How long will a 17Ah battery last in a heavyweight robot?

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Admin (Admin)
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Post Number: 12
Registered: 10-2004
Posted on Saturday, October 30, 2004 - 2:51 pm:    Edit Post    Move Post (Moderator/Admin Only)

This naturally depends on how quickly it is discharged but is also a bit more complicated than that. Firstly it depends on the robot, its motors, the amount of torque needed to drive it and how you drive it. A common set up in heavyweights is to use a pair of Bosch 750W motors at 24V. These motors have a current consumption of 40A at their nominal 750W output power. Let's assume an average consumption of 30A per motor for a 5 minute fight which adds up to 60A for 5 minutes or 60/12 = 5Ah.

You would naturally assume that a pair of 17Ah batteries would be far too big but no. The 17Ah is based on a 20hr discharge, as you discharge the battery more quickly, the effective Ah capacity falls. Our tests on Yuasa batteries give an effective capacity of 33% of their 20hr rating on a 5 minute discharge. Europa give 38% and Hawker Odyssey 43%. Thus, for the worse case Yuasa a 17Ah battery would only give 5.6Ah which happens to be enough for our example above.

In practice, most teams do use 17Ah packs although some do use smaller but largely depends on gearbox ratio, 2 or 4 wheel drive etc. It is worth mentioning that the NiCD Bot-Packs have an effective capacity of 82% on a 5 minute discharge which is why 3 x 3Ah packs in parallel (9Ah) replaces 17Ah of SLA. In fact many users report a longer running time than with SLA's.

If you need to work out the distance between centres of any two timing pulleys, then this calculator will eliminate the long calculations or trial & error for you.



  Timing Pulley Distance Between Centres Calculator  
  Large Pulley Teeth Number T  
  Small Pulley Teeth Number T  
  Pitch   mm  
  Belt Length   mm  
  Large Pulley PCD   mm  
  Small Pulley PCD   mm  
  Distance Between Centres mm  
  How to use the Pulley Distance Calculator  
  1. Enter the number of teeth on the largest pulley  
  2. Enter the number of teeth on the smallest pulley  
  Note: if 1:1 ratio, enter the same number of teeth in both boxes  
  3. Enter the belt tooth pitch in mm, i.e. T5 is 5mm, T2.5 is 2.5mm  
  4. Enter the belt length in mm  
  The resulting answer is shown in the bottom yellow box. For information, the PCD of the pulleys is also shown in the other yellow boxes.  
  In order to achieve the correct tension, one of the pulleys should be adjustable.  
  Disclaimer: Whilst we have taken evey care to ensure this calculator gives the correct answer, Technobots cannot be held responsible for any errors and their consequencies.