Help me pick an outrunner for my next project

As some of you may have seen my other posts, I'm a big fan of friction drive. I currently have a 36 volt Kollmorgen setup that I am very happy with (I've done around 1000 miles with it so far) and want to start a winter project using an rc motor (or two). Here is the drive unit I came up with for the first project (actually, this is the second one I made for my girlfriend with a stock Kollmorgen):



My main goals are:

1. Stealth. There are no clear ebike laws where I live and don't want to draw too much attention to myself.
2. Weight. On this project I would love to keep the weight to a minimum which will probably mean no slas like the first project. I would really like it to feel like a normal bike. I'm an ex-oldschool bmxer and still like to be able to hop up on to curbs when needed.
3. 25 to 30 mph top speed. I probably wouldn't use that kind of speed much but it would be nice to have available. My current project will do 20 to 22 mph.
4. Good hill climbing ability. We have a lot of hills in this area. Almost any ride includes at least one.
5. 12 to 15 mile range. Shouldn't be too hard since I get this much from three 7ah batteries now (I pedal a lot).

According to my calculations I would need 8067 rpms (with a 1.25" roller) to get to 30 mph. Are there any rc motors that will get me in that range on 24 volts?

I'm very new to the whole rc thing but I really think friction drive would be one of the easier ways of using the high rpms they produce.

I'm trying to stay a bit cheap too but I'm afraid to take a chance on some of the really cheap motor/controller combos on ebay.

Any suggestions on the motor, controller, and batteries needed for my goals from the rc gurus out there would be greatly appreciated.

Here is one of the cheap ones I was looking at:

http://cgi.ebay.com/aeolian-790kv-O...39:1|66:2|65:12|240:1318&_trksid=p3911.c0.m14

It lists the motor as putting out 920 watts! Is that possible? The Kollmorgen I'm using is rated at 400 watts (some list it as 300).

It's 790kv so it would run at 9480 rpms at 12 volts, right? Can these little things really put out that kind of power at that low of voltage? Assuming that's true that would give me a theoretical top speed of around 35 mph with a 1.25" roller.

What am I missing?

EVTodd said:

Here is one of the cheap ones I was looking at:

http://cgi.ebay.com/aeolian-790kv-O...39:1|66:2|65:12|240:1318&_trksid=p3911.c0.m14

It lists the motor as putting out 920 watts! Is that possible? The Kollmorgen I'm using is rated at 400 watts (some list it as 300).

It's 790kv so it would run at 9480 rpms at 12 volts, right? Can these little things really put out that kind of power at that low of voltage? Assuming that's true that would give me a theoretical top speed of around 35 mph with a 1.25" roller.

What am I missing?

Click to expand...

Assuming no controller limitations, the power curve will be parabolic with "x-intercepts" at 0 RPM and the no load speed and a maximum exactly half-way between those two intercepts. So, make sure you compare your "power requirements" curve against this curve in estimating speed; your speed in real life will be nowhere near the no-load speed, which becomes "more true" with higher velocities.

your speed in real life will be nowhere near the no-load speed, which becomes "more true" with higher velocities.

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I do realize the no load speed will be much higher than actual top speed which is why I said "theoretical" top speed. That, of course, is true with any motor.

I guess I'm hoping someone with rc motor experience can tell me if a little cheap outrunner like the one I'm looking at on ebay can really put out 3 times more power (well, watts anyway) than the kollmorgen I'm currently using. I guess I just need to bite the bullet and start experimenting. I don't think enough people have really tried outrunners in different configurations.

Get an outrunner that is twice as powerful as you think you need. The cheap ones are over rated, and the power in does not equal power out. Efficiencies of cheap outrunners can be anywhere from 60s to low 80s, not that great.

johnrobholmes said:

Get an outrunner that is twice as powerful as you think you need. The cheap ones are over rated, and the power in does not equal power out. Efficiencies of cheap outrunners can be anywhere from 60s to low 80s, not that great.

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Wow, that kind of stinks. So if a cheap outrunner says it will put out 920 or so watts you could realistically expect it to put out around 460? That's still pretty good from a motor that size especially if it can do that with only 12 volts. Maybe I'll do a dual motor setup, one on each side (two controllers with one running in reverse) like the old EV Warrior only much much smaller.

I keep thinking if I use two motors you'll always have one that pulls harder and in turn doing all the work. Anyone have any experiences with that issue?

Hey, a Hi-Koll. They can put out quite a lot more then their rated power, you must use an external controller. You can feed it 1.5+kw no problems, overspeeding is what causes problems.

http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=183
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=1434

Mathurin said:

Hey, a Hi-Koll. They can put out quite a lot more then their rated power, you must use an external controller. You can feed it 1.5+kw no problems, overspeeding is what causes problems.

