Using RC motors on E-bikes [Archive]
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Jeremy Harris
100 MW
With wheels, Miles, although the yearning to convert my paramotor from 120cc 2 stroke power into an EV is strong............
I built a simple drum dyno a few years ago, using an old car brake drum. I just turned the outside of the drum smooth and made a half wrap friction belt attached to a lever arm and spring balance for the torque measurement. Cooling was by directing a trickle of water from a hose into the drum centre, which worked OK as long as you were careful not to get the belt wet. RPM was measured using a mechanical contact tacho, one of those ancient things with a rubber cone you press against the shaft centre. It worked well enough.
I may resurrect it for this project, if I can find all the bits.
Jeremy
I built a simple drum dyno a few years ago, using an old car brake drum. I just turned the outside of the drum smooth and made a half wrap friction belt attached to a lever arm and spring balance for the torque measurement. Cooling was by directing a trickle of water from a hose into the drum centre, which worked OK as long as you were careful not to get the belt wet. RPM was measured using a mechanical contact tacho, one of those ancient things with a rubber cone you press against the shaft centre. It worked well enough.
I may resurrect it for this project, if I can find all the bits.
Jeremy
Fumesucker
100 W
johnrobholmes said:
You can use a very simple mechanism to dyno motors. Use something like a propeller to absorb the torque, which as Jeremy pointed out you can measure with a spring scale. RPM is no problem to measure these days.
Your "propeller" doesn't have to actually develop thrust, I made a whole series of different sized air movers with flat paddle type blades when I was testing motors a long time ago. A good quality hardwood that is free of knots and blemishes is fine for up to probably 10 kW or so. If you are really paranoid you can use aluminum plate.
I did some calculations with the ebike power spreadsheet and what you say matches well with the results I got, I'm taking that as a good sign.
I forgot to mention that after digging through my junk box (well, it's more of a large room actually) I found some toothed belt pulleys sufficient for about a 5:1 reduction, I'll probably try those out soon but I'll have to know the center to center distance before I can order a belt. Which basically means I'll need to have the motor in my hands before I can start designing the reduction gear system.
vanilla ice
1 MW
Jeremy Harris said:I will probably be aiming to build something a bit bigger than 6kW.............
Thats what I had in mind also, mebbe six 5kW motors instead of a single 40hp motorcycle motor. That way you take advantage of more massly produced commodity items, like you said "distributed" sort of like a pc farm vs. a single super computer.
John in CR
100 TW
JohnRob,
Thanks for that info about bell deflection on outrunners. That was something I never considered. Now the $55 2kw 700kv inrunner I've been eyeballing is looking even more appealing, especially considering that forced cooling using water jackets becomes relatively easy with off the shelf. For me it's the low price for the power that draws me to an RC solution. If I'm going to spend $800-1000 for a motor and controller, then I'd just accept the 20lbs+ weight penalty and go with an efficient motor already proven to handle 5kw continuous and much higher peaks. I just want high performance at the most reasonable price, not the lightest or most efficient bike.
John
Thanks for that info about bell deflection on outrunners. That was something I never considered. Now the $55 2kw 700kv inrunner I've been eyeballing is looking even more appealing, especially considering that forced cooling using water jackets becomes relatively easy with off the shelf. For me it's the low price for the power that draws me to an RC solution. If I'm going to spend $800-1000 for a motor and controller, then I'd just accept the 20lbs+ weight penalty and go with an efficient motor already proven to handle 5kw continuous and much higher peaks. I just want high performance at the most reasonable price, not the lightest or most efficient bike.
John
Tiberius
10 kW
Jeremy Harris said:Suffice to say that if I can get a cheap, light and powerful multiple motor proof-of-concept going OK, then I will probably be aiming to build something a bit bigger than 6kW.............
The key to this is avoiding the use of more than 75V DC, 50V AC......
Interesting point, that one. I notice the RC equipment tends to keep to 36 V or so, while a lot of e-bikers go to 72 V or more. It would seem at first that high voltage is better as it lowers the currents and the copper losses can be kept lower. In line with that thinking, I've gone for 72 V on the new bike.
But right now I am designing a DC-DC converter, and it is noticeable how the choice of electronic components goes down and the price goes up above 50 V. I'm having to review this idea that higher volts and lower current is best. In purely pragmatic terms, 50 V, 100 A may be easier to work with than 100 V, 50 A. Certainly if it is split into multiple parallel systems then it will be.
Nick
Jeremy Harris
100 MW
The low voltage RC stuff is definitely much cheaper than the high voltage stuff, massively so in the case of controllers.
