My crack at building the fastest hotrod 9C on the planet...

[UBMag]

Hello.

I have to say that I am a physics student, and not really a electrical engineer like a lot of you. Having said that, I hope you dont make to much fun of me when I get stuck on obvious electrical issues. I have been driving and hotrodding 9C`s for little over a year, and have kind of fallen in love with its simple, and cheap, construction (and its obvious limitations). I became a physics student for my love of challenging peoples individual "truths" about what is possible and what is not. I originaly planed to make this build all on my own, incognito, without community input, but realized I might need your hotwired brains to reach my goals.

Before build start I would greatly appreciate all input you might have for me to further map and adjust my goals and obvious obstacles! I am sure I have made mistakes in the planing, I just have not found them yet....

The project:

As the title the goal is to build the fastest (dragracing) 9C motor in existence. I do realize this is probably going to fail, but I want to make my crack at it never the less. I know most of you would have gone with a better motor, but the challenge is the fun part in my eyes. And if it works, the solutions could be transfered to any other more expensive and more potent DD hub.

Setting the Goal:

I have tried to look up and search for "the king of the hill" of 9C builds, but cant seem to figure out who holds the throne at the moment. All I know is that it must be here on this forum somewhere. I have not read it all so I am hoping for some input on who it might be, and what I am up against As far as I have seen we are in the 6000 watt-area. If I am wrong, please rectify me so I can adjust my aim!

Obstacles:

Enemy nr 1: Heat:
- "normal" heat buildup
- "excessive" heat buildup due to copper mass limitations

Enemy nr 2: Constructional weakness:
- Danger of warping axle and center stator "frame"
- Danger of warping side covers
- Frying hall sensors
- Burning out copper wire after exceeding its assumed power potential
- Excessive strain on bearings that might lead to failure
- Ripping apart spoke-flanges and holes
- Magnets delaminating from external ring due to heat

Background:

I know a post like this might be observed as a newbie "just blowing smoke". But I did have a crack at the project once before. That time I got around to about 4500 watts using 20s LiPo`s (pushing just above 60A max) before the metal holding the inside of stator warped due to heat and rendered the motor totally destroyed. So this time I am starting from scratch, and hopefully with a bit of community input will get the 1500W+ I need

 

[spinningmagnets]

The Pikes Peak racer used 111V on a 9C, and he also trained for roughly a year so he could add quite a bit of pedaling power for as long as possible. He cut ventilating holes in the sideplates to let the excessive heat out.

I believe ebikekit.com still sells a slower winding for their trike kit. You might not want to avoid informing Jason (the owner) that you intend to hot rod it, he doesn't want to be involved with that.

disassemble
beef up phase wires (search for the LFP thread)
swap in decent breaings, good ones are still fairly cheap
use a sensorless controller because halls cant take the heat
spray the stator with anti-corrosion spray
add a couple temp sensors, use the abandoned hall wires for the temp sensors (10K thermistor and LM35?)
reassemble with high-temp silicone for oil-cooling
add a pressure vent near the axle
gather performance/heat data
disassemble and drill holes in the sideplates
run identical tests with air-holes and no oil
post pics and data

If you do a good job with the pics and data (and allow me to use it in an article), I might be able to help with a financial subsidy, but I can't guarantee anything.

 

[Ypedal]

My neighbor's 9C is running 24S 3P ( 100v 15ah ) with an 18 fet Lyen with shunt soldered up to unlimited amps, pulls about 200 amps peak for a few seconds, with a skinny rider it will pass 90 kph on level ground.. gets hot.. FAST.. smells terrible after a few hot launches... but the damn thing just keeps on taking it.

 

[Punx0r]

Most of your potential problems listed are related to heat, which will all be negated by the same thing.

I doubt you'll warp the side covers or damage the axle or bearings. That's much more likely to happen due to vertical loading from a heavy rider or doing jumps. Upgrading the bearings is a good idea while it's apart, though.

Saturation is a real concern IMO and I'd love to know if you find out when it occurs...

 

[UBMag]

Yes, thank you Spinning Magnets for the input. I saw the article. What a motor build it is The oil cooling option is a very good and interesting idea. But I had planed another more unexplored and potent route in cooling. One that limits operational times and adds to cost though...

