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wrongprotocol
04-29-2009, 07:44 AM
Hey, first post here on these forums.

I recently started a Lawnmower/fertilizer-rover project but ran into an issue finding a motor/gearbox combo that will work with my setup.

I seem to like phidgets because it removes the electrical engineering component and allows us software engineers to just dig in :veryhappy:, in practically whatever language we want. it's also very easy to integrate into commercial app!

For previous (smaller) projects, I have been using the phidgets 8/8/8, servo-controller and high-current motor controller. If possible, I would like to use the same motor controller for this project. I have just been having trouble finding a motor/gearbox combo that would be suitable. I am also interested in using the phidgets high-speed-encoder to keep track of wheel position + speed.

I thought I found the solution with the parallax MotorMount and Wheel Kit with Position (http://www.parallax.com/Portals/0/Downloads/docs/prod/motors/27971-MotorMount-v1.0.pdf)

but after speaking with Alex @ Trossen for a while, he said I would not be able to use that kit w/ phidgets (the encoder signals are not compatible). He also said he did not think it would be able to push this heavy rover (max 100lbs with batteries and fertilizer-spreader and all the other goodies).

Edit: I have seen this project done a few times times with wheelchair/powerchair motors, but since I'm lacking the electrical understanding, I am not sure if those motors will work with the phidgets components.

Anyone have any suggestions?

Thanks in advance!

-Carmine

lnxfergy
04-29-2009, 08:08 AM
You mention 100lb weight for the robot -- thats really big.... add a cutting deck and that's really dangerous.. anyways - what kind of yard do you intend to mow? The motors required for a completely flat area will be significantly lighter duty than those required to scale a 35 degree incline.

How do you plan to navigate? Are encoders really necessary?

I think you will likely end up wanting something in the ballpark of wheel chair motors, current anywhere from 15-75A at stall... WAY more than the phidgets will handle.

-Fergs

wrongprotocol
04-29-2009, 08:21 AM
Hey Fergs,

Thanks for the reply,
the 100lb weight is a predicted max weight - the deck is built ontop of the lawnmower. I removed the wheels from the mower, build an angle-iron frame around it and [this part isn't done yet]plan to attach my own set of wheels to the angle-iron frame. Currently planning for swivel wheels in the front and fixed powered wheels in the back. This will not have to handle anything beyond a slight grade, no big inclines. Just a large area of flat land.

I will hold off on autonomous until everything works fine with R/C. Over the weekend i wrote some code to control a minibot along with a pan/tilt webcam with a logitech joypad over wifi. I also put in some sonar + IR rangefinding but I wont be using that until autonomous.

I went wifi because it's what I already have. the bot (as of right now is not a lawnmower, but just a rover) has a laptop on top with the phidgets stuff and webcam connected. I run the phidgets web interface on the laptop, and I encode and stream the video.

The rest of the processing is done on the computer in my house. I chose java as my language because I can prototype very fast in it. I can currently drive the small test-bot via my gamepad, see the sensor readings, and view streaming encoded video (with a .1 sec delay but that's good enough for a lawnbot).

If all goes well, I will add some simple autonomous logic. There isn't much to hit in this yard, it would just be important to cover all of the ground area.

Alex
04-29-2009, 08:25 AM
I think you will likely end up wanting something in the ballpark of wheel chair motors, current anywhere from 15-75A at stall... WAY more than the phidgets will handle.

It really depends though Fergs. If there is a PWM driven motor controller that can handle higher Amperage (ie. BaneBots has a 45A peak (http://www.trossenrobotics.com/store/p/4267-BaneBots-Motor-Controller-45A-peak-.aspx), but it's only 12A continuous), then you can easily hook it up to a Phidget Servo Controller. I'm saying "if" because I have no clue if there is one or not. I'm a little out of my element with this one, but I still wanted to throw the concept out there:)

wrongprotocol
04-29-2009, 08:48 AM
side question: 7 years ago, junior yr in highschool, we had a FIRST robotics team. Our bot was heavy, and we had used the powerwheels motor/gearbox. it didn't have to tread through grass but it had No problem moving that bot. I havn't done any with FIRST since then, so im not sure if they are using the same motor/gearbox kit. Anyone know about that? Would that be compatible with phidgets motor controller?

lnxfergy
04-29-2009, 08:50 AM
It really depends though Fergs. If there is a PWM driven motor controller that can handle higher Amperage (ie. BaneBots has a 45A peak (http://www.trossenrobotics.com/store/p/4267-BaneBots-Motor-Controller-45A-peak-.aspx), but it's only 12A continuous), then you can easily hook it up to a Phidget Servo Controller. I'm saying "if" because I have no clue if there is one or not. I'm a little out of my element with this one, but I still wanted to throw the concept out there:)

Sorry, I meant to say "phidgets motor controller" not phidgets in general. I'm sure there are servo-signal driven motor controllers that can source 20-30A continuous and 75A stall... look towards battlebot stuff.

-Fergs

lnxfergy
04-29-2009, 08:53 AM
side question: 7 years ago, junior yr in highschool, we had a FIRST robotics team. Our bot was heavy, and we had used the powerwheels motor/gearbox. it didn't have to tread through grass but it had No problem moving that bot. I havn't done any with FIRST since then, so im not sure if they are using the same motor/gearbox kit. Anyone know about that? Would that be compatible with phidgets motor controller?

