Know of any medium range drive systems for robot ?

I have found alot of small motors and gearboxes and alot of large expensive motors and gearboxes.
The small controllers ($15) only do like 2 amps and the large
controllers are like $300 the small motors are a $10-20 and the large ones $160 with gearbox.
So im stuck with $30 or a $460 drive system, i need something in the middle.
My robot will be relativly heavy (100lbs) but no need for speed, an inch or two a second will be enough. I do need accurate stearing, as my arm will have no rotation, instead rotate using the entire robot.
I would really prefer a tracked system, but i dont see any of those either.
So if you have any good links, please share them :-)
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Well, I'd say that $160 is still cheap. It is really a problem finding powerfull motors that are accessible pricewise. If your application allows for scavenged parts, you may want to create one or two search agents on ebay. It is hard, but I found one 12V DC motor with gearbox and controller (about 40rpm final) for $10 shipped. I was amazed that it worked when I got it.
Cheers
Padu
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On 6 May 2006 14:17:31 -0700, snipped-for-privacy@gmail.com wrote:

You might want to look at the children's electric riding toys for parts. You might find some of these at the goodwill, salvation army thrift stores, yard sales and such. Cheap variable speed battery powered drills from places like harbor freight might be of interest if you need the wheels to be independently operated.
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On Sat, 06 May 2006 23:49:51 +0000, Si Ballenger wrote:

1) cheap 2) on time 3) meets specifications
pick any two
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Know of an affordable controller that can power cordless drill motors ? I have actually already taken apart a harbor freight drill (had one). I am not really a electronics man (may be by the time my robot is done). I have thought of using a servo to control the variable speed, but im not sure if that would be exact enough.
It does come with HRFZ44N (transistor ?) on a heafty heatsink. I looked it up and its a : 49A, 55V, 0.022 Ohm, N-Channel UltraFET Power MOSFET Anyone know why its in there, and if/how i can use it ?
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On 7 May 2006 11:28:12 -0700, snipped-for-privacy@gmail.com wrote:

I would think you could actually use one of the small controllers to drive the power MOSFET in the cordless drill.
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Do you know how ? I dont know much about electronics. The mosfet has three wires. Cant be too difficult ? Is it just a power amplifier ? Im going to do some searches.
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snipped-for-privacy@gmail.com scribbled:

In this case it isn't really an amp. It is a simple switch that allows for higher power passthru than a generic transister. a signal on the gate allows current to pass from the collector to the emitter.
Transisters are really only amps at extremely low voltages. Above a certain voltage on the gate and they become solid state switches.
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On 7 May 2006 20:05:23 -0700, " snipped-for-privacy@gmail.com"

Assuming every thing is commonly grounded, it could be as simple as connecting the output of the small controller to the base of the MOSFET.
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Here is my new plan, two 343 oz-in servos modified for continuous rotation (these have 2 ball bearings). I will attach a sprocket to the servo wheel, and the drive wheels, and use about a 2:1 teeth ratio to double the torque. The wheels will have ball bearings and mounted on a single fixed axle.
That should be 686 oz-in at 30 rpm. Course have to divide that 686 by 6 for six inch wheels ... thats 114 oz at 6 inches right?, thats almost 10 lb of force ? It should move like 10 inches / second travel max, right ?
My robot will be 50-60 lbs.
If this sounds sane, does anyone know where i can get sprockets for servos.
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I have found the wheels at Northen Tools "2-Pc. Split Rim, Hub, 60T Sprocket Wheel Assembly - 10.5in. O.D." with ball bearings. All i have to do is mount a #35 sprocket to the servo wheel(thinking JB Weld), and mount the servo to tension the chain.
I know the sensor array I want to use, plan on using two laser pointers one pointing straight ahead (of the camera) and one on a servo. When i want to measure a distance, I will start moving the mobile pointer until the vision system only sees on red dot, then calculate the distance. A^2+B^2=C^2. Think it will work ? All this and the camera will be mounted to a pan and tilt mechanism.
I am still debating on the arm system to use. A lynxmotion arm would be easy and pretty nimble, but very weak. A custom arm would be slow and probaly only have one degree of freedom (plus bot freedom), probably just up/down and pinch. But it could do 10 pounds (or more). Maybe Both ! But which first ?
I really want to get to the software side. I havent been much into hardware in the past.
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On 9 May 2006 16:08:12 -0700, " snipped-for-privacy@gmail.com"

