Russ, you might want to test your BEMF system on locos with dual or more motors. Some systems have trouble with this, although they are often trying to “count” the transitions of commutator segments to get the true motor rpm, which is confused with 2 or more motors in parallel.
Regards, Greg
Thanks for the advice. You confirmed my first locomotive choice for testing which is the Aristo SD-45 with 4 motors. It works pretty well but I’m not trying to set exact speed based on the BEMF, I’m only insuring low speed operation. I knew that trying to determine RPM using BEMF from motors in parallel would be difficult and the circuit I made doesn’t have the resolution for it.
I’ve held the wheels when set to low speed and they will fight me to continue turning. With that locomotive I need to be careful not to get my fingers caught OR break the drive train. It’s very powerful. With BEMF maintaining low speed, I can turn up or down the main power supply for the track and it doesn’t affect the locomotive speed at all. I can’t wait to get the first prototype in the locomotive so I can run it with a bunch of cars behind it all at a nice steady crawl both up and down some large grades. I’ve basically incorporated PID closed loop control at low speeds. When it is running above a definable throttle setting I turn off BEMF measurement.
Right understand about not setting exact speed, so I guessed it’s not an issue with your design.
I will be interested to follow your progress… good luck to you.
Regards, Greg
What I do to measure Back EMF is turn off the motor controller’s PWM input. Reverse the direction lines. Then I measure the current sense line which normally tells me how much power I’m putting into the motor. Then I go back to powering the motor. When I run it in reverse with the PWM off it measures the motor’s output, which is small but measurable. Because I’m not counting pulses I don’t need to have the motor power off for very long but still get a useful reading. This gives me the minimum for realistic crawling but doesn’t induce motor noise like some other BEMF controllers.
I’ll add a receiver software switch that turns on and off the BEMF function because it may not work for some locomotives as you pointed out. It seems to work well in my testing so far though. I finally decided to pursue this and got the basics working in one evening! By tomorrow I’m hoping to have the first prototype running but since I started from scratch on the receiver it usually takes a bit of time to rewrite the radio protocols on new hardware.
Thought I would post a quick video showing Back EMF that enables crawl. Here is a demo of my test SD-45 (half disassembled) crawling along using the prototype board. The installable PC boards are coming Thursday. I can’t wait!
This evening I decided to take the prototype board in the SD-45 and plug it straight into my little Bachmann 2-4-2 switcher with a single motor. I had no hope of it running without tweaking the code as well as a lot of variables. Remember, this is early development still.
To my surprise not only did it work with no changes to variables, let alone code, but it very closely matches the SD-45’s speed in the first 3 throttle settings. This is very good news as the speed table routines do little at those low speeds. It looks like MU between very dissimilar locomotives will be possible.
Tomorrow I get the PC boards so I can do some real testing, including accessories. The next thing will be to see how the Dallee diesel sound board acts when the motor is being controlled with BEMF. I hope it doesn’t act strangely.
Here is a real train operation, low speed shunting. Aristo couplers aren’t as smooth as I would like but it works.
http://www.youtube.com/watch?v=Lw7XaC6_Ves
It is really working pretty well. I’m seriously thinking about making up a kit. Let me know what you think.
I’d be interested. Do you have a price point yet?
I would like this to be an open-source effort so it will be cheap. I need to cover any costs I have but, right now, the hardware cost for the transmitter with LCD display is about $120. I definitely want to make the software open source for this part of the application. The cost in parts for each receiver including a 30 amp motor controller is less than $80 and that is my current low quantity receiver board costs. The majority of the receiver price is the 30 amp motor controller.
It provides simultaneous control of 32 locomotives with 6 accessories and 100 non-locomotive (on/off) accessories primarily directed at turnouts and lighting. I have recently added Back EMF as the video shows and full control of 6 accessories including latched/momentary and default on/off. I also added speed tables to match speeds of dissimilar locomotives in hopes of adding MU capability next week. Each new feature takes me about a week so far assuming I maintain my current pace.
I will probably add a channel feature to allow you to take locomotives and transmitter to group gatherings where someone else may have a similar control. Because it will be open source I’m hoping others will develop for it in the end but I need to get it a bit further along first.
If parts were purchased in quantity the prices could be considerably less.
Looks interesting, Russ.
It will be a few years before I will be converting to R/C.
As a low budget operation, alternatives are always considered.
Ralph
I have my first run at MU consisting working now. It requires physically setting up each locomotive using the setup switch but default direction and low speed crawling is completely configurable. I’m working on a method to allow PC upload of the speed tables to match locomotives. During the physical setup the locomotives in the consist are all given the same address. Loco setup takes no more than 20 seconds assuming the speed tables are already done. Figuring those out takes a while! I’m hoping to make an interface to load them easily at least.
