8 Drive Motor Robot

[Dan Izzo]

My teammate started a poll on how many motors a robot is using to drive. One team responded to the "8 or More" category. Just wondering about what that robot can do if it's using that amount of motors for driving. If anyone from that team sees this, just let me know. I'm really curious here.

[GregT]

do all those motors really help? My team can not stall our motors, we have 2 and have tried with all our might to stall them- they just dont stop (wheels spin). I guess being so close to the weight limit has givin me a new view on motors

Greg

[Ken Leung]

Originally posted by GregT
do all those motors really help? My team can not stall our motors, we have 2 and have tried with all our might to stall them- they just dont stop (wheels spin). I guess being so close to the weight limit has givin me a new view on motors

Greg

A few things that determine how a drive train perform: Motor power, ratio, traction, and efficiency.

In the case you describe, your wheels start slipping when you try stalling the motors. This happen because your robot don't have enough traction.

In order to take advantage of more motors in the drive train, your robot got to have enough traction to take advantage of the extra motor power. That is why robots like 45 technokat's, or 308's, or 60's all lift goals up for more traction. By putting more weight on the powered wheels, they won't be slipping as easily, and that's when the extra motor power come into play.

That's one thing I see in robots this year... It seems like teams underestimate how important lifting goals are. You can only get so much traction from 130 lbs even with the best material on wheels/tread. That is why teams made a big deal out of FIRST's change of rules when they allow 15 degree or more wedge shape to lift goals up.

Also, with more motors in the drive train, you can gear the drive train to go faster without tripping the circuit breakers as easily. As a result, the robot can go much faster with faster free speed. With more motors sharing the load, you are drawing currents on more circuit breakers. Besides, the main 60 amp circuit breaker can handle a lot more amps than 60 during the 2 minute.

So, over all, more motors do help the drive train in speed and pushing force. It take a little work to get them working together, but not too hard from what I heard from the engineers.

[Digo]

This year I realized that the weight is a really important thing if you want traction.
In my grandpa's farm there was a truck that couldn't move because the tires were sliping on the wet sand. We put a lot of stones and sand bags on it and then we managed to drive it away.
I think it's important to be pretty close to the weight limit to have more traction, and I think its a good thing that since 2001 we don't have the "FeatherWeight in the Finals" Award.

[Greg McCoy]

It seems like an 8-motor drivetrain would pull an awful lot of current for little advantage over a 4 or 6 motor drivetrain. With 8 motors on drive I would think that you would pop the 60A breaker if you were running any other motors to pick up balls, grab goals, etc.

[CaptainPlaid]

Originally posted by Greg McCoy
It seems like an 8-motor drivetrain would pull an awful lot of current for little advantage over a 4 or 6 motor drivetrain. With 8 motors on drive I would think that you would pop the 60A breaker if you were running any other motors to pick up balls, grab goals, etc.

I agree. We have a four motor (drills and chips) drivetrain that is unstoppable when lifting on the goals in low gear. Putting 8 motors on a drivetrain would consume too much power and also limit you on the rest of your robot design. We use all pneumatics besides the four drive motors but if you were to have a go-home device or a ball picker you would need those other motors. We can drain a battery to radio cutout in one match and that is with only the four motors and the pump. Good luck on eight.
Also, one thing to keep in mind about polls is that you are not required to be truthful.

[ECarlson]

How are the 8 motors used? Are 4 used for normal driving, and 4 used for sideways motion, or perhaps 4 are used for steering?

Our robot uses 4.

[Perseus]

what else can a robot do then?


some one could have also just polled 8 or more

[Joe Taylor]

Yes, we made a drivetrain that used 10 motors and 4 pneumatics. the system had 4 independant wheels, each of which had a motor for "crab" style steering (2 window motors and two globe motors) the two rear wheels were powered with the atwood motors, and the two front each used a drill motor and a fisher price motor together (with some code limiting the power output of the fisher price motor so the speeds would match). each "wheel" was actually a short tank tread, and the pneumatic was used to retract the tread so only one point of it was touching the ground during "crab mode" steering. right now the system is all taken apart for some reworking with new treads, but when it's back up i'll take some pics for those who haven't seen it.

[ECarlson]

Originally posted by Joe Taylor
Yes, we made a drivetrain that used 10 motors and 4 pneumatics.

Wow! Yes, please post photos. Did your team miss out on Nationals this year? We just got back.
Robot problems in our first three matches kept us from placing well, but after a quick redesign, and some replacement parts, we were solid for the rest of our matches.