Yes the motor has an accessory shaft and it has a tach encoder. The encoder feeds the motor controller which in turn feeds the dashboard tach. The controller is set to limit rpms if necessary... which thankfully worked well when high gear blew half way down the track.

Does your motor have a stub shaft on the ass end? Some do, for an encoder or tach. If so, you could maybe cut a hole in your hood and let the little guy ride on top sticking up and out, like a blower in a ICE drag car.

 

Is it possible to put motor in cradle and use direct drive?

Is it possible to use planetary drive?

I think a smooth acceleration would be easier to control for max “unwasted rpm”.

An accelerometer could tell the controller of too much torque.

I know nothing of this, but I would think with electric drive, you should never brake traction.

 

For an old fashioned shunt/series wound motor, you should use a chopper control for supplying the armature and a stepped resistance for the field.

Trying to use any power transistor in the linear region for motor control is not advisable and it will burn up. Also, the chopper should use bipolar transistors (not IGBTs). If your motor isn't provided with special insulation, IGBTs will puncture the windings.

 

Yes, direct drive works. I originally built the car direct drive and put 1400 miles on it, but wound up adding a transmission. Electric can make a lot of torque, but gearing still helps. The low gear in my two speed transmission uses straight cut planetary gears.

Is it possible to put motor in cradle and use direct drive?

Is it possible to use planetary drive?

I think a smooth acceleration would be easier to control for max “unwasted rpm”.

An accelerometer could tell the controller of too much torque.

I know nothing of this, but I would think with electric drive, you should never brake traction.

 

On the subject of gearing for electric vehicles, the San Francisco transit agency (Municipal Railway) operates a fleet of 350 electric trolley buses which use 600 VDC from overhead wires.

The gear ratio between the DC traction motor and the rear axle of a 40 foot bus (or the center axle on a 60 foot bus) is about 11.60 to 1 and uses a double reduction. The first stage is in the axle housing and the second stage is a planetary hub on each wheel.

Double reduction axles are a specialty item and the axles for these buses were made by Raba in Gyr, Hungary. Meritor (formerly Rockwell) may be the only other one.

 

the chopper should use bipolar transistors (not IGBTs). If your motor isn't provided with special insulation, IGBTs will puncture the windings.

Do you have any literature to support your claim? Because I've never heard such a thing, and I couldn't find anything online that backs up what you say; to the contrary I can provide a sufficient supply of examples of IGBT motor choppers to establish that IGBT is an accepted norm technology used in industry for DC motor control.

 

Do you have any literature to support your claim? Because I've never heard such a thing, and I couldn't find anything online that backs up what you say; to the contrary I can provide a sufficient supply of examples of IGBT motor choppers to establish that IGBT is an accepted norm technology used in industry for DC motor control.

Skoda Controls in the Czech Republic *** built the entire propulsion system (the DC motor, chopper, and the controller) for our electric buses and they experimented with using IGBTs VS GTO thyristors. The objective was to minimize the size and weight of the smoothing inductor between the chopper and the armature.

IGBTs definitely reaked havoc on the windings (catastrophic insulation failures) and the testing was abandoned.

*** In 1999, Skoda operated a power device manufacturing plant for International Rectifier and they rank somewhere around 20 in the world for heavy the electrical manufacturing industry.

 

What happened at second 2.5?

 

At second 2.5, I shifted the car from low gear to high gear. At the time, the transmission had stock GM parts in it but apparently couldn't handle the torque, so the high gear clutches were slipping at that point and you can see that the motor RPMs went up a lot, then came back down as the clutches finally grabbed. The car had a 4.10 rear end at that time. Shortly after that I changed the rear end to a 2.73 gear, which helped to keep the motor RPMs low (and in the best power band), but put a lot more stress on the transmission. During testing with the 2.73, slipping was so bad that some of the clutches heated up and welded themselves together. After the latest transmission rebuild, shifting is very fast and solid. I shift at about 35-40 mph, and the car breaks 60 mph one second later.

In this video, you can watch the speedometer climb, the sweet spot is probably 40-60 mph. The transmission was slipping a bit on the shift, and the rear tires were still street legal drag radials that wouldn't hook at that power level. The car was limited to 80% power that day.

What happened at second 2.5?

 

In a IC engine, normally, you can not change the rpm/torque relationship.

So we use a gearbox to change that relationship, depending on velocity and torque needed for carriage.

An electric drive motor does away with all this. If the tires ever chirp with electric drive, you do not have the drive tuned properly. And you are wasting time and rpm(and rubber). You don’t want the rpm to go up, without the corresponding increase in velocity of carriage.

I believe your fastest run time will be when you apply torque slowly(compared to what you are use to), and to make sure that the carriage moves forward in the correct proportion to motor rpm.

The whole idea of electric drive is to deliver full power, but ONLY the power needed and no more.

The idea is to apply the most non slip torque thru run. You want to find that torque sweet spot thru-out runtime. This is possible with electric drive. You can hold the torque on the verge of slip.

