Custom Build With Golden Motors 3KW BLDC "Development Project"


New Member
Mar 15, 2015
In looking for a good motor I was pointed to this 3KW BLDC. I'm confident the motor will have more than enough power. I'm going to be very technical in my methods so I hope this thread will be helpful to those interested in utilizing this motor.

I estimate the cost of this project at approximately $2000

It is my opinion that the motor will need geared down quite a bit so I will be utilizing a custom built drive.

The Motor is Model# HPM3000
It is rated at 2/3 KW Continous and 6KW Peak.
The operating RPM is listed as 3000 to 5000 RPM.
You can find the complete specification online.

The first question to answer is how should the drive be configured.

Direct : Jackshaft or other means out using sprockets.

Geared: Using a configuration of gears and sprockets.

I have attached the datasheet for this motor to this post. It is like a dyno sheet for a gas engine.

After reviewing the data for the motor the question at hand can be answered mathematically.

If you find any errors in my calculations please advise so they can be corrected.

#1 Conversion of the tire rotations into MPH.

I'm going to skip through the math here but if you would like to know how this is calculated I will go through it.

Just ask.

The baseline I'm going to use is:

12.68 RPM of the tire = 1 Mph.
This is specifically for a 26" by 2.5" tire.
Calculation #2 " gear ratios "

This would be for example a 10 tooth sprocket on the motor and a 60 tooth sprocket on the wheel.

I know....we wouldn't do that, we would use a jackshaft and a smaller sprocket on the wheel.

I choose that example for simplicity of demonstrating drive ratio.

60 tooth sprocket divided by 10 tooth sprocket.
This is a 6:1 ratio.

The 10 tooth has to make 6 revolutions for the 60 tooth to make 1 revolution.

Ok that's the easy basics.

You should be able to calculate ratio and were using 12.68 wheel revs = 1Mph.

We also have the datasheet to use as a guideline for our design parameters.



New Member
Mar 15, 2015
I split this post up to make it easier to find and review specific data.

Let's get down to business.

Feasibility of Direct Drive " 6:1 Ratio "

A) Given 12.68 Rotations of the tire = 1 Mph
B) Given 6:1 gear ratio
C) Prefered speed range 2 Mph to 30 Mph
D) Motor Operating RPM 3000 rpm to 5000 Rpm

We will say were gonna pedal to 2 mph then use the motor.

2Mph = 25.36 RPM of the wheel.
25.36 * 6 = 152.16 RPM of the motor

10 Mph = 126.8 RPM wheel
760.8 RPM motor

20 Mph = 253.6 RPM wheel
1521.6 RPM motor

30 Mph = 380.4 RPM wheel
2282.4 RPM motor


Data from the data sheet.
Looking at the data sheet we can see that....

Motor Rpm of 2135 and a Torque load of 14.2 Nm

Will draw a current of 80.75 Amps.
Requires a power input of 3842 Watts
And Produces a power output of 3227 Watts
Having an efficiency of 84%

E) Given continuous rating of motor 3000 Watts
F) Given Peak Rating 6000 watts

3000 Watts at 48 volts = 62.5 amp current

6000 Watts at 48 volts = 125 amp current

There is only 1 unknown variable here...
( Torque Required to move bicycle at specified Mph)

Conclusion to example 1

It is my opinion that a direct drive with a ratio of 6:1 will not work with this motor.

The lower the motor Rpm the higher the torque load on the motor.

The higher the torque load on the motor the more current is drawn. Higher amp.

We know that at 2135 RPM of motor @ a Torque load of 14.2 Nm we will draw 80.75 amps.

Therefore at a lower RPM or a higher than 14.2 Nm our amperage draw us gonna increase.

We would like to continuously operate at around a 60 amp draw.
We should never exceed a 125 amp draw.

If we do the nearly $400 Motor is at risk of being toast.
The Sine Wave Controller is Rated at 200 Amps so I think the motor would be the first to burn.

Also we need to consider the load the batteries can Handel.

I could be wrong but my gut tells me otherwise.
I'm not an expert electronics engineer so if you are please explain if you disagree with this theory.

,152 rpm at the motor seems really slow unless the torque required to move the bicycle And operator is substantially less than.14.2 Nm.

If you are a statics and stress engineer please calculate for us the actual torque required at the wheel to move the bicycle at designated speeds.

As all ways your input is appreciated.

Mike B

New Member
Mar 23, 2011
Central CA
The maximum capability of the motor will not be used unless you are accelerating very hard or going very fast. The torque produced by the motor is what is needed to move the load. If the load is small the torque produced will also be small.

It like a car. Going down a level road at 60 MPH requires about 20 HP. Now the engine is capable of 200 HP but it's not producing that much to keep the car moving.

