i would like ot know how to put 2 cim motors into a dewalt tranny
You would need to build a custom gearbox that would accept 2 CIM’s and then insert that into a dewalt.
I just searched CD-media and found a few CADs of some 2 motor Dewalt gear boxes.
There is a white paper being written as we speak, (it may even be posted, I did not look) by TechEd3 (Mechanical Mentor from Buzz) on just that subject.
Buzz has used Dewalts and CIM combination for a few years with great success.
Think careful about this one. I know of a team that did this last year and had many transmission failures. The XRP trans is just not strong enough.
There is a stronger Trans from Dewalt on their bigger drill…
I designed that transmission model that is posted. However after talking to various people, if at all possible I would caution you not to run 2 CIMs into one dewalt. The stresses are too high for the transmission to handle. If you must run 1 dewalt per CIM for each wheel. Your best bet for a 2 CIM transmission would be to use a spur gear based transmission with dogshifter or ballshifter ala andymark or team 222. It is a bit more expensive but basically bulletproof. Also I would encourage your team to use as many prefabricated parts from andymark as possible in your transmission design as gears and such from there are cheaper than anywhere else unless being donated.
We did it in 2006 with no failures to the Dewalts. We built custom adaptor gearboxes to mount two CIMs. We used the 14 to 50 first stage reduction gears that came in the KOP trans to go from the CIMs to a single output shaft. The output shaft from the custom box drove the second stage planetary set in the Dewalt. We took the Dewalt first stage section out like the White paper Nothing But Dewalts describes for use with a single CIM motor. Instead of boring out the ID of the carrier sun gear and pressing it onto the CIM shaft, we made a custom aluminum adaptor that attached to the carrier sun gear using the four screws shown to attach the plastic top hat. This adaptor had a keyed ID that fit the keyed output shaft of the custom gearbox. The other thing that is important to do is to support nose of the Dewalt casting section. If you don’t the cantilever hanging out there will probably pull the small screws holding the Dewalt to the gearbox case out.
Dewalt Full Assembly.pdf (62.9 KB)
Assembly.pdf (52.6 KB)
Dewalt Full Assembly.pdf (62.9 KB)
Assembly.pdf (52.6 KB)
Hey a little off topic but what about using one of these. Would this be FIRST legal?
I would suggest reading the FRC manual…I can’t find any rule that would not allow it (unless it was too big or heavy; i.e. made the robot violate size and weight rules). Cost? Pass. Readily available? Pass. Looking at the specs, that axle would probably need to be trimmed, and some cheeseholing would be desirable, but those can be designed around.
Please note that this is based off of the 2008 rules and therefore can’t be used to determine legality for the 2009 or any other future game.
I have, I was just wondering if I missed something since I would think this would be a very good option for a robot (lawnmower transmissions). Its really cheap and its 3 speed, seems like a perfect replacement for a Dewalt if it is more reliable. Wonder what types of loads this thing can handle. Its so cheap maybe I will buy one.
It’s also really heavy. The specs say 7 lbs shipping weight.
According to the spec sheet this thing is a clutch-type transmission. So, you’ll need a way to both engage/disengage the clutch AND shift the gears. That’s kinda awkward and complex… However, it would allow you to shift gears at a standstill.
Its also non-reversing, whatever that means. (non backdrivable? or can it only turn one way?)
Not the best tranny for FRC. But if I ever build a go-kart I’ll look into these things
Yeah, it’s definitely useful for something…
but at that weight, size, ratios (7:1, 4.5:1 and 4:1 doesn’t provide wide range of shifting), and complicated operation… it’s not for a FRC robot.
Just to clarify, Buzz has been using DeWalts with a single CIM for the main drive for three seasons now, without any failure of motors or transmissions. However, we made modifications to the Joe Johnson NBD white paper to arrest certain concerns we had with the initial NBD design recommendations.
1- We do not cantilever the output sprocket/shaft, but support the output shaft on the outboard end with an additional bearing.
2- We fasten the output shaft to the end of the original transmission output shaft with 1/2-20 thread cross drilled and retained with a 1/8 hardened pin. We use the LH chuck retaining screw installed in the DeWalt output shaft, cut off flush to fill the void, so you won’t break the carbide drill as it comes through the inner wall.
3- Where the 3rd stage is removed from the DeWalt, we insert an alumininum spacer ring against the transmission shoulder that acts as a depth spacer as well as to maintain the transmission/motor shaft on the drive axis.
4- We turn down the output shaft of the CIM to .250, and bore out the sun gear to .2505 for a sliding fit onto the CIM output shaft. The length of this reduced shaft diameter should be equal to, or slightly longer, (for clearance) than the length of the sun gear.
5- We machine the “top hat” of mild steel, index four 5-40 tap holes to match the pin locations of the sun gear, and tap for 5-40 FH socket screws. We also broach a 2mm keyway in the 5/16 bore of the top hat to match the 2mm key on the CIM shaft, and key it. We also cross drill (1/8) the top hat/CIM shaft and insert a 1/8 roll or tension pin.
6- We clearance drill and countersink the sun gear with a carbide 82 degree #2 centerdrill (5/16 OD, 1/8 point) and then drill the four holes out with a #30 (.128) cobalt or carbide drill to provide clearance for the #5 screws.
7- We add a stiffening 1/8 x 1 3/4 tension pin to the shifter rod to prevent the 1/16" shofter rod from bending.
We are planning to experiment with a 2 CIM adaptation to the above to reduce the amp draw of the single CIM setup, which limited our “gearing up” the drive for speed this season for Overdrive. The only tradeoff is the weight added for the CIMs and adapter ot mount them. Based on the weight of the robot, friction coefficient of the wheels, and amperage available to power the motors, additional motors for the drive only help to reduce the amperage drawn to the motors. In other words, if you don’t trip the breakers, and the wheels slip on the carpet, more motors won’t equate to more push.
I have also included some pictures of the DeWalts taken after a season of two regionals, lots of shifting, two tough after-season Invitationals, and demos to elementary school groups. They are tough, light, cheap, and easy to shift. Everyone always asks how we get so much on our robot. DeWalts go a long way to lightening for more capability in other areas of the robot. PM me if you have any questions.
Looks like the pics didn’t attach, so PM me with your regular EMail address and I will send them to you if you want to look at them:)
Is there a chance you could put together and post a White Paper of your modifications?
you could try something similar to the robonauts’ V6 from 2006 just design it for 2 cims instead of 4
attached is a cad of one that i have been working on
Is that solidworks or sketchup?
SolidWorks, but i bet i could do it in SketchUp too! i turned on the contour modeling to give it more definition. more to come in the photo thread gallery thingy