My initial idea is to have a "2-phase cooling system". Where the first meassure of self defence is air cooling aided by internal fans (got the idea from a build here, but can not find it back), and the second is preassureized gas cooling. I have scetched a ruff idea for the setup in the picture (aspect ration and meassurements is a bit off, but the general idea is pretty much as in the drawing).

Air cooling:
I am not a hundrer on the air flow route, but I do want it to be forced threw the magnets-stator gap using highpreassure fans. It does not show in the drawing, but also have some kind of intake and extraction-aiding fins on the outside of the sidecover. I will move the 1-speed FW out by about 3 cm with a FW-spacer for clerance. One of the biggest drawbacks I can se with the way I drew it is that a total seal against the sidecover is impossible, but a partial wall to aid flow is a compromise that can work it fins, fans and wall cooperates correctly in the manner I think...

Gas cooling:
I was thinking to machine a small (2-3mm dia) hole in the axle center from the drive side, and route it from the inside of the sidecover threw 6 og eight copper tubes threw to the left side and have nozles situated just before the stator in the air-flow route. I have yet to decide on the gas, but it will need to be a cryogenic. I have had my eye on N2O for a while... The nozles would provide a spray of under -100 deg. celcius, so some kind of intelligent fast-switching controll-system based on multiple thermistors would be needed. I was thinking Arduino for that part. The fast temperature swings will accelerate metal fatigue considerably, but done correctly with enough flow, I think it has a shot...

 

[Ykick]

This kinda reminds me of that "Sow's ear" saying?

I ride 9C's and love 'em for their industrial similarities to an AK47. Cheap, plentiful and nobody cries if/when they melt down.

Upgrade phase wires, bearings and add large cooling holes with perhaps "fan shaped" attachments to move air at speed. For more performance, go 2WD with 9C's front and rear.

 

[gogo]

Subject: race ebike on dyno, flames and plasma! 40kw IN, 10hp OUT.
Do you want a street hotrod that drives around between 'runs', or a dragstrip dedicated machine?

 

[UBMag]

Subject: race ebike on dyno, flames and plasma! 40kw IN, 10hp OUT.
Do you want a street hotrod that drives around between 'runs', or a dragstrip dedicated machine?

That is a good one
Both please. Good Air Cooling system for cruising around town and commuting. And "Cryogenic mode" for racing. No "Trailerqueen" 10-second machine

 

[mat h physics]

Enemy nr 1: Heat:
- "normal" heat buildup
- "excessive" heat buildup due to copper mass limitations

Enemy nr 2: Constructional weakness:
- Danger of warping axle and center stator "frame"
- Danger of warping side covers
- Frying hall sensors
- Burning out copper wire after exceeding its assumed power potential
- Excessive strain on bearings that might lead to failure
- Ripping apart spoke-flanges and holes
- Magnets delaminating from external ring due to heat

IF this is a dedicated dragster, heat build up shouldn't be such a problem on short runs. Consider pre-cooling the motor before getting to the track, don't rule out using thermal insulating side covers. Cryogenic temps will reduce resistance to prevent heat generation in the 1st place, more power generated to the wheel. You will not burn out a copper wire, melt a solder connection or vaporize insulation, but not burn through copper. Expect parts to wear quickly, top fuel racers replace the aluminum connecting rods about every 7 runs.
Temp shock can be a problem on wire insulation, if cryo temps are used. See if "keystone" magnets are viable, ie no laminate. "Ripping apart spoke-flanges and holes", yes that maybe the real challenge limit for high torque on such a relatively small set-up.
You are looking at a great thermodynamics paper write up.

 

[Punx0r]

 

[Drunkskunk]

Sounds awesome. do you have a speed goal in mind, or just looking for as fast as you can get?

I think internal active fans may be more trouble than they are worth. you should be able to get better cooling by turning the cover into an active fan, adding blades so it draws air as it spins though cooling holes.
Also, a ram scoop and exhaust shroud should help pull air through faster.

Compressed gas isn't very efficient at cooling. Liquified gas is much better, but you would need to get the liquid into the hub.

Another idea that I haven't seen explored yet is adding heat sinks to the stator inside the hub, helping to pull the heat from the stator ring into the air channel for better cooling.

 

[Bob K]

If you are thinking of forced fluid cooling.....
If you use something more dense than a liquefied gas ( water)
and you impinge on you windings so as to turn the water to steam,
the phase change will remove more than ONE ORDER OF MAGNITUDE
more heat. Latent heat of vaporization can be your friend.
Pretty easy to calculate how much water you would need based on
wattage input. Pump up a 2 liter soda bottle with water and
70 psi and you have a cheap and efficient way to spray your windings
for an easy test. Just an idea. Best of luck to you!

