|
|
|
![]() |
|
|||||||
|
||||||||
![]() |
|
|
Thread Tools | Rate Thread | Display Modes |
|
|
|
#1
|
|||||
|
|||||
|
Re: pic: A more standard aproach
Quote:
Looks great, especially for the weight. I see other's concerns about the BB gearboxes under stress... I'm not too convinced thought that it would be that much of a problem (probably something that can be mechanically avoided.) One more question. You said 'that which is shown' is 35 lbs... Does that mean that a set of 4 would be 70 lbs? and does that 35 lbs include the chassis pieces shown? Great work. Jacob |
|
#2
|
||||
|
||||
|
Re: pic: A more standard aproach
I'm using 8 motors in the drive for a couple of reasons. I like the idea of the extra maneuverability and control that is provided, i know that this is more complicated program wise but it is less complex mechanically and is lighter. Two motors weighs less than a chain tensioner plus chain and sprockets. Mechanically it is much easier cause I don't have to mount everything separately and all the pieces are the same and there are fewer of them.
The motors would be two Fischer Price and two BaneBots (don't know if we have all these next year so...). I'm pretty sure that the trans could handle the load because there is a bearing at the bottom that all upward force and most lateral force would go into. I would worry a little about the carrier plate but if the modules are well protected I don't think it would be a huge problem. I got rid of the suspension cause of weight and the suspension is really complicated. I really liked the idea but it didn't seem needed for an actual first robot, plus this is much lighter and more importantly costs about half as much. The wheels cost $2.75 each instead of $100 each. And when I say "that which is shown" I forgot that I was only showing half of the bot. The entire thing, modules, motors, frame, everything weighs only 35 pounds. Of course with electronics this could be 10 pounds heavier but that still leaves much more than half the allowed weight to build on top of. Orders... jee hadn't thought of that. Thanks for the offer of help but I think I can handle it, however if I do need help. If you would like to CAD files just ask. Thanks very much for all the input. |
|
#3
|
|||||
|
|||||
|
Re: pic: A more standard aproach
Alex,
One thought I had after my intitial post is the problem of keeping the steering motors in alignment. It is an issue using two motors and chain for us. To keep all four tracking is going to take some processing power and sensors. |
|
#4
|
||||
|
||||
|
Re: pic: A more standard aproach
Just out of curiousity, how do you keep the wires on the drive motors from tangeling around the sverve module?
|
|
#5
|
|||||
|
|||||
|
Re: pic: A more standard aproach
We limit the travel to only one rotation plus a few degrees, max. This year we closed that down even further. The wiring comes right up out of the top of the module and the upper bearing point is a hollow tube which the wires run through.
|
|
#6
|
||||
|
||||
|
Re: pic: A more standard aproach
I was actually worried about how to keep the tubes in alignment. I was thinking of adding some sheets to the frame that would brace between the tubes vertically. And now that you mention it that is another good reason to use four motors, there is again less precision needed. While I do need precision to attach the motor mounts, I can think of an easy way to do that.
In this case since the module turning comes down through the top I can't run the wires through the bearing. I would run the wires up the inside of the module and then leave a large loop of wire to allow for turning before attaching directly above the module. I would also limit the turning of the module to keep the wire from tangling. |
|
#7
|
|||
|
|||
|
Re: pic: A more standard aproach
Quote:
We used this little piece of code to keep track of rotations: Code:
char encoder_turns(int pot, int last, int window) {
if(pot - last > 1023 - window)
return -1;
else if(last - pot > 1023 - window)
return 1;
return 0;
}
We then used 2 PI loops on each module (cw,ccw) to get it in the position we wanted. I could write a whole essay on control theory right here, but I think Jimmy's post "sums" it up: http://www.chiefdelphi.com/forums/sh...int#post617897 Quote:
|
|
#8
|
|||||
|
|||||
|
Re: pic: A more standard aproach
Seems to me that window lift motors - or a similar worm drive system - might be better for the steering motors. They rotate slowly - but maybe not slow enough - and have significant torque, and take the bumps pretty well. Plus, they are available cheap in surplus and reasonable in new.
Some newer types sometimes have integrated quadrature sensors (used for detecting objects during auto-close of the windows) that are sensitive and can be used to maintain steering alignment (along with a 'home' switch for recalibration). Some idle thought, is all. Don |
![]() |
| Thread Tools | |
| Display Modes | Rate This Thread |
|
|
Similar Threads
|
||||
| Thread | Thread Starter | Forum | Replies | Last Post |
| Standard vs. Custom Frame | brennerator | Technical Discussion | 62 | 23-12-2006 22:54 |
| Standard Joysticks | EricWilliams | Programming | 26 | 01-04-2006 22:59 |
| Standard Servos? | Matt Krass | FIRST Tech Challenge | 4 | 22-11-2005 08:09 |
| Developing a standard | Jack | Scouting | 23 | 03-01-2003 23:04 |