Alright. First off this is a nice forum and I've gotten good information from it. Lots of the ideas here are pretty spacy and non-realistic, but there is also some good engineering going on. The most valuable information I've run across is when people actually have created real working bikes and have used them for real uses (such as driving to work and having 1000+ miles on their setup). Actually that sort of information is actually invaluable. But altogether this is a nice forum and I appreciate its existence.
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Ok, so I have some questions. First off, to put things into perspective here is my goal:
I want a lightweight maneuverable, bicycle. Something that I can pick up and toss into the back of my truck. But I also want to use it for driving to work and other tasks during times of decent weather to reduce the wear and tear to my truck and save money and that sort of thing. That and improve my health a bit by getting outside and getting exercise.
I am thinking about a all-steel frame bike... something along the lines of a 'BMX Cruiser'-style bicycle... something with a long top tube and 20 or 24inch wheels and designed for adults. Nothing fancy, primarily because good quality steel BMX bikes are actually pretty affordable.
I live in a hilly area. Long hills of average steepness.
As far as power goes my ultimate goals are:
* 20-25 mph cruising range on flat ground with mild pedal assist.
(as a bonus occasionally going 30-35 on flat ground with heavy pedal assist would be great for a better workout and fun.)
* The ability to travel up moderate long hills at 7-15 mph with moderate to heavy pedal assist.
* 20 mile range.
So not a power house. My main concern, as far as expense goes, is making the batteries last. So I would like more higher voltage instead of higher amps, and having excess capacity so as not to drain the batteries each day. I am thinking for batteries the Ping (of ebay fame) Lifepo in 36 or 48 volt and 20 or 15 amp hours. The idea here is biggest bang for the buck.
Those batteries are not ideal, of course. I figure when those batteries wear out and I can justify a higher expense to myself I'd probably graduate up to the "Dewalt Nano"-style A123 batteries, which now seem to be available to hobbyists.
So my goal right now is to find a low-cost way to match those batteries up with a motor and achieve my power goals.
Oh, and keep it as simple as possible. I'd like the ability to inexpensively replace burnt out motors and broken bits without a great deal of fabrication or special parts.
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Oh, and the easy way out would be to purchase a hub motor from Ampedbikes or one of those new BMC 600watt geared hub motors. I like the BMC geared motors a lot, I think they are probably near ideal, however they are expensive. Also non-geared motors are nice, but they are very heavy. So I am thinking I should go with the complexity of a non-geared motor for the sake of saving weight and the ability to run the motor through multiple gears at the rear wheel.
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Right now I am aiming for a single-speed bike with a speed of about 16 mph until I get the basic design worked out and a working bike. If I like it then I will invest in a rear planetary hub system like the Alfine 8 speed hub and work out better gearing.
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So to match the batteries and power requirements I am aiming for a geared motor that is 36 or 48 volts, produces about 500-900 watts, and has rotating speed of less then 400 rpm at the chain sprocket.
(And to be honest I wouldn't mind replacing brushes. I just worry about efficiency)
So here are possibilities:
---- Cyclone-tw ---
They have these motors that include dual freewheels so that I avoid the expense of converting my crankset (pedal side) to a freewheel system (like a IPS captain system for tandem bikes, which should run about 150-200 bucks after everything is installed and running). They have various models they offer online that seem pretty nice. 24v at 600watts and 36v at 900watts. About 400 bucks. Probably closer to 500 bucks with custom mounts made, it linked up to the rest of the bike, and that sort of thing, I figure. Brushless is a big plus.
--- RC-based motor ---
These are cheaper and seem to be good quality, which are both big pluses. My biggest concern with them is the general very-high 'KV'.
You see the efficiency and weight is very good. But I figure if I have to have multiple gear reductions then the drive train losses will just throw any sort of efficient operation out the window. So I would probably want only a two-stage gear reduction system... a motor --> pully (or gear) then chainring ---> bicycle chain. I definately do not want some little RC motor buzzing about 15K with a 4 stage gear reduction...
