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pic: MOEnarch Swerve Drive
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Did you have any problems with the belt wrap?
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that gearbox has only slightly more than 90* of engagement but uses both thinner belt and smaller diameter pulleys. Given that, I would probably trust this arrangement. |
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10 - 20 ft/s is a pretty big gap there, Nathan :P
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Sdp pi suggests at least 6 teeth engaged on a pulley for full use of the belt strength, it looks like have sufficient engagement for that belt pitch.
I like how they packaged both motors in the drive module, it looks good. |
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Is it a fair assumption that you will be using 8 CIM drive with this.
If so, how are you planning to keep from popping your main breaker? Are you using current monitoring to keep yourself in a safe zone? |
Re: pic: MOEnarch Swerve Drive
I would consider changing the location of your digital encoder for a couple reasons.
First, as you tension the belt by moving your cim, it will change the engagement on the Digital encoder. Secondly, generally speaking those things don't appreciate a lot of side-loading. Third, if your belt slips, your wheel will no longer be aligned with the encoder reading. I'd consider a small lightweight bracket that places it directly over the primary shaft of the module itself, so you'll always know the true position of the module. This also relieves any side-pressure on it, and it can be coupled with something as simple as surgical tubing. It will probably be a wash weight-wise. |
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We did consider a bracket like you describe but it was just another part to manufacture and would also put the encoder in a more vulnerable location. If there is some unforeseen mechanical problem with it's current location we may go this route. |
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We did not experience breaker issues while also running an intake motor & compressor. We also did not perform any type of current sensing. |
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Churros are not recommended drive axles, but they work well for a quick prototype. We did have enough black hex VEXpro shafts on hand at the time. |
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This is all conjecture, but I highly recommend testing this type of encoder setup or it could come back and bite you. -Adrian |
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Free speed of CIM+MiniCIM motor combination geared 1:1 = (343 + 198) / (343/5310 + 198/6200) ~ 5604 rpm vehicle speed (with traction wheels) @ motor combo free speed = (pi*4*5604) / (720*12.75*40/18) ~ 3.45 feet/sec |
Re: pic: MOEnarch Swerve Drive
Getting there!
https://www.facebook.com/video.php?v...04577359603811 |
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Congrats on getting to the movement milestone though! |
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We actually tested this last year with a force gauge, it takes ~15% more force to pull/push the robot side to side or front to back (with locked wheels) because when you put it on a diagonal more nubs are touching the carpet per contact patch area. |
Re: pic: MOEnarch Swerve Drive
Looks like a happy happy joy joy moment. Some thing does not sound right when the module was rotating and driven. Those are wide wheels and may cause problems with amp draw on both drive motors and steering. Pay close attention to the tuning of the steering pid. You can have to much traction. For a fall back you might want to consider 1-1/2 or 1-1/4" Colsons. Next, get 4 of them on a frame and get programming. Then you will be half way there. Driver training is the last half. If you get it going before kick off, do you want to meet and do some swerve on swerve driving?
Note for the drive encoder, Do you really need quadrature? Wouldn't a tachometer solution be good enough? I do not now what the under side of the coaxial pulley looks like but, could you put some reflective tape strips on it and use a optical reflective sensor? We used a magnet solution last year and will use optical this year. |
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First I had to build The Bathroom Scale of Science, the "force gauge" we used to test this because the real one we had in the lab maxed out at 50lb. The bars that stick out from the sides are the handles and the X that crosses the face of the scale has 4 ropes that converge at a shackle that was placed around a 1x1 frame member on the robot in the bumper zone. The wheels were then locked by jamming a scrap between the spokes. The robot was pulled with the ropes remaining as horizontal, and the scale remaining as vertical as possible to the ground. A reading of ~120lb was observed on the scale. The wheels were then switched to those with diagonal tread, the same procedure was followed and a reading of ~140lb was observed. A ~15% increase. We also used a similar procedure to demonstrate how ineffective trying to drive out of a T-bone is. This time the wheels were unlocked and I pulled sideways acting as an opposing robot pushing from the oppisite side as our driver floored it (and the robot started to drive in a circle around me with a radius of the rope (~5ft)) you could see the scale instantly drop from a reading of ~140lb to something like 60lb (I don't remember the exact number but it was something drastic) We again used the test to determine that 2" wide 4" dia wheels were ~15% better than 1 inch wide wheels. Take 4 1" wide wheels, place them on the four corners of the robot, lock them, drag. Place 4 more 1" wide wheels on the same axles, lock them, drag. *All tests performed on actual FRC carpet |
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As for the encoders we debated this, but we haven't had very reliable results from magnetic sensors in the past, and there is not much room to mount an optical sensor under the pulley. We also had all the encoders we plan to use in stock so we just went with them. |
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Was the height of the horizontal rope above, below, or at the height of the wheel axes? |
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Hey Everyone!
This is just a quick update on the progress of the MOEnarch drive system. We have mounted the four modules onto the square chassis and it's working smoothly. This is the Facebook link to the video: https://www.facebook.com/video.php?v...type=2&theater As you will notice, the robot doesn't have any encoders on the modules just yet. We are looking to set those up by the end of next Monday and have a robot-centric swerve drive ready to go before Winter Break. |
Re: pic: MOEnarch Swerve Drive
Sounds like a swerve, kind of moves like a swerve, it must be a swerve. Welcome to the 3 degrees of freedom club.
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