I'm hoping to be able to make a reliable, efficient and powerful multi-motor and controller set up for much less than the cost of an equivalent single motor and controller. Hopefully it will be lighter as well. Keeping the voltage low doesn't present any real problems with the battery arrangements, as it just means breaking packs up into lower voltage sub-packs to supply each motor, rather than connecting them as a single high voltage pack.
Jeremy
I'm hoping to be able to make a reliable, efficient and powerful multi-motor and controller set up for much less than the cost of an equivalent single motor and controller. Hopefully it will be lighter as well. Keeping the voltage low doesn't present any real problems with the battery arrangements, as it just means breaking packs up into lower voltage sub-packs to supply each motor, rather than connecting them as a single high voltage pack.
Jeremy
MitchJi
10 MW
Hi,
But the smaller motors generally have a higher RPM so you will need more gear reduction. The costs will probably outweigh the savings plus it will be harder to get set up. Consider the hoops that Scott and Matt had to go through to get their RPM's down far enough. Then consider what increasing the RPM is going to do.
The chances of a sufficient volume of ebikes using two ESC's to cause a price drop highly unlikely.
Probably more likely (eventually) is increased volume of RC motors on Ebikes will cause a reduction in the prices of big escs.
eP said:
But the smaller motors generally have a higher RPM so you will need more gear reduction. The costs will probably outweigh the savings plus it will be harder to get set up. Consider the hoops that Scott and Matt had to go through to get their RPM's down far enough. Then consider what increasing the RPM is going to do.
eP said:
The chances of a sufficient volume of ebikes using two ESC's to cause a price drop highly unlikely.
Probably more likely (eventually) is increased volume of RC motors on Ebikes will cause a reduction in the prices of big escs.
I decided to keep things between 36V and 50V. For ebikes, the appropriate gauges for connecting wires are easily manageable and it doesn't make any difference to the motor losses, of course. As long as you can find a motor spec. to match your needs, I don't see any advantage to higher voltages, apart from perhaps simplifying battery pack charging arrangements.
Fumesucker
100 W
After much more head scratching I think I may have a handle on the multiple vs single motor gearing difference.
If you go from a single motor to a dual of the same power you should double your power, so all you have to do is use the e-bike spreadsheet someone kindly sent me to calculate the speed at double the power.
On level ground the spreadsheet shows 500 watts to give about 26 mph and 1000 watts to give about 34 mph.
So the gearing difference between a single motor and a dual motor setup of the same power to optimize for level ground should be 26/34 or 0.765.
A Scorpion 4025-10 turns 5144 rpm putting out 500 watts at 12V and 50 amps at an efficiency of 85%. For a vehicle speed of 26 mph with 20 inch tire that requires a gear down of about 11.6:1.
With two identical motors your gear ratio for each motor should then be 11.6 * 0.765 or 8.87:1, if you are optimizing for level ground.
With three identical motors the top speed on level ground would be 43 mph so the gearing would be 26/43 or 0.604.
Which gives us a gear ratio with our Scorpion example of 11.6 * .604 or 7.01:1.
For hill climbing I think the ratios will move somewhat closer to .5 for the dual motor and something under .5 for the triple. I'll work that out in a while.
If you go from a single motor to a dual of the same power you should double your power, so all you have to do is use the e-bike spreadsheet someone kindly sent me to calculate the speed at double the power.
On level ground the spreadsheet shows 500 watts to give about 26 mph and 1000 watts to give about 34 mph.
So the gearing difference between a single motor and a dual motor setup of the same power to optimize for level ground should be 26/34 or 0.765.
A Scorpion 4025-10 turns 5144 rpm putting out 500 watts at 12V and 50 amps at an efficiency of 85%. For a vehicle speed of 26 mph with 20 inch tire that requires a gear down of about 11.6:1.
With two identical motors your gear ratio for each motor should then be 11.6 * 0.765 or 8.87:1, if you are optimizing for level ground.
With three identical motors the top speed on level ground would be 43 mph so the gearing would be 26/43 or 0.604.
Which gives us a gear ratio with our Scorpion example of 11.6 * .604 or 7.01:1.
For hill climbing I think the ratios will move somewhat closer to .5 for the dual motor and something under .5 for the triple. I'll work that out in a while.
recumpence
1 GW
It would be very nice if this proves to work well for our application. I have been avoiding double motors because of my experience with twin motors in my RC models.
If multiple motors proves to give close to double output in bikes, it opens up many more options.
My skill is in mechanical design, problem solving, and machining. So, making the drive system is no problem for me. I fall down when it comes to the electronic end.