But the problem I am having with that seems that in order to get a RC motor to fit into that system I need to have a low KV... like 100-150. And the RC motors in that range are VERY powerful. Much more powerful then what I want and they would just obliterate my batteries. I already have a modified moped (oversized cylinder and racing exhaust) that goes about 45mph (60-100mpg, woot) and a 250cc Kawasaki Ninja that goes 85+ mph... I don't want to drop 2-3 grand on batteries to make my bicycle do the same thing.
So if I get a big HXT* or other motor with ~130Kv does it make sense to try to limit the current to it to 25-30 amps @ 36v? I don't really understand the nature of electrical motors that much, but I suspect that limiting the amps in that way will destroy the efficiency of the motor. Does there even exist a practical (read: off-the-shelf with some surgery) way to limit the current efficiently in that manner?
*http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142&Product_Name=HXT_80-100-B_130Kv_Brushless_Outrunner_(eq:_70-55)
They way I figure it if you need 4 stages to take a motor speed down your going to lose efficiency... Assuming a 3% loss for each belt/chain your going to have to run through and assuming a 85% efficient motor your going to see:
1 (power input) * .85 * .97 * .97 * .97 = 75% efficiency.
So the expense and the complexity of a system like that does not seem worth it to me.
--- NPC Gear Motors ----
http://www.robotmarketplace.com/products/NPC-T64.html
Probably outclassed by the Cyclone-tw.. these are brushed geared motors. I like them because the geared system is designed specifically to withstand abuse and the motors are designed for powering wheelchairs, among other things. So they are tough and the motors are cheap to replace (~60-70 dollars). I like the idea of tough design and not having to wait for stuff to ship from asia.
on a side note:
Oh if you want some serious power check out the MagMotors. They are lightweight brushed designs capable of extraordinary power output due to their magnets. Something like 4-5 HP (4000+ watts) in a 6 pound package at 24 volts. I went to Magmotor's website and they do have _brushless_ motors using similar magnets, but I can't find any information in pricing.
--- My1018 "Currie" motor at 36v ----
http://tncscooters.com/product.php?sku=106130
Nice and cheap. Relatively lightweight. But the power is a bit low and I have big questions on the reliability of the thing.
--- Dewalt 36v hammerdrill ---
http://www.amazon.com/gp/offer-listing/B0016A3MB2?tag=dewpowtooonl-20&camp=14573&creative=327641&linkCode=am1&creativeASIN=B0016A3MB2&adid=0W3HVNZGKNN5PKTRA8X6&
So you can find battery-less drills for around 50 bucks. Factory new ones for 80-100.
So they are extremely cheap and Dewalt has a very good reputation for reliability and strength. Not only that they have a all-steel planetary gear reduction system that reduces the RPM down to 0-400. Not only that they have a handy-dandy self-tightening chuck that can be used to hook up all sorts of adapters and whatnot. Such as:
http://www.dpxsystems.com/ProductDetail.aspx?ID=195
check out their video at: http://www.youtube.com/watch?v=y8abvlYHK3Q
(Although I don't plan on using DPX's system I like it a lot.)
So the older 24v model used by combat robots the world over. Very common, very popular. So you know it's very tough. They even have versions like the 'dustin' motor modified for high performance:
http://www.robotcombat.com/products/DCWD-D01.html
Although I don't plan on doing that, per say.
The thing about them is I am not sure about the specs. Dewalt clams a maximum power output of 750watts.. but that's probably near stall speeds, right? So what would they normally run at speed under load... something like 500 watts? I don't know. Like I said the 24v model is popular and I can find discussions were people are claiming 75% efficiency and 450 watts for those motors. The 36v motor shouldn't be any worse, I figure. Running higher volts it should be a bit more efficient if anything. Plus Dewalt relies heavily on reputation so having better battery life then their cheaper competitors is a critical thing (hopefully).
Oh, and the BIGGEST advantage, which in my eyes is huge, is that if I was to burn the motor out or ruin it's gearbox I can walk into virtually any hardware store in America and get a drop in replacement. This is a huge advantage. I'd be willing to spend a extra 200 dollars on batteries to counter any loss in efficiency over other motors to get the ability to do that.
------------------------------------------------
So any comments? How realistic do you think that I am being here?