Field weakening should never be needed if the drive is tuned right.

Also......you are delivering torque to only 50% of the area available.

Perhaps a smaller motor with drive on each wheel might be an improvement.

I believe there is a great future in electric drive.

When we get a real battery.

 

Skoda Controls in the Czech Republic *** built the entire propulsion system (the DC motor, chopper, and the controller) for our electric buses and they experimented with using IGBTs VS GTO thyristors. The objective was to minimize the size and weight of the smoothing inductor between the chopper and the armature.

IGBTs definitely reaked havoc on the windings (catastrophic insulation failures) and the testing was abandoned.

*** In 1999, Skoda operated a power device manufacturing plant for International Rectifier and they rank somewhere around 20 in the world for heavy the electrical manufacturing industry.

Why is it that IGBTs specifically were a problem? I don't know of anything special about them that would cause a problem. Other than turn-on/off time. If the turn-on/off time was too fast it would cause HV spikes, but that's a function of the drive circuitry, not the IGBT itself.

 

At second 2.5, I shifted the car from low gear to high gear. At the time, the transmission had stock GM parts in it but apparently couldn't handle the torque, so the high gear clutches were slipping at that point and you can see that the motor RPMs went up a lot, then came back down as the clutches finally grabbed. The car had a 4.10 rear end at that time. Shortly after that I changed the rear end to a 2.73 gear, which helped to keep the motor RPMs low (and in the best power band), but put a lot more stress on the transmission. During testing with the 2.73, slipping was so bad that some of the clutches heated up and welded themselves together. After the latest transmission rebuild, shifting is very fast and solid. I shift at about 35-40 mph, and the car breaks 60 mph one second later.

In this video, you can watch the speedometer climb, the sweet spot is probably 40-60 mph. The transmission was slipping a bit on the shift, and the rear tires were still street legal drag radials that wouldn't hook at that power level. The car was limited to 80% power that day.

Very cool, man. I envy. If you ever come to Houston to race, let me know.

 

My objectives are for drag racing, so it's all about squeezing out more performance in a variety of ways. I agree that tire spin is bad, but that can be fixed with tires, tire pressure, and chassis setup, including wheelie bars if necessary. ... then give it more power.

In the video, the motor amp limit was set to 1800A, rear tires were 315/35 drag radials, and it ran the 1/8th in 7.55 seconds at 84 mph. The tires wouldn't hook up above 1700A regardless of air pressure changes. The next trip out, slicks replaced the drag radials and the motor amp limit was increased to 2000A. After spinning a little on the first pass, the tire pressure was lowered from 15 psi to 14, and on the following passes, the tires hooked up at launch, and the car finished in 7.20 seconds at 87 mph.

I am still tuning a number of things in the car overall, motor power isn't even turned up all the way yet. The Zilla motor controller is probably tuned as well as it can be already, and has been proven for a long time by a lot of electric racers. Field weakening is one of the things on my performance roadmap, and will used when more when the other, easier changes have all been made. If a semiconductor solution cant do the job, it will be done with resistors instead.

I will develop a basic prototype to test at lower power with smaller motor to see what happens. Maybe it will let the smoke out, maybe not....

In a IC engine, normally, you can not change the rpm/torque relationship.

So we use a gearbox to change that relationship, depending on velocity and torque needed for carriage.

An electric drive motor does away with all this. If the tires ever chirp with electric drive, you do not have the drive tuned properly. And you are wasting time and rpm(and rubber). You don’t want the rpm to go up, without the corresponding increase in velocity of carriage.

I believe your fastest run time will be when you apply torque slowly(compared to what you are use to), and to make sure that the carriage moves forward in the correct proportion to motor rpm.

The whole idea of electric drive is to deliver full power, but ONLY the power needed and no more.

The idea is to apply the most non slip torque thru run. You want to find that torque sweet spot thru-out runtime. This is possible with electric drive. You can hold the torque on the verge of slip.

Field weakening should never be needed if the drive is tuned right.

Also......you are delivering torque to only 50% of the area available.

Perhaps a smaller motor with drive on each wheel might be an improvement.

I believe there is a great future in electric drive.

When we get a real battery.

 

I believe the secret to velocity is not amplitude of applied force, but the duration of applied force.

And I believe electric propulsion will prove it.

With todays processors, sensors, and drives, we can control and apply force like never before.

A pit stop will be a battery change and the programmer will be a valued racing team member.

When Wayne and his cohorts get this figured out, and others see what controlled power can do, hopefully it generates a lot more interest.

Theoretically, you should be able to control the wrinkle on a tire.

You might only be interested in run time, but all of you are doing very important work.

I wish you and your team much fame and success. You will have earned it.

I would think much of the heavy research is proprietary and not public,......waiting on a battery.

