OK, so we saw these really cool Andymark Nano Tube drive transmissions when they came out last year… We purchased a pair of the gear drive 3-shaft units in the fall with the intention of working on an off-season project. We never got around to this, and now that the season has begun, we are looking to use this as the basis for our drive. We are having some trouble in a couple areas that I would like to solicit opinions on.
First of all, the configuration of the Nano Tube makes it difficult to incorporate into an overall drive chassis with accommodations for bumpers all around. The fundamental problem is that the wheels stick out beyond the ends of the tubes. This means you can’t just put a structural member across the front and back that’s long enough to reach out to where the side bumpers need to go. The wheels interfere. ** If the tubes were maybe 4-5 inches longer (with the same wheelbase), it would be tremendously easier to incorporate into an overall frame**. We will need to come up with some way to extend the tubes in order to have a structurally sound chassis.
Second (and worse)… These tubes are designed for 6WD, with an 1/8" drop on the center wheels. While trying to assemble them into a frame tonight, we found a vexing problem. The two Nano Tubes are identical (there is no left and right). A consequence of this is that an unavoidable asymmetry is introduced. If you arrange the tubes so both centers are “dropped”, then the 2-wheel gearboxes are not directly across from each other ie: the front and center wheels are driven together on the left, and the rear and center wheels are driven together in the right. This will have an adverse affect on handling such that when the robot needs to push, it will not maintain a straight course.
What is really needed are two different styles (a left and a right) which Andy does not offer. We examined the possibility of reversing the components to create a mirrored version, but the features are not symmetrical and it would require a fair amount of machining to accomplish this.
Is there something obvious that we are overlooking here? We almost couldn’t believe it when we saw this… If we wind up with Mecanum drive this is a non-issue because we will not use the center wheels (and we can presumably de-populate the center axles and gear train). We are just not seeing how to make this work as intended for a 6WD robot !!
We liked the idea of the Nano tubes as well but also noted all the limitations you pointed out. Our solution was to custom mill 35 inch long tubes with no center drop. We’re using omnis on the corners. Two 27 inch long 3 x 1 inch endcaps complete the frame. Without a CNC mill this whole operations would be too labor intensive.
Wow… I am curious, If you went to all the trouble to custom machine new tubes, why didn’t you drop the center and run a conventional 6WD? It would seem like omni’s on the corners will be easier to push around than the drop center 6WD would.
I wish we had NC machining capabilities. It obviously gives you tremendous ability to recover from something like this.
I am surprised and disappointed in the deficiencies of the Nano’s. This was not at all apparent until we actually tried to use them !!
If you use the chain-driven Nano Tube setup, this is a non-issue (just move one of the chains to the other pair of shafts). With gears, I could see it being a bigger deal - but still, for a skid-steer (6WD) setup, I would want to chain the other shaft to the two geared ones anyhow. This allows for all of your motors’ power to be transferred to the floor regardless of which wheels are in contact. We are running the chain-driven Nano Tube with two chains per side to connect all of the wheels (we are using the longer Nano shafts and cutting off the excess to give us more space to mount two sprockets and a wheel to the shafts).
Though purely from an aesthetic point of view, left- and right-handed Nano Tubes would be sweet!
It was an especially attractive thought that the gear-driven tubes could eliminate chains, but you make a good point. If we chained the front and back together, then it would regain the symmetry. Presumably these chains would not be stressed too much (what about 25 instead of 35?)… It just kind of negates much of the beauty of the tubes.
Team 241 decided on the nanotubes with the built in gear drive of the center wheels. To get six wheel drive, we figured out that we needed to ADD the sprockets that normally come with the sprocket nanotubes to the gear-driven center wheel order. AndyMark’s folks knew exactly what we were trying to do and made sure we ordered the right sprockets and widgets.
Our students designed and built an “exoskeleton” out of 1" sq tube and connectors and bolted it right to the nanotubes they had assembled.
It’s only been 12 days and we have a sweeeett drive train and chassis already done ready for electrical component placement. We are probably 10 days ahead of where we normally are and we are pretty much guaranteed our drivetrain will stay aligned. Mentors did not have to touch a thing! What a great feeling.
If you mount the motors at the corners (look at the post by Taylor with 1529’s chassis) then you always have power available around the robot. The nano tubes are set up for a CIM mount directly into the geartrain.
This won’t work if you are wanting a 2 speed set up, but is very strong and quick with this arrangement.