There have been several comments posted regarding the ox and other GT3 belt driven systems seeking suggestions on how to reduce the rate of motion from the current 60mm per revolution to something smaller to improve resolution. The following concept should provide a simple drop-in solution that will cut the rate of motion in half and greatly improve the strength of the motors through simple gearing. Please accept this as a work-in-progress as I am still collecting parts for both it and the machine it will be attached to. Depth of the recesses for the FR188-ZZ bearings and the thickness any shims required along the 1/4" axle have yet to be determined. Basic Concept Parts Breakdown Y-Axis Attachment Note main belt tightening can be performed using existing slotted holes. Motor belt is tightened using short slots in the motor attachment plate. Note, this arrangement eliminates the substantial lateral forces that were originally imparted on the motor from the main belt. Tightening forces against the 55T O-belt need not be too significant. X-Axis Attachment It should be noted that with the square mounting pattern, the assembly can be oriented in several different positions but may require shimming with some orientations to resolve conflicts with adjacent bolts. The 55T belts and the 40T pulleys are being sourced from B&B. The 20T pulleys will be sourced from the parts store.
With a couple mods I could see this working on my machine..... hmmmmm. Does the 40 tooth pulley fit in there tight enough between the 2 flanged bearing that it limits side play? Might consider a couple bronze OilLite thrust washers if necessary. 2-1 reduction plus in my case the belt would help dampen the spur gear to rack.
I wouldn't trust it to stay centered on a geared system. As noted above, I still need to work out some shims as there is a couple mm of play in the system. As far as mounting on a geared system, I've already thought through that too as I plan to shift my system over to geared shortly after I get it built. By putting a pivot bolt in the mounting plate lined up directly with the motor shaft, the weight of the motor would be balanced on the pivot and all the spring tensioner would be doing is holding the spur gear against the rack. (It would also have to accommodate inertial forces causes by starting the motor but depending on ramping those forces should be easy to cover.)
Yeah that's what I was wondering, I was just looking to see if I could find some roller bearing thrust washer assemblies but I have only found them as small as 1/2" so far. I was thinking in my case the pinion is out a good distance on the shaft, I think there would be enough room for a collar and thrust washer then just extend the shaft out the back above the motor and add another thrust washer and collar on the outside, could adjust how far the shaft sticks out into the rack pretty easily and lock out most all the side to side play... Keep up the good work !!
Actually there shouldn't be any axial forces on the drive axle. All the force should be either radial or lateral. As far as shimming, I had just planned on using some small diameter 1/4" washers to snug up the 40T pulley between the two flanged bearings and as they are set opposed to each other, they should trap everything between the plates. I will however be using grooved axial bearings when mounting on the pivot bolt.
That looks like a nice start to a simple drop in bolt on upgrade, very nice! Changing this to a be a tensioner for a R&P system, could be a nice alternative (read less expensive) than others I have been able to find. Though the direct drive pinion on the motor works and should be "ok" for the motor bearings, having a separate tensioner\pinion on its own shaft would be nice Now I just have to keep track of all these cool ideas for when I start my build...
Hi Rick How's this creation coming along? As others have said, these gearing systems are around already, but really expensive. As I am toying with the idea of R & C, I await in anticipation. Gray
Sorry Gray but I haven't had a chance to take this any farther. I'm still putting together the OX to attach it to. And between work and cold weather that hasn't been proceeding along as rapidly as hoped. I do finally have all the parts though. The shim washers for this proved to be more of a challenge than expected. I'm having to drill out #10 washers because the 1/4" washers are too large of a diameter and rub the outer edge of the bearings.
This is a pretty old thread, however I am interested in using this on my OX build. I see some of the parts in he store, but not all. Any help with missing parts? Is there a kit?
Sorry no kit. There was a brief foray into speed reduction in the parts store but that was for speed reduction on C-Beam systems and it has been withdrawn pending a bit of rework. But that's really not a big issue. The parts links mentioned above still work or if you'd like to try something with a different reduction ratio there are plenty of sources of belts and pulleys out there to work from. B&B and SDP/SI have the best selection but they can be a bit pricey. Robotdigg is a lot cheaper but they only have GT2 belts and pulleys but these should be sufficient based on the lower forces within the reduction system. And of course there is always ebay. Using the center-to-center finder from SDP/SI will help you find the spacing between the two major holes and it's fairly easy to use it to work out the best possible belt/pulley combinations.
Hi, I'm a newbie. This is interesting stuff. I'm a long way from understanding all that was said so I hope my question doesn't insult you or make me look like an idiot. I can understand the belt tension on a direct drive could have a negative effect. It looks to me you have the same size 20 tooth pully on motor and at belt. That would eliminate the effect of the belt tension but I don't understand the other advantages. I'm assuming I'm missing some part of the idea. Only thing that comes to mind would have to do with tooth #'s aND how that effects size of pullys?? Regards, Rod
Actually it can have more significant belt tension issues than a regular Ox as the speed reduction pulleys also serve as a power doubler. Typically there will still be the same forces applied to the system (i.e. enough force to move the gantry and the bit through the material) but when additional force is required to power through harder materials that additional force has to come through main belt/pulley interface. The main advantage here is that the reduction gearing improves resolution by reducing the distance per step of the stepper without the power loss associated with increased microstepping. On an original Ox each turn of the stepper moves the gantry 60mm. With the reduction gears each turn of the stepper moves the gantry only 30mm thus increasing resolution. The 1:2 reduction in speed due to the pulley ratios however comes with a 2:1 increase in power. The benefit here is that smaller steppers can be used to achieve the same amount of power as the original direct drive ox which opens the system up to a much greater range of lower power driver boards.
Thanks, I hadn't thought about the increase in belt tension and can see the upside to that (I think). Your explanation is great. I hadn't thought about the advantages and savings of lower powered boards, ect... I will go back and open the design file. I got confused looking at the picture before so didn't take the time. I'm still a bit lost on how the reduction is achieved.
A 20 tooth pulley on the motor is turning a 40 tooth pulley at the opposite end which is connected to the drive shaft. So for every turn of the motor the drive shaft only moves half a turn and thus the drive pulley only makes half a turn rather than the full turn it would have made being direct drive.
Thanks, Light bulb in my head went on this time. Now the only thing I don't understand is why it didn't look right the first time I looked at it.
