Society of Robots - Robot Forum
Mechanics and Construction => Mechanics and Construction => Topic started by: Warhawk87 on July 14, 2010, 03:09:13 PM
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Hey everyone!
Stupid question, but how do I mount my front wheels so that they are free spinning but wont fall out.... My two back wheels are powered, and the wheels are connected to the shafts, so theres no problem there, but I cant think of how to mount the front wheels...
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you connect both wheels two an axle and connect that to a servo which will turn the axle. it might also be a good idea to have stoppers at the places that are the max. turn areas.
Hope this helps,
Patrick
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I dont want to power these wheels, so I would think that powering a servo would not work
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no, the wheels are unconnected to the servo. the servo turns the axle, not the wheels.
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servo
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the wheels should be free running, so you should connect the outer axle area to the servo, then ball bearings, with the inner part to the wheels.
Hope this helps,
Patrick
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I would rather try doing this without a servo.. Im just looking for a way to mount axels in a way that lets them spin freely but not fall out of the chassis and I think a servo would be a little overkill
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I think random robots was assuming you wanted to steer the front wheels, as that servo he mentioned was for steering the axle.
Having the axles in tubes and clamping down on the tubes could work.
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mhmm tight fit with some lube would let it spin and hold it... but i cant think of anything to clamp it... How do you guys do it normally? you have to do it for every 4 wheel 2 wheel drive robot dont you?
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Methods of securing the free wheels depends on the diameter of the axial. If small <3/16 inch then a collar with a set screw would work. Grind a small flat for the set screw to seat on.
For larger diameter axial then a hole could be drilled and a cotter pin inserted through the hole would hold the wheel on (just put a washer between the wheel and pin).
Another way is to thread the end of the axial and put a locking nut on (with a nylon insert or use two thin nuts and jam them together).
Or, cut a groove on the end of the axial for a 'C' clip.
Or, solder a washer or metal disk onto the end of the axial. Just take care not to melt the wheel hub if its plastic. This is the method I used on one of my small Bots. The axial was 1/8" piano wire and the wheel were vintage model airplane wheels about 1.5" dia.
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Thanks for the suggestions!
Methods of securing the free wheels depends on the diameter of the axial. If small <3/16 inch then a collar with a set screw would work. Grind a small flat for the set screw to seat on.
The axial diameter is 3 mm or about .12 inches, so this one might work... I guess i would drill a hole just big enough to let the axel spin, and use those collars on either side of the hole to stop it from moving back and forth... 2 problems that i see though,
There isnt much support for the axel if its held in at one point like that
It wouldnt be very economical to buy just 4 collars and i dont know where i would buy them in the first place
Thanks again!
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Hi,
There isnt much support for the axel if its held in at one point like that
If it's the center hung support for steering, it just needs to be done right. A small plate could by mounted with a bearing between the chassis and the plate for the vertical load and perhaps one or two for keeping the vertical steering "pin" in check. Then mount the 3mm axle on the plate.
It wouldnt be very economical to buy just 4 collars and i dont know where i would buy them in the first place
You can use electricians wire blocks (the proper English term escapes me) - those with 12 screw connectors in a block (usually white/semi-translucent, but comes in black too). Unscrew the two screws of each part and push the metal thingy out of the nylon (reinstall the screws before they go AWOL).
One of these each side of the wheel and a washer of a suitable size between connector and wheel should do.
These blocks are cheap (you may have some allready), comes in different gauges and you could even split them in half with a hacksaw, some patience and some bandages :-\
They're good for joining axles as well and for connecting a motor to an axle.
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The way im building this is steering is controlled by the direction and speed the back wheels are rotating with... So the front wheels just need to be locked into a static position without consideration for spinning the axel for steering.... Just clearing that up....
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casters?
(http://www.apartmenttherapy.com/uimages/sf/010809-casters.jpg)
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Shaft collars would work for basically any size of shaft.
You can order them from McMaster in that ID for 1.35 a piece. You also might be able to find them at Osh, but I'm not sure.
Depending on how hardened your axle is and what material it is you could possibly just bend it at a 90 degree angle.
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The way im building this is steering is controlled by the direction and speed the back wheels are rotating with... So the front wheels just need to be locked into a static position without consideration for spinning the axel for steering.... Just clearing that up....
Then you would be better of with casters as madsci1016 suggested, as the setup with a non turnable wheel will have to be dragged more or less sideways when it turns.
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Casters do sound good... And easier to mount probably.... Ill definetly look into that! Any suggestions for places to buy them?
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Hardware stores and furniture stores springs to mind. Or make them yourself :)