Any motors I am overlooking that I should pay attention to? Any nice, large RC motors with under ~1Kw power output at 24-48v ?
--Thanks.
-------------------------
Ok, so I have some questions. First off, to put things into perspective here is my goal:
I want a lightweight maneuverable, bicycle. Something that I can pick up and toss into the back of my truck. But I also want to use it for driving to work and other tasks during times of decent weather to reduce the wear and tear to my truck and save money and that sort of thing. That and improve my health a bit by getting outside and getting exercise.
I am thinking about a all-steel frame bike... something along the lines of a 'BMX Cruiser'-style bicycle... something with a long top tube and 20 or 24inch wheels and designed for adults. Nothing fancy, primarily because good quality steel BMX bikes are actually pretty affordable.
I live in a hilly area. Long hills of average steepness.
As far as power goes my ultimate goals are:
* 20-25 mph cruising range on flat ground with mild pedal assist.
(as a bonus occasionally going 30-35 on flat ground with heavy pedal assist would be great for a better workout and fun.)
* The ability to travel up moderate long hills at 7-15 mph with moderate to heavy pedal assist.
* 20 mile range.
So not a power house. My main concern, as far as expense goes, is making the batteries last. So I would like more higher voltage instead of higher amps, and having excess capacity so as not to drain the batteries each day. I am thinking for batteries the Ping (of ebay fame) Lifepo in 36 or 48 volt and 20 or 15 amp hours. The idea here is biggest bang for the buck.
Those batteries are not ideal, of course. I figure when those batteries wear out and I can justify a higher expense to myself I'd probably graduate up to the "Dewalt Nano"-style A123 batteries, which now seem to be available to hobbyists.
So my goal right now is to find a low-cost way to match those batteries up with a motor and achieve my power goals.
Oh, and keep it as simple as possible. I'd like the ability to inexpensively replace burnt out motors and broken bits without a great deal of fabrication or special parts.
-------------------------------------------------
Oh, and the easy way out would be to purchase a hub motor from Ampedbikes or one of those new BMC 600watt geared hub motors. I like the BMC geared motors a lot, I think they are probably near ideal, however they are expensive. Also non-geared motors are nice, but they are very heavy. So I am thinking I should go with the complexity of a non-geared motor for the sake of saving weight and the ability to run the motor through multiple gears at the rear wheel.
-------------------------------------------------------------
Right now I am aiming for a single-speed bike with a speed of about 16 mph until I get the basic design worked out and a working bike. If I like it then I will invest in a rear planetary hub system like the Alfine 8 speed hub and work out better gearing.
--------------------------------------------------------------
So to match the batteries and power requirements I am aiming for a geared motor that is 36 or 48 volts, produces about 500-900 watts, and has rotating speed of less then 400 rpm at the chain sprocket.
(And to be honest I wouldn't mind replacing brushes. I just worry about efficiency)
So here are possibilities:
---- Cyclone-tw ---
They have these motors that include dual freewheels so that I avoid the expense of converting my crankset (pedal side) to a freewheel system (like a IPS captain system for tandem bikes, which should run about 150-200 bucks after everything is installed and running). They have various models they offer online that seem pretty nice. 24v at 600watts and 36v at 900watts. About 400 bucks. Probably closer to 500 bucks with custom mounts made, it linked up to the rest of the bike, and that sort of thing, I figure. Brushless is a big plus.
--- RC-based motor ---
These are cheaper and seem to be good quality, which are both big pluses. My biggest concern with them is the general very-high 'KV'.
You see the efficiency and weight is very good. But I figure if I have to have multiple gear reductions then the drive train losses will just throw any sort of efficient operation out the window. So I would probably want only a two-stage gear reduction system... a motor --> pully (or gear) then chainring ---> bicycle chain. I definately do not want some little RC motor buzzing about 15K with a 4 stage gear reduction...
But the problem I am having with that seems that in order to get a RC motor to fit into that system I need to have a low KV... like 100-150. And the RC motors in that range are VERY powerful. Much more powerful then what I want and they would just obliterate my batteries. I already have a modified moped (oversized cylinder and racing exhaust) that goes about 45mph (60-100mpg, woot) and a 250cc Kawasaki Ninja that goes 85+ mph... I don't want to drop 2-3 grand on batteries to make my bicycle do the same thing.
