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Supario
08-29-2006, 01:12 PM
Hi,

Im building a new robot as part of a project in college. It will have a laptop and camera on board along with the usual encoders, sonars etc. so it will be fairly large (approx 40cm x 40cm , weight 10kg max) . Currently things are still in the design stage. I have the electronics/ control/ programming side of things figured out but I don't know much about the (electro)mechanical aspects of building something of this scale.

Q1. Is there any rough rule of thumb for calculating the minimum amount of torque a motor+gearbox should output to make a differencial drive robot with wheel diameter d and weight w move on a generally level floor ? I hope this question doesn't sound too dumb but having worked with tapedeck motors, plastic gears and small robots till now, I don't know how much torque is required to drive something of this size.

Q2. Will sticking four circular polycarbonate disks each of diameter 12cm and thickness around 0.4mm together and putting some rubber ring around it make for a wheel that is strong enough for the robot ? If not where can I get a suitable wheel? It has to be fairly firm because the robot will use odometric feedback.

Q3. How thick will the radius of the load bearing axles have to be assuming they are made of steel? What sort of bearing should be used ?

Q4. Is there any supplier/shop in India (Hyderabad or Bangalore especially) from who I can order suitable geared PMDC motors, preferably with encoders ? Alternatively is there any kind of junk equipment that could be cannabalized for motors of this kind ? Is www.robonence.com still an active supplier ? They've had just two items in their catalog for months.

Jabir
08-30-2006, 04:45 PM
Hi..
I had made a bot weighing about 5.5 Kg. Used 2 kgcm steppers with 3:1 deduction gears with Differential steering .
Speed was very low. I tested it with a max of 8 KG ..It worked fine!

http://www.roboticsindia.com/modules.php?name=Forums&file=viewtopic&t=1544

1. U can use relations of rolling friction. Refer Engineering Mechanics by Shames or Beer and Johnston.

2. U can find good wheels from a hardware shop. Use castor wheel tyres. Ask for rubber not nylon.

3. About the shaft ,Take a dia 10 mm man :wink: . If u try to design it mechanically u will surely get a value less than 3mm!!!Believe me. We can’t make such a shaft by turning. Use ball bearings. U can find them from any automobile shop.

4. I don’t know!!:lol: :lol:

PS: Use Aluminium anywhere possible instead of Steel.:idea: Surely reduce weight.

Regards
JABIR

Supario
08-30-2006, 07:44 PM
Hi Jabir,

Thanks for your reply. I was looking at the photos of ROBOFORK. Real nice robot. Where did you get those gears used in the geartrain ? For the body I plan to use polycarbonate/acrylic sheets and aluminium channels for reinforcement and attaching the motors to, steel was just for the axles.

Jabir
09-02-2006, 02:13 PM
Hai supario , sorry for the delay. I was very busy for the last 2 days.

I got the pinions from Coimbatore , from an Electronics shop. The big gear is made in the college workshop, in a universal milling machine. Since u are not mech , I don’t recommend it. Search in coimbatore.

In my opinion, there is no need for such a complicated body. Just use a plywood sheet.

Try viper motors. I heard they are very tourquey .:idea:

If u wishe I am ready to send u my report . There is a lot of mistakes. but sometimes it will help u.

Regards
JABIR

Supario
09-02-2006, 05:47 PM
Hi,

I'd really appreciate it if you could send a me copy of your report ( supario AT gmail DOT com) . Was the pinion on ROBOFORK similar to those found in mechano/errector sets ?

Thanks,
Supario

Jabir
09-03-2006, 03:21 PM
I have just send it.

JABIR