Newbie: Using 24V wheelchair gear motors with the propeller?

Carlos Villegas

Dear colleagues,

I, once again, turn to this invaluable resource to get information on what is a very new topic for me, robot building. FYI, my background is software.

I bought the propeller educational kit to get my hands on the hardware of this incredible chip a while back.

My goal is to build a little robot for tough terrain (i.e. easy there, no so tough, just the backyard) inspired from the book "Build your own all -terrain robot" by Brad Graham and Kathy McGowan.

Here's my immediate question (but please feel free to give advise to somebody that needs it and is listening/reading at %110):

Once I buy a pair of 24-Volt gear motors,

a) Do I need to get an H-bridge for the gear motors?

b) How do you get a PC application to control the gear motors (i.e. is the H-bridge and/or propeller chip involved)?

As you can see I'm a little lost but I'm eagered to learn and willing to do practically anything to reach my goal. Took and electronics class last semester and have a soldering station.

Any help will be immensely appreciated.

Sincerely,
Carlos Villegas

Mike Green

a) You need some kind of switching circuit to control the power to the motors. If you want them to be reversible, you need something like an H-Bridge. You can do this with relays as well as with switching transistors (if you're not in a hurry). If you want to control speed, you need something like a transistor switch. If you want speed control and reversibility, you really need an H-Bridge.

b) You still need some kind of switching arrangement. If you want speed control, you need some hardware to do PWM (pulse width modulation). That can be a Propeller or a Stamp or SX microcontroller or other logic circuitry. To control this from a PC requires some kind of interface, probably USB to serial or USB to parallel or USB to HID (human interface device) that's connected to your control circuitry. If it's not a USB to serial adapter, you may need a bit of programming on the PC side. If it's a USB to serial interface, the PC software side is a bit easier and you have more choices of software you can use for development.

rjo_

Carlos,

The HB-25 is perfect... works exactly the way it is supposed to and doesn't much care what motor you hook up. No fancy code either. Just flat out works. The only problem is the voltage, which is nominally rated at up to 14 volts. But knowing the engineering at Parallax... I wouldn't be surprized if it worked just fine. If it were me... I'd just hook it up and see... but I like excitement!

I'll scrounge around for a similar motor and do a fried egg test. Or... I could send you one of mine ... if you promised to video the experiment!!!

Rich

Carlos Villegas

Mike,

Thanks for the information. It points me in the right direction.

Based on the information you've provided me, I've created my understanding of how things are connected (component diagram). See if you can see the attachment included in this post to answer a question I have about still needing a microcontroller.

c) It seems that a USB-to-serial interface is the best way to go. So my PC app will connect via USB to a microcontroller?

d) With a USB-to-serial what software choices are available. I ask this just to make sure I'm on the same page.

e) Any good, easy and not-to-expensive microcontrollers you recommend?

Carlos Villegas

Rich,

Is the HB-25 an H-bridge or a microcontroller or a little of both? It really looks good from a technical point and is getting good reviews too.

I'm a little concerned that I'll burn it if I attach 24V to it. Which now I understand why you want the experiment videotaped.

My 24V gear motor for testing is on its way !!!

Paul Baker

The HB-25's max rated voltage is 16V, so it wont be able to drive your wheelchair motors at thier rated voltage. If you are capable at underdriving them (most DC motors do at a lower speed) you could use the HB-25 if the continuous current is less than 25A and the surge current is less than 35A, if this is exceeded the fuse on the HB-25 will blow and require replacement.

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

bennettdan

Carlos,
I have used these motor controllers for wheelchair motors before
http://www.ifirobotics.com/victor-883-speed-controller-robots.shtml
they run on 24vdc and they can be ran by the Propeller, BS2, SX and they interface just like a RC servo.

Carlos Villegas

bennettdan,

Wow, so the Victory 883 will do it! Excellent. Thank you very much for pointing this out.

I'm going to assume your name is Dan, if it is not, please excuse me in advanced.

Dan, so what's the easiest way (and economical, I know, I know, I'm asking for too much) to produce a PWM signal to feed the Victory 883?