 

[itchynackers]

Enemy nr 1: Heat:
- "normal" heat buildup
- "excessive" heat buildup due to copper mass limitations

Enemy nr 2: Constructional weakness:
- Danger of warping axle and center stator "frame"
- Danger of warping side covers
- Frying hall sensors
- Burning out copper wire after exceeding its assumed power potential
- Excessive strain on bearings that might lead to failure
- Ripping apart spoke-flanges and holes
- Magnets delaminating from external ring due to heat

IF this is a dedicated dragster, heat build up shouldn't be such a problem on short runs. Consider pre-cooling the motor before getting to the track, don't rule out using thermal insulating side covers. Cryogenic temps will reduce resistance to prevent heat generation in the 1st place, more power generated to the wheel. You will not burn out a copper wire, melt a solder connection or vaporize insulation, but not burn through copper. Expect parts to wear quickly, top fuel racers replace the aluminum connecting rods about every 7 runs.
Temp shock can be a problem on wire insulation, if cryo temps are used. See if "keystone" magnets are viable, ie no laminate. "Ripping apart spoke-flanges and holes", yes that maybe the real challenge limit for high torque on such a relatively small set-up.
You are looking at a great thermodynamics paper write up.

If this is a 1/4 mile machine, Mat has it right here. Skip the gas/air cooling stuff. Go with water or oil, since heat generation will be limited to seconds. Pre-cool the motor (ice bags?). Get a higher speed motor (9x7). Run it at mega volts. In my opinion, your biggest problem will be keeping the controller from blowing.

 

[Punx0r]

Subject: race ebike on dyno, flames and plasma! 40kw IN, 10hp OUT.
Do you want a street hotrod that drives around between 'runs', or a dragstrip dedicated machine?

Very interesting. Clearly there's no point exceeding 10kW input on a 9C.

 

[UBMag]

Thank you for all the input so far. I will take a "sitdown" and do some maths on the different options tomorrow. As more of you mentioned I also belive one of the keys is in the precooling to get the windings resistance down as low as possible. I will need to look into the actual numbers for what is possible. It will never become a superconductor, but it's worth taking a closer look at.

I also recently read a very interesting paper on cooling electrical compressormotors using their own compression work to cool the internals within the motor itself, resulting in overall increased efficiency. Some clever conclusions was made outside the obvious.. Not really the same thing, but some principles might be valid here if I remember correctly. I have to take another look and find the reference paper.

So far I have standing on my floor: a big bottle of nitrous, two motors, a CA3, a bunch of bits and bobs, and 148 volts of LiPo...

 

[fellow]

You have a bottle of N20 you say? Aim to the motor, connect the solenoid with the temp sensor inside. When t>50'C, keep the solenoid switch open .

 

[grindz145]

big shoes brother

http://endless-sphere.com/forums/viewtopic.php?f=2&t=12356

 

[grindz145]

Enemy nr 1: Heat:
- "normal" heat buildup
- "excessive" heat buildup due to copper mass limitations

Enemy nr 2: Constructional weakness:
- Danger of warping axle and center stator "frame"
- Danger of warping side covers
- Frying hall sensors
- Burning out copper wire after exceeding its assumed power potential
- Excessive strain on bearings that might lead to failure
- Ripping apart spoke-flanges and holes
- Magnets delaminating from external ring due to heat

IF this is a dedicated dragster, heat build up shouldn't be such a problem on short runs. Consider pre-cooling the motor before getting to the track, don't rule out using thermal insulating side covers. Cryogenic temps will reduce resistance to prevent heat generation in the 1st place, more power generated to the wheel. You will not burn out a copper wire, melt a solder connection or vaporize insulation, but not burn through copper. Expect parts to wear quickly, top fuel racers replace the aluminum connecting rods about every 7 runs.
Temp shock can be a problem on wire insulation, if cryo temps are used. See if "keystone" magnets are viable, ie no laminate. "Ripping apart spoke-flanges and holes", yes that maybe the real challenge limit for high torque on such a relatively small set-up.
You are looking at a great thermodynamics paper write up.

