most effiecient motor

I've been reading around and have come to the conclusion that it would be a waste to have access to a machine shop and not take advantage of it. So I've decided to take the plunge and make an attempt to fit an rc motor to my bike. I'm going to try to keep the reduction to a one stage, so I'm looking for the lowest kv motor I can find that would be able to keep me going at a steady 25-30 mph.. So basically I'm looking for a low kv, highly efficient motor to pair up with the hv110 thats coming in the mail. I've been looking at the Turnigy HXT 80-100-B because it's 130kv, but was wondering if such a powerful motor would run as efficiently as a smaller motor that is being pushed harder. What I'm looking for is the most effiecient way to cruise at 25-30 mph, acceleration is not quite as important as efficiency. oh, one more parameter: inexpensive is preferable!

Joel

Joel,

What part of the bike are you planning to drive?

well, I'm in the brainstorming stage right now (obviously, I haven't even chosen a motor), but I'm thinking I'm going to make a rear-wheel drive system similar to your "emoulton" project except chain-driven. The main thing that is stumping me is how to keep it simple (and inexpensive-I'm a student), but also not have to pedal along with it at full speed!

joel

So, you mean a real one-stage reduction as opposed to what is usually referred to here as one-stage (one-stage gearbox plus reduction to wheel/crank)?

I don't think those cheap Turnigy motors are very efficient but, if acceleration isn't so important to you, you can find a way to limit the current to keep the heat down.

yeah, I'm thinking with a 130kv motor, 36 volts, and 26" tires, a 1:10 ratio for the two gears would get me at about my target cruising speed. (~36mph theoretical, but <30mph in reality). It seems fairly straighforward, am I missing something?

joel

Yes, 9t to 90t would do it. You can get a 90t sprocket here: http://www.electricscooterparts.com/sprockets.html

Sprockets less than 11t start to get a bit inefficient and noisy, though.

It would certainly be a cheap and easy way to get started.

Since you listed inexpensive as one of your criteria perhaps this motor might work for you.

http://www.hobbycity.com/hobbycity/store/uh_viewItem.asp?idProduct=7870&Product_Name=TGY_AerodriveXp_SK_Series_63-74_170Kv_/_3250W

thanks for all the responses!

Okay, two more questions, if I did get a motor such as the Turnigy HXT 80-100-B would it be less efficient because it's not being driven very hard, or does the efficiency just have to do with the rpm's it's running at? (I'm wanting to hit the motor's peak efficiency at 25-30 mph) Also, would running a 9 tooth pinion be so inefficient that it would be a better idea to move to a two stage reduction system? Or would that cancel out the benefits?

Joel

ps miles your bike is sick

Peak efficiency would be at a certain percentage of the no-load speed (around 85%-90%) and also a specific amp draw. You've got the speed bit right.

Probably still more efficient than going to a 2 stage system but 11t to 110t would be better.

The problem with cheap motors is that you usually get what you pay for. They tend to use cheap magnets and cheap steel in the rotors, which causes eddy currents to develop around the impuities. These eddy currents cause power-robbing heat to generated. If you want small, and super efficient, you are going to have to spend a bit more.

The HXT might be fine, however, as it is pretty big, as RC motors go, so it will be taxed less in an ebike application. Personally, I like the German-designed Hackers. They are also manufactured now in China, but they use the best magnets and high-quality steel in the stators.

A couple of points to keep in mind when you are choosing your gearing. If you gear this for 30 mph, that means your throttle will be have to be wide-open. That can get tiring.

The second option you might consider is to make use of the bike's gearing, which means you can get away with a lot less power to get similar performance. To do this, you can drive a 2nd chainwheel on the crank. This option requires that you use a freewheel on the crank, as the pedals would move with the motor othrwise, but this isn't as daunting a task as it sounds. Several of us are looking to do exactly that. Check out the Freewheel crank resources thread.

-- Gary

I second Gary's opinion/advise

Gram for gram, test after test Hacker has proven to be one of the most efficient motors in the RC world.
There has been plenty of actual in the field 3rd party unbiased independant test data that has proven this.

MicroDan's are also at the top of the list but they may be too small for what you are looking for.