Switching controllers do amazing things also. Say you are going fairly slow but up a steep hill. The motor is running slow so it doesn't need much voltage, but the load is high so it needs a lot of current. For this example lets say the motor is rated at 80 amps max and you need 60 to get up the hill. The battery can provide 60 amps at 60 volts. But the speed is slow so the motor only needs 20 volts (back EMF)

The controller is actually a high efficiency power converter and will provide those 60 amps to the motor. But since only 20 volts are needed the current drawn from the battery is only 20 amps.

Pretty cool eh?

In short, the power delivered by the motor is determined by the load


New Member
Mar 15, 2015
Yes Mike it is very cool.
And as far as that back EMF thing there are people out there coupling two similar motors and by capturing out of phase currents can output more power from the driven motor than what's out into the system.

For the most part what your saying is correct.

I still haven't quite wrapped my head around this whole low rpm with an electric but it's correct.

I spoke with Golden Motors and all though there not giving a direct answer for gear ratio they pretty much concur with what your saying.

Only addition is lower rps means more current draw due to higher load.

So I'm still pondering what ratio to run initially.

I think this motor is larger than most used on bikes and has more power.

I'm wondering what the disadvantage would be to a larger gear reduction.

Would I loose top speed, or just run higher rpm throughout the system.

What ratios are people with similar setups running.


Sep 8, 2014
BC, the first thing you need to establish is the power and speed capability of the motor.
Then just decide how fast you want the bike to go, within those power limitations.
It's 3kw, that equals 4 HP. The info above: The operating RPM is listed as 3000 to 5000 RPM. This sounds like the motor is happiest between those two.
It's not a great lugger, but makes lots of power spun up. I say let 'er spin.
Personally I wouldn't care to go 40 on a bicycle, so maybe I would set it up to go 32. My gearing choice would hit 32 at at its top RPM.
On our very cool gearing calculator program, available on the forum somewheres, with 26" wheels, it works out like this..
With a 4 to 1 primary drive ratio, with sprockets - like 12/48, then a jackshaft sprocket with 16 teeth driving a rear with 48 on a 26" you get a drive ratio of 12 to 1.
With all that power it should romp over any hill and will hit 32.2 mph @5000 RPM.
At 5000 = 32.2
At 3000 = 19.3
At 1000 = 6.4
So you would be hitting your stride right at 20, top out at 32.
This stuff might help you arrive at a workable gearing adjusted to your own preferences of course.
That bike will not lack grunt power geared this way. The lowish gearing will help avoid high motor temps and avoid overloading the controller, also.
Good luck, I'll be watching how it comes out!
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Mike B

New Member
Mar 23, 2011
Central CA
Yes, you really need to tell us what you have in mind for the project.

How fast? On/off road? Do you care about legal? Is it going to have pedals?

If you just want to go 30 MPH you can do that with a 1 KW hub motor, bolt it on and be down the road. No transmission, no mounting problems and looks like a bicycle.


Active Member
Sep 25, 2008
You could custom center mount a hub motor and use a jackshaft to power freeweel cranks using the bikes normal drivetrain and gears. Or run direct to the rear wheel. It would line up. gear ratio would be 1:1? just checked out the gm motor. looks good. that should work perfect. what kind of volts and ah are you planning?
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New Member
Mar 15, 2015
Hello all.
I appreciate the replies and suggestions.

My application is as follows. I'm looking to put this on a full suspension MB. The bike I'm looking at has a nice spot where I think everything will fit nicely. Once I buy the bike I'll have a better idea how I'm going to arrange everything.

This motor I'm sure has more than enough power for this application. I'm looking to travel around 25 to 30 Mph on average. I need extra power because this will be my primary means of transportation. And a lot of my riding will be uphill for several city blocks.

I spoke with a tech at Golden Motors and found out that Mike is pretty much right on. The Motor isn't rated for 3000 / 5000 rpm but it is configured for 3000 or 5000 rpm. They can configure the motor any way I would like but the standard configuration is 3800 rpm. That would be top continuous RPM. And the motor would only be spinning that rpm if it had enough power to drive me that fast.

I was also told that the sine wave controller has built in protections that will keep the motor from overloading.

All of this is good news because it makes this setup much simpler and cheaper to build the drive for.

As I said before I am a CNC Machinist with full turning and milling capability so I will be machining the motor mounting and drive components.

Mike recommended a 5:1 Ratio for this motor and that's about right on. I decided I'm going to start around there.

I don't care for the jackshaft setup. I don't want to run all that power through the bicycle gears or rely on a freewheel.

I'm going to machine a housing that the motor will mount to. The housing will also mount to the bicycle frame. On the motor shaft I will be putting a 10 T Sprocket for #35 chain. The 410 and bigger chain is just too big and heavy for me. I think #35 will be fine.

I will be putting a countershaft in the housing with a 20 t sprocket to reduce the motor to 2:1 ratio. On the other side of the countershaft I will utilize a 10t sprocket. That will output to a sprocket I will be running mounted to the disk break bolt circle on the rear wheel.
Probably between 30 and 36 t.

The greatest thing is if I want to change the gear ratio I can easily by changing a cheap sprocket.

I looked at Helical gears which are expensive and require a new housing to change the ratios.

