Using RC motors on E-bikes [Archive]

[Miles]

Yes, that's what Matt did with his AXI motor and it seems to be working fine. It's a pity we can't mount the motors to take advantage of the ambient airflow.

Vented motors on bikes does worry me, it's the reason I went for an inrunner. I just don't know how much of a problem accumulation of magnetic debris would be, in practice.

 

[docnjoj]

Another problem with vents is they make the motor frame less stiff, thus increasing the NOISE level!!!!!!! Aaargh!
otherDoc

 

[safe]

The Cooling Issue

I created a full thread on the issue of cooling called "How To Ice Up Your Motor". It was a long and drawn out discussion. Some things discovered:

Ice is very effective because you can do things like pre-cool the shell and that gives more time before the motor heats up. If you were to have externally applied icing all the time that would be effective too, but just pre-cooling alone is not bad. (a good place to start)

Air is a funny thing.... heat transfer off the surface of a still air steel plate is VERY low... like 25 times slower than water... but if you have air blowing past the plate with enough speed you can get better cooling. The argument about transfer of heat from core to shell needs to be seen in light of turbulent flow in between the two... the transfer is better than you think. This means that if you could really keep the shell COLD all the time that your heat transfer might be pretty good. The shell transfers it's heat to the outside edge many times faster than from the edge to the air. (that's why water cooling is so effective, the boundry condition for heat transfer is improved so much and the water can carry so much more heat away based on volume)

Also, I've actually tested the idea of pre-icing the motor and I've found that it's without doubt very effective. In situations where I would normally get my motor to the breaking point of overheating, with the pre-icing I end the ride with a luke warm motor. I was very pleased with it.

Anyway... that's my two cents worth... ice is impractical for most situations, but for those that can do it you do get very good results...

Fast moving air is better than still air.

Water is better than fast moving air.

Ice is better than water.

 

[TylerDurden]

The Heating Issue

I created a full thread on the issue of cooling called "How To Ice Up Your Motor". It was a long and drawn out discussion. Some things discovered:

Ice is very effective because you can do things like pre-cool the shell and that gives more time before the motor heats up. If you were to have externally applied icing all the time that would be effective too, but just pre-cooling alone is not bad. (a good place to start)

Air is a funny thing.... heat transfer off the surface of a still air steel plate is VERY low... like 25 times slower than water... but if you have air blowing past the plate with enough speed you can get better cooling. The argument about transfer of heat from core to shell needs to be seen in light of turbulent flow in between the two... the transfer is better than you think. This means that if you could really keep the shell COLD all the time that your heat transfer might be pretty good. The shell transfers it's heat to the outside edge many times faster than from the edge to the air. (that's why water cooling is so effective, the boundry condition for heat transfer is improved so much and the water can carry so much more heat away based on volume)

Also, I've actually tested the idea of pre-icing the motor and I've found that it's without doubt very effective. In situations where I would normally get my motor to the breaking point of overheating, with the pre-icing I end the ride with a luke warm motor. I was very pleased with it.

Anyway... that's my two cents worth... ice is impractical for most situations, but for those that can do it you do get very good results...

Fast moving air is better than still air.

Water is better than fast moving air.

Ice is better than water.

Ever seen an outrunner?

 

[eP]

The Cooling Issue

I created a full thread on the issue of cooling called "How To Ice Up Your Motor". It was a long and drawn out discussion. Some things discovered:

Ice is very effective because you can do things like pre-cool the shell and that gives more time before the motor heats up. If you were to have externally applied icing all the time that would be effective too, but just pre-cooling alone is not bad. (a good place to start)

[CUT]

Anyway... that's my two cents worth... ice is impractical for most situations, but for those that can do it you do get very good results...

Fast moving air is better than still air.

Water is better than fast moving air.

Ice is better than water.

Hi Safe

What about shorter copper path ?
New motor topology - less copper loss = less heat.
http://endless-sphere.com/forums/viewtopic.php?f=7&t=4778

Best regards

 

[John in CR]

OK, the temptation of 8hp in just a few pounds of weight is just too hard to resist. Can the electronic braking on these RC controllers be used to create regeneration, or are these motors too hard to turn that a freewheel is required in the event of a dead battery?

I'm also thinking that the big HXT motor with 130rpm/v turns slow enough to go with only a chain and large sprocket at the wheel using a #35 or 40 chain, or just accept the weight penalty and put my Comet torque converter in the middle for automatic gearing and great hill climbing ability.

For added durability, I'd add an extra set of bearings to support both ends of the motor shaft so the motor's bearings don't "see" the side load. Then add a blower turbine directly on the motor shaft for additional cooling.

Yikes. Now I need a lot more Lifepo4's.

John

 

[dirty_d]

what about using that #219 chain, racing go carts with motors that spin like 15,000rpm use that, they also make very big #219 sprockets so getting the right ratio would be easier than with #35.

 

[eP]

what about using that #219 chain, racing go carts with motors that spin like 15,000rpm use that, they also make very big #219 sprockets so getting the right ratio would be easier than with #35.

15000 rpm at what motor diameter ?

4000-6000 rpm is needed working rpm range IMHO

 

[John in CR]

...4000-6000 rpm is needed working rpm range IMHO

At 130rpm/v for the HXT 80-100-B, that's 6240rpm at 48volts and 4680rpm at 36v. Don't these decrease with a load? That's why I believe for some of these motors gearing them down may be unnecessary.

 

[docnjoj]

I vaguely remember seeing 85 rpm/volt with one of those AXI jobs. Could be just "old eyes", however!
otherDoc

 

[eP]

...4000-6000 rpm is needed working rpm range IMHO

At 130rpm/v for the HXT 80-100-B, that's 6240rpm at 48volts and 4680rpm at 36v. Don't these decrease with a load? That's why I believe for some of these motors gearing them down may be unnecessary.