So if I get a big HXT* or other motor with ~130Kv does it make sense to try to limit the current to it to 25-30 amps @ 36v? I don't really understand the nature of electrical motors that much, but I suspect that limiting the amps in that way will destroy the efficiency of the motor. Does there even exist a practical (read: off-the-shelf with some surgery) way to limit the current efficiently in that manner?
*http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=5142&Product_Name=HXT_80-100-B_130Kv_Brushless_Outrunner_(eq:_70-55)
They way I figure it if you need 4 stages to take a motor speed down your going to lose efficiency... Assuming a 3% loss for each belt/chain your going to have to run through and assuming a 85% efficient motor your going to see:
1 (power input) * .85 * .97 * .97 * .97 = 75% efficiency.
So the expense and the complexity of a system like that does not seem worth it to me.
--- NPC Gear Motors ----
http://www.robotmarketplace.com/products/NPC-T64.html
Probably outclassed by the Cyclone-tw.. these are brushed geared motors. I like them because the geared system is designed specifically to withstand abuse and the motors are designed for powering wheelchairs, among other things. So they are tough and the motors are cheap to replace (~60-70 dollars). I like the idea of tough design and not having to wait for stuff to ship from asia.
on a side note:
Oh if you want some serious power check out the MagMotors. They are lightweight brushed designs capable of extraordinary power output due to their magnets. Something like 4-5 HP (4000+ watts) in a 6 pound package at 24 volts. I went to Magmotor's website and they do have _brushless_ motors using similar magnets, but I can't find any information in pricing.
--- My1018 "Currie" motor at 36v ----
http://tncscooters.com/product.php?sku=106130
Nice and cheap. Relatively lightweight. But the power is a bit low and I have big questions on the reliability of the thing.
--- Dewalt 36v hammerdrill ---
http://www.amazon.com/gp/offer-listing/B0016A3MB2?tag=dewpowtooonl-20&camp=14573&creative=327641&linkCode=am1&creativeASIN=B0016A3MB2&adid=0W3HVNZGKNN5PKTRA8X6&
So you can find battery-less drills for around 50 bucks. Factory new ones for 80-100.
So they are extremely cheap and Dewalt has a very good reputation for reliability and strength. Not only that they have a all-steel planetary gear reduction system that reduces the RPM down to 0-400. Not only that they have a handy-dandy self-tightening chuck that can be used to hook up all sorts of adapters and whatnot. Such as:
http://www.dpxsystems.com/ProductDetail.aspx?ID=195
check out their video at: http://www.youtube.com/watch?v=y8abvlYHK3Q
(Although I don't plan on using DPX's system I like it a lot.)
So the older 24v model used by combat robots the world over. Very common, very popular. So you know it's very tough. They even have versions like the 'dustin' motor modified for high performance:
http://www.robotcombat.com/products/DCWD-D01.html
Although I don't plan on doing that, per say.
The thing about them is I am not sure about the specs. Dewalt clams a maximum power output of 750watts.. but that's probably near stall speeds, right? So what would they normally run at speed under load... something like 500 watts? I don't know. Like I said the 24v model is popular and I can find discussions were people are claiming 75% efficiency and 450 watts for those motors. The 36v motor shouldn't be any worse, I figure. Running higher volts it should be a bit more efficient if anything. Plus Dewalt relies heavily on reputation so having better battery life then their cheaper competitors is a critical thing (hopefully).
Oh, and the BIGGEST advantage, which in my eyes is huge, is that if I was to burn the motor out or ruin it's gearbox I can walk into virtually any hardware store in America and get a drop in replacement. This is a huge advantage. I'd be willing to spend a extra 200 dollars on batteries to counter any loss in efficiency over other motors to get the ability to do that.
------------------------------------------------
So any comments? How realistic do you think that I am being here?
Any motors I am overlooking that I should pay attention to? Any nice, large RC motors with under ~1Kw power output at 24-48v ?
--Thanks.
