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Author Topic: Need help with wheel placement and turning ???  (Read 2674 times)

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Offline BajanickTopic starter

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Need help with wheel placement and turning ???
« on: August 16, 2008, 05:29:35 PM »
 I am planning on building a rover bot using wheelchair motors and four pnuematic wheelbarrow style wheels. I would like to use tank style steering. What is the best wheel placement for this type of setup so the wheels dont drag, or should I go with some type of 4 wheel drive for this setup to be effective?

Thanks.


Offline Rebelgium

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Re: Need help with wheel placement and turning ???
« Reply #1 on: August 16, 2008, 06:17:34 PM »
the wheels will always drag in differential drive ("tank style"). But the wider you place the wheels the less drag.

Quote
or should I go with some type of 4 wheel drive for this setup to be effective?
If you're going with differential drive, you'll need 4wd eitherway. 2wd won't work.
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Offline MarkBrown

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Re: Need help with wheel placement and turning ???
« Reply #2 on: August 16, 2008, 06:50:00 PM »
By wheel dragging, do you mean the left wheel rotating when turning right, causing the right to drag?  If that is the case, couldn't you just have the right wheels rotate the opposite direction at the same rate or a slightly slower rate then the left?
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Offline BajanickTopic starter

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Re: Need help with wheel placement and turning ???
« Reply #3 on: August 16, 2008, 07:07:14 PM »
The previous bots I have built used tank steering where the two wheels turn the opposite direction to turn the bot, but these where only 2 wheeled with castors.
 I will probably need to devise some kind of 4 wheel drive using bike chain or somthing of the sort.


Offline Rebelgium

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Re: Need help with wheel placement and turning ???
« Reply #4 on: August 17, 2008, 09:33:17 AM »
The previous bots I have built used tank steering where the two wheels turn the opposite direction to turn the bot, but these where only 2 wheeled with castors.
 I will probably need to devise some kind of 4 wheel drive using bike chain or somthing of the sort.



yes, but imho using 4 (weaker and cheaper) motors is much better and easier then using two more powerfull motors with chains/gears/... to make it 4wd
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Offline BajanickTopic starter

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Re: Need help with wheel placement and turning ???
« Reply #5 on: August 17, 2008, 05:29:26 PM »
Yea but I have 2 wheelchair motors and they are very expensive. I might just use the configuration they are in with the 2 rear castors that way I can use the tank style steering but 4 wheel drive would be cool. :)

Offline ArcMan

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Re: Need help with wheel placement and turning ???
« Reply #6 on: August 18, 2008, 07:16:52 AM »
Cool is certainly a worthy goal for any robot, but what do you really need?  Most robots have differential drive with one or two swivel casters.  There is a reason for this.  It provides the best robot movement control.  IMO, you should use this unless you have a really good reason not to - like really rough, muddy terrain that would require tank treads or 4WD.  Is this the case for your robot?

Offline BajanickTopic starter

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Re: Need help with wheel placement and turning ???
« Reply #7 on: August 18, 2008, 07:01:08 PM »
Yes, I want it to be an all terrain radio controlled bot. Thas why the large pneumatic tires. I guess I can either go with 4 WD with tank steering or 2 WD with car type steering. The 2 WD system might be a little cheaper cuz I would not need a controller that does mixing.

Offline Gertlex

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Re: Need help with wheel placement and turning ???
« Reply #8 on: August 18, 2008, 07:41:07 PM »
4WD Tank-style sounds like a good choice for what you're doing.  It's quite robust.  Doesn't sound like you need particularly fine control either; that's something hard to achieve with this style of drive.  A few points: make sure the design makes it fairly easy to set up the chain for driving.  (as opposed two aluminum plates on each side with 2"spacers for 1.75" wide wheels, or some such)

I also feel that turning is much easier and less "painful" to watch if you minimize weight.  You'll probably want to tweak the speeds too to get the bot to drive straight (on flat ground).  Motor tolerances and weight distribution are both potential sources for your robot veering.
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