 

BR-549, thanks for your kind comments. My main goal is really to have fun, and maybe push the boundaries a bit in the process. The car is already fast enough that it's raising eyebrows at the track and outrunning most of the street muscle cars with ease. I am a member of NEDRA, National Electric Drag Racing Association, and as you suggest one of our goals is to raise awareness of what electric can do. Many people think of electrics as glorified electric golf carts that are sleepy in performance. NEDRA shatters that concept.

For my field weakening interest, railroads have been using it for a long time, GE Electrak tractors, and a few electric racers do too. I would like to advance that technology if possible, by using semiconductor and better controls to, as you put it, control the wrinkle on the tires.

It seems to me that, at least in theory, gradually bringing in field weakening at an optimal rate is going to average out to a better result than the old fashioned, crude but proven method of resistors. There ought to be a way to do this, but I recognize the potential down-sides as Glenn Holland has suggested. A test setup will help to understand this better, using a smaller motor that I don't mind destroying.

So returning to my original post & question, is the mosfet it? Can it's ohmic region of operation handle variable current shunting, while getting hit with an 18 khz PWM square wave pulse? Any suggestions for other component choices?

I believe the secret to velocity is not amplitude of applied force, but the duration of applied force.

And I believe electric propulsion will prove it.

With todays processors, sensors, and drives, we can control and apply force like never before.

A pit stop will be a battery change and the programmer will be a valued racing team member.

When Wayne and his cohorts get this figured out, and others see what controlled power can do, hopefully it generates a lot more interest.

Theoretically, you should be able to control the wrinkle on a tire.

You might only be interested in run time, but all of you are doing very important work.

I wish you and your team much fame and success. You will have earned it.

I would think much of the heavy research is proprietary and not public,......waiting on a battery.

 

You should hook up with John Metric from Texas, find LoneStar EV Racing. He has built two street legal electric drag cars that are very fast, and has just started testing his electric dragster, built with 4 motors. He runs at the Houston Motorsports Park.

Very cool, man. I envy. If you ever come to Houston to race, let me know.

 

It seems to me that, at least in theory, gradually bringing in field weakening at an optimal rate is going to average out to a better result than the old fashioned, crude but proven method of resistors. There ought to be a way to do this, but I recognize the potential down-sides as Glenn Holland has suggested.

So returning to my original post & question, is the mosfet it? Can it's ohmic region of operation handle variable current shunting, while getting hit with an 18 khz PWM square wave pulse? Any suggestions for other component choices?

While i still consider mr hollands's assertion that IGBTs will be detrimental to your motor to be bogus, i do think that BJTs will be a better choice. It is much easier to get linear mode operation out of them. Operating MOSFETs or IGBTs in their ohmic region is like trying to balance an egg.

 

I don’t believe I would try a SS device right off. To switch your field weakening resistor in.

I would try an old fashion relay with a short adjustable timer. Millisecond range.

This could be your proof of concept experiment.

When you do decide to try SS device, use same kind as in drive first.

There are several up to date power experts here. State your motor control problem on the Embedded Systems forum. Link it to this one.

They might have other strategies for the problem.

 

Ok I've given it some thought and here's what i would try first:

Your controller appears to be acting as a low side switch already, that's good. I am remotely familiar with these types of controllers and to my knowledge they are constructed of a bank of FETs acting in parallel, mounted to a common heat sink. They control current throughput (or "effective applied voltage" depending how you look at it) via PWM at a fixed frequency (although some may shift the PWM freq to maintain better efficiency through some RPM ranges). That's also good.

So I would continue using the resistor; i would choose the lowest value, highest power resistor that one would select for a multi-contactor "stepped" shunt resistor selection. I would wire from M+ on the controller to the armature, then from the armature to the field, and then from the field to M- on the controllef, putting the field on the low side of the circuit. Then i would connect the resistor between armature and field, and from the other side of the resistor to a beefy FET, and from the fet to ground. Then i would tap into the controller's gate drive circuit to get its PWM signal (so that the resistor's PWM will always be synced with the motor's PWM).

Now you need to design a simple circuit which goes between the controller's gate drive circuit and the resistor FET, to adjust PWM duty cycle independent of the controller's duty cycle. Once you do that, you have effectively created a "variable resistance" in parallel with the field (more accurately a variable current shunt) without all the pain and anguish of trying to operate FETs in linear mode. Also on it gives much more freedom with respect to heat sinking; trying to dissipate all that power from little semiconductor packages with frying them would be tough. However heat sinking a dumb resistive load should prove much easier.

Assuming for a minute that what has been said about IGBTs and/or FETs being destructive to motors is correct (which i still do not believe ), this arrangement should alleviate that concern as you will be controlling a resistive load and not the motor.

 

Ok, first off, I'm not really qualified to speak to the microprocessor controlled systems you are contemplating but I have an old school idea that may be of interest.
A form of resistance element that increases in resistance over a period of a few seconds AND has approx. the right value of resistance to work with the DC motor windings can be found in an element from an electric cook top or in submersible type water heater element.
Just a thought I think you could investigate. Small, cheap and rugged too!