Worst case scenario you could connect two together and run them off one board.· Or you could use tank-treads instead and use the existing drive-system minus the wheels.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Chris Savage Parallax Tech Support csavage@parallax.com
No, I meant actually connect two Sumobot chassis together...The Servos could run off other I/O pins and you could parallel the two power sources to double your capacity.· Of course, this would make the Sumobot larger than the regulations allow so...
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Chris Savage Parallax Tech Support csavage@parallax.com
Note the nice thing about having two wheels and a 'dragger' ball is that you can steer by driving the wheels at different speeds. When you add 2 more wheels, now you may have to steer the 'front' two wheels -- trying to 'drag' them from side to side to steer gets much harder.
I suppose that more depends on whether the additional pair of wheels are powered or un-powered. If one designs the side-pairs to operate in tandem, there really shouldn't be too much "drag", I wouldn't think.
If the front motors are linked mechanically (by mini-chain or belts) to newly installed rear wheels, then it can even be done with just two motors. I've seen miniature ladder chain used very successfully in this kind of operation on a lightweight, low speed robotic platform.
When the wheels are powered in tandem you essentially have "skid-steering".· Dave here in Tech Support has two BOE-Bot chassis mounted together and all four servos are powered.· It's like tank treads without the tracks.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔ Chris Savage Parallax Tech Support csavage@parallax.com
I was going to make all 4 wheels powerd to that it would give the bot more pushing power. Well thats the idea anyways. I'm just haveing trouble conecting the extra two wheels to the board so that they work. We now have the idea to conect the extra wheels to the white board but I'm programer and I don't know anything about conecting wires·and circuts.
Hmmm... tank track method seems more usable.. crossing lines, the basic VEX robot design, from their own manual, uses 4 'inline skate' type wheels,
driven in differential mode.. each side, being driven by one servo.. (I.e. left side wheels driven by same, right driven by same.)
simply by driving both wheels using a oOo-style gearing, with the center larger gear as the drive. (so both smaller gears turn the same way)
Drawback! even this method, applies major drag to the outside edges of the wheels. it won't always turn. (and, an attempt to speed-up the
robot, applying a chain drive, instead of the gears, required far more torque, than the servo could apply. o=O=o )
Even a tank track method would require a little drag trying to turn sideways. I've even gone as far as to drive BOTH sides of the track assembly,
with the chain drive, to compensate.)
Another crossing of lines, the TAB Sumo-BOT, uses a O-Ring track assembly. (===), with a worm/wheel assembly driving only one side of the
track. I imagine, you could drive the single track assembly off the servo.
Hmm.. I am curious, though.. Why shouldn't you be able to drive 2 servos off the same digital signal? after all, the control signal, is a simple pulsed stream,
and the servos only read the frequency of the pulses.. Time to see if I can pull this off with the BOE, and a couple of VEX motors, to see...
I don't see how, the servos will interfere with each-other. they may run at different speeds. (nature of all mechanical things.) and you may end-up
with one dragging, or pulling on the other.. but, digital signals are always shared, inside a computer. (across different devices, address paths, etc.)
It would stand to believe, you should be able to drive the signal pins of 2 servos off the same signal source.
I guess you could drive two servos from one signal, just keep in mind that sometimes the servos don't have the same rpm...
I'll have to compensate for drift on my VEX servos in my tankbot...
Sending one servo 1000 (2ms) and the other servo 500 (1ms), they are mounted on different sides and therefore rotates in different directions, will not make my bot go straight...
So does two servos with the same pulse really turn at the same rpm ???
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Living on the planet Earth might be expensive but it includes a free trip around the sun every year...
Experience level:
[noparse][[/noparse] ] Let's connect the motor to pin 1, it's a 6V motor so it should be fine.
[noparse][[/noparse] ] OK, I got my resistors hooked up with the LEDs.
[noparse][[/noparse]X] I got the Motor hooked up with the H-bridge and the 555 is supplying the PWM.
[noparse][[/noparse] ] Now, if I can only program the BOE-BOT to interface with he Flux Capacitor.
[noparse][[/noparse] ] I dream in SX28 assembler...
Just for the heck of it, and since the SAME discussion about driving two motors from the same motor line, on the VEX,
(www.vexfan.com , motion subsystem discussion), I decided to take a whack at it.
Since both motor modules (or, in Parallax terms, Constant Rotation Servos) draw their main power from the same
source, they should also have no problem drawing from the single pulse signal. I had a spare servo, and a spare
motor module for the VEX, and hooked them up in parallel. A single pulse signal sent to both, turned the motor
module at a rate of speed, and the servo to a specific position. No problems, and no loss of power, speed, or torque.
I'm now looking to make a 4WD frame, using VEX parts, to make a BOT capable of crossing over rough terrain,
with all 4 motor modules running off the single pulse for forward or backward, and a simple steering assembly for
turning the front end wheels. Kinda like prototyping a Jeep drivetrain, with independant motors at each wheel.