I am looking forward to how it proves out.
Matt
If multiple motors proves to give close to double output in bikes, it opens up many more options.
My skill is in mechanical design, problem solving, and machining. So, making the drive system is no problem for me. I fall down when it comes to the electronic end.
I am looking forward to how it proves out.
Matt
Fumesucker
100 W
I checked and the ratios for a ten percent grade were so close to 5:1 and 3.3:1 that in the real world it would make no difference.
Fumesucker said:
Fumesucker, this one doesn't sound right.... Wind resistance goes up with the square of the speed - power to overcome it goes up with the cube.... What proportion of the 500 Watts is your wind resistance power requirement?
Jeremy Harris
100 MW
Interesting motor in that link, Miles. Be nice if motors like that were to become available retail, but somehow I doubt that they will.
I've been doing more motor and controller comparisons, to try and work out the "best bang for my buck" for a multi-motor proof of concept system, but without opting for anything too cheap and nasty. I can't afford to risk megabucks on something that's state of the art, either.
I've come down to a selection based on four criteria; continuous power, total price for a motor and controller, watts per kg and watts per £. The short-list of motors is:
Tower Pro 5330 10T - 80A max, 60A best eff, 215kV, 679g, about £25
HXT 73-64 - 75A max, 60A best eff, 200kV, 790g, about £35
HXT 80-85A - 125A max, 110A best eff, 250kV, 1230g, about £75
The choice for affordable controllers comes down to just one or two, although they seems to be supplied under several different names and prices. The one I've opted for is supplied by http://www.budgetrc.co.uk and seems to get reasonable reviews (it looks like it's also sold as the Turnigy Pentium and a few other names). It will handle 125A max, 100A continuous at up to about 28V and costs around £30. I opted not to use the very cheap "super simple" controller in the light of the comments here about it being a bit flaky.
The benchmark comparison figures for each of these motors and the above 100A controller, when run from a 24V supply, are:
Tower Pro 5330 10T - Continuous power = 1920W, total price = £55, watts/kg = 558, watts/£ = 26
HXT 73-64 - Continuous power = 1440W, total price = £65, watts/kg = 635, watts/£ = 22
HXT 80-85A - Continuous power = 2400W, total price = £100, watts/kg = 565, watts/£ = 24
Despite the higher power of the HXT 80-85A, the best motor in terms of price, power per £ and power per kg looks to be the Tower Pro 5330 10T, so it looks as if that will be the one.
All told, building the spreadsheet to compare lots of motor/controller combinations has been interesting, as it's highlighted the impact of the motor and controller specs when combined as a system.
Jeremy
I've been doing more motor and controller comparisons, to try and work out the "best bang for my buck" for a multi-motor proof of concept system, but without opting for anything too cheap and nasty. I can't afford to risk megabucks on something that's state of the art, either.
I've come down to a selection based on four criteria; continuous power, total price for a motor and controller, watts per kg and watts per £. The short-list of motors is:
Tower Pro 5330 10T - 80A max, 60A best eff, 215kV, 679g, about £25
HXT 73-64 - 75A max, 60A best eff, 200kV, 790g, about £35
HXT 80-85A - 125A max, 110A best eff, 250kV, 1230g, about £75
The choice for affordable controllers comes down to just one or two, although they seems to be supplied under several different names and prices. The one I've opted for is supplied by http://www.budgetrc.co.uk and seems to get reasonable reviews (it looks like it's also sold as the Turnigy Pentium and a few other names). It will handle 125A max, 100A continuous at up to about 28V and costs around £30. I opted not to use the very cheap "super simple" controller in the light of the comments here about it being a bit flaky.
The benchmark comparison figures for each of these motors and the above 100A controller, when run from a 24V supply, are:
Tower Pro 5330 10T - Continuous power = 1920W, total price = £55, watts/kg = 558, watts/£ = 26
HXT 73-64 - Continuous power = 1440W, total price = £65, watts/kg = 635, watts/£ = 22
HXT 80-85A - Continuous power = 2400W, total price = £100, watts/kg = 565, watts/£ = 24
Despite the higher power of the HXT 80-85A, the best motor in terms of price, power per £ and power per kg looks to be the Tower Pro 5330 10T, so it looks as if that will be the one.
All told, building the spreadsheet to compare lots of motor/controller combinations has been interesting, as it's highlighted the impact of the motor and controller specs when combined as a system.
Jeremy
Hi Jeremy,
Might be worth investigating the larger motors here: http://www.suppomodel.com/ Maybe you would get a good deal if you ordered a couple, as samples, direct from the factory.....