At some point I may add on the fly consisting, allowing creation of locomotive groups. I would need to handle default direction for each locomotive while in the consist in the transmitter. I’m going to do consisting manually for a while to see how much interest the folks here have in it.
I set up part of the overall speed table for my Aristo RS-3 and SD-45 to work together. What wildly different locomotive speeds they have! Is the latest RS-3 version geared so high? The RS-3 is at least 2x as fast as the SD-45 at top speed. The RS-3 speed curve isn’t very linear either. I do have it creeping along with Back EMF though. For its weight it can drag around some cars at low speed now.
I’m going to equip my Bachmann 2-4-2 switcher again. It seemed to have a speed range and curve much more like the SD-45. That would look funny in a consist but what the heck. If that one goes well I guess I’ll start converting over all the locomotives I have.
My plan was to have speed tables completed by the weekend. I got it done! It is possible to enter in min and max with 4 additional points in between to create a custom, six point speed curve. Then you can transmit it to the individual locomotive via radio. It works great. I am able to join up my SD-45, RS-3 and Bachmann 2-4-2 steam engine together and have them operate together.
I am going to do a lot of testing on various friend’s railroads but I think I all the core development work complete.
I will see what people ask me to add now. BTW, the Bachmann switcher can run so slow that its wheels look more like a clock work, taking 5 minutes for a single revolution when I really slow it down! The multi-motor diesels are slow but not that slow! Now that it is running on the track it will actually spin the wheels at that slow clock speed when I couple it to a stationary object.
Here is a slower shunting video using the rough running Bachmann 2-4-2. I will warn you, the locomotive is running slow so it is a bit tedious to watch:
http://www.youtube.com/watch?v=Ze2J7dilVIo
So far I can easily adjust any locomotive I have tested to operate at a similar slow speed and still have all the normal throttle range with a smooth transition between all speeds.
I hope to have some additional video from testing at a friend’s railroad this weekend. It will be 100% battery power. Should be interesting!
That is admirable slow speed performance!
Regards, Greg
A buddy loaned me an Aristo FA with the DCC plug (2007 vintage) and with a little playing with the variables I have it running pretty slow as well. Not quite as slow as the Bachmann but nice. The RS-3 and FA perform the same even though they are about 10 years apart in manufacture. The FA did require some rewiring to fix factory errors, the front MU connector was wired to the speaker lines on the main board, the speaker simply wasn’t wired, which was good as it would have been connected to where the MU should have been and burned up on first use of battery.
With all the talk of MU consisting on the fly from other people, I guess I will look at adding that to my RC as well. Everything else is working nicely. I just received some four line LCD displays that will significantly increase the amount of information I can display on the transmitter. I may look into adding custom engine names rather than just loco numbers.
The transmitter now supports 8 character engine names as well as an additional four digit number. I changed the display layout so that in normal operation both lines are dedicated to engine operation. When non-locomotive accessories are selected the second line changes and they can be modified. All while still maintaining basic control of the current selected locomotive (or consist). Early next week I will have the prototype boards designed for the transmitter. Everything will easily plug together, LCD, keyboard, processor, encoder and push buttons. Here are a few screen shots of the transmitter: Pennsylvania SD-45 locomotive being controlled (bell on):
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/sd-45_screen_shot.jpg)
Shot of antenna flashing during transmit:
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/sd-45_transmit_screen_shot.jpg)
Pennsylvania RS-3 locomotive being controlled (whistle/horn on):
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/rs-3_display_screen.jpg)
Accessories being controlled while RS-3 locomotive is still running:
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/accessory_display_screen.jpg)
Here is a picture of the new transmitter pcboard. Makes it very easy to plug in the LCD and keyboard. The two switches, encoder and power are all simple plugs as well. There are RS232 drivers onboard for connection for both programming as well as PC interface for AI railroad control. These pictures just show one driver installed. The case is a $4.99 Radio Shack project box (6"x4"x2") to give some scale. The cover with transmitter board:
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/HPIM2983.jpg)
The cover removed, showing all wiring:
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/HPIM2982.jpg)
I wish I could find a cheap project box that had a 9V battery compartment! I need to secure the battery for normal use. Perhaps a velcro strap screwed/fastened to the case. The project box does have a dividing panel at the bottom that should work well.
I decided to add a battery compartment by placing a metal divider panel. I put electrical tape along the edge since it was sharp. I would have rather used plastic but I didn’t have a piece handy. Here is a picture:
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/HPIM2988.jpg)
Here is a picture of the front with a face lift:
(http://i68.photobucket.com/albums/i27/rmcintir/Robotics/HPIM2987.jpg)
Looking good Russ. I enjoy your posts, but don’t understand most of them!
I’ve been following your progress and I like what I have seen so far. Looks to be simple to operate. Any idea on when it will be available yet as either a kit, boards or complete?
Thanks.