The frame, is actually already built. Using 4 10cm long pieces of 1/4" surgical tube. (clipped a replacement band
pair for a slingshot.) There's my suspension & shock absorber system.
the steering system is still in development.
gelfling,
Where I could see a problem is in the case of two servos being mechanically "slightly different" due to manufacturing irregularities, part differences, wear-and-tear, etc. Depending on your configuration, this could cause binding, excessive wearing, and other "bad stuff" ... without any easy way to correct the problem.
Just a thought...
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Truly Understand the Fundamentals and the Path will be so much easier...
Post Edited (Tom Walker) : 7/14/2006 8:45:37 PM GMT
Comments
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Chris Savage
Parallax Tech Support
csavage@parallax.com
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Chris Savage
Parallax Tech Support
csavage@parallax.com
I suppose that more depends on whether the additional pair of wheels are powered or un-powered. If one designs the side-pairs to operate in tandem, there really shouldn't be too much "drag", I wouldn't think.
If the front motors are linked mechanically (by mini-chain or belts) to newly installed rear wheels, then it can even be done with just two motors. I've seen miniature ladder chain used very successfully in this kind of operation on a lightweight, low speed robotic platform.
The other option of course are "omni-wheels" whcih will offer little or no resistance whether powered or un-powered, if you can stand the monetary "pinch":
http://www.acroname.com/robotics/parts/R98-4CM-POLY-ROLLER-3.html
Regards,
Bruce Bates
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Chris Savage
Parallax Tech Support
csavage@parallax.com
http://www.omniwheel.com/cgi-bin/plugins/MivaEmpresas/miva?plugins/MivaMerchants/merchant.mvc+Screen=CTGY&Store_Code=KCWD&Category_Code=Transwheel2
driven in differential mode.. each side, being driven by one servo.. (I.e. left side wheels driven by same, right driven by same.)
simply by driving both wheels using a oOo-style gearing, with the center larger gear as the drive. (so both smaller gears turn the same way)
Drawback! even this method, applies major drag to the outside edges of the wheels. it won't always turn. (and, an attempt to speed-up the
robot, applying a chain drive, instead of the gears, required far more torque, than the servo could apply. o=O=o )
Even a tank track method would require a little drag trying to turn sideways. I've even gone as far as to drive BOTH sides of the track assembly,
with the chain drive, to compensate.)
Another crossing of lines, the TAB Sumo-BOT, uses a O-Ring track assembly. (===), with a worm/wheel assembly driving only one side of the
track. I imagine, you could drive the single track assembly off the servo.
Hmm.. I am curious, though.. Why shouldn't you be able to drive 2 servos off the same digital signal? after all, the control signal, is a simple pulsed stream,
and the servos only read the frequency of the pulses.. Time to see if I can pull this off with the BOE, and a couple of VEX motors, to see...
I don't see how, the servos will interfere with each-other. they may run at different speeds. (nature of all mechanical things.) and you may end-up
with one dragging, or pulling on the other.. but, digital signals are always shared, inside a computer. (across different devices, address paths, etc.)
It would stand to believe, you should be able to drive the signal pins of 2 servos off the same signal source.
Stephen (gelfling6)
I'll have to compensate for drift on my VEX servos in my tankbot...
Sending one servo 1000 (2ms) and the other servo 500 (1ms), they are mounted on different sides and therefore rotates in different directions, will not make my bot go straight...
So does two servos with the same pulse really turn at the same rpm ???
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Living on the planet Earth might be expensive but it includes a free trip around the sun every year...
Experience level:
[noparse][[/noparse] ] Let's connect the motor to pin 1, it's a 6V motor so it should be fine.
[noparse][[/noparse] ] OK, I got my resistors hooked up with the LEDs.
[noparse][[/noparse]X] I got the Motor hooked up with the H-bridge and the 555 is supplying the PWM.
[noparse][[/noparse] ] Now, if I can only program the BOE-BOT to interface with he Flux Capacitor.
[noparse][[/noparse] ] I dream in SX28 assembler...
/Bamse
(www.vexfan.com , motion subsystem discussion), I decided to take a whack at it.
Since both motor modules (or, in Parallax terms, Constant Rotation Servos) draw their main power from the same
source, they should also have no problem drawing from the single pulse signal. I had a spare servo, and a spare
motor module for the VEX, and hooked them up in parallel. A single pulse signal sent to both, turned the motor
module at a rate of speed, and the servo to a specific position. No problems, and no loss of power, speed, or torque.
I'm now looking to make a 4WD frame, using VEX parts, to make a BOT capable of crossing over rough terrain,
with all 4 motor modules running off the single pulse for forward or backward, and a simple steering assembly for
turning the front end wheels. Kinda like prototyping a Jeep drivetrain, with independant motors at each wheel.
The frame, is actually already built. Using 4 10cm long pieces of 1/4" surgical tube. (clipped a replacement band
pair for a slingshot.) There's my suspension & shock absorber system.
the steering system is still in development.
Stephen
Where I could see a problem is in the case of two servos being mechanically "slightly different" due to manufacturing irregularities, part differences, wear-and-tear, etc. Depending on your configuration, this could cause binding, excessive wearing, and other "bad stuff" ... without any easy way to correct the problem.
Just a thought...
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Truly Understand the Fundamentals and the Path will be so much easier...
Post Edited (Tom Walker) : 7/14/2006 8:45:37 PM GMT