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I do indeed use an external ecrazyman controller at 36 volts on my hi koll. The photo is the drive for my girlfriend's bike which has the stock controller running at 24 volts. I really like the Kollmorgens a lot and I'm sure it can handle more power than I'm giving it.

I'm just trying to see how far I can take the friction drive thing with an rc motor now. The small size and weight is very appealing to me. That and I have a spare bike to play with. :lol:

Wow. No one here has any experience with lower priced outrunners and controllers?

OK, yes a friction drive can work fine with an RC motor. A friend of mine is using a AXI 5345 with a friction drive and it works great! He is actually seeing 48mph with a 2 inch roller on 48 volts! That motor pulls 4,000 watts at roughly 80% efficiency.

The issue is quality versus cost. Low cost tends to give you low performance. But, you don't need to spend a fortune either.

If you are going with an RC setup, I would recommend the Castle Creations HV110 controller with a Astro Flight servo tester as a throttle.

Matt

recumpence said:

OK, yes a friction drive can work fine with an RC motor. A friend of mine is using a AXI 5345 with a friction drive and it works great! He is actually seeing 48mph with a 2 inch roller on 48 volts! That motor pulls 4,000 watts at roughly 80% efficiency.

The issue is quality versus cost. Low cost tends to give you low performance. But, you don't need to spend a fortune either.

If you are going with an RC setup, I would recommend the Castle Creations HV110 controller with a Astro Flight servo tester as a throttle.

Matt

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Matt, thanks for the info. I have been meaning to get back with you to get your input.

Wow! I thought I was going to extremes with friction drive. Not even close! 48 mph is just plain nuts! :lol: Do you have any photos of your friend's bike? What kind of batteries is he using?

I just did some price checking on the AXI motors and they look like they are around $285 or so. I was hoping to find something around $100 for the motor and the same or less for the controller. Any good brands out there in that range? I don't quite need that kind of speed so something a little less powerful would be fine.

Ok... More looking on the web tonight and I found this one:

http://www.unitedhobbies.com/UNITED...HXT_63-74_200kv_Brushless_Outrunner_(Eq:5240)

And this controller:

http://www.hobbycity.com/hobbycity/...roduct=7341&Product_Name=SuperSimple_100A_ESC

Would this combo work?

At 36 volts that motor would turn 7200 rpms which would probably be enough for what I want. Heck, if I went back up to a 2 inch roller 24 volts might be enough for 30 mph.

The motor would work fine. I would not recommend the controller, they suck at staying in sync.

johnrobholmes said:

The motor would work fine. I would not recommend the controller, they suck at staying in sync.

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Good to know. How about this one? http://www.unitedhobbies.com/UNITED...ct_Name=TURNIGY_Plush_100amp_Speed_Controller

I have heard of one guy using that controller. It burned out after a while.

Basically, from what I have seen and experienced, you can skimp a bit on the motor, but not the controller (unfortunately).

Matt

My HexTronik PRO 120A ESC I've been using has been working well for me so far. Be sure to get the USB programmer and Support Doccuments/program it makes setup a breeze and lets you test the system while hooked to the computer while displaying the rpm. Sync seems pretty good so far, It keeps up through gear changes and when the motor is overloaded. The bad news is that it's only good to ~24v, has a wonky throttle map that goes from nothing to full really quick, and I don't know if it lives up to it's current spec. (only using 20A or less right now) Oh yea, startup is really rough.

Marty

All of those cheap controllers are horrible at keeping sync. Honestly I can only recommend a Castle sensorless for safety reasons. I just never felt that I could depend on any other brand because of false startups and failed accelerations. I went through all of the different Hobby Wing built controllers with no luck (HXT, tunigy, sentilion, OEM RC, etc) I have yet to use the sensorless module on the Infineon controllers however. Isn't an RC controller, but they are relatively inexpensive.

I suggest a Castle HV 85 or 110.

EVTodd said:

...
Maybe I'll do a dual motor setup, one on each side (two controllers with one running in reverse) like the old EV Warrior only much much smaller.

Click to expand...

Great minds think alike! :wink:
http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=6877&p=104322&hilit=cybien#p104322

I also tried a turnigy sentilon 100A hV speed controller. It is hobby city's best and didn't work out of the box. After I got it to work it didnt sink well even with a turnigy brand motor. I went with the Castle Creations 85A HV Speed control and it seems to work beautifully so far. If you're considering something from hobby city you may also want to pick up the turnigy aerodrive wattmeter, it works fine with my set up and can control your speed controller (Verified with Caslte Creation) while providing some good information, volts, watts, servo pulse.

EvTodd,

There is alot of used AXI's and Hackers on rcgroups.com for sale forum, theres also alot of 30-40 amp controllers too. I missed a few HV-85's and HV-110's that sold before I discovered them. If you use one of the lower voltage controllers, what battery setup are you planning on running?