If this is a 1/4 mile machine, Mat has it right here. Skip the gas/air cooling stuff. Go with water or oil, since heat generation will be limited to seconds. Pre-cool the motor (ice bags?). Get a higher speed motor (9x7). Run it at mega volts. In my opinion, your biggest problem will be keeping the controller from blowing.

Good advice from someone who I trust would know

 

[Modbikemax]

Hello.

I have to say that I am a physics student, and not really a electrical engineer like a lot of you. )

All the 'Ginger beers' are out writing Apps. We are the ones who get the job done. :wink:

 

[hydro-one]

if u like the 9c get a 50mm stator cromotor(same 23 pole pairs) scheme but twice the width stator). imo the 9c is just too small for performance. i use less wh on my rides with the bigger motor, and the torque is out of this world at 250amps 110v. no heat issues and i can wheelie at will. if you have to go 9c grab a 12x5 wind that is one hot moto....put it in a very small wheel i run a 17" motorcycle rim and that seems perfect. that will help alot with heat. and volt up , phase upgrade and couple thermocouples (bbq thermometer?). oil cooling with pipes would allow you to flog that all day but i cant imagine having oil leaving out of my bike (water yes.....)

hope that helps..

 

[UBMag]

I am amazed with the response and amount of good solutions suggested. I am still working on my resarchpaper on the different parameters and hypoteses of the build, hopefulle comming to one theoretically best way of proceeding with the experiment. Especially I have to calculate the "exact" theoretical thermodynamic potential of each solution, and cryogentic material option in relation to this particular application. This is a ongoing prosess that requires me to brush up on a lot of different parts of my curicullum, so it takes time... No better way to learn physics than actual challenges :lol:

So I figured I would build one motor with only air cooling for benchmarking in the meantime. Controller choices above 132volts also seems to be a real challenge for this application. Still looking, but might come down on a Lyen (if I decide to limit to 132 volts hot)...

For benchmark-motor I went 12 awg since it is easiest. I think I need to try to get more into the "9Cryo"-motor. 10K Thermistor. - DONE

 

[John in CR]

You got one of the 2 real limits, which is the skinny axle. The other is stator saturation, not by heat but by current and the limited flux it can create.

For the most power, since we are limited by voltage, you wanted the fastest wind for the most power (powers is rpm X torque). Max torque is the same for all the different winds and is determined by the steel and magnets, not the copper. Then since you're pretty limited in max power, you'd want to use the smallest wheel for the most torque applied to the ground.

Cooling for a drag race is fairly easy. Getting the stator cold before the start with a compressed is a good touch, and then maybe add a powerful blower that cranks up at launch. Toolman2 measured that he got 1000W of savings in decreased copper resistance using a 70W leaf blower mounted just outside his outrunner forcing big air through the stator of one of his motors.

Why the smallish motor though? This isn't like a little fuel injected 4 cylinder that can be modded to do big power and beat a V8. You're torque limited no matter what you do, so a bigger motor with only minor or no mods can slaughter you without even pushing to full saturation. If it's just an exercise in getting the max out of your favorite 9C that's a fun learning project. You're severely limited by the motor though if the quest is for extreme power. eg I push my hubmotor at 27kw peak input, and with my simple cooling hacks it's unstressed enough to have no heat issues riding as far as I want as my daily rider. In straight stock form I ran it at 16kw without issue, so despite pushing probably 100lbs or more greater load, even in stock form I would fly by your 9C in any race you come up with.

If it's only for short drag racing, then pushing a motor to its limits is fine, because economy isn't a concern and 20 seconds of heat is fairly easy to deal with at these relatively low power levels. Keep in mind that at absolute max power of a motor the efficiency will be only 50%, so they aren't useful in that setup anywhere other than in a drag race.

 

[UBMag]

You got one of the 2 real limits, which is the skinny axle. The other is stator saturation, not by heat but by current and the limited flux it can create.

For the most power, since we are limited by voltage, you wanted the fastest wind for the most power (powers is rpm X torque). Max torque is the same for all the different winds and is determined by the steel and magnets, not the copper. Then since you're pretty limited in max power, you'd want to use the smallest wheel for the most torque applied to the ground.

Cooling for a drag race is fairly easy. Getting the stator cold before the start with a compressed is a good touch, and then maybe add a powerful blower that cranks up at launch. Toolman2 measured that he got 1000W of savings in decreased copper resistance using a 70W leaf blower mounted just outside his outrunner forcing big air through the stator of one of his motors.

