View Full Version : Need a motor?

07-16-2009, 06:42 PM
I found this and ordered some for my electric trike project. These are very high quality brushless DC motors with built in controller designed to run on 24 VDC. They turn counterclockwise only which is perfect for direct driving the spindle of my mill. Max rpm is 2800, continuous rated power is 300 watts which is a little more than 1/3 hp and peak power is around 800 watts so speed regulation should be very good. Of course it will need a 24vdc power supply capable of supplying at least 15 to 20 amps. The controller probably has a low voltage cutout that will turn off the motor at around 16 to 18 volts. It is temperature protected as well.

They are made by Danaher Motion in the USA, Kollmorgen brand, and were intended for use on electric bicycles but somebody goofed and they have the wrong rotation. Cost is 79.95 from:


I'll let you know how it runs when I receive my order but it is controllable from zero to 2800 rpm with full torque at all speeds. To control it all you need is a 5k ohm pot.


Forrest Addy
07-16-2009, 07:51 PM
Wonder why they can't be reversed? Maybe there's a shunt on the board that if opened or slosed will reverse the controller's switching logic

I bet Evan finds it.

07-16-2009, 08:53 PM
Mount it on the right side and it will rotate properly, won't it?

07-16-2009, 08:57 PM
Shaft rotation reversible by reversing power leads. According to the ad.

07-16-2009, 09:01 PM
You have the wrong ad. That only applies to brush motors.

07-16-2009, 10:54 PM
If its like most brushless motors, it should have three leads. Should be able to reverse any two to change the phase of power input. This has worked for me in the past with brushless motors I use in my combat robots.

07-16-2009, 11:24 PM
Not when it has an integral controller. The controller decides how the phases are activated and in what order. Changing the polarity will simply make it do nothing since the controller will have the wrong polarity. It's just like a brushless computer fan motor in that respect.

I am quite sure that with this motor all you need to do is pull off the rear cover to expose the PCB with the hall sensors. Even if there are no provided links or jumpers to change direction, switching the wiring on the PCB to any two hall sensors will reverse the rotation. Almost certainly though there will be a pin on the controller chip that sets the direction of rotation. In that case it will be a simple matter of bringing out another wire that will act to reverse the direction when it is grounded or brought high.


Even if it cannot be reversed it is a very good price for a high quality brushless motor, especially considering that it includes the controller and is trivial to connect. With the peak power overhead it has it will provide maximum torque even at 10 rpm or at full speed. With that sort of regulation it will behave like a much more powerful motor in most circumstances. It would also make an excellent motor for a small CNC lathe as it would be very easy to control the spindle from the computer. This will also be the case on my mill.

07-16-2009, 11:30 PM
I've read that there's a pin on the controller chip which can be grounded to reverse these 'backwards' motors. The chip is alledgedly common and datasheets are available online. I haven't chased it any further.


Forrest Addy
07-16-2009, 11:30 PM
Tole ja Evan would have an answer

J Tiers
07-16-2009, 11:37 PM
It may depend on the cheapness of the motor. They may not put in all the hall sensors, if they know it's for one direction. Then it may not be able to reverse without adding or moving parts.

But, if it wasn't found out until they were assembled, it might be that the cost of rework is more than the cost of scrapping to salvage and re-making them, even if they WERE fairly easily reversed.

07-16-2009, 11:38 PM
I've read that these can be reversed at the field windings as well. So they may not be using discrete sensors. I believe there's a way to determine rotor position by monitoring voltage on the unpowered phase.

J Tiers
07-16-2009, 11:49 PM
I've read that these can be reversed at the field windings as well. So they may not be using discrete sensors. I believe there's a way to determine rotor position by monitoring voltage on the unpowered phase.

There is, and even on the powered phase..... But not all do that "sensorless vector" stuff, its more in VFDs still.

Some of the motors HAVE only one phase...... at least for fans.

Given that the thing has a speed control, most likely it has regular sensors. We've done 150HP 5 phase drives with that sort of sensor-based control and a special PM motor. Not that hard compared to the sensorless stuff.

07-17-2009, 12:07 AM
It can be reversed. It is the same motor they make for Currie Electric Bicycles except they turn the wrong way. It was a large custom order from Danaher for Currie and they got it wrong. The markup on a lot of 10,000 from Danaher is so small that any sort of rework would be too expensive when you consider all the expenses involved. It may be a sensorless design but I doubt it. Sensorless motors with only three phases won't always start by themselves. They sometimes require a spin to find the right phase sequence. That wouldn't be a problem for motors sold in Europe for electric bikes since they require that all power assisted bikes must be started from a standstill by pedal power only until it reaches 3 kph. The US and Canada however allow the motor to start motion from a standstill as long as it has an automatic cutoff when any brake is applied.

07-17-2009, 01:32 AM
These are pretty nice little motors. I picked up a pair off ebay a few years ago when they were even cheaper. We are still running one on my son's mini-go kart and it hasn't given us a lick of trouble in 3 years of misuse :)
There are reversing instructions on either the v is for voltage or endless sphere forums. Have fun, Rob.