Ill start this thread up too, it concerns gearing. I know that putting different-sized sprockets on the drive train alters the gear ratios, but Im a bit less clear on the issue of gearboxes. So: what exactly do they do, are they needed on all robots, and if so, can they be bought/scrounged or do they have to be made from scratch? (Ill be using 24v 150W gold motors btw)
Gearboxes are basically exactly the same as sprockets but they gear by the teeth of a cog binding together. The gearing works on exactly the same principle as the sprockets.
A gearbox is just a housing for gears. Gearboxes can have 1 or many stages of reduction, dependant on the motor and gearing required.
They can be made from scratch and/or scrounged (bit harder) but for a 24v gold you could easily use sprockets or timing pulleys to gear the motor down.
and for 24v golds, i would reckkomend between 7:1 and 10:1 gear reductions for starters
My old feather used 12:1 new one uses 8:1 but with smaller wheels so its about the same speed and power on 24V. See web site for more info
http://www.teamturbine.co.ukhttp://www.teamturbine.co.uk
Gear ratios mean nothing without equating the wheel size as well. doubling the wheel diameter has the same effect as halfing the gear ratio.
GORD
One thing that puzzles me about the gear ratios: if a 7:1 ratio needs 1 sprocket to be 7x bigger than the other, how do they fit inside a feather thats 10-12cm tall? (taking that height as an example)
its the number of teeth that needs to be 7x more.
ie a sprocket with 10 teeth beside a sprocket with 70 teeth.
Some low machines use dual stage gearing to achieve a high gearing.
for instant
4:1 gearing leading into
3:1 gearing woul equal
(4*3=)12:1
As used by Tornado and Panic Attack methinks.
Typically for a single-stage reduction, you choose the largest possible output sprocket or gear that will fit inside the diameter of the wheel (including the chain if applicable) and then the smallest possible input sprocket or gear attached to the motor.
We use somewhere between 3.5:1 and 4:1 (cant remember exactly) on big nipper becasue we only use 75mm dia wheels. Gordon is right if you use smaller wheels then you can use a smaller gear ratio with gears at smaller rated torques, the gears/sprockets and wheels are all smaller and therefore save weight but at the expense of having less surface area in contact with the ground, so less grip, which has to be compensated for in other ways.
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