Sprockets will keep things cheap simple and compact so my bicycle will still look like a bicycle.

Just need to decide how to camouflage the battery.


New Member
Mar 15, 2015
Boy it's pretty quiet in the electric section.

I've been working on some sketches to figure out how I'm going to mount this motor.

This motor is pretty big. About 7 inches in diameter.
The bike I'm thinking about is full suspension and where the Seat tube would intersect the bottom bracket housing there is a small section of tube used for the mounting of the shock absorber.

To fit this motor I'm thinking I will have to remove that section of tube and build the shock absorber mount into the motor housing / mount. Kinda like the bikes where the mid drive includes the bottom bracket.

If I do build this it seems this bike will have tremendous power. The 3kw motor seems like a lot. I'm guessing my top speed could easily end up around 50Mph or more.

For strength I think I will add some long triangular side plates from the motor housing back to the dropouts on the frame.

To stiffen the frame up some.

I'm just wondering if this motor is too much for a bicycle and maybe I'd be better off with the 1500w version.

What do you guys think


Active Member
Sep 25, 2008
I think you might be the first person on here to try one of those most people just get a magic pie its a lot less headache.


New Member
Mar 15, 2015
I've looked at the hub motors and I'm sure there great. I think I'm just looking for more. And to me what is a headache for most it the part I really enjoy.

Dollar for dollar if you look at what it cost for the hub motors. It's about 400 with the wheel. Still got to spend $$$ on the battery. And that's for about 1000w.

From my experience with gas bikes I know bicycle wheels don't last long. Bent rims broken spokes whatever. Then it's another 200 to fix that problem every time it occurs.

It's 268 for the motor and 260 for the 200 amp sine wave controller. About 530 plus shipping so somewhere around 650. And that's for 3kw continuous 5kw peak.

Considering I am a mechanical engineer and have full access to CNC lathes and Mills which gives me the ability to make anything I want for the cost of the materials.

I'm thinking I can build a bike similar to the Stealth Bomber for less than $2000.

It won't have high gear pedaling but I'm not planning on pedaling much. And I want to keep the bike looking like a bicycle as much as possible. Performance wise I'm pretty confident the Stealh Bomber has a very similar sized motor.

I'm guessing it will be more than most want to ride.

I'm thinking I can take the 26" hyper havoc full suspension mountain bike and fit it with this motor. I will defiantly add disk brakes front and back. Most likely my rear drive sprocket will be mounted to the disk brake hub of the wheel. I have done this before and it works very well.

The rotor for the rear disk brake will be mounted to the sprocket. The spacing is tight I know but I'm sure I can fit it. Just gonna have to run a 30 or 32 T rear sprocket.

If worse came to worse I'm sure I can build a custom rear swingarm. I certainly plan on adding support like side plates if I do stick with the bicycle swingarm. That's one of the things I like about this bike. If you look at the triangle the back end makes its not real tall. Some faceplates would add plenty of strength and not be huge.

If you look at the center of the Bike , the way the suspension is tied in, and the space above the bottom bracket it looks very feasible to machine a motor housing / suspension bracket combination that includes the drive fits well and can be completely hidden by the side plates.

The plates I vision would mount to the housing and basically cover most of the triangular back frame. Probably just a bit smaller so they fit on the inner dimensions of the triangular frame.

Thus making the whole thing look like a fancy dressed up full suspension mountain bike. Also the shape of the main frame would fit some batteries Nicely and also be able to be covered by plates.

I need to do some more research on batteries. If I am able to take a bunch of the RC Lipo packs and put several cells in series to get the voltage of 48 which is easy enough and say 5 to 10 amp hours by running the series groups in parallel then I can shape the battery to fit in that front section of frame.

I just don't know what to do for a battery management system and the charger.

At this point it's a bunch of figures and sketches right now. I'm figuring it'll take me two months to build all this but it'll be ready for summer.

Considering a stealth bomber is 10000 and I'm looking at about a 2000 for this build I'm saving a **** of a lot of cash to have the same thing.

And who knows maybe I'll end up with a marketable product. At least maybe sell the design work.

To me this is interesting and fun. I've learned a lot all ready and by the time I'm done I'll have learned a whole lot more.

Education is priceless.

No kit or out of the box rig will give me all if that.
Sky's the limit here.

I'd definitely be interested in any suggestions or ideas you guys might have.

Big Country


Well-Known Member
Dec 23, 2007
Kalamazoo, MI
looking forward to seeing what you come up with big country. I am on my 4th electric bike and love em. I don't have the talent most of the others do so i am into simple set ups but i have a blast


Electric Enthusiast
Dec 11, 2014
Austin Tx
I will totaly bamboozle any Swing arm making processes that I can,
Arent those batteries known to start fires? I suspect thats what the battery management is for :p
I Dont know anything about battery management systems, but what ive heard is that lifepo4 and manganese are the way to go for batteries

or mayhaps you can figure out how to use Ultra capacitors In lieu of the Batts :3