SAW-US, A Build Diary

[Sportball]

Thanks for the advice, I must admit the wheels are a bit overkill but they fit perfectly on the motor shafts and appear to gave a lot of grip, I would hate to have to replace them with a bottletop or such like. Let's do a full weigh in and see how we get on.

I will have a play with the trimming and see if that will give me a straight line drive.

Thanks again..

[Sportball]

I have decided to amend the title of this post to "A Build Diary", this way I can keep all the posts in one place and anyone interested can follow.

Saw-Us is now at prototype MK2. I have ordered and received my weapon servo, a GWS PARK HPX F, after reading a recommendation. Lucky thing was it arrived in a plastic box approx 110mm x 300mm. With a little modification this box has become the shell, I am a little oversize on the width and weigh in at around 175g but it is a step in the right direction.

I have a question regarding the weapon servo. I have connected it via a live mains feed direct from the battery with the neutral and signal coming from the receiver but it is causing strange behaviour in my drive motors. Quite often after, operating the flipper, the motors spin on there own making the robot either drive backward or go into a spin. When I operate the flipper again they stop and I gain control. It appears to happen more if I drive forward and operate the flipper at the same time. I have a mode 2 Spectrum DX5e and the motors are driven via the right stick whilst the flipper is forward / backward on the left stick....any ideas.

PS photo to follow.

[BeligerAnt]

In order to diagnose the problem you may have to take a few steps backwards.
Is your battery fully charged?
If you disconnect the servo completely does the robot behave?
Even if you twiddle the left stick?
If you connect the servo to the receiver in the normal way (all 3 wires) do the motors behave?
With the servo connected how you want it, does it behave if you operate the flipper only whilst stationary?

It doesn't sound as if you have anything unusual in your setup, so it should work eventually...

[Sportball]

I will do some more investigation and let you know. In the meantime please see some photos:

[Sportball]

In order to diagnose the problem you may have to take a few steps backwards.
Is your battery fully charged?
If you disconnect the servo completely does the robot behave?
Even if you twiddle the left stick?
If you connect the servo to the receiver in the normal way (all 3 wires) do the motors behave?
With the servo connected how you want it, does it behave if you operate the flipper only whilst stationary?

It doesn't sound as if you have anything unusual in your setup, so it should work eventually...

Hi Gary, I had another play and could it be something as simple as the batteries running down? By adding the servo it obviously drains the batteries quicker than when is was motors alone, the problem only starts after around 15mins of operation. When I disconnect the servo the motors behave. I have tried connecting the servo direct to the reciever but it makes the ESC led flash as I guess it is drawing too much current.

[peterwaller]

The problem you are describing is as I think Gary suspects judging by what he has asked you to do is almost certainly caused by the battery voltage dipping.
Any battery has what is known as internal resistance which means the more current you draw the more the voltage decreases. The current drawn when driving motors isn't constant so you will get short dips in the battery voltage. The voltage regulator that supplies the 5 volts to the receiver has to have a certain voltage above the 5v (dropout voltage) to operate correctly so if the battery voltage is dipping below that voltage it is likely to cause the receiver to malfunction. Because the battery you are using is a low capacity only 110amH they are more suseptible to voltage dips (high internal resistance) and any way if the battery is 110maH and you are drawing an average of say 1A the battery will be getting flat after around 6 mins of operation. The 5v regulator on most controllers is normally only able to supply about 100ma for the receiver and the HPX F can draw as much as 1.5A at 5V which explains why is dosn't work if you run the servo from the receiver. The only solutions I can see is a larger capacity battery, a lower power servo or an extra 5v regulator capable of delivering 1.5A but you will still be flattening the battery but the servo will draw less current on 5V.

[Sportball]

Thanks for the input, it may not be a problem when it comes to competition. The batteries last around 15-20mins with no problem and this is with my son going overkill with the flipper. With a round lasting 5mins I guess I just need to bring a spare set.

[BeligerAnt]

The cells you linked to originally http://www.technobotsonline.com/lipo-po ... -3.7v.html have a continuous discharge rate of 2C or 220mA. Any more current load will cause the voltage to drop.
Something like this: http://robotbirds.com/catalog/product_i ... ts_id=4053 rated at 25C discharge (2.75A) will perform much better.

Fights are limited to 3 minutes and generally last much less so you would be OK with a spare set of batteries for a competition, but I would suggest getting some with a much higher discharge rating.

[Rhys]

How can technobots get away with selling that rubbish and calling it high discharge! When has 2C ever been high discharge? Get onto hobbyking and get something with 10 times the discharge for a quarter of the price. Why everybody isn't just running nanotech batteries these days is beyond me.

[Sportball]

Thanks, I only chose those due to the weight. I will look elsewhere next time