I suspect you will break the servos and be out the $$ as they probably can't handle the shaft side load of driving the chain sprocket if directly connected. If you want a cheap strong little geared motor you can get a 6v B&D cordless screwdriver at walmart for ~$7.
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My desires for using a servo are i can use the ssc-32 servo controller i already need. Servos can do forward, backwards, proportional movement internally.
The servos i have in mind for the drive are hs-805BB dual ball bearing. They pull 1.2A max. They cost $40 each. I can buy metal gear sets for them if they do strip out for $20.
If i use motors, i will have to get some kind of controller for them with a RS232 interface. Then get a power controller. Then get the motors, then get the gearboxes, and get it all to work. While some of the motors come with gear boxes and even wheels, the cheapest Ive seen are $160 and they are relatively high speed. (14ft/sec) I only need an inch or two/sec.
I looked at the controller mentioned, and its 1/3 the price ive seen for large ones but still $100 (with speed control extra ?).
To make things worse i dont understand electronics, and dont understand how a h-bridge works or how to make one porportional, so i cant do it mayself.
I think ill just try the servos, if they dont seem strong enough, ill use them for the arm or accessory.
What I need to do it with motors is a motor controller that takes servo input and porportionally controlls the motor. then i could use some cordless drills.
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On 9 May 2006 18:18:39 -0700, " snipped-for-privacy@gmail.com"

The below link has inexpensive motor and servo controllers that probably can be connected to the same serial port. You should be able to have the motor controller drive the MOSFET transistor in a variable speed drill.
http://www.pololu.com/products/pololu/#motocon
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Everyone thanks for the advice. I have ordered my parts. I am going to try the servos first. But since my wheels will use chain/sprocket, i can change my plan easy. I will probably move to cordless drills with a controller. I was thinking maybe the scc32 can 'drive' a motor controller too since it says its output is servo/TTL ? I may have to learn more about electronics also. Worst case i end up with two extra MEGA-SERVOS ;-) Sure i can make use of them ;-)
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Status report:
frame constructed, wheels mounted. pincher ... pinching
I am about to mount my drive servos, i believe that they will work excellent so long as i dont have to go up steep inclines or run 'over' stuff. The large (11.5") wheels have ball bearings, and while on carpet the slightest force to the sprocket on the wheel generates movement. I have modified one servo to continuous rotation (805BB), it has a tab you can remove around the POT, and i cut the anti-rotation tab off. the POT is adjusted for standstill at 1500, and the servo reassembeled. The servo provides an amazing amount of torque, easily enough to move the robot on hard or carpeted flat surfaces. It also turns proportionally with the difference of the PWM. Being the wheels themselves are half the weight so far, makes the robot pretty stable, about like a table. :-)
At first i tried to hot glue the servo wheel to the metal sprocket, but hot glue wont stick to the metal. So im gonna go back to the original idea of JBWelding it on, better make sure its right, cause i doubt ill get them apart. Ill post back later and tell how well he moves with it all.
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Just letting you all know, the servo works fine, it has enough torque to run over my foot, although running over a foot makes a two wheeled robot very tipsy ! I hope the servo lasts my experiments. If not i have found places to buy new gears ~$2 or metal gears ~$20. They can go from a snails pace to a pretty good speed. At the lower speed the robot will stop when it run onto something (like a screwdriver) but if you up the PWM it will run over stuff up to a couple inches although it really jerks when it comes off !
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I am working on a problem a lot like this one. I decided to go with a bigger drive system (350 W electric scooter motors @ ~$20 and HB 25 @ $50).
Here is a good site for finding parts:
https://sdp-si.com/eStore /
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snipped-for-privacy@gmail.com wrote:

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Although the servos work as well as i could have hoped so far, thanks for the ideas for version 2, or maybe a retrofit. But knowing how much torque and speed the servos can generate, i would be afraid of seriously breaking something with larger motors.
I guess your using two HB-25s ?
snipped-for-privacy@earthlink.net wrote:

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On Sat, May 06, 2006 at 02:17:31PM -0700, snipped-for-privacy@gmail.com wrote:

Take a look at our new RX50 h-bridge - it might be just what you are looking for:
http://www.bdmicro.com/rx50/
These h-bridges are designed to run in the 30 amp range. What voltages are you looking to use? Note that by using higher voltages you can handle the same amount of power at lower current. This allows you to use smaller wires, connecters, etc and handle the same amount of power delivery.
-Brian
--
Brian Dean
ATmega128 based MAVRIC controllers
  Click to see the full signature.
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