The bigger powerwheels *might* be able to carry 100lbs for an extended time... but with a shortened life (especially when you add treaded wheels). That said, those motors are really cheap and thus inefficient... so shorter runtimes + higher current (still higher than the phidgets motor controller can handle most likely).

Alex had a good call on phidgets servo + servo-pulse motor controller...

-Fergs

wrongprotocol
04-29-2009, 09:05 AM
If there is a PWM driven motor controller that can handle higher Amperage (ie. BaneBots has a 45A peak (http://www.trossenrobotics.com/store/p/4267-BaneBots-Motor-Controller-45A-peak-.aspx), but it's only 12A continuous), then you can easily hook it up to a Phidget Servo Controller.

I'm a bit confused - why a servo controller instead of the motor controller? can it handle higher current than the 'high-current motor controller' ? or is it because it can send data?

I have been calling around asking about the wheelchair motors to get an idea of price and if they are even available. But I still face the problem of figuring out how to use it with the phidgets. I dont know enough to integrate the banebots speed controller with one of the the phidgets devices.

Alex
04-29-2009, 09:50 AM
I'm a bit confused - why a servo controller instead of the motor controller? can it handle higher current than the 'high-current motor controller' ? or is it because it can send data?

I have been calling around asking about the wheelchair motors to get an idea of price and if they are even available. But I still face the problem of figuring out how to use it with the phidgets. I dont know enough to integrate the banebots speed controller with one of the the phidgets devices.


There are several ways of controlling a DC motor. One way is like this:

http://www.trossenrobotics.com/images/SubCatImages/USBPWMMotorControl.jpg


This setup uses two controller boards. You have a servo controller and a DC motor controller. The DC motor controller needs signals from the servo controller (PWM or pulse width modulation) to control the speed and direction of the servo.


From the Motor and Servo Controllers page (http://www.trossenrobotics.com/store/c/2664-Motor-Servo-Controllers.aspx):


Controlling a DC motor (http://www.trossenrobotics.com/store/c/2882-DC-Motors.aspx) from a computer is best done as a two stage process. Servo controllers (http://www.trossenrobotics.com/store/c/2665-Servo-Controllers.aspx) output a PWM signal which the DC motor controller accepts. This allows a developer to custom build a solution for their needs much easier than trying to hunt for the perfect integrated solution. A servo controller can be chosen that has the type of connection and API needed while a DC motor controller (http://www.trossenrobotics.com/store/c/2666-DC-Motor-Controllers.aspx) can be selected separately to match the motors being driven.

lnxfergy
04-29-2009, 09:51 AM
I'm a bit confused - why a servo controller instead of the motor controller? can it handle higher current than the 'high-current motor controller' ? or is it because it can send data?

I have been calling around asking about the wheelchair motors to get an idea of price and if they are even available. But I still face the problem of figuring out how to use it with the phidgets. I dont know enough to integrate the banebots speed controller with one of the the phidgets devices.

The idea is this: the servo controller takes input from your computer and outputs a signal (low current, low voltage), that then is input into a motor controller. Where a hobby servo would normally turn this signal into a position output, the motor controller takes this signal and instead turns it into a motor speed. The servo controller doesn't even touch the motor, just sends a signal to the motor controller (since the motor controller lacks the easy-to-use USB interface you seek with the phidgets)

EDIT: alex beat me to the punch.. so.. yeah, what he said!

-Fergs

robologist
04-29-2009, 09:58 AM
In refernce to above, there are a number of high current motor controllers that accept a servo pulse as a drive signal. So the use would be to have a phidgets servo signaller control a third party battlebots type h-bridge to drive something like wheelchair motors. I made a quick survey of NPCRobotics (http://www.npcrobotics.com/products/index.asp), which sold wheelchair motors to the battlebots folks, and their motors were typically 24 volt, and had stall currents from 60 to 200 A. I'm thinking that Fergs was pretty close on estimating current, most would be in the 60-80 A range. Now the Phidgets HC motor control you have does appear to be meant for 12 volt operation, so if you take 24 volt motors and run them at 12, that also halves their current draw. So your 60-80 Amps becomes 30-40, almost getting close to the Phidgets HC. If you can make some sort of cut off circuit, fast blow fuse, or whatever, you almost might get by with it. But it would seem to be cutting it a bit close (pun intended).

Edit : ok, fine so everbodies awake this morning and ahead of me.

wrongprotocol
04-29-2009, 10:16 AM
sweet, i really appreciate all this info.

Thanks a lot! The servo controller -> speed controller seems to be the route I want to take. I'll look into trying to find maybe a 12V motor instead of the 24. If I can't, I will try what robologist mentioned.

Thanks again guys! I'll keep you posted!

Adrenalynn
04-29-2009, 10:36 AM
I use the RS80D motor controller, and the RS160D on another project. 2x80A and 2x160A @ 12-48v+. PWM driven, 2.5 channels each. Big nasty crazy motor controllers made for combat robots. Tougher than you'd ever believe, and intended for R/C. Plug 'em in and go.