I'm not sure what mean unnecessary. Would you like to elaborate it ?
You should also keep in mind motor like HXT are not 90% range efficient. Theirs max efficiency is about 80%.

Best regards

 

[Miles]

You should also keep in mind motor like HXT are not 90% range efficient. Theirs max efficiency is about 80%.

Using the specification here: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5142
The peak efficiency appears to be 11% for 36V

 

[John in CR]

You should also keep in mind motor like HXT are not 90% range efficient. Theirs max efficiency is about 80%.

Using the specification here: http://www.unitedhobbies.com/UNITEDHOBBIES/store/uh_viewItem.asp?idProduct=5142
The peak efficiency appears to be 11% for 36V

Maybe I'm looking into the wrong motor. How are you guys coming up with these efficiency numbers? That internal resistance number is surely a typo. From a theoretical standpoint why would a larger outrunner be any less efficient than smaller ones? Isn't it their simplicity that leads to such high efficiency? Also, Suppo makes a similar sized motor, and they claim a 90% max efficiency and 86% efficiency over a fairly wide power range. What am I missing?

 

[dirty_d]

the resistance for that HXT is indeed a typo, its 32 milliohms, i already graphed that motors performance, its very similar to the AXI motor, the peak efficiency was over 90%.

here are the graphs, first is 100A limit, second 50A limit.

 

[eP]

the resistance for that HXT is indeed a typo, its 32 milliohms, i already graphed that motors performance, its very similar to the AXI motor, the peak efficiency was over 90%.

here are the graphs, first is 100A limit, second 50A limit.

Lets look at TP5330 real datas:
http://myhobbycity.com/showthread.php?t=345&page=2

Kv = 254 rpm/V
Rm = 24.5 miliohms cold, at 1A
Rm = 63.4 miliohms at 70A, warm
Io = 1.5A @ 7V,
1.9A @ 10.5V,
2.2A @ 14V,
2.4A @ 17.5V,
2.6A @ 21V,
2.7A @ 24.5V,
2.8A @ 28V,
2.9A @ 31.5V,
3.1A @ 35V,
3.3A @ 38.5V,
3.5A @ 42V

HXT motor are more similiar to TP motors than to AXI.

No way 90%+ efficiency.
If HXT has more or less Rm=32mohm cold so you can safely assume it has at least 60 mohm warm Rm.

 

[eP]

Maybe I'm looking into the wrong motor. How are you guys coming up with these efficiency numbers? That internal resistance number is surely a typo. From a theoretical standpoint why would a larger outrunner be any less efficient than smaller ones? Isn't it their simplicity that leads to such high efficiency? Also, Suppo makes a similar sized motor, and they claim a 90% max efficiency and 86% efficiency over a fairly wide power range. What am I missing?

ACF -advertising correction factor

 

[John in CR]

ACF -advertising correction factor

ACF I can accept, but what about "The peak efficiency appears to be 11% for 36V"? Doesn't that need an HCF, hyperbole correction factor? For me efficiency is more of a cooling factor than a range factor, and what I'm after is maximum power in minimum size and cost. A $149 fist sized motor on a low slung homemade bike that leaves everything but the sportiest car or motorcycle in its dust from a stoplight is exactly the WOW factor needed to introduce EVs to Costa Rica.

John

 

[Miles]

Of course, I was only making fun of the sloppy attitude towards posting specifications - it's everywhere.

 

[recumpence]

Miles,

I spoke with Dave from Astro Flight yesterday. He is making me one of the 6 turn motors. So, I will be able to give my impression of that motor soon.

I will need to mod my power unit to make it fit, though. But, I think it will run better than my AXI.

Matt

 

[Miles]

Matt,

Good move. I have a 12t which I'm using with a single stage reduction. Certainly, my 3210 works beautifully with the HV 85 controller.

We should also work on them to morph their servo tester into a throttle control - they seem to have an eye on the ebike market, now.

Exciting times

 

[Kraeuterbutter]

hey..
have you seen this ?
http://www.powercroco.de/24N28P6530.html


weight: 960g
80 rpm/Volt
he has build that motor for a bicycle

with 24Volt its around 1300 rpm under load

yes, the efficience-numbers are not at 90% like on the motors from towerhobbies mentioned here.
BUT: i also doubt this 90% a little bit..
very often (specially cheap motors) motors are far overrated when it comes to efficience..
claims of 93% and when tested on a professional motor-test-stand (for example Plettenberg does do this) you see, that some even not reach 80%
so: this 80% are real 80% Dr. Ralph Okon measured, you can trust this values..
and with that low kv (80 rpm/V) you can maybe safe some more %-points at gearing

oh:
he has also build "some" other motors:
http://www.powercroco.de/navigation.html

 

[Miles]

Another plus for the Astro Flight inrunners is the ease of adding a decent heat sink

 

[Miles]

hey..
have you seen this ?
http://www.powercroco.de/24N28P6530.html

Yes. I had a correspondence with him, about it, 2 years ago

 

[docnjoj]

Bob Boucher rules! Also, lets not forget Samarium Cobalt stands up to heat much better than Neodyme! I've used his stuff since the 60s, for electric glider competition! The motors could sizzle grass when they landed, but we dunked them in ice water and went on to fly again!
otherDoc

 

[Miles]

Yes, he was the real pioneer with this stuff.

The new Scorpion motors/kits are claimed to have "Neodyme" magnets rated to 200 deg. C, though.......
http://www.innov8tivedesigns.com/Scorpion_Motors/
I'm waiting for the 55mm series to come out...