it and gear it down... not great for efficiency.