piclist 2000\11\13\111213a >
Thread: How to control a motor
face BY : Dan Michaels email (remove spam text)

Tom Handley wrote:
>   Dan, I took a look at that Nikko Hummer and I've had similar problems. My
>car has a mechanical lever to switch between high and low grear ratios but
>even then, the ratio doesn't supply much torque at the low end. This car
>uses an H-Bridge but no PWM in the original. Their "Turbo Boost" is simply
>bumping the motor voltage from 6V to 12V. The front steering is a motor that
>drives the wheels to one side or the other with a limit switches made out of
>a cheap PCB with wiper arms. Anyway, I quickly decided to throw that out and
>start from scratch...

I was off looking at the RadioShack cars this weekend. I noticed
some of the 4WD trucks have a high-low switch on the differential
- indicating gear-switching. Not sure how many feet/sec the cars
go in low-gear. Of course, no one at RS can ever answer any
"technical" questions, but the high-gear on these cars is 500ft/min,
much below the 1200+ for the racers, so low-gear may be usable.
However, you seem pretty low on the RC-car route.

Also, I noticed RS and others have an M1 tank, with cat-treads
and a motor for each side - just the sort of thing you were after.
Have you checked this out? Probably pretty slow and torque-y.

Most of these 4WD jobs with low-gear say they can climb 37-45deg
slopes. sounds like plenty of torque. I wonder if the new year's
offerrings have addressed the slow-speed/high-torque issue better
than in the past.

>   Again, the problem is torque and the gear ratio. I'm using the 16F876's
>PWM but I have to ramp up the PWM duty cycle quite a bit to get it to roll
>and then back down to track my target tach speed. Right now it takes about
>6-8 ft...

As mentioned, maybe the new year's 4WD trucks or the M1 tank do
better in the torque arena.

>   I'll have to admit I'm addicted and, due to the modular nature of my
>`hacks', I can easily use them on another platform. I would love to get into
>"Battle Bots" but it takes lot's of money and time and I really don't
>consider those robots, just R/C toys on steroids ;-)

I figure about the "best" battle bot would be a thing with a
circular scythe that would stick out and flip over the enemy from
the side. [Leonardo invented this 500 years ago for hacking
enemy troops in two - but all you had to do was shoot the horse
that pulled it].

I think it would be fun to build an autonomous bot that would
wander around on its own and map the terrain. Come back home
for re-charging.

- danM

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Subject (change) How to control a motor

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