Note, I have the propeller development kit already. Is there an example PWM spin program that is compatible with the Victory 883?

Your hungry-for-information (and humble) robot·newbie friend,

Carlos

Mike Green

If the controller mentioned by bennettdan really accepts a servo control pulse (like the HB-25), you can use any of the several servo control library objects for the Propeller. There's one in assembly that can handle 32 servos and one in Spin that can handle 4. Check out the Propeller Object Exchange library which you can reach from Parallax's main Propeller page (look on the right side of the page for the link).

bennettdan

Carlos,
It is Dan and I have not used the Propeller much but have used these with the Stamps·and the propeller should work even better.
How do you plan to tell the Propeller to control the 883, computer control (wireless) or a input like a Pot?·Maybe we can answer with better details.
Also do you know how a standard RC servo works if not you can get a good ideal how it works with the WAM textbox from parrallax it is written for the Basic Stamp 2 but has a good section on how to control the servos this will get you up to speed on the control of servos, which the Victor 883 uses the same wiring and signals to control as a standard servos that way you could use it in a RC application.
http://www.parallax.com/dl/docs/books/edu/Wamv2_2.pdf
This is the link to the WAM text look for the Servo control section.

Post Edited (bennettdan) : 6/20/2007 2:24:59 AM GMT

grindel

The easiest way for me to control motors using a PWM signal driving a Electronic Speed Control was to get the parallax servo controller, it required no knowledge of programming to get started. I also learned some programming to control it. Now I am slowly growing into micro controllers for object avoidance...although right now I still need to experiment to safely interface with the prop.
www.parallax.com/detail.asp?product_id=28823
$40...not too bad.

Hope that helps

Carlos Villegas

Dan,

First of all, thank you for: http://www.parallax.com/dl/docs/books/edu/Wamv2_2.pdf I've found it to be in very helpful learning tool on how the pieces fit together. It also was helpful to know that I the motor I plan to drive can be controlled similar to a servo, right?

With respect to your questions:

How do you plan to tell the Propeller to control the 883? I want to control it from a computer (onboard the mobile robot). By the way, what is "input like a Pot"? I want to power the system with a 24V of battery.

Carlos Villegas

Carlos Villegas

Mike,

So based on the previous post by Dan, does it sound like the Vicotry 883 accepts a servo control pulse (like the HB-25)?

Carlos Villegas

Carlos Villegas

grindel,

Wow, that certainly qualifies as an inexpensive solution to produce PWM.

Would the Parallax servo controller (www.parallax.com/detail.asp?product_id=28823) be compatible with the Victory 883 Motor Control?

I apologize if this question just doesn't make since... I'm learning as I go.

Yours truly,
Carlos Villegas

Mike Green

Carlos,
I looked at the 883's datasheet and it seems to accept a standard 1-2ms servo pulse. The Parallax Servo Controller would work with that as well as the Propeller. They sell some kind of adapter cable for controllers other than their own. I can't figure out what this cable does though. Maybe you can call or e-mail them to find out.

Post Edited (Mike Green) : 6/20/2007 4:42:21 PM GMT

bennettdan

Carlos,
The 883 controller is actually controlled just like a regular Forward and Reverse motor ESC (electronic speed controller) on RC cars it accepts the same pulses that a servo would so you can hook the 883 into a RC car reciever and then control your motor that way but the propeller can output the same signals to control servos, ESCs and the 883. The motor controller converts the signals into a PWM output that varies the voltage and polarity to the motor for speed and direction control.

Mike Green,
I use a standard 14" servo extension cable to link my 883 to my Stamp but I think the pinout is not the same as a regular servo and I had to swap two of the pins out of the extension cable so it would be the same as the standard servo I think they made the wiring on the 883 different so they can sell you the Cable.

Carlos Villegas

Thank you everybody for your help on this subject. The discussion contain herein has been of most value to me and hopefully others.

My Servo Controller is on it's way. And soon I will complete all the parts to start embarking on the wonderful journey of robot building [noparse]:)[/noparse].

Most sincere thank you to Mike, Dan, grindel, Paul and rjo_.

Carlos Villegas