Why the smallish motor though? This isn't like a little fuel injected 4 cylinder that can be modded to do big power and beat a V8. You're torque limited no matter what you do, so a bigger motor with only minor or no mods can slaughter you without even pushing to full saturation. If it's just an exercise in getting the max out of your favorite 9C that's a fun learning project. You're severely limited by the motor though if the quest is for extreme power. eg I push my hubmotor at 27kw peak input, and with my simple cooling hacks it's unstressed enough to have no heat issues riding as far as I want as my daily rider. In straight stock form I ran it at 16kw without issue, so despite pushing probably 100lbs or more greater load, even in stock form I would fly by your 9C in any race you come up with.

Thank you for your input. I have not decided on wheel size, but as you say, the smaller the better i guess.

Wow, 1000w more mechanical power based solely on lowered winding resistance? That is a good number for any air-cooling system. What kind of motor was he using? (just asking to get a feel of what kind of efficiency-percentage increese we are talking). You would not happen to have a link to that thread (if any?).

The reasson for using the 9C was really cost. Like someone nicely put it before, "the AK47 of hubs" disposable and cheap. Also by coosing a motor with a limited potential, it makes it much easier and cheaper to find batteries and controller for the job, without blowing the bank. The important part for me is really to use it as a research experiment for learning, not to create the worlds most powerfull motor. And if I am lucky enough to find a "optimal" solution as a result, it is highly likely that it can be fransfered into another more powerfull DD hub, with similar results. Just now I am studying magnetism and induction (as part of my "classic physics" course) so I figured this could help me to accelerate my learning curve by practical experiments.

The ultimate goal is to use it on a light racing frame with as low weight as possible, and see what kind of performance is the limit for this particular motor. And hopefully set a upper real world performance benchmark for this motor.

edit: Yes, the axle is a problem. I am considering designing a new sidecover with a bigger bearing for side-axle cable exit. But it might just be that the copper meets its maker before the 12 gauge... Will have to try and find out i Guess

 

[spinningmagnets]

But it might just be that the copper meets its maker before the 12 gauge

I recall one builder used a lathe and bored the entire length of the axle all the way through. Two phase wires exited one side (or possibly four paired wires for less wasted air space), with one phase wire plus the other small wires out the other side. But I agree 12-Ga should be enough for most of the hot-rodding mods.

"The helpful 9C wire upgrade thread, explicit DIY pictures."
http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=24547

 

[John in CR]

Toolman2 never gave us details or pics that I know of, just that he/they measured the actual benefit, and I'd trust his statement despite the fact that I'm held to a different standard. I'm pretty sure his was using the leaf blower at one end to blow into an RC type outrunner.

Exterior blades at the perimeter on the exhaust side of a hubbie can get a lot of air through the motor if you're turning good rpms. Interior blades almost touching the stator are effective at increasing the velocity and turbulence at the stator and end windings where it is needed most.

Inductance and magnetism...It sounds like you need a 2nd motor with a high speed wind, so you can study the practical effects of inductance on our controllers...Try your hand at some big toroidal coils on yours phase wires and fun stuff like that. The project you defined is firmly in the domain of Thermo Dynamics classes not inductance and magnetism.

I have some big hubbies that snack on controllers due to very low inductance. I made a set of toroidal coils using large speaker magnets as the cores, but I have no way of measuring any benefit other than the controller never blew. If you run across anything that might be helpful in that regard, please let me know, because I found little. Another idea is to cast 3 toroid cores using magnetite and epoxy. The kids have fun collecting magnetite for me at the beach using big magnets, so I can get plenty if it makes sense.

FWIW, the best way I've found to get the most copper through an axle is using magnet wire, so the 3 phases don't need 3 individual insulators and you can get a round harness with 3 electrically isolated phases plus halls.
Hints...stagger the ends of the phases to make it easier the get started through the turn. I used silicone for lubrication, which cured to become a seal. The hardest part for me was getting all copper strands well connected, so leave the outer ends unconnected (though marked which are for which) and check continuity of each strand to the others from the outside after you get the inside terminated. I ended up with slightly better than 10ga through my 9C axle pretty easily using that method with magnet wire varnish, 1 layer of electrical tape stretched thin and tight (to get it nice and round before heat shrink) and 2 layers of quality heat shrink as my harness insulation through the axle.