Available in UK, here: http://www.allelectricrc.co.uk/suppo-motors-108-c.asp
Might be worth investigating the larger motors here: http://www.suppomodel.com/ Maybe you would get a good deal if you ordered a couple, as samples, direct from the factory.....
Available in UK, here: http://www.allelectricrc.co.uk/suppo-motors-108-c.asp
Jeremy Harris
100 MW
Thanks for those links, Miles. I'd taken a look at the Suppo site before, but couldn't find any detailed info or prices, so hadn't really considered them as an option.
I think I may go for the TowerPro motors for my experiment, unless I can get a good deal on a big Suppo and suitable controller. There's a part of me that suggests going for the more expensive, more powerful, HXT though.............
Jeremy
I think I may go for the TowerPro motors for my experiment, unless I can get a good deal on a big Suppo and suitable controller. There's a part of me that suggests going for the more expensive, more powerful, HXT though.............
Jeremy
Jeremy Harris
100 MW
Miles,
Many thanks for that link, it's very reassuring to read that review on the motor, although the link is broken, I managed to dig out the test review from the HobbyCity forum. There are some other good reviews on that forum, too. Here is some of the text of the Tower Pro 5330 review that I've cut and pasted:
Apart from the odd effect when heavily loaded (which might need some looking at in a vehicle application) this motor looks to be good value.
Jeremy
edited to add:
Whilst digging around in the link Miles provided, I came across mention of the Double AXI 5330 motor. This is two AXI 5330 motors mounted on a common shaft and driven by two controllers. Googling around found a few useful snippets that show that this arrangement does give double the power of just a single motor, which is reassuring for my idea of coupling motors together.
Jeremy
Many thanks for that link, it's very reassuring to read that review on the motor, although the link is broken, I managed to dig out the test review from the HobbyCity forum. There are some other good reviews on that forum, too. Here is some of the text of the Tower Pro 5330 review that I've cut and pasted:
Apart from the odd effect when heavily loaded (which might need some looking at in a vehicle application) this motor looks to be good value.
Jeremy
edited to add:
Whilst digging around in the link Miles provided, I came across mention of the Double AXI 5330 motor. This is two AXI 5330 motors mounted on a common shaft and driven by two controllers. Googling around found a few useful snippets that show that this arrangement does give double the power of just a single motor, which is reassuring for my idea of coupling motors together.
Jeremy
Fumesucker
100 W
Miles said:
Good catch, you're right, I misread something apparently.
Note the "Performance by KPH" and "Resistance breakdown" sections.
26/39 is 0.666
Fumesucker said:
I thought it must have been something like that.
How are you getting on with the spreadsheet? Let me know if you have any suggestions for improving it. I've got several ideas, but not that much time to devote to it, at the moment...
Fumesucker
100 W
Miles said:
A "Watt hrs/mile" and "Watt hrs/km" readout would be nice.
Very informative piece of work, I've enjoyed playing with it.
On edit: A "Human Input" option would be nice too.
Good ideas. I had the "Human Input" option in mind, already. A "Headwind" option might be useful too, perhaps?
I didn't write this but I have tweaked it a bit, and have always intended expanding it. If anyone else wants to help, then....
I didn't write this but I have tweaked it a bit, and have always intended expanding it. If anyone else wants to help, then....
The lower the KV the easier is is to deal with, well at least gearing. A nice thing about this is you can use the shaft on the mounting plate side like Scott did already. http://www.endless-sphere.com/forums/viewtopic.php?f=6&t=5168&start=0
I would love to use this!
Model: HXT80-100-B
Wire Turns: 8
Resistance: 32ohm
Idle Current: 2A
ESC Required: 130A
Input Voltage : max. 48V
Kv : 130 rpm/V
Weight: 1570g
Shaft: 12mm
Voltage Range: 20-48v
Non Load Current: 2.0A
Maximum Power: 6500W
Equivalent: 60-80cc Gas Engine
I would love to use this!
Model: HXT80-100-B
Wire Turns: 8
Resistance: 32ohm
Idle Current: 2A
ESC Required: 130A
Input Voltage : max. 48V
Kv : 130 rpm/V
Weight: 1570g
Shaft: 12mm
Voltage Range: 20-48v
Non Load Current: 2.0A
Maximum Power: 6500W
Equivalent: 60-80cc Gas Engine
Fumesucker
100 W
Yes, a "Headwind" option could prove useful.
And I agree that the lower the KV, the easier the gearing becomes.
And I agree that the lower the KV, the easier the gearing becomes.
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